By Greta Petry

     Do men have larger brains than women? University anthropologist Dean Falk is about to publish a scholarly paper that she says will put this subject to rest once and for all.

     According to Falk, an internationally recognized expert in human brain evolution, it’s true: Men around the world do have bigger brains than women. However, she says, this is nothing for them to get swelled heads about. Male rhesus monkeys also have bigger brains than female rhesus monkeys. Whatever males are using their extra neurons for, she says, it’s not the higher cognitive abilities—like abstract thinking, judgment and reasoning—that separate us from the monkeys and make us distinctly human.

     Falk is describing research for an article that is being published in the Journal of Human Evolution this spring. Co-written with a former graduate student, Nicholee Froese, M.A.’95, Donald Sade of the North Country Institute of Natural Philosophy of Mexico, N.Y., and Bruce Dudek, a University at Albany professor of psychology, this paper tackles the thorny question of whether or not there are sex differences in brain size after body size is taken into account. In her term project for Falk’s graduate seminar on brain evolution, Froese reanalyzed data already available and established that, indeed, men have larger brains than women of the same body size.

     “Once this paper is out, the question will be settled. ‘Yes, males do have bigger brains,’ Falk said, adding, “This is an important finding because, until now, this question has been extremely controversial. We’ve now extended Froese’s work to ask the same question about rhesus monkeys. The findings turn out to be the same for monkeys as for people. It’s almost weird how close the numbers are. The important question is, what are the evolutionary implications?” 

     Falk and her co-authors hypothesize that males have bigger brains than females because they process visual information and construct mental maps of their environments differently than females, as is the case for certain rodents (known as voles) in which males travel widely to find mates during the mating season. Rhesus monkey males migrate to new social groups when they reach sexual maturity and presumably need keen visual and spatial abilities to do so. So too might have the ancestors of humans, Falk hypothesizes.

 






Dean Falk and graduate student Art Sansone measure the brain sizes of female monkeys by using mustard seeds.
 



    In a few rare species of Old World monkeys, females rather than males do the migrating. Graduate student Art Sansone and Falk are just beginning to study brain size of these female monkeys, and how they compare to those of males of the same body size that do not migrate. Sansone measures brain size by filling the crania of macaques with mustard seed. Then he measures the leg and arm bones from the same skeletons to estimate body size. 

     Falk, who is perhaps best known for her “radiator” theory of brain evolution, joined the University faculty in 1988. She contends that the brain size of man’s ancestors began to increase dramatically once hominids stood erect and developed a network of cranial veins capable of cooling the brain. Those blood vessels control brain temperature in the same way that a radiator cools a car engine. Falk’s 1992 book, Braindance, popularized that theory. 

     Falk’s cutting-edge research in the area of human brain evolution, which is funded by the National Science Foundation, took an interesting turn last spring when she was invited to provide a commentary in Science magazine on a report of a surprisingly small brain for a nearly three-million-year-old fossil from the human family. The report by Glenn Conroy of Washington University in St. Louis and his colleagues showed that the fossil’s brain was small in comparison to published cranial capacities for other fossils. This was odd because these other specimens looked as if they should have had smaller instead of larger capacities than the new specimen.

     In her commentary, Falk noted that all of the published cranial capacities of early hominids needed to be re-evaluated and suggested that the new specimen also raised a number of questions about the timing and mode of human brain evolution. After writing her commentary, Falk began to reanalyze the cranial capacities for all of the specimens of early hominids that she has in her collection. This research, begun with graduate students John Guyer and John Redmond, initially focused on reconstructing the details and sizes of the brain as reflected on casts of the insides of the brain case, called endocasts.

 

Graduate student John Guyer prepares an endocast to be used to study the size and details of the brain.

 

    The effort has now been joined by Conroy and Professor Horst Seidler and colleagues of the Institute of Human Biology at the University of Vienna who use sophisticated computer imaging to produce three-dimensional models of the cranium called “virtual endocasts.” Falk reconstructs the endocasts by hand in her laboratory and then sends them to St. Louis and Vienna to be compared to their corresponding three-dimensional images generated from computed tomography scans of the original fossils. As Conroy’s Science report predicted, this international team has uncovered flaws in the accepted brain measurements for some of our earliest relatives.

     “The received wisdom is the belief that brain size in our own genus, Homo, took off and doubled during the last two million years,” said Falk. “We think that our revised cranial capacities will change the big picture. The timing during which brain size in our relatives increased dramatically occurred over a much longer time, i.e., it began closer to three than to two million years ago.”

     Given the contentious nature of paleoanthropology, the road to having this revised evolutionary timeline accepted will be rocky, Falk predicts. “Because our findings contradict widely held published views, they are going to be controversial,” she says. Falk and her graduate students presented their findings at a conference last summer in Spain and found strong interest among leading paleoanthropologists. Falk also discussed their findings at a symposium on evolutionary anthropology at the Max-Planck Institute in Leipzig, Germany, in November.

     “It means revising the whole bottom of the hominid fossil record, turning it upside down. Even more exciting,” said Falk, “is that we are finding interesting differences in the frontal and temporal lobes of the brains of different species of early hominids, and this could have implications for one of the most debated questions in paleoanthropology—namely, which fossils are ancestral to humans and which are not.” 

University anthropologist Dean Falk, center, and graduate students John Guyer, Linda Bussell, Art Sansone and John Redmond (left to right) examine early hominid skulls.


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