Just as some animals have done before us, humans could shrink to adapt to rising temperatures caused by climate change. At least that’s the theory put forward by a paleontologist Scottish. The mammals that live in hot regions are smaller size than those who live in cold regions. This would be particularly the case for the first horseswho lived about 55 million years ago.
” The reasons are not fully understood, but it is likely, in part, that smaller animals have a larger surface area relative to their volume than larger animals and can therefore dissipate excess heat better “, explains Professor Steve Brusatte, paleontologist at the University of Edinburgh, quoted by the English newspaper The Guardian. According to the researcher, these elements can lead to a “plausible” hypothesis that humans will be able to shrink to adapt to rising temperatures under the effect of the global warming.
The availability of resources is also a determining factor
This theory is of interest to other scientists. In July 2021, researchers from the University of Cambridge in (UK) and the University of Tübingen (Germany) published a study in the journal NatureCommunications.
The authors of the work studied the size of the body and the brain over 300 human fossils. According to their estimates, temperature represents one of the main factors causing the change in size of human bodies over the last million years. Clearly, the climate hot could lead to less body build, while the cold climate would produce larger bodies.
The impact of global warming on human size could however have other causes, for example, the availability of food and resources. This is the counter-argument formulated by certain researchers, in particular Professor Adrian Lister of the Natural History Museum in London, also quoted by The Guardian.
Will global warming cause humans to shrink?
Bergmann’s rule, which states that species living in cold climates tend to have a mass higher body, can it apply to human evolution? Yes, says a study today, even if this thesis is subject to caution.
Article of Celine Deluzarchepublished on July 17, 2021
In warm-blooded animals such as mammals or birds, it has long been observed that body size is correlated with temperature. This is called Bergmann’s rule, after the 19th century German biologiste century Carl Bergmann who enacted this rule in 1847. According to this principle, animals with a smaller ratio between the surface area and the volume of the body have less heat loss and are therefore better adapted to the cold. This purely empirical rule, however, suffers from many exceptions. the largest land animal known, the African elephant, thus lives in a warm environment.
Is Bergmann’s rule valid in humans?
However, many studies have taken up this rule to find out if it could apply to humans. With often contradictory results, some finding a correlation between body temperature and size, others not. A 2013 study trying to make a global synthesis has itself come to mixed results, the groups of thenorthern hemisphere roughly matching Bergmann’s rule but not the southern hemisphere groups. According to its authors, a temperature difference of at least 30°C or 50° latitude to observe significant differences.
A new study published in NatureCommunications became interested inapplication of Bergmann’s law in humans, not in space but in time. ” During the last two million years, the average weight of the Homo species has increased from 50 kilos to 70 kilos on average, and his brain has tripled in sizeattests Manuel Will, of the University of Tübingen in Germany and main author of the study. Many hypotheses have been put forward to explain this evolution, such as diet, competitive or social factors, or the level of technological advancement. But no evidence has yet been provided to support these assumptions. »
The average temperature, the main factor of variation in body mass
The researchers therefore wondered whether the climate could have played a role in the increase in human corpulence. They examined nearly 300 fossils aged from one million years to 10,000 years and compared them to past climatic variations. They thus found that the Men of the Pleistocene average and Neanderthalwho lived in colder environments, actually had a higher body mass than theHomo sapiens modern, appeared 30,000 years ago.
” The average temperature alone is three times more important than the other variables on the variability of body mass in the different groups “, attest the authors. On the other hand, the latter found only a weak correlation between the climate and the brain size. ” For the latter, the climate may have played a marginal role “, explain the authors. Humans living in drier places with less vegetation, for example, tend to have larger brains, possibly because they had to develop more complex techniques to hunt larger animals living in these savannahs, they suggest. .
Will global warming make humans smaller?
Should we then conclude that the global warming will make us shrink? Certainly not in the short term: It would take thousands of years to begin to see any effects of warming. “, tempers Andrea Manica, co-author of the study, on the site NPR. ” And even if that happened, the change would be minimal, on the order of a kilo for a warming of 2°C. “, he calculates. In reality, we observe rather the opposite, that is to say that Men tend to be bigger and bigger and bigger, in large part because of changes in diets (more protein and of calories).
Does the evolution of species accelerate when the climate cools?
CNRS article published on 04/29/2017
Using a new model of phenotypic evolution, researchers have assessed, over a period of 80 million years, the evolution of the size of mammals and birds as a function of temperature. Unexpectedly, they found that the rate of change in body mass of both classes of animals was higher during cold climatic periods.
The way in which climatic changes influence the morphology species is still largely unknown. The theory of adaptive radiation places biotic factors (in the forefront of which is competition for access to food resources) as the main criteria for the phenotypic evolution of species. This theory, which has played an important role in the development of models of phenotypic evolution, however, has largely ignored the importance of factors abiotic (CO concentration2 of the’atmospheretemperature, etc).
In a study recently published in Pnastwo researchers from the Institute of Biology at the École Normale Supérieure (Ibens) are proposing a new analysis tool capable of better evaluating the influence of environmental variables on theevolution of species. To illustrate their methodology, the scientists focused on body mass variations in mammals and birds from -80 million years ago to the present day.
Focus on molecular phylogeny
For this, they used reconstructions of global average temperatures over geological time as well as molecular phylogenies almost complete with mammals and current birds. The researchers then compared various scenarios for the evolution of body masses along the branches of these phylogenies. Over the past 80 million years, they have found that the body mass of these two classes of animals changes more rapidly each time the climate cools. “Cold geological periods could be linked to rapid and abrupt environmental changes, unlike warmer periods which would be associated with more ecological stability”believes Hélène Morlon, a researcher in ecology scalable to Ibens and co-signer of the article.
Beyond unexpected conclusions, the rate of molecular evolution being, as a rule, higher when temperatures increase, this study demonstrates the relevance of a methodology based on molecular phylogeny to study the evolution of traits (size weight, metabolismetc.) of large groups of species.
From a fundamental point of view, this methodology could indeed help the scientific community to determine among a wide range of biotic and abiotic factors those that most influence the phenotypic variations of species. “Analytical tools such as this one should notably make it possible to measure over geological time the respective role of a set of environmental parameters on theevolution of species »illustrates Julien Clavel, postdoctoral fellow at Ibens and main author of the article.
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