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First Primates: Expert Q&A

  • Posted 07.15.08
  • NOVA scienceNOW

On July 15, 2008, Mary Silcox answered selected viewer questions about our earliest primate ancestors, what it's like to do fieldwork, and other matters paleontological. Please note we are no longer accepting questions.

Dr. Mary T. Silcox

Dr. Mary T. Silcox is an Associate Professor of Anthropology at the University of Winnipeg, Canada. Full Bio

Photo credit: Courtesy Mary T. Silcox

Dr. Mary T. Silcox is an Associate Professor of Anthropology at the University of Winnipeg, Canada. Silcox's research program centers on understanding the earliest phases in the evolution of the Order Primates, which includes lemurs, monkeys, apes, and us. As a paleontologist, she uses fossils to answer questions about why our order branched off from the rest of mammals to take its own, unique evolutionary course. Silcox and her colleagues do fieldwork to collect fossils of early primates from Wyoming and Montana, and use both traditional methods (e.g., light microscopy) and high-tech approaches (e.g., ultra-high-resolution X-ray computed tomography) to study them. Silcox earned her Ph.D. in Anatomy from the Johns Hopkins School of Medicine in 2001 and was a postdoctoral fellow at Penn State University.

Q: Do you like doing fieldwork? What's the coolest thing you've ever found? Sophia, Baltimore, Maryland

Mary Silcox: Yes, I love doing fieldwork! Finding fossils is hard work, but when you come across the bones or teeth of an animal that no one else has ever seen, the feeling is extraordinary. I also really enjoy the camaraderie of doing fieldwork. My colleagues and I camp when we work in Wyoming or Montana, and we have a great time together. Probably my favorite thing about fieldwork is being with an interesting group of people, all working towards a common goal.

I like small things, so for me the coolest fossil I have ever found was a lower jaw of an animal called Picromomys. In the NOVA documentary, we talked about an animal called Dryomomys, which was a pretty tiny animal, only a bit bigger than a mouse. Picromomys was even smaller than that—it only weighed about 10 grams, a third the size of Dryomomys. In fact, Picromomys is in the running for the smallest primate ever known, much smaller than any primate alive today. It is also an incredibly rare animal; there are only about 10 specimens known from its family. So while the fossil I found might not have looked like more than a tiny splinter of bone with a couple of shiny dots on it, to me that's as cool as it gets!

Q: Today we see a fantastic diversity of primates inhabiting the Earth. How is the evolutionary (or phylogenetic) diversity of primates distributed across our planet? Which processes have led to the current pattern of species distribution? Paulo B. Chaves, Vití³ria, Espí­rito Santo, Brazil

Silcox: There are three main factors that affect primate diversity and distribution. The first is climate. Primates are ancestrally tree-living, fruit-eating animals. That means that they tend to be diverse and broadly distributed during periods when the world is warm and wet and there are lots of tropical forests, and less diverse and more restrictively distributed when the world is drier, colder, and less heavily forested.

The time period we were talking about in the NOVA program was a very good time to be a primate. The area in Wyoming where Jonathan Bloch was doing research, which is badlands today, was a lush tropical to subtropical forest. Just to give you some idea of how different the world was from today, there are actually primates known from the same time period that lived on Ellesmere Island! Today, non-human primates are mostly restricted to a belt around the equator where there are still tropical to subtropical forests.

There are some primate groups that can live outside of a forest, however, which brings me to the second factor that affects primate diversity and distribution: adaptation. Some primates have developed features that have allowed them to live in more sparsely forested, or even unforested, areas. Gelada baboons, for example, don't have to spend any time in the trees—they eat grass and can move very effectively on the ground. Humans are another great example of this. We certainly wouldn't be able to live in places like Winnipeg (where I live) if we were restricted to areas with tropical forest!

Geography is the third critical feature to primate diversity and distribution. The incredible diversity of lemurs on Madagascar, for example, is a product of the fact that it is separated from Africa by very deep water. Monkeys and apes never made it to Madagascar, which allowed lemurs to diversify into a broad array of different forms without facing competition from other types of primates. The same is also true of South America, where we see an extraordinary diversity of monkeys, but no apes, because they never made it across the Atlantic Ocean, at least until humans transported them there.

Q: How did the fossils get into the granite? Since granite is volcanic, how would fossils survive? Great program! Thank you. Anonymous

Silcox: The fossils that Jonathan Bloch and Doug Boyer were preparing out of rock were actually coming from limestone, a sedimentary rock, not granite. You're absolutely right—it would be surprising to get fossils like these out of granite. It's actually surprising to be finding concentrations of such well-preserved bones at all. Jonathan Bloch and his colleagues have suggested that these deposits originated with short-lived ponds that may have served as pit-traps to small animals. Small animals would get stuck in depressions in the landscape where there were ephemeral concentrations of water, and then get covered over very quickly so that they ended up preserving unusually well.

Q: Approximately where in the line of ancestors shown on the Web site [see Meet Your Ancestors] did the lineage of bonobos and chimpanzees diverge from ours? Roger Neyman, Forest Grove, Oregon

Silcox: The bonobo-chimp lineage would have branched off between Dryopithecus and Australopithecus. Dryopithecus is the closest animal we have in the fossil record to the common ancestor of African apes (gorillas, chimpanzees, and bonobos) and humans. Australopithecus is a member of our own family—we know this because it has features that show that it walked upright on its hindlimbs, which is something that none of our close primate kin can do. Our family (including Australopithecus) is thought to have branched off 5-7 million years ago from our common ancestor with bonobos and chimps.

Q: What would you say to well-educated people (college-degreed & graduate-degreed) who continue to believe the "Bible Creation Story" rather than accept overwhelming scientific evidence? Donald Gayman, Clarkston, Washington

Silcox: In my opinion, the primary cause for this debate is that people are confusing two fundamentally different ways of learning about the world. Religion has faith at its core, and faith is all about belief without questioning. Individuals who believe in a strict interpretation of the Bible have an easy answer to every piece of potential evidence for evolution—God did it.

Science, on the other hand, is about questioning everything. It doesn't depend on faith; it depends on amassing evidence to support a hypothesis, and being open to changing your mind if new evidence arises that points in another direction. Science can't answer questions about topics, like the existence of God, for which it is impossible to collect evidence. And religion can't provide us with empirical data about topics, like the evolution of humans, which belong in the realm of science. They represent fundamentally different ways of knowing, and I would say that anyone who tries to answer religious questions with science, or scientific questions with religion, is doing a disservice to both.

In terms of how I approach this when I am talking to a creationist, I think it is very important to be respectful of people's religious beliefs. All I ask is that no matter what your beliefs are, you educate yourself about the evidence that exists for evolution, and think honestly about what it means.

Q: If primates developed from a shrew-like ancestor, does this suggest that we are related also to rodents? Is this why we often use rats in genetic experiments before human testing? Ian Cameron, Calgary, Alberta, Canada

Silcox: Humans are actually fairly closely related to rodents. As I noted above, our closest living relatives are tree shrews and colugos. The next branch out is a group called Glires, which includes rodents and rabbits, so we are more closely related to rodents than we are to things like dogs, horses, cows, etc. However, shrews are actually not rodents—they belong to a group called Eulipotyphla (informally referred to as insectivores) that also includes moles and hedgehogs. We are more distantly related to this group. I think we tend to draw mouse or shrew analogies to our fossils because they are the small, furry animals that we are most familiar with. However, even though they may have looked kind of like these living animals, plesiadapiforms were their own critters, with features that we don't see in any animals alive today.

In terms of why rats are often used in genetic experiments, I think that it is mostly because they are fairly easy to breed and keep in a lab environment. Scientists' choices of research animals often have more to do with logistics than anything else—that's why we know more about the genetics of fruit flies than any other group on Earth!

Q: Thanks for your program. About when did primate and feline branches diverge? I read that our DNA is closer to cats than to dogs. Anonymous

Silcox: I'm not quite sure where you would have read this, because most modern authorities agree that cats and dogs are more closely related to one another than either is to humans and other primates. Cats and dogs are usually placed together in a group called Carnivora. This is part of a larger group called Laurasiatheria that also includes bats, hoofed animals (like cows and horses), and insectivores. We are part of a group with tree-shrews, colugos, rabbits, and rodents called Euarchontoglires. Laurasiatheria and Euarchontoglires probably branched off from one another about 90-100 million years ago, so that would be when our evolutionary path diverged from that of felines.

Q: What color were our first primates? Michael, Carlisle

Silcox: Unfortunately, it is impossible to know for sure. My guess is that the first primates were probably fairly uninteresting colors. This is because the most primitive primates alive today don't have full-fledged color vision, so we think that the earliest primates probably didn't either. Animals that can't see in full color tend to be less attractively colored than animals that can. Most mammals can't see in full color, for example, and are uninteresting shades of brown—this is obviously a contrast to birds, which can see in color, and are much more interesting hues. So our earliest kin were probably brownish or grayish in color.

Q: do you have eny monkes Natalia, Grade 1, Texas

Silcox: No, unfortunately I don't have any monkeys. On the one hand, I would love to have a monkey as a pet. Or even better a lemur, like Zoboomafoo! However, I know that it wouldn't be a very good idea. Monkeys are wild animals. Dogs and cats make good pets because humans have been breeding them to have features that make them good pets for a long time—over 10,000 years in the case of dogs. Think how much nicer a pet a dog is than a wolf! Monkeys haven't been bred to have human-friendly features, so they don't always make good pets. Also, when people go into the wild to try and capture monkeys to be pets, sometimes members of those monkeys' families get hurt in the process. Therefore, although I would love to have a monkey or a lemur as a pet, I make do with going to visit my favorite primates at my local zoo.

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