8.IV: Chapter 8 Summary

By 200 million years ago, our ancestors were mammals.  They had survived the worst mass extinction of all time, and their bodies were highly adapted to life on land.  Evolution was guided by the harsh climate of the post-extinction period, the consolidation of all continents into one grand Pangaea, and the towering presence of dinosaurs.  The Mesozoic appearance of fruit trees also greatly shaped our past.  In a less direct way, the geology of the Mesozoic Era impacted us with the accumulation of major oil reservoirs.

From the earliest mammals, we inherited our warm-bloodedness, our good sense of hearing, and, damn them, our body fat.  Warm-bloodedness was an especially significant and complex trait.  It involved the co-evolution of several supporting features, including teeth for chewing, legs for running, and efficient hearts and lungs.    

Mammals were unlike any other class of animal.  Not only did they give live birth and care for their young, but their brain had reached a new level of complexity with a neocortex.  After the dinosaurs went extinct about 70 million years ago, the mammalian family tree radiated into a multitude of orders, including ours, the primates.  In early primate evolution, again a host of traits co-evolved and reinforced each other.  By this time, many of the defining traits were mental or behavioral:  heightened senses and motor skills, prolonged infancy, emotional bonds, and social group life.

By the time of the catarrhine primates 35 million years ago, physical features included grasping fingers with opposable thumbs, full color 3D vision, and teeth that your dentist would recognize (well, okay, Count Dracula’s dentist).  Primate vision and manual dexterity were demanding on the brain and encouraged an especially advanced neocortex. 

As young ones took longer to mature, they required more intensive parental care.  Mothers stepped up to the plate.  The life of a mother became deeply intertwined with the lives of her children, from pregnancy to nursing to supervision and education.  The physical states of pregnancy and lactation actually promoted neurochemical bonds of love in the brains of mother and child.  There were several models of mating behavior and gender roles, varying from species to species. 

Living in cooperative groups forced the evolution of social intelligence.  Monkeys learned to recognize each other’s facial features and expressions.  They developed social hierarchies and had to understand how they and their peers ranked within the group.  Long before there was wealth or power, there was social status, and primates cared intensely about it.  When we gossip with friends or watch reality TV shows, we see human social situations overflowing with drama – the ambition, the power plays, the cheating and the backstabbing!  We might shake our heads and wonder what kind of society we live in today.  The truth is, it’s nothing new.  Not by fifty million years.  

Back to Section 8.III: Mammals And Primates

Up to CHAPTER 8: THE LAST FEW 100,000,000 YEARS

Continue to Chapter 8 Human Ancestor Image Gallery

Chapter 8 Margin Notes (Blog Posts)

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