Climate Change Impact on Humans

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According to recent research, the average body size of humans has fluctuated significantly over the last million years and is linked to a changing climate.

About the Research

• A team of researchers led by the University of Cambridge in the United Kingdom and the University of Tübingen in Germany gathered measurements of brain and body size for more than 300 fossils from the Homo genus or family, to which modern day humans (Homo sapiens) belong.
• The team used this data, combined with a reconstruction of the Earth’s regional climates from the last million years and determined what temperature, precipitation and other climate conditions each of the fossils, spanning the last million years, would have experienced when it was a living human.
• The study found a strong link between temperature and body size, showing that climate was a key driver of body size during that period.
• Researchers also looked at the impact of environmental factors on brain size.

Major Findings

• Impact on Body Size
  • Researchers found that climate, mainly temperature, has been the main driver of changes in body size for the past million years.
  • Colder, harsher climates were linked to larger bodies, while warmer climates were linked to smaller bodies.
    • Larger bodies can buffer individuals from cold temperatures as the larger a person is, the smaller the surface compared to volume, so one can conserve heat more efficiently.
    • This relationship between climate and body mass is consistent with Bergmann’s rule, which predicts a larger bodyweight in colder environments and a smaller body weight in warmer environments.
    • This is observed in animal species such as bears. Polar bears living in the Arctic weigh a lot more than brown bears living in comparatively warmer climates.
  • This is a relationship that is found in many animals and even among contemporary humans.
  • Now scientists know that it was a major driver behind the changes in body size over the last million years.
  • For the current climate change, researchers have held that it is unlikely that it will dramatically impact human body sizes for now.
  • The changes referred to in the research happened over thousands of years or tens of thousands of years, so a few years of climate change will do little to the bodies or brains.
• Impact on Brain Size
  • According to experts, Homo sapiens are 50 per cent heavier with the brain three times larger compared to earlier species such as Homo habilis. However, the reasons behind such changes are still debated.
    • Homo sapiens emerged around 300,000 years ago in Africa, but the Homo genus, which includes Neanderthals and other extinct, related species such as Homo habilis and Homo erectus, has existed for much longer.
  • 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.
  • It proves that different factors determine brain size and body size and they are not under the same evolutionary pressures.
    • Climate did have a role in brain size, but there was so much variation in brain size that it cannot be explained by environmental changes.
  • However, climate explains changes in brain size much less than it does for body size.
    • It means that other factors such as added cognitive challenges of ever more complex social lives, more diverse diets and more sophisticated technology were likely the main drivers of changes in brain size.

(Image Courtesy: Guardian)

• Continued Evolution
  • 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 humans 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.

Impacts on Animals

• Climate change is shrinking some of the planet’s animals and also changing their physical features.
• North American migratory birds have been getting smaller over the past four decades and their wingspan wider.
  • It is suggested that the shrinking body sizes are a response to climate warming, with temperatures at the birds’ summer breeding grounds increasing roughly 1 degree Celsius over the course of the study.
  • In an analysis of 70,716 dead birds representing 52 species logged between 1978 and 2016, researchers found that 49 saw statistically significant declines in body size.
• According to another study, ectotherms (cold-blooded animals like toads, turtles, and snakes that rely on environmental heat sources) are already changing a lot with the rising temperatures.
  • Both aquatic and terrestrial ectotherms have been shrinking with common toads’ size and condition decreasing as temperatures rose 1.5 degrees Celsius over a 22-year period.

Source: CNN