UNIVERSITY OF CAMBRIDGE
- The average body size of humans has fluctuated significantly over the last million years and is strongly linked to temperature.
- Colder, harsher climates drove the evolution of larger body sizes, while warmer climates led to smaller bodies.Brain size also changed dramatically but did not evolve in tandem with body size.
An interdisciplinary team of researchers, led by the Universities of Cambridge and Tübingen, has gathered measurements of body and brain size for over 300 fossils from the genus Homo found across the globe. By combining this data with a reconstruction of the world’s regional climates over the last million years, they have pinpointed the specific climate experienced by each fossil when it was a living human.
The study reveals that the average body size of humans has fluctuated significantly over the last million years, with larger bodies evolving in colder regions. Larger size is thought to act as a buffer against colder temperatures: less heat is lost from a body when its mass is large relative to its surface area. The results are published today in the journal Nature Communications.
Our species, Homo sapiens, emerged around 300,000 years ago in Africa. 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 trait of the evolution of our genus is a trend of increasing body and brain size; compared to earlier species such as Homo habilis, we are 50% heavier and our brains are three times larger. But the drivers behind such changes remain highly debated.
“Our study indicates that climate – particularly temperature – has been the main driver of changes in body size for the past million years,” said Professor Andrea Manica, a researcher in the University of Cambridge’s Department of Zoology who led the study.
He added: “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. We now know that the same climatic influences have been at work for the last million years.”
The researchers also looked at the effect of environmental factors on brain size in the genus Homo, but correlations were generally weak. Brain size tended to be larger when Homo was living in habitats with less vegetation, like open steppes and grasslands, but also in ecologically more stable areas. In combination with archaeological data, the results suggest that people living in these habitats hunted large animals as food – a complex task that might have driven the evolution of larger brains.
“We found that different factors determine brain size and body size – they’re not under the same evolutionary pressures. The environment has a much greater influence on our body size than our brain size,” said Dr Manuel Will at the University of Tubingen, Germany, first author of the study.
He added: “There is an indirect environmental influence on brain size in more stable and open areas: the amount of nutrients gained from the environment had to be sufficient to allow for the maintenance and growth of our large and particularly energy-demanding brains.”
This research also suggests that non-environmental factors were more important for driving larger brains than climate, prime candidates being the added cognitive challenges of increasingly complex social lives, more diverse diets, and more sophisticated technology.
The researchers say there is good evidence that human body and brain size continue to evolve. The human physique is still adapting to different temperatures, with on average larger-bodied people living in colder climates today. Brain size in our species appears to have been shrinking since the beginning of the Holocene (around 11,650 years ago). The increasing dependence on technology, such as an outsourcing of complex tasks to computers, may cause brains to shrink even more over the next few thousand years.
“It’s fun to speculate about what will happen to body and brain sizes in the future, but we should be careful not to extrapolate too much based on the last million years because so many factors can change,” said Manica.
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At last we know why the world is full of fat stupid people..
People who believe in dangerous man-made climate change already have very small brains.
What? The only constant is change? Even evolution isn’t static? Oh the humanity!
About all I can get from this is that smart people know how to get out of the sun better.
Many also fly south like the birds for winter!
Birds are smart, especially parrots which are really smart for a bird, and some humans. They can have a 200+ vocabulary and use it correctly.
“Researchers have used data on skeletal remains to calculate how the average height of Englishmen rose or fell over 2,000 years of history. Using data from skeletal remains of men aged between 21 and 49 years from a range of archaeological excavations conducted in different parts of England during the last 30 years, they reconstructed a man’s full height from data recording the length of his femur. …Their working paper reveals that Englishmen became taller when Britain was under Roman occupation (200-410 AD), with average height rising from 167 cm to 170 cm (or 5 feet 5 inches). The researchers suggest this rise in average height coincided with the Romans’ improved water supply and sanitation systems and a more varied diet at this time. After the Romans left Britain in 410, heights did not deteriorate immediately but fell from 600 onwards. The paper highlights previous research suggesting that health may have deteriorated when populations moved out of the towns and cities set up by the Romans, abandoning their more hygienic water supplies and waste disposal systems. Plague and pestilence then became common and infectious diseases are known to have increased at this time, with archaeological evidence also suggesting that diets were inadequate.
Average heights of men started to go up again after the Norman Conquest of 1066, says the paper. By the end of the early medieval period, heights had increased to 172 cm, increasing to 173 cm in the 1100s, edging closer to heights achieved at the start of the 20th century. The paper suggests that a warmer climate may have contributed to good general health among the population, noting that records for 901 until 1100s show that England ‘saw the warmest weather of the millennium’. Over this period of 200 years, average heights increased by more than 5 cm, says the working paper.
After 1200, heights started to decline, and archaeological evidence shows that at this time, the rural populations were decreasing, farmland had become degraded and there were shortages of crop seeds. It also notes that other research has suggested temperatures turned colder over the century, with weather becoming far more changeable until the early 1300s. The early 1300s started with the Great Famine (1315-1317) which may have exaggerated the decline in average heights, but the paper says men had started getting shorter several decades before.”
A much better record of heights and temperature, although of just modern man, that shows the complete opposite correlation. This was height rather volume but likely due to diet so I suspect body weight would have shown a similar increase with warmth and better diet.
Interesting comparison with wombats. There are two extant species in the genus Lasiorhinus. The northern and southern hairy -nosed wombat. Both are endemic to semi arid inland regions of Australia. The one living in warmer climes (warmer winters) is about 20% heavier than the southern.
The common wombat is about the size of the southern hary-nosed wombat. It lives in cooler areas at altitude on the mainland as far north as Queensland, and in Tasmania. The Tasmanian population (much cooler) are usually 20% smaller than mainland animals.
All three species are rotund little buggers that are furry and burrow, unlike humans, but it does show it’s not as simple as retaining body heat.