| Chapter 2: | Humans |
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away from our own houses on another street. It was community defense. With nothing to gain individually from scolding these errant adolescents, we knew instinctively that public safety is good for the community, and we each shouldered our weapons to uphold it. This kind of aggression, supporting the community beyond self-interest, is part of being human, but not uniquely so: We share community defense with many other primates. As for the youths, we will return to them shortly.
Bones
This is an exciting time to be a primatologist. New discoveries of ancient bones, new methods of analysis, new theories and ways to test them, and the whole new genre of DNA analysis add daily to the understanding of human evolution. The downside is that anyone whose last biology course was more than 10 years ago is likely to be badly out of date. Here, therefore, is a review of current thinking about human evolution.
To understand who human beings are and how they came to be what they are today, primatologists and evolutionary biologists look to humans’ closest relatives, other primates. The closer the taxonomic relationship, the more likely that animals will have a similar biology. Genetically, humans’ closest living relatives are the two chimpanzee species, the common chimpanzee and the bonobo (once known as the pygmy chimpanzee). Humans are only slightly more distantly related to gorillas. But contrary to the common understanding, humans are not descended from chimpanzees, or even from a chimpanzee-like ancestor. For example, the last common human-chimpanzee-gorilla ancestor was not a knuckle-walker, as is commonly pictured. Biomechanical analyses of the shoulders, elbows, hands, vertebral column, hips, knees, and feet show that human ancestors never walked on all fours; humans evolved from an upright-positioned arboreal climber that walked on two legs when on the ground, as gibbons and orangutans do today (Hart & Sussman, 2009; Lovejoy Lovejoy, Suwa, Simpson ,Matternes , & White, 2009; Schmitt,