Mammals came to existence roughly one hundred million years ago. Mammal females make much larger investments into offspring and are choosy about mates.

Males tend to be competitive for access to receptive (ovulating) females and therefore to be bigger and stronger. Earliest primates evolved about fifty million years ago with major changes: having eyes on the front, which allowed for depth perception, and opposable thumbs, which made it possible to grab and hold things.

Early hominins, directly ancestral to humans, appeared about five million years ago in Eastern Africa and lasted about three million years. They ate primarily fruit and nuts.  They were bipedal - walked upright, which was energy efficient and helped to spot food, mates, competitors, and predators. They also were slow, small, vulnerable to predation, and formed social groups, though with limited cooperation. Their brain size was one-third of the modern human brain weight, and they left no stone tools. They had a high level of sexual dimorphism: males were twice as big, which was driven by male-male competition. They did not pair-bond, and mothers wean kids after five years, letting juveniles be independent with a high probability of dying (Miller 9/11/2022).

The earliest Homo evolved about two million years ago with dramatic differences in brain, body, and behavior. The brain of Homo erectus was three-fourths the size of Homo sapiens, they used elaborate tools. The body was almost identical to ours, shaped for long-distance endurance running. However, bipedality did not allow them to sprint faster than quadrupeds. For the upright position some other defining morphological traits were selected: flexible waist and side-facing shoulder, which aided throwing skills and therefore hunting (Wong 2014). They added regular meat to the diet, used fire for cooking also fibrous plant foods, and for warmth and protection. They were moving toward pair-bonding with accompanying reduction in sexual dimorphysm and longer care for young - ten to fifteen years. Females care for multiple children at a time with the help of the father, kin, and the highly cooperative group - the alloparents. Cooperative breeding predates the significant enlargement of the brain. Women who lived decades after menopause had likely doubled the survival of the young. Our empathy likely comes from the group care for children, in Homo. They became numerous and migrated all over the Old World.

Anatomically, modern humans emerged one-fifth of a million years ago. However, behaviorally, we have existed for less than a tenth of a million years - with complex societies and warfare (Hrdy 2009) . About ten thousand years ago most human groups turned to agriculture. They settled with larger villages, built sturdier houses, accumulated wealth, had hierarchies, dramatic diet changes and new diseases. Within a few thousand years of agriculture, large cities emerged. And about a hundred years ago technology started to change the environment of evolutionary adaptation, creating new conditions for selection. 

Cultural anthropologists study modern traditional societies that live off the land and other foragers did for two million years, like !Kung (South Africa) and Hadza (East Africa) but also in Asia and South America. They are highly mobile, live in simple huts in small groups, have only essential belongings, cooperate, have gender roles, and help together with children. Women gather plant food over large areas, returning over and over to the plants with ripening fruit and bringing them back to the camp every day. Men travel on foot for hunting days long. Women provide sixty to eighty percent of food weight.

!Kung people of Kalahari Desert live in a climate ranging from freezing to 110 degrees Fahrenheit. They are the masters of survival in their habitat. They have a self-sufficient economy, except for iron, minimal possessions are owned exclusively by individuals, shared and exchanged. They forage less days than they spend on other tasks, and a lot on leisure activities like composing songs, singing, playing musical instruments, dancing, sewing beaded patterns, telling stories, visiting, thinking or daydreaming, and simply resting. They have no hierarchy, with women equally involved and important, and the leaders take their position because of their abilities and respect. They know over five hundred species and use over a hundred kinds of plants for food. Men are loving fathers, they build huts, hunt with poisoned arrows to provide for about thirty percent of animal food, and gather about twenty percent of plant food. Women gather fruits, berries, vegetables, nuts, melons, beans, roots, and prepare food. Mongongo nuts with their outer fruit are abundant and constitute half of the diet. Their diet is very healthy by modern standards, it is extremely low in saturated fats, salt, and sugar, which saves these people from many diseases. If young !Kung win a fifty-fifty chance to escape deadly infections before they are fifteen, they live till fifty-five on average, dying usually from respiratory diseases and malaria (Shostack 1981).

References:

Dr. Lynne Miller, lecture notes, September 2022.

Wong 2014 - Rise of the Human Predator

Hrdy 2009 - Meet the Alloparents

Marjorie Schostack, Nisa, 1981.