Are humans more closely related to gorillas or baboons? To understand how living things are related to each other, evolutionary biologists sort out
which traits are shared or different between different species. Using this information, they can put together a “tree of life”. A tree of life is a lot like a family tree except that instead of showing how family members are related a tree of life shows how different species are related. Generally, the more traits two species share, the more closely related they are to one another. Based on the tree of life to the left, do you think humans are more closely related to gorillas or baboons? Hint: the more branches there are between species, the more distantly related they are to one another.
To demonstrate how a tree of life (or phylogeny) is built, the EOG brought primate skulls to the New Haven Cooperative High School’s AP Biology Class. We asked the students to look at the different primate skulls and describe their traits. After all the observations were made, the students worked together as a group to assemble the tree of life for these primates. Using observations and measurements of only a few traits (such as presence or absence of a forehead, tooth number, tooth shape, how the skull connects to the vertebral column, and the presence or absence of a chin) the students were able to reconstruct the evolutionary relationships between howler monkeys, baboons, gorillas, Homo erectus, and humans. In doing this, the students learned how evolutionary biologists are able to sort out the evolutionary relationships among different species. The kids also learned which single trait is unique to modern humans as compared to other primates (including other extinct human species): the presence of a chin!
We visited the Common Ground After-School Program to teach the students about how animals have evolved to avoid being eaten by predators. For a detailed description of the activity see: Night at the Peabody 2012.
As in our activity at Common Ground Animal Adventure Camp: Week 1, we ran an activity at the Peabody Museum summer camp that emphasized the fact that animals evolve mouthparts that allow them to eat the food that is available to them in their environment.
We introduced mouthpart evolution by asking the campers to look at pictures of different types of animal skulls. By looking at the different skulls, the campers were able to infer what types of food different animals eat. We then played a game to illustrate how animal mouthparts evolve.
Carrot Island and Bean Island
Campers were randomly assigned to be a bird with a chopstick beak or a bird with a skewer beak. We started the game with three skewer birds and three chopstick birds on “bean island” and three skewer birds and three chopstick birds on “carrot island.” Carrot island had carrots for food and bean island had dried beans for food. We used flour to draw the island perimeters in the grass.
Which type of bird do you think collected the most food on each island?
After each round of the game, the group on each island that collected more food gained a new member to their population. If the skewer birds collected more carrots on carrot island, the skewer bird population grew by gaining a new teammate. In contrast, if the chopstick birds did not collect as many carrots, they lost a member of their population. The same applied to bean island. At the end of the game, we found that the population on carrot island evolved skewer beaks, whereas the population on bean island evolved chopstick beaks.
Not only does this demonstrate how mouthparts evolve to allow animals to successfully take advantage of the food available to them, but it also shows that evolution depends on the environment. In short, there is not one “right” type of mouthpart. Rather, different types of mouthparts are advantageous under different environmental conditions and this leads to the evolution of diverse traits.
We ended the activity by relating the results of the game the famous example of beak evolution in the Galapagos finches (see Animal Adventure Camp: Week1 for a detailed description of Galapagos finch evolution).
We ended the activity by asking the campers to take one last look at their chopsticks or skewers. As it turns out, some of the chopsticks and skewers had a pattern drawn on them and others did not. We asked the campers whether having a pattern on their faux mouthparts influenced how much food they were able to collect. The campers told us that whether there was a pattern or not on their mouthpart did not influence how hard or easy it was to collect food.
We explained to them that just like the pattern on the skewers or chopsticks did not make it harder or easier to collect food, in nature, animals often have traits that are neutral, rather than adaptive. Take for example, eye color in humans. Some people have brown eyes and some people have blue eyes, but people with brown eyes don’t see any better than people with blue eyes. So, in humans, eye color is an evolutionarily neutral trait.
Why are Some Animals so Ornate?
Throughout nature, we see that some animals have very elaborate traits, while others are more subtle in appearance. Take for example, the peacock. Why is it that male peacocks have such huge, colorful tails, but a sparrow is relatively drab in appearance and has such a short tail?
We asked the campers at Common Ground to think about this question and write down some possible answers. Here is one camper’s insightful answer:
This camper was right on the ball! It is true that in cases in which animals are very ornate this is often to attract a mate. In these animals, the more ornate you are, the more likely you are to mate. This is one component of what scientists call sexual selection. Scientists have demonstrated this phenomenon in many experiments. One of the most famous experiment involved changing the tail length of male widowbirds, birds with very long tails, and then recording which males mated the most. It turns out that in the widowbirds, females prefer males that have long tails. The scientists discovered this by changing the tail lengths of widowbirds and then recording which males mated the most, they were able to show that the males with the longer tails mated the most. To read the original study click here
But the question remains: Why are only some animals ornate, while others, like the sparrow, are so drab? To try to answer this question we played a game.
Capture the Tail
In this game, campers were assigned to play the role of a long tailed bird, a short tailed bird, or a predator. To simulate the different length tails, we clipped long and short ribbons to the campers shirts. We then played a “capture the tail” game. If the predators could pull off the tail, then the “bird” was “out.” What do you think happened?
Well, not too surprisingly, the predators had a much easier time capturing the long tails than the short tails. What does this tell us about why some animals might have long tails, while others have short tails? One reason is that, just like in the game, having a long tail makes an animal more at risk for predation.
After the game, we talked about the results with the campers and we explained that in many cases, very ornate animals tend to live in places where there are very few predators. Since these animals are at low risk of predation, they are able to evolve these ornate traits. In contrast, a sparrow, for example, is confronted with all kinds of predators: hawks, cats, dogs, etc. Therefore, it is important for the sparrow to be inconspicuous. That’s why sparrows tend to be brown and small and have short tails.
We also explained to the campers that sometimes only one of the parents is ornate, while the other is drab in appearance. These differences often have to do with which parent takes care of the babies. If the mother takes care of the babies, but the father doesn’t, it is important that she doesn’t draw too much attention to herself because this could attract predators that might not be harmful to her, but could attack the small babies. Usually, when the male and female of a species look very similar, both parents take care of the babies. Compare the pictures of the male and female bird of paradise to the male and female sea gull. Who do you think takes care of the babies in these two different types of birds?
Why Do Animals Have Different Types of Mouths?
Birds have beaks, cats have sharp teeth, and rabbits have buckteeth. Why do different animals have such different types of mouths? Animals have different types of mouths because different animals eat different types of food. Imagine if you wanted to eat a carrot but all you had was a straw. It would be pretty difficult to eat the carrot using a straw, a fork would work much better. On the other hand, if you wanted to drink some juice, it would be a lot easier to drink it using a straw than a fork. Animals have evolved mouths that help them eat their food so they can grow strong, survive, and have babies. For example, hummingbirds have a straw-like beak that they use to drink nectar from plants, while rabbits have big front teeth that help them nibble carrots. A rabbit would be in trouble if it tried to eat a carrot using a hummingbird beak!
By looking at different animal’s mouths, we can guess what they eat. Take a look at the animal skull pictures below. What do you think these animals might eat? Hint: think about how the animal’s mouth could act like a utensil. Did you notice that the bird’s beak looks kind of like tweezers? This tweezer-like mouth is very important for the bird because it helps it pick up small seeds from the ground. The bird’s mouth looks pretty different from the cat’s mouth, huh? The cat’s sharp teeth wouldn’t be as useful for picking up little seeds in the grass. However, the cat’s sharp teeth are important for the cat because cats eat meat and they need sharp teeth to cut through the meat, kind of like a knife.
What Can Skulls tell us about what Different Animals Eat?
At the Common Ground Animal Adventures Camp, we demonstrated how different animals have evolved different types of mouths by showing the campers skulls of cats, pigs, birds, orangutans, gorillas, humans, turtles, Neanderthals, etc. and asked them to look at the mouths of the skulls and try to figure out what the animals might eat.
The Best Beak for Beans
Next, we played a game with the campers to demonstrate how different mouthparts have evolved in different animals. In this game, we separated the campers into 3 groups and gave each group a different utensil: forks, chopsticks, or wooden skewers. We then scattered dried beans on the ground and had the teams use their utensils to collect as many beans as they could in a five-minute period. When the five-minutes were up, each group tallied up the number of beans they collected. The team that collected the fewest beans went “extinct” and so the members of this team had to join one of the other teams. We played the game for several rounds and in the end one team collected the most beans…by a long slide! Do you think it was the spoon team, the chopstick team, or the skewer team? We finished up by the activity by relating the outcome of the game to the real life case of bird beak evolution in the Galapagos Finches.
A Real Life Example of Evolution: THe Galapagos Finches
Scientists think that a very, very, long time ago there was originally only one type of finch on the Galapagos islands. This one type of finch flew to the islands from the mainland. Once on the islands, the finches stayed, they found food to eat and had babies. These baby finches shared a lot of traits with their parents, however, some of the babies had slightly bigger beaks and some had slightly smaller beaks. As it turned out, big beaks were slightly better for eating big seeds, while small beaks were slightly better for eating small seeds. Over a very long time the finches with big beaks evolved even bigger beaks, that were even better for eating the big seeds on one island, and the finches with the small beaks evolved beaks that were even smaller and even better for eating small seeds on different island. Eventually, these finches evolved into different species. Now there are 15 different finch species on the islands.
The Galapagos finches were first found by Charles Darwin, the scientist that discovered the theory of evolution, which is why we sometimes call them “Darwin’s Finches.” Darwin discovered these finches a long time ago, in the 1800’s, but even today, scientists are going out to the Galapagos Islands to study these finches so that we can better understand how evolution works.
If you are interested in learning more about current research on the Galapagos finches then check out these links:
What makes Living things both Similar and Different?
Why do some people have brown eyes and other people have green eyes? Why do dogs walk on four legs and birds walk on two? Why do horses eat grass and spiders eat flies?
The simple answer to these questions is that all living things, whether they are your best friend or a humpbacked whale, are different from one another.
But what makes us all different?
It turns out that there is a special genetic code that is in all the cells in our bodies and this code is different in almost all living things.
Still, you have probably noticed that even though you are different from your best friend, you are more similar to each other than either of you are to a jellyfish. This is because there are more differences between your genetic code and a jellyfish’s genetic code than there are between you and your friend.
Evolutionary Biologists are interested in trying to understand how changes in the genetic code have made us different from jellyfish, jellyfish different from snakes, snakes different from ladybugs, and so on.
One of the reasons Evolutionary Biologists are so interested in understanding how changes in the genetic code can lead to changes in the characteristics of living things is because scientific research has shown that all living things have evolved from a common ancestor that lived on the earth about 3.8 billion years ago. This means that a very, very long time ago there was only one living thing on earth, but gradually, over many, many, many, many, many, many, many, many, years, mutations that changed the genetic code gave some of these living things new characteristics that helped them to survive and reproduce in new environments and this process led to the evolution of all the diverse living things on earth.
To illustrate how a small change in the genetic code can dramatically change the behavior of an organism, our group brought nematodes to the Science Fair Sunday at “The Children’s Museum” in West Hartford.
Nematodes are round worms that can be either free living or parasites. We used the free-living nematode Caenorhabditis elegans for our demonstration. C. elegans commonly lives in decomposing organic matter, where it eats bacteria. Under laboratory conditions, these worms can display two very different behaviors. Either they eat as a group (clump) and move constantly from food patch to food patch (disperse), or they like to eat alone and stay in the first place they find food. In addition, worms that clump are pickier about what they eat, whereas the solitary foraging worms don’t care.
During our activity, children were allowed to see the differences between these two types of living worms through a compound microscope. We then explained to them that a single mutation in the genetic code (a change in the DNA from T to C) was responsible for the striking behavioral differences. We used a poster board to illustrate in more detail how differences in the genetic code makes each organism unique, how differences between species arise from differences in the genetic code, and how, thanks to our shared ancestry, there are common features to all living organisms.
As part of the “Big Food: Health, Culture, and the Evolution of Eating” exhibit at the Peabody we set up a booth at the Peabody Family Day to demonstrate how eating can drive evolution
What we decide to eat can lead to the evolution of our food. For example, in some places, there are rules about fishing that say that fishermen are only allowed to catch fish that have reached a certain size and the littler fish have to be thrown back. Since the big fish are being caught, but the little fish are being thrown back, this can lead to the evolution of smaller fish. How do you think this happens? Well, since the small fish are never caught and eaten they escape human predation. As long as the smaller fish have babies that are also small, none of the small fish will ever be caught, and overtime, the population of fish will be made up of all small fish.
To illustrate the way our eating habits can lead to evolution, we played a game with the visitors to the Museum. We gathered groups of kids and their parents and we gave them the option to chose one pretzel from a “population” of pretzels. Some of the pretzels were small and some were large. In general, people chose the larger pretzels over the smaller ones. After everyone had chosen a pretzel, we asked them to describe how the pretzel “population” had changed. It was immediately obvious that the pretzel “population” was now dominated by small pretzels. If these small pretzels had actually been fish, then the small fish might start mating with each other and have babies that would also be small fish, and eventually the population would be made up of mostly, or all, small fish. Any fish that grew too large would be caught and fished out of the population. Eventually, fishers would not be able to fish at all because all the fish would be too small. What do you think would happen if the fishermen threw back more of the large fish?
To show visitors how predation can lead to the evolution of camouflage, we played the butterfly camo game described in detail in the “Night at the Peabody” post.
Since different animals eat different types of food, they have evolved different types of mouth parts. We demonstrated how very different mouth parts can be by bringing in a bunch of live invertebrates for the kids and parents to feed. We brought in caterpillars, moths, crabs, and tarantulas. By putting the caterpillars under the microscope, thefamilies could watch up close to see how the caterpillars use sharp, teeth-like, mandibles to crunch away at their food. They use their mandibles almost like gardening shears! In contrast, the moths (the grown up caterpillars) have a long-straw like mouth called a proboscis that they use to drink nectar from flowers. To simulate nectar, we fed the moths a mixture of sugar and water so we could watch them drink with their proboscis. The kids were also given the opportunity to feed crabs with microscopic sea monkeys and watch as the crabs used both their claws and their filter-like mouth parts to gobble up the tiny sea monkeys. But the real hit of the feeding zoo had to be Cynthia and Megan: two very polite tarantulas!
The kids and parents were able to feed Cynthia and Megan crickets and watch how they used their poisonous, syringe-like, fangs to paralze their prey. Once Cynthia and Meghan had had their fill of yummy crickets, they were gracious enough to let each and every kid confront their arachnophobia (or curiosity) by holding them and petting them. Besides learning about how different animals use different mouth parts to eat their food, the visitors to “Family Day at the Peabody” also learned that there are some pretty nice spiders in the world.
Sponsored by the John’s Hopkins Center for Talented Youth, April 14, 2012
Strategies to Escape Ending up on a Dinner Plate
How do living things avoid getting eaten? One way critters can escape predators is to hide by blending in with their surroundings, a strategy called camouflage. For example, if a butterfly is black and rests on a black tree trunk, then it will be able to hide better than if the butterfly is white. If a bird with a taste for delicious butterflies came along, it would have a much easier time finding the white butterfly than the black butterfly.
Camo Relay Race
To demonstrate how butterflies use camouflage to escape predation we played a game.
For this game, we spread a mixture of hundreds of white and black paper butterflies over either white or black construction paper sheets. Each team was given a set of tweezers and a plastic cup. One by one, each team member had to run towards the table where the butterflies laid and, using their tweezers, pick three butterflies as fast as possible, then run back and hand the cup and tweezers to the next person. The game ended after 5 minutes and each team was asked to count the total number of butterflies picked, and the proportion of white and black butterflies in the cup. After writing the numbers on the board, we discussed the results as a group, allowing the kids and parents to make the connection between the color of most of the butterflies the team picked, and the color of their background. What do you think they found?
After the camouflage relay race, we showed the kids and parents pictures of the famous case of industrial melanism in the Peppered moth and explained that this is a real life example of evolution.
A real Life Example of evolution: Industrial Melanism
In the case of industrial melanism, smog from factories during the Industrial Revolution killed the white lichen on the trees, turning them from white to almost black. Before then, the white lichen on the trees gave the bark a white appearance and the white Peppered moths were able to escape getting eaten by camouflaging on them. When the trees darkened because of the pollution, the white moths became easy targets for predators and the few lucky black moths in the population suddenly had an advantage because they were now able to hide on the black trees. These black moths survived to have more black babies, and their black babies had black babies, and so on, until pretty soon the population of moths evolved to become black!
I Spy a Butterfly
To illustrate how well camouflage works as a way to hide from predators, we played an “I spy” game in which the kids were shown an image of a nature scene and asked to find the well-hidden butterfly or insect. When the kids thought they could see the insect they raised their hand and the first one to do so came to the front and pointed out to the rest of the group where the hidden insect was in the image. To see if they were correct, we then removed the background so everyone could plainly see the insect and where it had been hiding.
Hide and Freak
Camouflage is not the only way that animals are able to escape getting eaten. Another way that an animal can escape predation is by startling the predator. In this case, an insect with a drab appearance looks like a non-threatening meal to the predator. However, when the predator comes along, the insect opens its wings and reveals a startling coloration or pattern that causes the predator to hesitate long enough for the insect to fly away. This is called a startle response.
Insects also use color to warn predators that they are poisonous. For example, the Monarch butterfly extracts toxins from its food when it is a caterpillar and it stores these toxins in its body. A predator that eats a poisonous monarch gets sick and spits out the butterfly. Eventually, the predator learns to avoid brightly colored insects because they might be poisonous. This is called warning coloration. “Might be poisonous” is an important concept here because some insects are brightly colored but are not poisonous. These insects trick the predator into thinking they are the poisonous type so the predator won’t eat them. This is called mimicry. One of the most famous examples of mimicry is the case of the monarch and the viceroy. Monarchs are poisonous and so the Viceroy mimics the Monarch in order to scare off predators. For a long time, scientists thought that the Viceroy was not poisonous and so it tricked predators into not eating it by looking like the Monarch. This type of mimicry is called Batesian Mimicry. Recently, however, scientists have found evidence that the Viceroy may actually be poisonous too. Therefore, it may be the case that the Monarch and Viceroy mimic each other in order to send a clear message to predators: Orange and black coloration=poisonous! This type of mimicry is called Mullerian Mimicry.
To show the kids examples of all the types of strategies insects use to avoid getting eaten, we showed them specimens of real insects from the Yale Peabody Museum.