Natural selection favours lighter pigmented skin in northern regions

Biology Questions On Cancer

1. What are the causes of skin cancer?

2. Why are Caucasians more at risk of skin cancer than other populations?

3. At what age does skin cancer typically occur? Is the incidence of skin cancer greater in youth or old age?

4. Does the amount of UV light reaching the Earth vary in a predictable manner (Figure 6-3)? If so, describe the pattern you observe.

5. What latitude receives the greatest amount of UV light (Figure 6-3)? The least?

6. Based on these data (Figure 6-3), where might you expect to find the most lightly pigmented and most darkly pigmented people on the planet? Be as specific as you can.

7. Provide a rationale to your answer above (i.e., why did you think that more darkly pigmented people would be found in those areas)?

8. Interpret Figure 6-4 and the trend it describes.

A. Is skin reflectance randomly distributed throughout the globe? If not, how would you describe the pattern?

B. Restate your findings in terms of skin color and UV light (instead of skin reflectance and latitude).

C. How closely do these findings match the predictions of your hypothesis (Question 6)?

D. Some populations have skin colors that are darker or lighter than predicted based on their loca­tion. Their data point falls somewhere outside of the line shown in (Figure 6-4). What might ex­plain the skin color of these exceptional populations? Propose a few hypotheses.

E. Hypothesize why different skin colors have evolved.

9. Hypothesize why different skin colors have evolved. Based on what you know, what factor is most likely to exert a selective pressure on skin color?

10. Review your answer to Question 3. Keeping your answer in mind, how strong a selective pressure do you expect skin cancer (UV-induced mutations) to exert on reproductive success?

11. Based on this information, does your hypothesis about the evolution of skin color (Question 9) seem likely? Why or why not? How does skin color meet, or fail to meet, the three requirements of natural selection outlined above?

12. Based on Branda and Eaton’s results (Figure 6-5), what is the apparent effect of UV light exposure on blood folate levels?

13. What is the apparent effect of UV light on folate levels in these test tubes? __________________

14. How is folate linked to natural selection?

15. All other things being equal, which skin tone would you expect to be correlated with higher levels of folate? _________________________________________________________________________

16. Based on this new information, revise your hypothesis to explain the evolution of human skin color.

17. What would happen to the reproductive success of:

A.light-skinnedperson living in the tropics? _________________________________________

B. light-skinned person living in the polar region? _____________________________________

C.dark-skinned person living in the tropics? _________________________________________

D. dark-skinned person living in the polar region? _____________________________________

18. Predict the skin tones expected at different latitudes, taking folate needs into consideration. Use the world map (Figure 6-6) to indicate the skin tone expected at each latitude (shade the areas where populations are darkly pigmented).

19. Can folate explain the variation and distribution of light- and dark-skinned individuals around the world?

20. How is vitamin D linked to natural selection?

21. Which skin tone allows someone to maintain the recommended level of vitamin D? ________________

22. Based on this new information, revise your hypothesis to explain the evolution of the variation and distribution of human skin color.

23. Taking only vitamin D into consideration, what would happen to the reproductive success of:

A. light-skinned person living in the tropics? _________________________________________

B. light-skinned person living in the polar region? _____________________________________

C. dark-skinned person living in the tropics? _________________________________________

D. dark-skinned person living in the polar region? _____________________________________

24. Predict the skin tones expected at different latitudes, taking only vitamin D needs into consider­ation. Use the world map (Figure 6-8) to indicate the skin tone expected at each latitude (shade a region to represent pigmented skin in that population).

25. Can vitamin D alone explain the current world distribution of skin color? ____________________

26. Using principles of natural selection, predict the skin tone expected at different latitudes, taking ul­traviolet exposure, vitamin D, and folate needs into consideration. Use the map (Figure 6-9) to indicate skin tone patterns at different latitudes (shade regions where populations are expected to be darkly pigmented).

27. Are UV light, vitamin D and folate needs sufficient to explain the current world distribution of skin color? ___________________________________________________________________________

28. How might you explain that Inuits, living at northern latitudes, are relatively dark-skinned (much more so than expected for their latitude)? Propose a hypothesis.

29. Conversely, Northern Europeans are slightly lighter-skinned than expected for their latitude. Pro­pose a hypothesis to explain this observation.

Biol 1100L

Spring 2014

Please note that this manual is a work in progress and was compiled specifically for the ISU Biology department. It changes each semester/session depending on the interests of the instructors. It is

a free and unpublished manual that has not seen reviewers or editors; there are errors.

The first step in the acquisition of wisdom is silence, the second listening, the third memory, the fourth practice,

the fifth teaching others.

~Solomon ibn Gabirol (1021 -1058 AD)

1-1

Biol 1100L Ecology1 Lab 1

1. Define hypothesis using your textbook.

Name:_______________________________ Section:____

In lab this week you will gather observational data about arthropod distributions and ecol- ogy, describe their niches in terrariums, construct a hypothesis, make a prediction, and calculate the diversity (Shannon-Weiner Diversity Index) for each niche type. Arthropods are a major component of all terrestrial ecosystems and their behavior has been the object of many famous ecological studies. All arthropod species are in the Kingdom Animalia and Phylum Arthropoda but they are in many different classes, orders, and families. A large proportion of arthropods are plant detritivores, i.e. organisms that feed on dead and decaying plant material. These organisms hasten the conversion of biomass to soil, speed up rates of nutrient cycling, and as a result, increase the productivity of ecosys- tems. In this lab you will learn about three very important ecological concepts: diversity, niche and the competitive exclusion principle. Diversity can be measured in a number of different ways, and you will use the Shannon-Weiner Diversity Index. The niche is a set of environ- mental factors necessary to the continued existence of a species. The niche describes anything you might be able to think of that an organism requires. This includes what it eats, where it eats, when it eats, when it sleeps etc. The competitive exclusion principle states that two species with identical niches cannot coexist indefinitely (Gausse 1934). It makes sense that species that coexist will have different niches. If they didn’t they would either be in the process of going extinct or driving their competitor into extinction. The way species subdivide niche space has been called niche partitioning.

Figure 1-1. Diagram of an arthropod terrarium.

Part 1. Defining Niches

One of the members of your group will obtain a terrarium and poking / digging tools from the west end of the lab. Do not do anything to the terrarium yet. Note the overall structure of the terrarium ecosystem (Fig. 1-1). As a group talk about the different ways the species of arthropods could partition this niche space to avoid identical niches. Be prepared to present your group ideas to the class. Decide as a class on 4 distinct niches that would be good to use. All groups of students must use the same niches to continue with the exercise.

2. What is an example of a hypothesis (see textbook)?

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Biol 1100L Ecology1 Lab 1

3. What are the niches you and your classmates identified for the terrarium? 1___________________ 2___________________ 3___________________ 4___________________

4. As a class construct a hypothesis about arthropod abundance and diversity of each niche.

Table 1-1. Abundance of arthropod types from ter- rarium #_____.

Arthropod Niche

1 2 3 4 cricket isopod millipede bess beetle tenebrio beetle other 1 other 2 Total Abundance

5. As class make a prediction about arthropod abundance and diversity of each niche.

Part 2. Data Collection

Observe your terrarium. Carefully, without disturbing the other niches, search one niche for arthropods. Be gentle and care-

ful (we don’t want to harm any of the arthropods). As you find an arthropod place it in the plastic holding chamber.

6. Fill in the appropriate niche/arthropod cell in Table 1-1 with count data using tick marks. NOTE: do not count dead arthropods.

Repeat for all the niches.

Part 3. Data Analysis

To calculate diversity biologists use indices that are based on mathematical equations. For this lab you will use the diversity spreadsheet linked to Moodle to calculate the Shannon-Wiener Index (H’) which is calculated as -Σ(pi ln pi). This index is an indicator of the evenness and richness (i.e. number of arthropod species and the abundance within each species) within an environment. H’ ranges upwards from 0. The 0 value indicates a single species and increases as richness and evenness increases. When you have completed your observations, each group will provide their niche totals from Table 1-1 to the class.

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Biol 1100L Ecology1 Lab 1

7. Calculate a class average using the Excel spreadsheet linked to Moodle for each arthro- pod type in each niche and enter that average into Table 1-2.

8. Using the class averages, cal- culate Shannon- Wiener Diver- sity Index (H’) for each niche using the Ex- cel spreadsheet provided and fill in Table 1-3.

Table 1-2. Average abundance of arthropod types from all terrariums studied.

Arthropod Niche

1 2 3 4 cricket isopod millipede bess beetle tenebrio beetle other 1 other 2 Total Average Abundance

Table 1-3. Shannon-Wiener Diversity Index (H’) for each niche.

Niche H’ 1 2 3 4

9. In a complete sentence and in your own words define the Shannon-Wiener Index (H’). What two important factors are taken into account by the Shannon-Wiener Diversity Index?

10. Did you conclude that your prediction was true or false for the diversity of arthropods per niche?

11. Did you accept or reject your hypothesis?

12. In retrospect would you have modified your selection/distinction of niches?

13. Did the taxonomic descriptions in the appendix appear to agree with the niches you saw the arthro- pods in?

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Biol 1100L Ecology1 Lab 1

Cricket Class: Insecta Order: Orthoptera Family: Gryllidae

Bess Beetle Class: Insecta Order: Coleoptera Family: Passalidae

Darkling Beetle Class: Insecta Order: Coleoptera Family: Tenebrionidae

Isopod (Pill bug) Class: Malacostraca Order: Isopoda Family: Armadillidiidae and Porcellionidae

Millipede Class: Diplopoda Order: Spirobolida Family: Spirobolidea

This group of insects is closely related to grasshoppers that are in the Family Acrididae. Most species of crickets overwinter as eggs. All crickets have auditory organs on their front tibia. The male cricket rubs its wings together to make a chirping sound. The young cricket, or nymph, looks like an adult except that it is smaller and not sexu- ally developed. Crickets are generally scavengers that will eat essentially anything.

These are large (32-36 mm long) shiny black beetles. The mouth is adapted for chewing wood. Passalids are somewhat social and their colonies live in decaying logs. The adults can produce a squeaking sound by rapidly rubbing their third legs against their fifth abdominal sec- tion. All beetles undergo larval and pupal stages before emerging as adults.

These dark brown flying beetles are also known as dark- ling beetles. Most tenebrionids feed on plant matter of some kind and often live in cornmeal, dog food, cere- als, and dried fruits. The Tenebrionidae is the fifth larg- est family of beetles with over 1000 species in North America.

These organisms are actually crustaceans and are closely related to crabs and lobsters. The name isopod literally means equal-legs. Individuals in this group are often found under boards and decaying wood. They eat wood and logs as they decay. Isopods breathe with gills so they must live in an area that is constantly moist.

Millipedes are elongate wormlike animals with many legs. Most millipedes have 30 or more pairs of legs. They tend to avoid light since they have eyespots on their heads that are sensitive to light. They live on dead leaves or other decaying material.

14. Do you feel you have made an adequate description of niche space of these arthropods? Why or why not?

15. Which niche was most diverse? Why do you think this is the case?

2-1

Biol 1100L Population Ecology Lab 2

Name:_______________________________ Section:____

Part 1. Population Study

A summary of mortality, survivorship, and ex- pectation of further life by age, is called a life table. The most straight forward type of life ta- ble starts with a cohort of young organisms and follows their fortunes through their lives, until the last one dies. Because cohort data are usu- ally difficult to obtain, most life tables are calcu- lated using other kinds of information. If we can obtain mortality rates by age of a population we can, after the appropriate assumptions and cal- culations, construct a life table (called a time- specific table, versus the age-specific cohort table). A frequent approach, and the one used here, is to use age at death to estimate mortal- ity rates and calculate the other vital statistics from that. Tables produced in this way are age- specific, even though the cohort is composite, made up of individuals that started life in differ- ent years. The study of human populations is called de- mography and is a branch of science called population ecology. A population is defined as a species (interbreeding individuals) within a de- fined area. In this lab, we will be exploring the Idaho Falls population. Using the data that was collected from the Rose Hill Cemetery of Idaho

Table 2-1. Life table of the Idaho Falls population pre-1930 and post-1970. Where x is the beginning age of the age class, nx is the number alive (survivors) at age x, lx is the proportion of survivors at age x, dx is the number dying (mortality )within the age class x, and qx is the mortality rate (that is, dx/nx).

Table 2-2. Data collected from the Idaho Falls Rose Hills Cemetery during Spring 2010. Also known as mortality (dx) pre-1930 and post-1970 of the Idaho Falls popula- tion.

Falls (Table 2-1), the life table (Table 2-2), and the survivorship curves (Fig. 2-1) constructed you will answer a few questions.

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Biol 1100L Population Ecology Lab 2

1. Look at circle A on Figure 2-1. Why do you think there is a steep decrease in survivorship for the pre-1930 population?

2. Comparing pre-1930 and post-1970 populations, has the proportion of people surviving through an age class increased or decreased for the Idaho Falls population (excluding the last two age classes)?

3. What has changed since pre-1930 to make an increase in survivorship possible?

4. Do you think this is similar for the entire US population?

Figure 2-1. Proportion (as a percentage) of survivors (lx) at age x of the Idaho Falls population pre-1930 and post-1970.

A

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Biol 1100L Population Ecology Lab 2

Part 2. Ecological Footprint

Lifestyle in advanced nations like the US depends significantly on the direct or indirect burning of fossil fuels. Many people in less developed nations, however, do not depend on large-scaled burning of fossil fuels. Imagine a subsistence farmer in an undeveloped country living in a mud hut without electricity or running water. The family is fed from the small herd of animals and crops adjacent to its dwelling. The family does not own a car, and travel to the next village requires an ox and a cart. The family does not own any electrical appliances or electronic media. Consider another family in a more developed part of the world but less developed than North America or Western Europe. The family has electricity in its small home, but it does not own a car and has just bought its first TV. The father rides his bike to a nearby village for work. The mother walks to the local village market three times a week for local produce and meat. The atmospheric CO2 level was approximately 280 parts per million (ppm) before the industrial revolu- tion and is now 393 ppm (in 2005 it was 387 ppm). A greenhouse gas, CO2, is emitted from a variety of sources, many of them associated with the burning of fossil fuels. For example, when you drive a car, the exhaust emissions include CO2. When you heat or cool your home the required energy often comes from the burning of fossil fuels in power stations. But have you ever stopped to think that your diet may play a role in CO2 emissions? If you eat meat and shop for it at a supermarket chain, there is strong chance that the source of your T-bone steak is a distant slaughterhouse. In winter, the lettuce that makes up the bulk of the salad you eat may be shipped from tropical locations. Your steak and lettuce than travel by truck to reach your supermarket delicatessen or produce counter, contributing to CO2 emissions along the way. In 2007 the biosphere had 11.9 billion hectares of biologically productive space corresponding to roughly one quarter of the planet’s surface. These 11.9 billion hectares of biologically productive space include 2.4 billion hectares of ocean and inland water and 9.1 billion hectares of land. The land space is composed of 1.6 billion hectares of cropland, 3.4 billion hectares of grazing land, 3.9 billion hectares of forest land, and 0.3 billion hectares of built-up land.

One of the ways that you can visualize your own personal impact on the ecology of the planet is to calculate your Ecological Footprint. In this activity you will use the Global Footprint Network to determine your Ecological Footprint.

5. Use the Global Footprint Network glossary to define the following; 1) gha, 2) biological capacity (biocapacity), 3) biological capacity per person, and 4) ecological footprint.

http://www.footprintnetwork.org/en/index.php/GFN/

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Biol 1100L Population Ecology Lab 2

6. What kinds of behavior reduce Ecological Footprints?

7. Use the Global Footprint Network website to calculate your footprint. You must enter “Detailed Information”. Fill in Table 2-3.

Table 2-3. Your Ecological Footprint. http://www.footprintnetwork.org/en/index.php/GFN/page/calculators/

Food Shelter Mobility Goods Services Planets GHA Carbon Dioxide

8. Look at Figure 2-2 A and B: A. What is the biocapacity per person for the USA? B. What is the Ecological Footprint of consumption for the USA. C. How do these numbers compare to the majority of the world?

10. Look at Figure 2-2 D and E: A. Is the USA a creditor or debtor nation? B. What is the USA’s Ecological Footprint percentage over domestic biocapacity? C. What is the USA’s Ecological Footprint percentage over globally available biocapacity? D. How do these numbers compare to the rest of the world? E. How can the USA become a creditor nation if our domestic consumption is 8 gha per person

but our domestic biocapacity is 3.87 gha per person and the global biocapacity is 1.78 gha per person?

9. How does the USA’s Ecological Footprint of consumption (Figure 2-2 B) compare to Ecological Footprint of production (Figure 2-2 C) and how does this compare to the majority of the world?

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Biol 1100L Population Ecology Lab 2

11. Look at Figure 2-2 F: A. Is the USA a net importing or exporting country?

B. How many gha do we import each year? C. Could the USA Ecological Footprint be reduced if our net import of biocapacity were reduced?

Questions for Discussion:

12. Earlier you saw that the pre-1930’s Idaho Falls population had lower survivorship than the post 1970’s population. Do do you think the trends shown for pre-1930’s Idaho Falls’ population could be similar to those of present day developing nations?

13. If our entire US population was considered a developing nation pre-1930’s, what does this tell you about future consumption and carbon footprints of today’s developing nations?

14. Do you think this is sustainable?

2-6

Biol 1100L Population Ecology Lab 2

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Biol 1100L Population Ecology Lab 2

3-1

Biol 1100L Biodiversity Lab 3

It is estimated that there could potentially be 30 million species on Planet Earth. The two million species that have been described and named are organized into three domains (Figure 3-1); Bacteria, Archaea, and Eukarya. These domains are further organized into smaller and smaller groupings. Today you will learn more about this system of organization and over the next five labs you will be introduced to a variety of organisms.

Part 1. Systematics

The study of the diversity of organism and of the relationships between them is the scientific field of systematics. Systematics is important because it creates the foundation upon which all other biological disciplines are based. Phylo- genetic systematics provides methods for infer- ring evolutionary relationships. Relationships are inferred by distinguishing between charac- ters that represent an ancestral condition for the organisms in question and those that represent the derived condition. Shared derived charac- ters among organism are evidence of common ancestry. A phylogenetic tree (Figure 3-2) is graphical representation of the evolutionary re- lationship between taxa.

2. Who are you and your hypothetical sister’s most recent common ancestors?

Figure 3-2. Each node along a branch of the phylo- genetic tree represents a population that lived at a particular point in time. The root is the original popu- lation. Nodes mark the population that split to pro- duce two daughter populations. The tips represent the populations that are currently living (extant).

Imagine that you have a sister and a cousin. Your sister and you share ancestors, your mother and father. You and your sister share other ancestors too as do you and your cousin. These may include your father’s or mother’s parents, their parents, and so on. Evolutionary biologists refer to the ancestors two individuals

share as common ancestors (held in common or shared). You are more closely related to your sister than to your cousin because your most recent common ancestors with your sister (your mom and dad) lived more recently than your most recent common ancestors with your cousin (your grandparents). We can use similar reasoning in thinking about the evolutionary relationships among populations and species.

Name:_______________________________ Section:____

Figure 3-1. A phylogenetic tree of the three domains of life.

1. In the following diagram label the arrows most recent common ancestor and the root.

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Biol 1100L Biodiversity Lab 3

3. Who are you and your hypothetical cousin’s most recent common ances- tors?___________________________

4. Who are you more closely related to, your sister or your cousin? Why?

5. Who lived more recently your most recent common ancestors with your sister, or your most recent common ancestors with your cousin?___________________________

6. In the diagram: A. Which arrows (x, y, or z) point to the

most recent common ancestor of 1 and 3?

B. Which arrow points to the most recent common ancestor of 1 and 2?

C. Which lived most recently, the most re- cent common ancestor of 1 and 3, or the most recent common ancestor of I and 2?_____________________________

D. Is 2 or 3 more closely related to the 1? _______________________________

E. Draw an arrow on the diagram showing the direction of time.

Part 2. Taxonomy

The discipline of systematic encompasses the field of taxonomy which is the classification, de- scription, and naming of groups of organisms. Since the 18th century, biologists have sub- scribed to a standard protocol for the descrip- tion, naming, and classification of organisms. Classification is a utilitarian product of system- atics, a tool that provides names for groups of species and serves as a way to retrieve in- formation. It allows people across the country and world to communicate more efficiently with each other.

The fundamental unit of classification is the species. Most often a species is defined as a group of individuals that are capable of inter- breeding under natural conditions producing fertile offspring.

In formal biological classification, species are grouped according to estimates of their simi- larity or relatedness. Such groups are called taxa (singular, taxon). The taxa are listed in a hierarchical pattern. The most commonly used groups in the system of zoological classification are shown in Table 3-1 (listed from the most in- clusive to the most exclusive):

In this system, the animal kingdom is divided into a number of phyla (singular, phylum). Each phylum is divided into classes, classes into or- ders, orders into families, families into genera (singular, genus) and genera into species. A classification developed for a taxon will be af- fected by the particular characters used, the

Table 3-1. Example of a taxonomic classification. Taxa Syringa American Elk Domain Eukarya Eukarya Kingdom Plantae Animalia Phylum or Division Magnoliophyta Chordata

Class Magnoliopsida Mammalia Order Rosales Artiodactyla Family Hydrangeaceae Cervidae Genus + specific name

= species name

Philadelphus lewisii

Cervus canadensis

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Biol 1100L Biodiversity Lab 3

relative weight given, and how they are ana- lyzed. If different characters or weighting is used a different classification will arise.

Animals have two types of names, common and scientific. Every animal taxon has a unique scientific name that is used throughout the world. Common names are less precise and can cause confusion because the name can be used for several different species. Also, the ma- jority of species do not have a common name. The scientific name of a species is binomial and is always italicized. The name consists of two words the genus name and the specific name. For example the American Elk’s scientific name is Cervus canadensis.

A dichotomous key (Figure 10-3) is a device used to identify an organism through several steps. At each step (called a couplet) a choice must be made between two alternatives based on the presence of certain characters. Usually the characters are morphological (that is they are based on the form or shape of an organ- ism). Each alternative will lead to another cou- plet or to the name of the identified organism.

7. Use the key in Figure 3-3 to determine the phyla of unknowns A-D: A._______________________________

B._______________________________

C._______________________________

D._______________________________

Figure 3-3. Dichotomous key to some of the animal phyla. Adapted from a key made available by the UCLA Marine Science Center.

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Biol 1100L Biodiversity Lab 3

Part 3. Flowers and Trees*

SimBio1 EvoBeaker™ Flowers and Trees is a computer simulation program to help guide you through the process of understanding how inheritance, variation and the origin of new variation can, over time, produce biodiversity. The exercise relies on an example using a wild flower called columbine.

8. Observe Figure 3-4:

A. What is the common and species name of this flower?

B. What kinds of animals do you think access the nectar in columbine nectar spurs?

Figure 3-4. The columbine flower, Aquilegia flavescens.

A. Designer Flower

Launch SimBio EvoBeaker. Select Flowers and Trees from the Lab options and Designer Flower from the drop down Experiment Menu. The model columbine populations you will ex- periment with live on a series of peaks in the Rocky Mountains in Western North America. These peaks are shown as squares on left side of the EvoBeaker window. Because our model columbines thrive only at high-mountain peaks, peaks are islands of good habitat floating in a sea of poor habitat.

Columbine seeds typically do not travel far. In- stead, they drop to the ground near their par- ents. The mountain peaks in our model are far apart, so columbine seeds rarely move from one peak to another. A seed can make such a trip only if it gets picked up an extraordinarily strong wind, or if it stuck to the hoof of an elk or the foot of a hiker.

There are 8 flower traits that you will look for in the model columbines. To see the traits,

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Biol 1100L Biodiversity Lab 3

double click on one of the tiny flowers, such as the one on Peak 1. You will see a Trait Editor window appear. This window contains an enlarged view of the flower, plus the 8 traits listed in pull-down menus.

Find the trait listed as Anthers. The columbine you found on Peak 1 has white anthers. To mutate the flower so it has yellow Anthers select Yellow from the pull-down menu next to the word Anthers. Go to each of the other traits and mutate them back and forth between their two states. As you do so, ex- amine the changes in the enlarged cartoon flowers until you are familiar with what each of the traits looks like.

When you are done, close the Trait Editor window.

B. Growing Trees

Imagine that only one of our seven peaks is inhabited by columbines, and that as this population evolves over time, seeds occasionally make the long trip from one peak to another to establish a new population. If you could watch this happen over hundreds of generations, what would you see? Evo- Beaker summarizes the events you would witness in a diagram called a phylogenetic tree.

To see this, go to the Experiment menu and select Growing Trees The ancestors of the columbines in our mountain range blew in as seeds several years ago and landed on one of the peaks. You can see the population of flowers now living there. Click on the GO button to let time advance until the original population splits into two populations. Then stop the model by clicking on the STOP button.

Each year as the model runs, all the old flowers set seed and then die. The following spring, the seeds sprout, grow up, and flower. Normally seeds stay on the mountain peak of their parents, but once in a long while, a fierce storm comes through and carries a seed from one peak to another, es- tablishing a new population, which you just watched happen. Look at the evolutionary tree in the Note- book panel.

9. Describe how the division of one population into two is represented in the tree diagram.

Every so often, a mutation happens in an individual flower in one of the populations. The program indicates this by changing the color of the tiny icon that represents the individual flower. The model is rigged so that new mutations quickly spread through the population in which they arise. Continue run- ning the model with the GO button until you see the color of the flowers on one of the peaks change. When the change has spread through all flowers on that peak, STOP the model.

10. In addition to the change in color of the little flowers in the Peaks, describe how the change in a trait is represented on the evolutionary tree diagram. (Hint: it is shown in two places on the tree diagram - look at both the tree itself and at the pictures of the flowers at the branch tips.)

11. As the changes were happening, time was moving forward. Aside from the time scale on the left, how is the movement of time represented in the evolutionary tree?

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Biol 1100L Biodiversity Lab 3

Each time a seed blows from one peak to another, we say that the tree diagram splits. The tips of the two resulting branches are the two new populations, drawn at the top of the tree to show that they are currently alive. The base of the two branches come together to show that both new populations came from the same parent population. This parent is the most recent common ancestor of the two new populations. Continue running the model until populations have become established on a couple of other peaks, and then stop the model.

Time is shown at the bottom of the main window. Run the model until 1000 years have gone by. Be patient - evolution takes time. Watch the action both on the mountain peaks and on the evolutionary tree. At the end, look at the pictures of the flowers at the tips of the tree branches. Pick a flower picture at the tip of the tree diagram (representing one of the living mountain peak populations). Follow its branch all the way to the base of the tree.

12. Does the flower picture at the tip reflect all the trait changes that occurred among its ances- tors?___________

C. Building and Reading Trees

In the Experiment menu, select Simple Evolving Flowers. The setup here is the same as last time, except that there are only 1 mountain peaks and traits for each flower. The Notebook on the right will still show the evolutionary tree as it grows, but now no changes will occur unless you make them happen. Start the model running by clicking on the GO button. Let time advance for 40-60 years so there is a little trunk at the bottom of the tree. Then stop the model by clicking on the STOP button. In Part 3.B. you watched as mutations appeared on their own in the columbine populations. In this experiment. You will play mutator, changing the traits of flowers at your whim. Start by changing the anthers of one of your flowers from white to yellow. To do that, double-click on one of the flowers in the Peak I population. A Trait Editor window will appear. Change this flower to have anthers that are yellow by selecting Yellow from the Anthers pull-down menu. Don’t change any other traits right now. Close the Trait Editor window. Run the model again for 40-60 years by clicking on the GO button. Look at the evolutionary tree. Notice that, as in the last experiment, there is a label showing when the new trait appeared. Note also that the picture at the top shows the current living population with the new trait. Your evolutionary tree should now look like the one shown here. The evolutionary tree traces the 80 or so previous generations that are ancestors of your current Peak 1 popula- tion.

13. What color are the anthers of the present population? ________________

14. What color are the anthers of the ancestral population? ________________

15. There are no storms modeled in this experiment. Instead, you will establish new flower populations on the other peaks yourself by traveling with seeds stuck to your hiking boots. Before doing this, draw a diagram of what you think the evolutionary tree will look like when you carry a seed from Peak I to establish a new population on Peak 2. You don’t have to draw pic- tures of the flowers at the tips, just use the names of the populations.

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Biol 1100L Biodiversity Lab 3

Now go ahead and carry a seed from Peak I to Peak 2 by clicking on a flower in Peak I, holding your mouse button down, and dragging the flower to Peak 2. Start the model running again and run it for 40-60 years . Stop the model and look at the tree. 16. Was your diagram prediction correct?____________

Over time, new traits could arise in the population on either mountain peak that make the flowers on the two peaks look different. 17. What will the tree diagram look like if the flowers on Peak 1 mutate to have pointy petal tips.

Change the petal tips of a flower on Peak I to “pointy” (using the Trait Editor). Close the Trait Editor and run the model for another 40-60 years. Compare the pointy-petal diagram on the screen to the one you drew. 18. Was your pointy-petal diagram prediction correct?__________

Now click and drag one of the flowers from peak 1 to 3 and run the model for 40-60 years. Make the following changes happen, being sure to run the Model for 40-60 years between each one.

• The population on Peak 3 acquires dark petals

• 40-60 years • A hiker carries a seed from Peak I to

Peak 4

• 40-60 years • The population on Peak 4 acquires long

spur bottoms • 40-60 years

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Biol 1100L Biodiversity Lab 3

1©2008, SimBiotic Software for Teaching and Research, Inc. All Rights Reserved.

19. Draw the resulting diagram: A. Label:

• b - most recent common ancestor of the populations on Peak 1 and Peak 3 • c - most recent common ancestor of the populations on Peak I and Peak 2 • d- most recent common ancestor of the populations on Peak 3 and Peak 2

B. Approximate the amount of time shown on screen between: • Peak I population and b _____________ • Peak I population and c _____________ • Peak 3 population and b _____________ • Peak 3 population and d _____________

20. Have more years passed since the Peak 3 population split from Peak I at b, or since the Peak 3 population split from the Peak 2 population at d? _______________________________________

21. Have more years passed since the Peak I population split from Peak 3 at b, or since the Peak I population split from Peak 2 at c? ___________________________________________________

22. Is the population at b a descendent of c or is the population at c a descendent of b? ________________

23. Given how much time has passed from each ancestral population to the current populations on the mountain peaks, write down the order of relationships (which population is most closely related to which other) among the four currently living populations. Next explain why they have that rela- tionship based on the amount of time that has passed from each common ancestor.

4-1

Biol 1100L Animal Diversity Lab 4

Part 1. Sponges & Cnidaria

Sponges are primarily marine organisms and as adults are sessile, filter-feeders. They have a cellular level of organization comprised of specialized cells that perform specific functions. Cells are held loosely together and supported by spicules. They can reproduce asexually by budding but they also release eggs and sperm. Most sponges are poisonous or protected by their spicules, and are rarely eaten by other animals. There are about 10,000 sponge spe- cies.

1. Define multicellular and heterotrophic:

2. Observe the sponge species on display. A. Sketch two: B. Draw the direction water moves into the

sponge.

3. View a prepared slide of a sponge spicule. A. Sketch one spicule at 40X.

B. What is a spicule for?

Cnidarians are radial symmetrical, they have two distinct tissue layers (epidermis and gas- trodermis) separated by a mesoglea and en- closing the gastrovascular cavity that has one opening that functions as both the mouth and the anus. They exist in both the medusa and polyp form. Polyp: cylinders that adhere to the substratum with tentacles extended. Medusa: umbrella-shaped, but free moving. There are about 9,000 cnidarian species.

Name:_______________________________ Section:____

The domain Eukarya (eukary- otes) includes plants, fungi, ani- mals, and many unicellular organ- isms that all share one important trait: the presence of a nucleus in their cells. Today we will focus on the animals (Figure 4 -1). Animals are defined as those eukaryotic organisms that are multicellular and heterotrophic. Bilateral ani- mals with three distinct tissue lay- ers can be further divided into two groups, the deuterostomes and protostomes. When protostomes develop into an embryo they form a mouth first whereas the deuteros- tomes produce the mouth second.

Species: _________________ Species: _________________

Specimen: _________________

Magnification:_______________

Figure 4-1. Phylogenetic tree of some of the major animal groups.

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Biol 1100L Animal Diversity Lab 4

4. Observe a live Hydra using a dissecting scope. A. Sketch:

B. Explain how it moves and what types of tissues must be present to enable it to move?

5. View at 40X a slide of a cnidarian larva. A. Sketch:

B. What is the adaptive significance of mo- tile larvae?

Part 2: Deuterostomes

A. Echinoderms

Sea stars, brittle stars, sand dollars, sea urchins and sea cucumbers make up the echinoderms. All echinoderms live in the marine environment. As adults, most have a water-vascular system tube feet, and an endoskeleton covered by an epidermal layer. They usually have obvious pentaradial symmetry. ~ 6,500 species

6. Observe the echinoderm species on dis- play. A. Sketch two:

B. Drawn dotted lined over sketchs to show pentaradial symmetry.

B. Chordates

The tunicates, lancelets, fishes, amphibians, reptiles, birds, and mammals make up the chordate animals. All of these animals, at some stage of their lives, share the following characters: a notochord, a single, dorsal, tubu- lar nerve cord, and a post-anal tail.

~44,000 species

7. Observe the variety of chordates on display in lab. A. Fill in Table 4-1 with a 1 if a characteris-

tic is present or a 0 if it is not.

B. Label the nodes and fill in the taxa names on Figure 4-2 using Table 4-1. Helpful hint: scales of fish and reptiles are the product of convergent evolu- tion.

Specimen: _________________

Magnification:_______________

Specimen: _________________

Magnification:_______________

Species: _________________ Species: _________________

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Biol 1100L Animal Diversity Lab 4

Part 3: Protostomes

A. Flatworms, Annelids, & Molluscs

Flatworms include both free-living (planarians) or endoparasitic (tapeworms and flukes) spe- cies They are unsegmented and cephalized with bilateral symmetry and incomplete guts. There are about ~ 25,000 species of flatworms and the majority are parasites.

8. Observe the flatworm species on display. A. Label each of the following drawings (A-C) with the flatworm species:

B. How does the morphology of the non- parasitic forms compare to the parasitic forms?

Annelids are the segmented worms and in- clude the leeches and earthworms. They have a closed circulatory system, and a well- developed nervous system. There are about ~ 17,000 species of annelids.

9. Observe the live leech and aquatic worms. Describe the way each moves.

Molluscs are a large and diverse group of fresh and marine animals that includes snails, slugs, clams, oysters, squid, and octopi. They have muscular foot for locomotion. A mantle enclos- es the internal organs and gills. They usually have shells. There are about ~ 95,000 species of mollusc species.

10. Observe the mollusc species on display. A. Sketch two: B. Label the foot on each.

Table 4-1. Characteristics of some chordate groups.

Taxa no to

ch or

d

bo ny

s ke

le to

n

ve rt

eb ra

e

ja w

s

le gs

am ni

ot e

eg gs

sc al

es a

nd /o

r f ea

th er

s

tunicate lancelet hagfish lamprey shark fish amphibian reptile bird mammal

A.__________B.___________C.____________

Species: _________________ Species: _________________

Figure 4-2. Evolutionary tree of some chordate groups.

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Biol 1100L Animal Diversity Lab 4

B. Roundworms and Arthropods

Roundworms include the vinegar eels, root and soil nematodes, intestinal roundworms, trichina worms, hookworms and heartworms. Most are microscopic but a few are quite large. Soil- inhabiting nematodes are especially abundant, many million living in a shovel-full of garden soil. The parasitic nematodes infect both plants and animals, causing crop and domestic ani- mal losses as well as significant human health problems. There are about ~ 25,000 species of roundworms.

Arthropods are animals that have a segmented body, appendages that are paired and com- posed of seven jointed segments, and a chi- tinous exoskeleton. These include the spiders, crabs, insects, potato bugs, shrimp, millipedes, and centipedes. The exoskeleton provides pro- tection (both in water and on land), mechanical rigidity, and joints that permit complex move- ments driven by muscles. There are over a mil- lion (1,000,000) described species.

11. Observe the roundworm and arthropod spe- cies on display. Label each of the following drawings (A-G) with the species name and describe some of their life history:

C. Species_______________ Life History:

D. Species_______________ Life History:

E. Species_______________ Life History: F. Species_______________

Life History:

A. Species_______________ Life History:

B. Species_______________ Life History:

G. Species_______________ Life History:

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Biol 1100L Natural Selection Lab 5

Part 1. Survival

In this activity, you will repeat an important observation that helped Darwin develop his theory of natu- ral selection. Populations cannot grow indefinitely, and therefore not all of the offspring will survive to reproduce. You will determine the number of individuals produced by ten generations of a plant species assuming that every seed produced by every plant of every generation survives and grows into a mature plant that also produces seeds. Obtain half of a fruit from your instructor and count the number of seeds that it contains. Multiply the number of seeds by two to obtain the total number of seeds in the entire piece of fruit.

We will assume that each seed will grow into a plant. 1. Write this number in column five, row one of Table 5-1 and the Natural Selection workbook linked

to Moodle. Use the ‘Important Notes’ on the next page to find the number of fruits that your plant will produce. 2. Write this number in column three, row one of Table 5-1 and the Natural Selection workbook linked

to Moodle. 3. Fill in Table 5-1 with the numbers generated by the Excel spreadsheet.

Name:_______________________________ Section:____

The fundamental premise of the theory of evolution is that the form and behaviors of a species are not fixed, but can instead change over time. Nature selects the individuals who have the variations that, on average, allow them have more offspring. In addition to natural selection (which is not a random process), four other mechanisms of evolution have been described in detail; these are mutation, genetic drift, gene flow, and non-random mating. Evolution via these mechanisms has been corroborated in essentially every branch of biology, including genetics, molecular biology, microbiology ecology and so on. Clearly, Darwin’s contribution to biology was one of fundamental importance.

The overall objective of this lab is to observe the phenomena that Charles Darwin used to sup- port his theory of “Natural Selection.” Instead of “evolution,” Darwin used the phrase “descent with modification,” but he actually coined the term “Natural Selection.” In On the Origin of Spe- cies, he wrote:

“Can we doubt...that individuals having any advantage, however slight, over oth- ers, would have the best chance of surviving and procreating their kind? On the other hand, we may feel sure that any variation in the least degree injuri- ous would be rigidly destroyed. This preservation of favorable variations, I call Natural Selection. “ Note that Darwin capitalized natural selection, but it is not a proper noun and should not be capitalized.

Evolution by natural selection has been described as two observations and one inescapable conclusion; 1) populations cannot grow indefinitely, and therefore not all of the offspring will sur- vive to reproduce and 2) populations present heritable variation. These observations led Darwin to the inescapable conclusion that individuals within a population will have an unequal reproduc- tive success (differential reproductive success). Natural selection is a process that results in a some individuals leaving more offspring than others because those individuals have traits that are better suited to their environment. In this lab, you will participate in activities to illuminate the two observations, and explore for yourself the “inescapable conclusion,” which logically follows from the two observations.

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Biol 1100L Natural Selection Lab 5

Important Notes: Table 5-1 is based on the following assumptions and information: • All of the seeds from your piece of fruit are planted, grow, mature, reproduce to produce new

seeds, and die within one year. • Each plant needs one square meter (1 m2) of Earth’s surface to complete its one-year life cycle. • The average number of green peppers per plant is eight, the average number of apples per tree

is 2,000; the average number of kiwi per tree is 120; the average number of limes per tree is 293, and the average number of tomatoes per plant is 13.

• The number of fruits produced in each generation (column 4) is the product of the number of plants in that generation (column 2) multiplied by the number of fruits per plant (column 3).

• The number of seeds produced in each generation (column 6) is the product of the total number of fruits in that generation (column 4) multiplied by the number of seeds per fruit (column 5). This number is equivalent to the total number of plants that comprise the subsequent generation (i.e., next row in column two).

Use the results shown in Table 5-1 to answer the following questions: 4. How many generations will it take for this plant to completely cover the land surface of the planet,

assuming that the land surface of Earth is 1.5x 1014 m2 ?

Table 5-1. The number of plants produced by a single ____________________________ fruit through several generations, assuming that all seeds develop into mature plants that also survive and reproduce.

Generation Number of Plants in population Number of Fruits per Plant1

Number of Fruits in this Generation

Number of Seeds per Fruit

Total Number of Seeds produced by this Genera- tion2

Parental unknown 1

1 2

3

4

5

6 1This number will be the same for each row. 2Because all seeds survive and develop into mature plants, this number is equivalent to the number of plants in the population for the subsequent genera- tion.

5. How many generations will it take for this plant to completely cover the entire surface of the planet, assuming that the total surface area of Earth is 5.11 x 1014 m2?

6. What observation did you make during this activity that was similar to the observation made by Charles Darwin when he described natural selection?

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Biol 1100L Natural Selection Lab 5

Part 2. Heritable Variation

You are well aware of the diversity among human beings, but sometimes the variations among indi- viduals of other species are not as obvious. Populations present heritable variation. In this investi- gation you will study individual variations in size among members of a sample population.

Obtain 24 peanuts and measure the length of each in millimeters. Record your measurements in Table 5-2.

Determine the variability of lengths among the peanuts by determining the range of measure- ments. The range is determined by subtracting the length of the smallest individual in your sam- ple from the length of the longest individual.

Range = ____________________

Divide the range into five or six equal intervals, as shown for the example population data in col- umns one and two of Table 5-3.

7. Complete Table 5-3 by creating a frequency distribution using your own data in the columns la- beled “Actual Population.”

Table 5-2. Lengths of individuals in a sample of 24 peanuts. Individual

Length (mm) Individual

Length (mm)

Individual

Length (mm) Individual

Length (mm)

0 1 2 3 4 5 6 7 8 9

10

6-10 11-15 16-20 21-25 26-30

Interval (Length in mm)

Fr eq

u en

cy

Figure 5-1. Frequency diagram of the sample data shown in Table 5-3.

Table 5-3. Length frequency distributions of individuals in two populations of peanuts.

Example Population Actual Population

Range (mm) Individuals (#) Range (mm) Individuals (#)

6-10 2

11-15 6

16-20 10

21-25 4

26-30 3

8. Use the graph paper provided, make a frequency diagram (as shown in Figure 5-1) using the data you collected. Label the diagram Figure 5-2, provide a complete and accurate figure caption, and label the axes correctly.

9. What are the definitions for 1) variant, 2) variable, 3) variance, and 4) heritability found in the text- book?

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Biol 1100L Natural Selection Lab 5

10. Is there variation in length among the peanuts you measured? Name two factors that might be responsible for the variation in peanut lengths.

11. Of the two sources of variation, which are heritable traits that could be inherited by the next gen- eration of peanuts?

12. Which of the sources of variation is important for evolution?

13. Describe an experiment you could perform to determine if the variation you observed is heritable.

14. What observation did you make during this activity that was similar to the observation made by Charles Darwin when he described natural selection?

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Biol 1100L Natural Selection Lab 5

Table 5-4. Change in population size of three types of beans (black, white, tan) after four generations of reproduction while exposed to hunting.

Generations

1 2 3 4

B la

ck B ef

or e

20

A fte

r

W hi

te B ef

or e

20

A fte

r

Ta n B ef

or e

20

A fte

r

Part 3. Reproductive Success

In this activity, we will investigate the fate of beans that vary in color when they are being actively “hunted”. We will assume that hunting is a form of selection and that variation in bean color is heritable. This exercise will demonstrate that individuals within a population can have an unequal reproduc- tive success (differential reproductive success).

Collect three cups (one with 20 black beans, the other with 20 tan beans, and the final with 20 white beans) and a piece of carpet.

15. What color is your carpet?_____________________________

16. What is your hypothesis and prediction?

One person in the group will track of the number of beans of each color. This person is the bean counter. Each remaining team member is a bean hunter.

The bean counter will mix the three bean types together in one cup. The hunters should now close or cover their eyes while the bean counter pours the beans onto the

carpet and spreads them randomly over the entire surface. When the bean counter, says “hunt!” the hunters must open their eyes, quickly take two beans (one

with each hand), place the beans to the side of the carpet, and close their eyes again. The bean counter will quickly rearrange the

beans on the carpet and then once again give the hunters the signal to hunt.

This process will be repeated until a total of 40 beans have been removed from the carpet by all the hunters combined.

17. In the “After” rows of Table 5-4, Record the num- ber of beans of each color remaining on the car- pet.

Before you continue, assume that: • Beans are asexual. They do not need to

mate and produce offspring with another bean.

• Beans breed true. A tan bean produces only tan offspring, a black bean produces only black offspring, etc.

• Each surviving bean has three offspring. • The parent bean dies after reproducing.

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Biol 1100L Natural Selection Lab 5

For example, if you have 15 tan beans, 4 white beans and 1 black bean left after hunting, the next generation will have 45 tan beans (15 x 3), 12 white beans (4 x 3), and 3 black beans (1 x 3). Calculate the number of offspring of each color of bean left on the carpet. This will be the second

generation of beans (generation 2 column, “Before” row).

18. Record the values in the column for generation 2 and the “Before” row of Table 5-4.

Collect the number of beans for each color that you calculated for question 15. You should once again have 60 beans.

Repeat the full procedure until you have completed the table for all generations.

19. Which bean type was represented more than the other types after four generations of selection?

20. Why is the assumption that bean color is heritable important?

21. Based on the observations made while completing activities two and three, state the “inescapable conclusion”.

22. Briefly describe a scientifically verified example of natural selection. See textbook.

6-1

Biol 1100L Evolution of Human Skin Color1 Lab 6

Ultraviolet (UV) light is electromagnetic radiation having a wavelength in the range of 10 nm to 400 nm (Figure 5-1). The wavelength is shorter than that of visible light, but longer than X-rays. UVA (315-400 nm), UVB (280-315 nm), and UVC (100-280 nm) can all damage collagen (important skin and hair portien) and vitamin A. UVA can cause indirect DNA damage Ozone in the ozone layer fil- ters out UV wavelengths from about 200 to 315 nm but enough UVB still makes it through to cause sunburn and direct DNA damage. But UVB between 295 and 297 nm is required by humans. UVB photons are needed to sustain skin photosynthesis of vitamin D3 in low-UVB environ- ments, and resulted in the evolution of depigmented skin. However, too much UV radiation can cause problems. Dark pigmentation is necessary to protect folate. Photoly- sis of folate is caused by UV radiation and by oxygen free radicals generated by UVA. Cell division, DNA repair, and melanogenesis all compete for folate; under high UV ra- diation conditions and poor diet this competition can be severe.

Part 1: Skin Cancer

“Stop it!” called Tatiana, playfully. Her boyfriend, Zach, was inspecting her skin very carefully. “Look,” he answered her, his voice taking on a more serious tone.

“Today a woman walked into the clinic for her annu- al physical. Everything about her seemed fi ne. She leads a balanced lifestyle, she eats well, she exer- cises: she’s healthy! But as she was about to leave, I noticed a mole on her arm. It had many of the warn- ing signs of skin cancer. So, I removed the mole. This woman now has to wait for the lab results to see if it was cancerous. If it is, maybe we caught it early

Name:_______________________________ Section:____

Figure 6-2. Examples of skin cancer from the American Academy of Dermatology.

Figure 6-1. The electromagnetic spectrum in nanometers. Ultraviolet light has wavelengths between 10 and 300 nm.

enough to treat it, and maybe not. Either way, her life is changed. I just want to make sure you don’t have any suspicious moles (Figure 6-2), okay?”

Tatiana relented and allowed Zach to examine her skin. She asked: “Do only white people get skin cancer?” “No, people of all skin tone can get skin cancer, but it does occur more frequently in Caucasians.” 1. What are the causes of skin cancer?

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Biol 1100L Evolution of Human Skin Color1 Lab 6

2. Why are Caucasians more at risk of skin cancer than other populations?

3. At what age does skin cancer typically occur? Is the incidence of skin cancer greater in youth or old age?

Part 2: Pigmentation and UV Light

Humans were initially lightly pigmented. About seven million years ago, humans and chimpanzees shared a common ancestor. Since that time, the two species have evolved independently from one another. It is generally assumed that chimpanzees changed less over that time period than humans— because they have remained in their original environment. Chimpanzees are therefore often used as a surrogate to make inferences about the physical and behavioral attributes of our common ancestors. The skin of chimps is light and covered with hair. From this observation, it has been inferred that our earliest ancestor was also probably light-skinned and covered with hair. Since humans and chimps diverged, humans left the protection of trees and adapted to a new environment (the open savannah). This change in habitat required several adaptations. Life on the savannah provided little shade and so little protection from the sun, and required a more active lifestyle (i.e., hunting as opposed to pick- ing fruits). It is also hypothesized that the social interactions and strategizing required for successful hunting favored the development of a large brain, which consumed a lot of energy and generated heat. An increased number of sweat glands and loss of body hair evolved to dissipate heat. This created a new problem, as the light skin became exposed and vulnerable to the sun’s damaging ultraviolet (UV) radiation.

A. Melanin: Natural Sunscreen Skin cells that produced a pigment called melanin were advantaged because melanin is a natural sunscreen; it absorbs the energy of UV light and shields cells from the radiation’s harmful effects. Such cells were favored in evolution and now all human skin cells can produce this pigment. People vary in their skin tone due to differences in the distribution, quantity, size, and type of melanin found in their skin cells. As you might suspect, people with dark skin tend to have larger and more numerous melanin-containing particles in their skin. This provides protection from the sun’s UV rays. Many genes are known to affect the production of melanin and cause skin color variation in humans. While skin color is an inherited characteristic, the fact that many genes code for this trait explains why children do not always exactly match their parents’ skin tone. Tanning is the process of producing more melanin in the skin in response to ultraviolet exposure, and does not require a change in the genetic code (if a parent gets a tan, the off spring will not be more pigmented).

Why are human populations differently pigmented? What caused the evolution of an array of different skin colors?

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Biol 1100L Evolution of Human Skin Color1 Lab 6

4. Does the amount of UV light reaching the Earth vary in a predictable manner (Figure 6-3)? If so, describe the pattern you observe.

5. What latitude receives the greatest amount of UV light (Figure 6-3)? The least?

6. Based on these data (Figure 6-3), where might you expect to find the most lightly pigmented and most darkly pigmented people on the planet? Be as specific as you can.

Figure 6-3. Distribution of UV Light across the Globe. A map of the world on which the UV-light Index has been superimposed. The latitudes are shown on the left (latitude helps define a location on Earth, specifically how far north or south of the equator a site is). Figure obtained from the National Oceanic and Atmospheric Adminis- tration. Graph retrieved 18 October 2009 from http://www.cpc. ncep.noaa.gov/products/stratosphere/uv_index/ gif_fi les/uvi_world_f1.gif. Th is U.S. Government material is not subject to copyright protection within the United States.

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Biol 1100L Evolution of Human Skin Color1 Lab 6

7. Provide a rationale to your answer above (i.e., why did you think that more darkly pigmented people would be found in those areas)?

B. Distributions of Skin Color

8. Interpret Figure 6-4 and the trend it describes. A. Is skin reflectance randomly distributed throughout the globe? If not, how would you describe the

pattern? B. Restate your findings in terms of skin color and UV light (instead of skin reflectance and latitude). C. How closely do these findings match the predictions of your hypothesis (Question 6)? D. Some populations have skin colors that are darker or lighter than predicted based on their loca-

tion. Their data point falls somewhere outside of the line shown in (Figure 6-4). What might ex- plain the skin color of these exceptional populations? Propose a few hypotheses.

E. Hypothesize why different skin colors have evolved. Based on what you know, what factor is most likely to exert a selective pressure on skin color?

Figure 6-4. The skin reflectance of populations located throughout the world. Skin reflectance is a measure of pigmentation. The more a skin reflects light, the lighter it is in tone. Panel B of Figure 2 in Barsh (2003). Graph originally captioned as “Summary of 102 skin reflec- tance samples for males as a function of latitude, re- drawn from Relethford (1997).” © 2003 Public Library of Science. This is an open-access article distributed under the terms of the Public Library of Science Open- Access License, which permits unrestricted use, distri- bution, and reproduction in any medium, provided the original work is properly cited.

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Biol 1100L Evolution of Human Skin Color1 Lab 6

9. Hypothesize why different skin colors have evolved. Based on what you know, what factor is most likely to exert a selective pressure on skin color?

Part 3 – Natural Selection and Evolution of Skin Color

Based on the information provided so far, it seems reasonable to hypothesize that darker skin evolved to protect against the harmful effects of UV light. In particular, individuals who lacked optimal pigmenta- tion for tropical latitudes had a greater risk of skin cancer and death. Until fairly recently, this was the leading hypothesis about the evolution of skin color. However, there is a problem with this hypothesis. Let’s see if you can find it. Here is some basic information on evolution by natural selection. Evolu- tion is a change in the gene pool of a population of organisms from generation to generation. Natural selection is but one of several mechanisms by which evolution can take place. Through natural selection, populations evolve and become adapted to their specific environment. Natu- ral selection will occur if the following three conditions are present:

• Variation: The organisms in the population vary with regard to a trait. • Heredity: Variation in the trait has a genetic component transmissible to off spring. • Selective Pressure & Differential Reproductive Success: Some traits increase the odds of

surviving to reproductive age and successfully producing and rearing off spring in a given envi- ronment. Such traits are more adaptive.

Those organisms having the better adapted trait leave more off spring behind—they are “naturally selected.” In the next generation, this adaptive (and inherited) trait will increase in frequency and will be represented in a greater proportion of the population. At this point, the genetic makeup of the popu- lation is different from that of the starting population: the population has evolved. Evolution is really a “number’s game”: the organisms that reproduce the most “win” because their traits will be dispro- portionally represented in the next generation. Note also that individuals do not evolve. They either breed more effectively or less effectively, depending on already existing differences in their traits. Only populations evolve or change over time. 10. Review your answer to Question 3. Keeping your answer in mind, how strong a selective pressure do you expect skin cancer (UV-induced mutations) to exert on reproductive success?

11. Based on this information, does your hypothesis about the evolution of skin color (Question 9) seem likely? Why or why not? How does skin color meet, or fail to meet, the three requirements of natural selection outlined above?

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Biol 1100L Evolution of Human Skin Color1 Lab 6

A. Folate: A Different Way of Looking at It

Since skin cancer tends to occur after age 50, it has little impact on reproductive success. Conse- quently, skin cancer probably exerted little pressure on the evolution of skin color. Some other factor must explain the range in pigmentation that is observed in the human population. For years, this fact was overlooked by the scientific community, and the consensus was that dark skin had evolved as pro- tection against skin cancer. In 1991, the anthropologist Nina Jablonski was skimming though scientific journals when she came upon a 1978 paper by Branda and Eaton.

Branda & Eaton’s paper measured the folate concentration in two human test groups. This paper in- vestigated the effects of sunlight on an essential chemical found in our body: folate or folic acid (one of the B vitamins). Folate is an essential nutrient for DNA synthesis. Folate levels in humans are deter- mined by two things: (1) dietary intake and (2) destruction through alcohol consumption or ultraviolet skin exposure. Since cells reproduce at a fast pace during pregnancy (and hence, there is a lot of DNA replication), the highest levels of folate are needed during pregnancy. Folate deficiencies during preg- nancy can lead to anemia in the mother and malformations of the nervous system (neural tube defects in particular), gastrointestinal system, aorta, kidney, and skeletal system in the fetus. There is also a high rate of miscarriages. In addition, folate deficiency has been linked to spermatogenesis defects (inability to form sperm) in mice and rats (Mathur et al., 1977), and anti-folate agents are being inves- tigated as a form of male contraceptive (Cosentino et al., 1990). The results are shown in Figure 5-5. One group (called “patients”) was exposed to UV-light, while “normals” were not so exposed. Folate was iso- lated from blood and placed in a test tube. Half of the test tubes were exposed to UV light for 1 hour. The folate concentration in the samples was measured. The results are indicated in Table 6-1. Patients were exposed to UV light for at least 9 hours every day for 3 months. The difference between the two groups was statistically significant (P< 0.005). Brackets rep- resent the standard error of the mean.

Figure 6-5. Levels of blood folate (nanograms per nanoliter) in people exposed and not exposed to UV light. From Branda, R.F., and Eaton, J.W.(1978). Skin color and nutrient photolysis: An evolutionary hypothesis. Science 201: 625–626.

Table 6-1. Folate concentrations in four samples of human plasma before and after a 1 hr exposure to UV light in vi- tro. From Branda, R.F., and Eaton, J.W.(1978). Skin color and nutrient photolysis: An evolutionary hypothesis. Science 201: 625–626.

12. Based on Branda and Eaton’s results (Figure 6-5), what is the apparent effect of UV light exposure on blood folate levels?

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Biol 1100L Evolution of Human Skin Color1 Lab 6

13. What is the apparent effect of UV light on folate levels in these test tubes? __________________

14. How is folate linked to natural selection?

15. All other things being equal, which skin tone would you expect to be correlated with higher levels of folate? _________________________________________________________________________

16. Based on this new information, revise your hypothesis to explain the evolution of human skin color.

7. What would happen to the reproductive success of: A. light-skinned person living in the tropics? _________________________________________ B. light-skinned person living in the polar region? _____________________________________ C. dark-skinned person living in the tropics? _________________________________________ D. dark-skinned person living in the polar region? _____________________________________

18. Predict the skin tones expected at different latitudes, taking folate needs into consideration. Use the world map (Figure 6-6) to indicate the skin tone expected at each latitude (shade the areas where populations are darkly pigmented).

Figure 6-6. Prediction of skin tone distribution with respect to foalte needs. Map of the world from http://commons. wikimedia.org/wiki/File:World_map_blank_black_lines_4500px_monochrome.png, CC BY-SA 3.0.

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Biol 1100L Evolution of Human Skin Color1 Lab 6

19. Can folate explain the variation and distribution of light- and dark-skinned individuals around the world?

B. Vitamin D: Still Another Way of Looking at It

Folate can explain why dark skin evolved, but it cannot account for the evolution of light skin. Another factor must be at play. Vitamin D3 is essential for normal growth, calcium absorption, and skeletal de- velopment. It is particularly important in maintaining and repairing healthy bones and teeth. Its role in calcium absorption makes it essential in maintaining a healthy heart, blood clotting, a stable nervous system, and an effective immune system. Deficiencies manifest themselves as rickets (softening of the bones), osteoporosis, and osteomalacia. It can lead to death, immobilization, or deformities. Women have a higher need for this nutrient during pregnancy and lactation due to their need to absorb calcium to build the fetal skeleton. Humans can obtain vitamin D3 by one of two means. They can consume it in certain foods (fish liver oil and to a lesser extent, egg yolk). Alternatively, skin cells have the ability to synthesize it from a cholesterol-like precursor. However, this process requires the energy of UV radia- tion. Theoretical research on the dose of ultraviolet radiation required to produce vitamin D3 suggests that for moderately to darkly pigmented individuals (Figure 6-7):

• There is enough sunlight reaching the tropics (approximately 5° north of the Tropic of Cancer to approximately 5° south of the Tropic of Capricorn) to meet all of a human’s requirement for vita- min D3 throughout all months of the year. Th is is indicated by the dotted area on the map. Note: Vitamin D3 is not produced to toxic levels when high quantities of sunlight are present.

• In the area indicated by narrowly-spaced obliques, there is not enough ultraviolet light to synthe- size vitamin D3 in human skin for at least 1 month of the year;

• In the area indicated by widely-spaced obliques, there is not enough UV light for the skin to syn- thesize vitamin D3 in any month of the year

Figure 6-7. Amount of UV light available to synthesize recommended levels of vi- tamin D for a moderately to darkly pigmented person at various locations around the world. Source: reprinted from Th e Journal of Human Evolution 39(1), Jablonski, N.G., and G. Chaplin, Th e Evolution of human skin col- oration, pp. 57–106, Figure 2, copyright.

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Biol 1100L Evolution of Human Skin Color1 Lab 6

20. How is vitamin D linked to natural selection?

21. Which skin tone allows someone to maintain the recommended level of vitamin D? ________________

22. Based on this new information, revise your hypothesis to explain the evolution of the variation and distribution of human skin color.

23. Taking only vitamin D into consideration, what would happen to the reproductive success of: A. light-skinned person living in the tropics? _________________________________________ B. light-skinned person living in the polar region? _____________________________________ C. dark-skinned person living in the tropics? _________________________________________ D. dark-skinned person living in the polar region? _____________________________________

24. Predict the skin tones expected at different latitudes, taking only vitamin D needs into consider- ation. Use the world map (Figure 6-8) to indicate the skin tone expected at each latitude (shade a region to represent pigmented skin in that population).

Figure 6-8. Prediction of skin tone distribution with respect to Vitamin D3 needs. Map of the world from http:// commons.wikimedia.org/wiki/File:World_map_blank_black_lines_4500px_monochrome.png, CC BY-SA 3.0.

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Biol 1100L Evolution of Human Skin Color1 Lab 6

25. Can vitamin D alone explain the current world distribution of skin color? ____________________

Evolution by natural selection is a process of compromise in which costs are minimized and benefits are maximized. Both light and dark skins have costs and benefits. As you are probably now realizing, adopting one level of pigmentation has trade-offs.

26. Using principles of natural selection, predict the skin tone expected at different latitudes, taking ul- traviolet exposure, vitamin D, and folate needs into consideration. Use the map (Figure 6-9) to indicate skin tone patterns at different latitudes (shade regions where populations are expected to be darkly pigmented).

Figure 6-9. Prediction of skin tone distribution with respect to both folate and Vitamin D3 needs. Map of the world from http://commons.wikimedia.org/wiki/File:World_map_blank_black_lines_4500px_monochrome.png, CC BY-SA 3.0.

27. Are UV light, vitamin D and folate needs sufficient to explain the current world distribution of skin color? ___________________________________________________________________________

28. How might you explain that Inuits, living at northern latitudes, are relatively dark-skinned (much more so than expected for their latitude)? Propose a hypothesis.

29. Conversely, Northern Europeans are slightly lighter-skinned than expected for their latitude. Pro- pose a hypothesis to explain this observation.

1 This lab was adapted from “The Evolution of Human Skin Color” by Annie Prud’homme-Généreux, National Center for Case Study Teaching in Science. Copyright held by the National Center for Case Study Teaching in Science, University at Buffalo, State University of New York, all rights reserved. Used with permission.