The Elements of Evolution (61-22-5) Continuing Human Evolution

 Continuing Evolution

From early Homo species to archaic Homo sapiens 300 TYA there was a trend toward robustness which finally reached a plateau, then gradually declined. Early humans had thick skulls and muscular physiques. They were incredibly strong. The humans that traveled out of Africa 200,000 years ago were less beefy than those 100,000 years earlier, though more robust than humans today.

Most populations of early moderns gradually became more gracile: a trend that dramatically ratcheted 10,000 years ago, at the end of the last Ice Age. This includes a 10% reduction in brain size: from over 1,400 cm2 to an average 1,300 cm2.

There are exceptions. Some populations, including Australian aborigines, retained relative skeletal robustness. The generally accepted explanation is that hard times made for hard humans.

Early on, muscle mattered more. With more advanced tools, muscle mattered less. The facility to manipulate the environment allowed hominins to evolve into a relatively weak, gracile species.

There were many epigenetic changes in the brain development of moderns. Modern humans are more susceptible to organic mental illnesses, such as autism and schizophrenia, than their hominin predecessors.

There were also numerous changes in epigenetic regulation of genes in the immune and cardiovascular systems. Meantime, the digestive system remained relatively unchanged.

Environmental changes affected early moderns. Some were self-imposed. Exterminating all the local large game necessarily changed strategies for getting food.

Early agriculture was haphazard. The first farmers suffered nutritional stress; a surefire ticket to smaller body size.

Social changes may have played a role, though characterizing how those changes translated to a slenderer physique is speculative. Changes in foraging may have lessened the benefit of strength-based competition between men for mates: size mattered less than resource acquisition, which was more a matter of smarts.

Various forms of agriculture took hold at distinct times in various regions of the world, yet humans tended to become more gracile regardless of where or how they lived.

The one constant for all was an average increase in global temperature from the end of the Pleistocene. A warming climate is likely to have been a causative agent in human downsizing. In many parts of the world, numerous nonhuman animals also declined in size contemporaneously.

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Human evolution is ongoing.

Pigmentation changes are rather easily accomplished epigenetically. This accounts for the distinctive variations among human subspecies which have emerged.

The thick, straight, black hair that typifies east Asians arose within the past 30,000 years. Red hair has an even more recent origin, as a lightened variant of brown hair.

Earwax and sweat glands, both traits from related genes, have changed in the past 25,000 years. Stinky armpits and sticky earwax are old school. The innovation, found in east Asians, is flakier, drier earwax and less pungent body odor.

In the past 5,000 years, the skin, hair, and eye colors of Europeans have lightened, owing to local climate. Sexual preference for blond hair and blue eyes has made them more common. Meanwhile, Africans in malaria-infested areas developed greater resistance to the disease.

10,000 years ago, human teeth were 10% larger than today. As eating softer cooked foods became the norm, teeth and jaws shrank, generation by generation.

Lactose tolerance is another recent dietary adaptation to consuming dairy products and has independently evolved at least 5 times in different human subspecies in the past 5 millennia. Other adaptations related to consuming interspecific milk, which is not especially wholesome, have also occurred, including in the microbiome.