A major question of human evolution is, given that we are 98.8% genetically the same as a chimpanzee, and that we diverged as a species in a relatively short period of time, how is that you and I are able to play the piano? (I can't actually play the piano, but I could.) How can we be so similar to our relatives, and be so different in our capacity for social behavior, abstract thought, and reasoning, which has made humans stand out so drastically from any other animal? Our DNA sequences are only 1.2% different, but what a whopping 1.2%. A study published this week in the journal Genome Research attempts to shed some light on that question. And like so many things, it's all about timing.
It appears that in the part of the brain responsible for the higher functions humans tend to be famous for — the prefrontal cortex — development happens much, much slower than in macaque monkeys and chimpanzees. Slower, but at a much higher level. The study suggests that the drawn out toddler years, when we can just barely fend for ourselves and basically still need our parents to do everything for us, are crucial to how we are so similar, but so different, than other apes.
Researchers — led by Philipp Khaitovich at PICB, a joint institute of the Max-Planck Society and Chinese Academy of Sciences — studied postmortem brain tissue samples from the three species, to watch for variations in gene expression, which is how our genetic material manifests itself over time. They found revelatory results in the genes that control development of synapses, the structures that allow information to travel through the brain.
The forming of synapses in the brain happens throughout life, but really, the overwhelming majority happens in the very early stages of development, which is actually kind of depressing. Basically in the first five or so years of life, the brain is building its operating system, learning how to send information, and deciding what parts of the brain it's really going to need and what parts it really isn't (quaintly called "pruning").
For monkeys and chimps, this takes a couple of months. More or less out of the womb, they're wired and ready to go. Humans, however, are squishy little dunderheads that need mommy for a really long time compared to most animals.
According to the team's results, in this five years of slow development, the genes' expressions that lead to synaptic development go through the roof, radically changing what the smartypants part of the brain is capable of. Voila. Monkey eats poop; Chopin plays Nocturnes.
This study suggests that sometime in the last 4-6 million years, perhaps around the time we split from the Neanderthals, we developed this unique way of wiring our brains more slowly, and as a result, our unique cognitive traits. And then Skyrim.
Reference: Xiling Liu, Mehmet Somel, Lin Tang, Zheng Yan, Xi Jiang, Song Guo,Yuan Yuan, Liu He, Anna Oleksiak, Yan Zhang, Na Li, Yuhui Hu, Wei Chen,Zilong Qiu, Svante Pääbo, and Philipp Khaitovich. 2012. Extension of cortical synaptic development distinguishes humans from chimpanzees and macaques. Genome Research.
photo credit by Flickr user juhansonin under Creative Commons.