Ruminations: Evolutionary Influences

"Our study indicates that climate -- particularly temperature -- has been the main driver of changes in body size for the past million years."
"We can see from people living today that those in warmer climates tend to be smaller and those living in colder climates tend to be bigger."
"Over a long tine, yes, we would expect a decrease in body size [due to climate change]."
"But the effects that we describe occurred over thousands of years, so a few years of warming will do little to body size. But if we were to keep changing temperature and keep them there for a long time, then yes, one would expect such changes."
"Brain size was not affected by temperature, but it was affected by long-term climatic stability."
"The likely rationale for that is that brains are expensive, and you need reliable resources to maintain them."
Professor Andrea Manica, researcher, Department of Zoology, Cambridge University

Human fossils illustrating the variation in brain (skulls) and body size (thigh bones) during the Pleistocene period.

Over 300 fossil samples were studied by scientists to track the fluctuation in human body size over thousands of years of evolution linked to climatic conditions. The research team discovered a clear link between people who live in colder environments and the size they attained; larger bodies being the result in contrast to people living in warmer regions being smaller in size, a trend that continues to this day.

Where people who live in cold environments tending to have larger body sizes than those in warmer areas of the globe.

The average person of Dutch descent as an example stands 6 feet in height whereas the average person living in India tends to be on average 5 foot, 5 inches in height. For the study, the researchers from the Universities of Cambridge in the U.K. and Tubingen in Germany, note that for every degree of warming, a corresponding 0,87 percent decrease in body mass occurs.

In other words, a 2C warming would result in a body size decrease of one kilogram (2.2 lbs.) for someone whose weight comes in at 60 kg (132 lbs.) A similar trend sees the reverse emerge; for every degree of cooling, body size increases by 0.87 percent.

A larger body size results in a person's mass to surface area ratio being greater, therefore more heat efficient, so less warmth is dissipated than with smaller sized people.

This trend, according to Professor Manica, would tend to continue as climate change sees the soaring of global temperatures. Published in Nature Communications, the study concluded that brain size also changed over time; not, however, evolving in tandem with body size.