Local weather has modified the scale of our our bodies and, to some extent, our brains too – Watt Up With That?
PICTURE: SKULL: – LEFT: AMUD 1, NEANDERTHAL, 55,000 YEARS AGO, ~ 1750 CM³ – CENTER: CRO MAGNON, HOMO SAPIENS, 32,000 YEARS AGO, ~ 1570 CM³ – RIGHT: ATAPUERCA 5, MITTELPLEISTOCEN HOMO, 430,000 YEARS AGO, … more CREDIT: MANUEL WILL
- The average height of humans has fluctuated greatly over the past million years and is heavily dependent on temperature.
- Colder, harsher climates led to the development of larger body sizes, while warmer climates led to smaller bodies. Brain size also changed dramatically, but did not develop along with body size.
An interdisciplinary research team led by the Universities of Cambridge and Tübingen has collected measurements of body and brain size from over 300 fossils of the genus Homo found worldwide. By combining this data with a reconstruction of the world’s regional climate over the past million years, they have determined the specific climate each fossil experienced when it was a living human.
The study shows that the average height of humans has fluctuated widely over the past million years, with larger bodies developing in colder regions. It is believed that a larger size acts as a buffer against colder temperatures: a body loses less heat when its mass is large in relation to its surface area. The results are published today in the journal Nature Communications.
Our species, Homo sapiens, originated in Africa about 300,000 years ago. The genus Homo has existed for much longer and includes the Neanderthals and other extinct related species such as Homo habilis and Homo erectus.
A defining characteristic of the evolution of our species is a trend towards increasing body and brain size; Compared to earlier species like Homo habilis, we are 50% heavier and our brains three times larger. But the drivers behind such changes remain highly controversial.
“Our study shows that climate – especially temperature – has been the main driver of changes in body size over the past million years,” said Professor Andrea Manica, researcher in the University of Cambridge’s Department of Zoology, who led the study.
He added, “In the people living today, we can see that those who live in warmer climates tend to be smaller and those who live in colder climates tend to be taller. We now know that the same climatic influences have been at work over the past million years. “
Researchers also looked at the influence of environmental factors on brain size in the genus Homo, but the correlations were generally weak. The brain size tended to be larger when Homo lived in habitats with less vegetation, such as open steppes and grasslands, but also in more ecologically stable areas. Combined with archaeological data, the results suggest that people living in these habitats hunted large animals for food – a complex task that may have fueled the development of larger brains.
“We found that different factors determine brain size and height – they are not under the same evolutionary pressure. The environment has a much greater influence on our body size than our brain size, ”says Dr. Manuel Will from the University of Tübingen, Germany, first author of the study.
He added: “In more stable and open areas, there is an indirect environmental impact on brain size: the amount of nutrients extracted from the environment had to be sufficient to allow the maintenance and growth of our large and particularly energy-intensive brains.”
This research also suggests that non-environmental factors were more important in powering larger brains than climate, with the lead candidates being the additional cognitive challenges of increasingly complex social life, more diverse diets, and more sophisticated technologies.
The researchers say there is good evidence that the size of the human body and brain is constantly changing. The human body still adapts to different temperatures, with taller people on average now living in colder climates. The brain size of our species appears to have shrunk since the beginning of the Holocene (about 11,650 years ago). The increasing reliance on technology, such as the outsourcing of complex tasks to computers, can cause brains to shrink even further over the next millennia.
“It’s fun to speculate about what will happen to body and brain size in the future, but we should be careful not to extrapolate too much to the past million years as so many factors can change,” said Manica.