London, July 30 (ANI): Two new studies have suggested that our ancestors' brains expanded from a mere 600 cubic centimetres to about a litre some 2.5 million years ago, because the ice age helped to cool the brains to let off steam and grow.
About a decade ago, biologists David Schwartzman and George Middendorf of Howard University in Washington DC hypothesized that our modern brain could not have evolved until the Quaternary ice age started, about 2.5 million years ago.
They reckoned such a large brain would have generated heat faster than it could dissipate it in the warmer climate of earlier times, but they lacked evidence to back their hypothesis.
Now, according to a report in New Scientist, hints of that evidence are beginning to emerge.
Climate researcher Axel Kleidon of the Max Planck Institute for Biogeochemistry in Jena, Germany, modelled present-day temperature, humidity and wind conditions around the world using an Earth-systems computer model.
He used these factors to predict the maximum rate at which a modern human brain can lose heat in different regions.
He found that, even today, the ability to dissipate heat should restrict the activity of people in many tropical regions.
According to Kleidon, if keeping cool is a problem now, it would have been even more challenging - perhaps too challenging - 2 or 3 million years ago when temperatures were a few degrees warmer than today and air-conditioning units were harder to come by.
A new study by Schwartzman and Middendorf suggests that a small drop in global temperatures may have made a big difference.
The pair used basic equations of heat loss to estimate how fast the small-brained Homo habilis would have been able to cool off.
Assuming overheating limited the size of H. habilis's brain, they then calculated what drop in air temperature would have been needed for Homo erectus to be able to support its bigger brain.
They found that a drop in air temperature of just 1.5 degrees Celsius would have done the trick.
Given the timescales involved, it may be near impossible to match definitively the onset of an ice age with speciation, but a 1.5 degrees C drop is consistent with the cooling climate of the time, according to Middendorf.
According to psychologist David Geary at the University of Missouri in Columbia, being able to cool bigger brains would have lifted the brakes on expansion. (ANI)