After researching the somatosensory (touch), auditory and visual systems in the brains of squirrels and monkeys at Vanderbilt, Krubitzer received her Ph.D. in 1989 and was set to proceed to M.I.T. on a National Institutes of Health postdoctoral fellowship. Then came the decision that altered her path in science and led her to the studies that ultimately brought her the MacArthur award. "About a month or so before I was supposed to go to M.I.T., I realized that I had always been interested in evolution. So I told John Kaas, I don't want to go to M.I.T. And he said, 'What?' I said, 'I want to go to Australia to work on platypuses and spiny anteaters'--the mammals whose ancestors branched off early in evolution. The ancestors of humans branched off relatively late. The animals I wanted to study had ancestors that branched off about 150 million years ago, and two of these are in present-day Australia.
"So John was pissed off at me for a day, and then he said, 'OK.'" Kaas helped Krubitzer with an appointment to the Vision, Touch and Hearing Research Centre in Queensland, Australia, where she conducted research into the cortical structure of the brains of these descendants of early mammals. She has no doubts that her decision was right.
"Going to Australia was the best thing I ever did. Today John Kaas will say the same thing. He'll tell me, 'Leah, at the time I was a little worried about you. But it was the best thing you ever did.' And it was, because it changed my thinking."
The technical paper that she published in 1995 as a result of her Australian studies--"Organization of Somatosensory Cortex in Monotremes: In Search of the Prototypical Plan"--demonstrated that, as Krubitzer describes it, "There are features of [brain] organization that are retained in all species. And these serve as constraints and have served as constraints for building a brain, because you simply cannot get rid of them. Some of the common features of the neocortex that all mammals possess are primary and secondary sensory processing areas and patterns of interconnections between common neural structures.
"The other thing we found was that even the changes that occur in a number of different lineages of animals take the same form. They're independently evolved, but they look really similar. This suggests that the brain can't do just anything. It doesn't change randomly in any way, but instead must be highly constrained."
Krubitzer's combining of evolutionary theory with developmental neurobiology, based on comparative neuroanatomical studies, has brought into view a common substrate of the brain in all animals, including humans, that provides both the opportunity for evolutionary changes and limits what may develop.
Part of what makes Krubitzer so fascinating a scientist is that she can describe this from a variety of perspectives, from the genetic modifications that are involved in brain evolution to the changes in neural development that can occur to the animal behavior that is exhibited. Breaking through narrow specialization of the various fields of biological investigation, Krubitzer provides a breathtaking window through which you can begin to glimpse the incredible complexity of the whole phenomenon of animal evolution.
One example is her description of how brain evolution and brain development fit together. "Another way to understand how a brain gets built is to understand how it develops, because the evolution of the adult cortex is really the evolution of the development of the cortex. What's being changed in the course of evolution is something in the developing nervous system. There's some sort of genetic change that alters the developing nervous system. Such changes are ultimately realized in the adult form. Although it's the adult form that's being selected for by the environment, what's really being selected for is the [genetic] program that generates the adult form, the developmental program."
Krubitzer sees all mammalian brains as having "a common plan of organization that was inherited from a common ancestor." While she admits that there's no way of knowing what that ancestor was, she says that its brain type was probably closest to that of a hedgehog.
Sitting with Leah Krubitzer and considering one's own brain's hedgehog inheritance is a humbling experience. And from Krubitzer's point of view, it should be. "Humans aren't so special. We are certainly constrained by the same things other mammals are. We'd like to think of ourselves as different--that we just sort of popped up and that this doesn't apply to us. Well, it absolutely applies to us."
Then comes the conclusion that perhaps has drawn the most interest to Krubitzer's work. "Our future evolution, or more precisely our nervous system evolution, is highly constrained. Evolution is a tinkerer. But there are a limited collection of pieces and bits that it can make something with. I can't predict what's going to be selected for and selected against because I don't know what the future holds. But I can tell you how your brain might change. I can tell you what you won't lose. I guarantee it."
Asked to provide a specific example, Krubitzer says, "You're not going to grow a new hemisphere in your brain. You're not going to do a ["Star Trek"] Dr. Spock mind-meld. All you have to do is look at the history and you can predict the future pretty well."
But Krubitzer, in her latest studies, is doing much more than predicting the future of brain evolution; she's giving it a helping hand. Working in collaboration with Zoltán Molnár of Oxford University, Krubitzer is attempting to alter the developing nervous system of marsupials in a way she believes is consistent with evolution. The two are attempting to generate new brain parts, or functional regions, in the brain, by significantly modifying the organization of an existing brain in a manner consistent with actual brain evolution.
One such alteration includes changing the actual size of the neocortex, a portion of the brain that has increased dramatically in humans. The neocortex is thought to be involved in perception, cognition, learning and memory.
An outgrowth of all Leah Krubitzer's work is her appreciation for the incredible complexity of all life forms, of their evolutionary success.
When it comes to humans' special capacity for language, Krubitzer doesn't see it as necessarily so special. "Animals have pretty complicated communication systems. Ours may be the most complicated. But I don't know of any species of mammal that doesn't communicate at one level or another."
She regards the attempt to measure other animals by human standards as a fundamentally flawed view of life. "The biggest problem of studying the nervous system is the nervous system through which we study it, right? We take all of our prejudice and our biases and our notion of intelligence with us, and guess how it works out? We humans are way up here and every other animal is a degraded form of us.
"But they've evolved independently. You still hear people, even really smart people, talk about more evolved and less evolved, as if there's this scale of nature and everything is evolving toward a human state. But the little tiny insectivore has adapted well to its environment. It's existing. It's alive. It's not extinct. That's a successful animal, right? Most mammals on the face of the earth are not large-brained. We're the exception. You don't have to have a huge brain to be successful in an evolutionary sense."
Krubitzer's egalitarian view of the evolutionary tree caused her to conclude in her most renowned paper in which she most succinctly summarized her findings--"The Organization of Neocortex in Mammals: Are Species Differences Really So Different?"--with a quotation from a naturalist writing from Cape Cod in 1949. She agrees to read it out loud:
"We patronize them [other animals] for their incompleteness, for their tragic fate of having taken form so far below ourselves. And therein we err, and greatly err. For the animal shall not be measured by man. In a world older and more complete than ours, they move finished and complete, gifted with extensions of the sense we have lost or never attained, living by voices we shall never hear. They are not brethren; they are not underlings; they are other nations, caught with ourselves in the net of life and time, fellow prisoners of the splendor and travail of earth."
When Leah Krubitzer finishes reading this, she looks up. Though it is certain that she has read this passage many, many times, she is as moved as if it were the very first time. That, more than anything, is Leah Krubitzer's true genius.
Ralph Brave, a senior editor at the Sacramento News & Review, is an occasional contributor to UC Davis Magazine. Photo by Neil Michel/Axiom.
