杏吧原创

Watch a human brain morph into a 鈥淏oskop鈥� brain

Compare the two brains side-by-side

I鈥橵E been waiting for someone to write this book for years. I almost wrote it myself 鈥� twice 鈥� but was distracted by other projects. Now and have written a much-needed book on big brains.

Big Brain is a popular account of how brains enlarge, in both evolutionary and developmental terms. Bigger doesn鈥檛 necessarily mean better, the authors caution, when you鈥檙e comparing one human with another; after all, , at 1230 cubic centimetres, was merely average in size. Size definitely matters when comparing one species with another, however. The great apes have pint-sized brains, at less than 473 cc, and so did our hominin ancestors as recently as 2.5 million years ago. In the million years that followed, brain size slowly doubled (contrary to the spurts suggested by the authors). Then about 750,000 years ago, brain size began to increase more rapidly. By 200,000 years ago, Homo sapiens were on the scene with brains three times as big as those of our ape cousins.

That鈥檚 how the story usually goes, and it leaves us thinking that our big brains mark the high point of evolution. A century ago, however, in the Boskop region of southern Africa, a few skulls were discovered that would have housed a brain 30 per cent larger than our own. The discovery led to much speculation in the 1920s that a bigger-brained human subspecies wandered South Africa 30,000 to 10,000 years ago.

Lynch and Granger suggest these bigger-brained humans, dubbed 鈥淏oskops鈥�, were forgotten by history because their very existence threatened our egos. With their large prefrontal cortices 鈥� the parts of the brain involved in high-level cognitive tasks 鈥� the authors suggest that the Boskops may have been capable of impressive mental feats: 鈥淲ith their perhaps astonishing insights, they may have become a species of dreamers, with an internal mental life literally beyond anything we can imagine.鈥�

It鈥檚 a fun idea, but one that anthropologists dismissed long ago. In the 1950s it was shown that the Boskop skulls were barely different from those of modern peoples such as the San and Hottentot. What鈥檚 more, the Boskop brain was actually smaller than the high end of modern humans, which is about 2000 cc.

Watch a human brain morph into a Boskop brain

Compare the two brains side-by-side

The strength of the book lies in the neuroscience, especially its treatment of neural plasticity and the 鈥渁ssociation areas鈥� of the brain. These areas grew at a disproportionate rate as bigger brains evolved, and the authors suggest that it is their size compared with that of our sensory regions that largely distinguishes humans from other animals.

We cook food, travel around the globe and build houses, roads and bridges. Those abilities have their basis in language, and language itself may be a result of our association region 鈥� all thanks to our bigger brains.

Human Evolution 鈥� Follow the incredible story in our comprehensive special report.

The Human Brain 鈥� With one hundred billion nerve cells, the complexity is mind-boggling. Learn more in our cutting edge special report.