Einstein's brain — so far from ordinary in its intellectual achievement — might reveal a telltale anatomical signature. Size alone certainly could not account for his brain power.
"Here was somebody who was clearly very clever; yet his overall brain size was average," Witelson said. "It certainly tells you that, in a man, sheer overall brain size can't be a crucial factor in brilliance."
Never had Harvey given away so much brain.
Witelson and her colleagues carefully compared the 40-year-old tissue samples with dozens of normal male and female brains in her collection. She also compared them with brains from eight elderly men to account for any changes due to Einstein's age at the time of his death.
She found that one portion of Einstein's brain perhaps related to mathematical reasoning — the inferior parietal region — was 15% wider than normal.
Witelson also found that it lacked a fissure that normally runs along the length of the brain. The average human brain has two distinct parietal lobe compartments; Einstein's had one.
Perhaps the synapses in this area were more densely interconnected.
"Maybe this was one of the underlying factors in his brilliance," she said. "Maybe that is how it works."
She took it as confirmation of her suspicions about the anatomy of intelligence. If there were differences affecting normal mental ability, they would show up in the arrangements of synapses at particular points in the brain.
Einstein, she was convinced, had been born with a one-in-a-billion brain.
"We suggest that the differences we see are present at birth," Witelson said. "It is not a consequence of environmental differences."
She turned again to the brains in her refrigerator. Wherever she looked, she began to see evidence of how microanatomy might underlie variations in mental abilities.
As she matched the brain specimens to the intellectual qualities of their owners, she discovered that differences in the size of the corpus callosum were linked to IQ scores for verbal ability, but only in women. She found that memory was linked to how tightly neurons were packed, but only in men.
Witelson determined that brain volume decreased with age among men, but hardly at all among women. Moreover, those anatomical changes appeared to be closely tied to a gradual decline in mental performance in men. "There is something going on in the male brain," she said, "that is not going on in the female brain."
Brain Conquers All
Last year, a worried farming couple brought their youngest child to McMaster University Medical Center.
They were no longer certain whether their child was a girl or a boy. The youngster had traits of both, as occurs in about one in 5,000 births. In this child, nature had devised a living test of gender and the brain.
The medical experts determined that the child's body was a composite of normal and abnormal cells. Some had a girl's usual complement of two female sex chromosomes. Many, perhaps due to a mutation, had only one female chromosome and consequently were almost male.
"Which cells got to the brain?" wondered Witelson, who was called in as a consultant. "You have to consider the sex of the brain."
The doctors all suspected the child's brain was masculine. There was no way to know for sure. They could not safely take a sample of neural tissue to biopsy.
Until recently, reconstructive surgery based on a doctor's best guess was the rule in such cases. But in Hamilton, they counseled patience, Witelson recalled.
"We said, 'Let the child's behavior tell us what sex the child is.' "
Given time, she believed, the brain would reveal itself.
COLUMN ONE | MAPPING THE MIND