7.VI: Summary

Over the last few tens of millions of years, primates evolved into apes.  Apes are identified by a few physical characteristics making them different from monkeys.  They are especially notable for their arms, which are adapted for hanging and swinging from branches.  Most apes share rain forests with monkeys, but occupy slightly different niches.  Despite their greater size, apes’ suspensory behavior gives them advantages in the treetops.

Socially, apes continued to evolve in the direction of having larger social groups but fewer children with longer lifespans.  The great apes developed larger brains with spindle neurons, unique brain cells associated with social intelligence and self-awareness.  An enlarged cerebellum enabled greater motor abilities.  

The Neogene Period, 23 to 3 million years ago, was a veritable age of apes, with tens of species enjoying incredible success across Africa, Asia, and Europe.  Their habitat shrank significantly when the Earth experienced a permanent trend of drying and cooling.  Forests receded to the equatorial regions, and apes left Europe to follow the forests.  Only five small genera of apes remain today.  Four of them continue to dwell in rain forests of Africa and Asia.  They are highly specialized for that ecosystem, and have accordingly limited habitats. 

The fifth ape, hominins, tried a different strategy.  They forged into the cooler, drier habitats of eastern and southern Africa.  Hominins diverged from a common ancestor with chimpanzees at some controversially-dated point of time on the order of ten million years ago.  For unknown reasons, they had already started to develop unique traits such as erect bipedalism and reduced canines.  Those physical features proved to be advantageous in woodlands and savannas.  Hominins found a valuable new source of nutrition in roots.  They also ate seeds, nuts, and probably even some meat.

Hominins, of course, were human ancestors.  Instinctively, we do not yet honor the earliest hominins with the label “human”.  There are legitimate biological reasons for this distinction, but these ancestors had reached the point of separating us from the rest of the animal kingdom.  The best-known and most recent hominin genus was Australopithecus, which arose four million years ago.  Australopithecine apes were curiously hybrid ground-walkers / tree-climbers about the size of modern chimpanzees.

Great apes have a theory of mind; we are able to conceive of other minds as having different perspectives from our own.  This makes social life infinitely more complex.  We can see past our differences and cooperate for a greater good.  At the same time, we can also lie, cheat, and take advantage of each other.  Since we relate to each other as individuals but can only accommodate a limited number of relationships, ape morality draws a sharp distinction between an in-group and out-groups.  In chimpanzees and humans, this effect is complicated by a unique social structure with multiple males.  Competition occasionally leads to deliberate acts of murder, even within a community.

The point of hominin speciation is a special juncture in our ancestral history.  It is a moment to speculate about the dichotomy of human nature.  We are inherently animalistic, but we are also so clearly unique.


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