Karen Sears explores the history that shaped life as we know it.
Let’s look past the flesh-eating beetles, shall we, and focus on the big picture of what’s happening in the laboratory of Karen Sears: She’s examining the evolutionary forces that influence what she calls the “morphological diversification” of mammals, from ear bones to limbs....
Okay, so maybe it isn’t so easy to look past the flesh-eating beetles. Truth be told, the work of Sears, a professor of integrative biology in LAS, is not for the squeamish, nor can you call it a typical career path. Sears’s mother likes to recall how, when Sears was just a girl, she was asked what she wanted to be when she grew up.
“A paleoanthropologist,” came the reply, and though that’s not exactly what she turned out to be, it’s along the same lines as her work today as an evolutionary biologist.
“Most kids go through the dinosaur phase, and those of us in paleontology, we just never outgrew it,” jokes Sears in her laboratory in Morrill Hall.
Today, Sears has become one of the more well-known evolutionary biologists in her field. That beetle colony in her laboratory, though it may make the skin crawl, is in fact a vital tool by which Sears examines the skeletons of rodents and other animals. Those skeletons and other features are helping her shine new light on how mammals—including humans—have evolved over millions of years.
Her work has gained widespread attention. Sears’s research has been featured in Extreme Mammals, a national touring exhibit through the American Museum of Natural History, and in April she appeared on PBS in Your Inner Fish, a three-part series exploring how “hidden within the human body is a story of life on Earth,” according to PBS.
Sears’s contribution to the series (in the second episode, subtitled Your Inner Reptile) is an exploration of how humans have ancient connections to reptiles. Sears explores how the reptilian ear evolved into a mammalian ear, with parts that reflect the modern human ear.
Millions of years ago, Sears explains, the reptiles that evolved into the first mammals had jawbones comprised of many bones put together. During the evolution of mammals, three of those bones migrated up the creature’s head to form the malleus, incus, and stapes, a more effective combination of bones otherwise known as the “definitive mammalian middle ear,” she says.
That’s merely a description of the evolution that occurred, however, so Sears turned to the gray short-tailed opossum to help determine how it happened. It turns out that the opossums are born with a reptilian jaw took place during the evolution of reptiles into mammals. As the opossums grow, three bones migrate, reptilian-like, from their jaw to form the middle ear.
With that in mind, Sears and her lab members (graduate student Dan Urban in particular) have been studying opossums in hopes of explaining what happened at the very dawn of mammals.
“We think that perhaps some changes in cell behavior, perhaps cell death, might have been involved in the breaking off [of bones] from the jaw,” she says. “We’re currently starting to look at some of the genes that might be involved in that process.”
The middle ear is just one of the many projects Sears is working on. She works with a team of four graduate students, and, with funding from grants from the National Science Foundation and other sources, Sears explores how various aspects of mammals have evolved. They travel as far as Trinidad to study bat wings, for example, and they are currently examining how hands and feet in mammals evolve to reduce the number of digits. For example, they see evidence that in prehistoric times, as choked jungles gave way to open grasslands, animals such as horses reduced digits in their feet to become better runners.
Sears’s lab also conducts research with biomedical implications. They are studying thalidomide, the drug that was introduced in the 1950s to reduce morning sickness in pregnant women but actually resulted in thousands of deaths and gruesome birth defects. What Sears noticed, however, is that while humans and primates respond very strongly to thalidomide, rodents do not.
“We want to understand what goes wrong during development when it’s introduced, and why different organisms respond differently,” Sears says. “Actually, thalidomide is the drug of choice now for leprosy in many areas of the world. So it’s being used again, and we’re starting to see more babies being born with thalidomide-generated defects. It’s still a global problem that we’re facing.”
With the PBS series, however, her research on the ear garnered more attention than any other project so far. She realized it at a recent press event in California, where PBS rolled out its upcoming shows, and Sears was asked to participate in a press conference to promote Your Inner Fish. Her comments were blogged by TV Guide, and she brushed past members of Sesame Street and Downton Abbey.
After all that, however, Sears appears most excited about simply continuing her work. “What really excites me now with the rise of evolutionary biology is being able to look at patterns and explain them, and explain why they happen, and why did this happen instead of that,” she says. “What really drives me is understanding not only the history of mammals on our planet, but our own evolutionary history, because we are mammals too.”
By Dave Evensen