Cold Weather and Bigger Brains

Bob Holmes of the NewScientist has a report on brain size and hominid evolution, in which it is hypothesized that modern human brains could only expand when the air temperature was cold enough to allow for adequate heat dissipation—a glacial maximum for example. He writes:

For all its advantages, the modern human brain is a huge energy glutton, accounting for nearly half of our resting metabolic rate. About a decade ago, biologists David Schwartzman and George Middendorf of Howard University in Washington DC hypothesised 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 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 (Climatic Change, vol 95, p 405).

One of the big questions surrounding the research is whether or not the climate data has the kind of resolution that is necessary to support the hypothesis:

Given the timescales involved, it may be near-impossible to match definitively the onset of an ice age with speciation, but a 1.5 °C drop is consistent with the cooling climate of the time, says Middendorf.

It is an intriguing idea and bears more investigation but I suspect it may be one of many variables driving brain size expansion at the time.


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Brain Evolution in Early Primates

Work by University of Florida vertebrate palaeontologists Mary Silcox and Jonathan Bloch suggest that the early primate brain may not have evolved in quite the way we think it did. The story, in Science Daily, has this to say:

"Most explanations on the evolution of primate brains are based on data from living primates," said lead author Mary Silcox, an anthropologist at the University of Winnipeg and research associate at UF's Florida Museum of Natural History. "There have been all these inferences about what the brains of the earliest primates would look like, and it turns out that most of those inferences are wrong."

Researchers used CT scans to take more than 1,200 cross-sectional X-ray images of the skull, which were combined into a 3-D model of the brain.

"A large and complex brain has long been regarded as one of the major steps that sets primates apart from the rest of mammals," said Florida Museum vertebrate paleontologist and study co-author Jonathan Bloch. "At our very humble beginnings, we weren't so special. That happened over tens of millions of years."

It is generally thought that the plesiadapiformes were not true primates but perhaps led to them. These earliest primates relied much more on sense of smell than later primates did.