Pygmies show growth plasticity is key to human evolution
While the stature of pygmies is well-suited to tropical rainforests, the mechanisms underlying their growth remain poorly understood. In order to decipher these mechanisms, a team of scientists from the CNRS, IRD and UPMC studied a group of Baka pygmies in Cameroon. Their findings revealed that their growth rate differed completely from that of another pygmy cluster, despite a similar adult height, which implies that small stature appeared independently in the two clusters. This work is published on 28 July 2015 in Nature Communications.
Sure, but so…?
The scientists were thus able to show that although the body size at birth of the Baka was within normal limits, their growth rate then slowed significantly until the age of three years. Their growth curves subsequently paralleled global standards, with a growth spurt at adolescence and an adult size achieved on average at the same time as that seen throughout the world. However, they never made up for this initial retardation. On the other hand, pygmies in the eastern cluster were born with a smaller body size, so that their small stature resulted from growth processes different from those of the Baka.
The pygmy morphology of these populations thus results from two different mechanisms, which may be linked to an imbalance between the growth hormone and the two IGF that has allowed them to adapt to rainforest conditions, under a mechanism of convergent evolution.
These pygmy clusters thus split apart between 8,000 and 13,000 years ago, which shows that human growth can evolve within a relatively short period of time. This growth plasticity may have played a determining role in the spread of Homo sapiens outside Africa, allowing this species to adapt rapidly to new environments.
Wow. So different mechanisms explain why people are short.
And this is key to human evolution?
Oh, by the way, would readers like to hear about all the other things that are key to human evolution? Here you can find out more about
Human evolution, we are told, began in a genetic coding error (a doubling error) half a billion years ago. Or else accelerated gene regions (HARs), human specific regulation of neuronal genes, or just plain novel genes are invoked.
In other accounts, humans evolved to “outrun the fastest animals on earth.” Alternatively, parasites made us what we are. One source informs us that men evolved sturdier features due to fighting over women (and beards to demonstrate their ability). We learned to walk upright in order to hit each other.
Ah yes, walking. There is a “uniquely human” way of walking upright and there’s no shortage of theses as to why: carrying infants or scarce resources, and saving energy strut the stage. Or it is due to climate change or rough terrain? Don’t assume a “chimpanzee starting point,” counsels one expert. Talk about advice that peers would be reluctant to heed…
These explanations tell us that bipedalism offers considerable advantages. Yet humans were the only creatures to adopt it with no backward glance. If we ask why that is, we will be rewarded only with announcements of the discovery of further ancient advantages. And on that point, we are already convinced.
Bipedalism, we are told, also resulted in nakedness, because of our need to cool down. But we are assured elsewhere that nakedness evolved as a way of controlling parasites. And another source suggests that “hairier is better” for that purpose.
Similarly, the human hand is simply a byproduct of changes to the shape of our feet. Or maybe not. Did stone tools really change human hands? Darwin speculated on this, which makes the idea canonical today. Curiously, while many claim that apes use and shape tools like humans, few speculate why doing so had no such dramatic effect on their hands.
We are told by others that fighting “may have” shaped the evolution of the human hand. One academic offers, “I think there is a lot of resistance, maybe more so among academics than people in general — resistance to the idea that, at some level humans are by nature aggressive animals.” Resistance? Really? Among academics and pundits, that is surely the conventional view!
And the human brain? … More.
All of this stuff is supposedly critical. Which means it all happened randomly, right?
Why pygmies might be tempted to sue: Why does being short make one responsible for key moments in evolution?
Shortitude can be a real advantage (when one slips on the ice, one falls a much shorter distance), but it can be a real disadvantage (the likelihood of falling off a ladder is greatly increased = why was that person on a ladder anyway?).
Who funds this stuff? Could we fund their local children’s hospital instead? How about a civil rights drive (see vid below). Why wouldn’t that be a better use of the science (or any) dollar than yet another nonsense speculation about the key driver of human evolution?
See also: The bones tell vastly different stories
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