Morgan points out that all the other primates that stand up on occasion have a habitat that is wet rather than dry. The proboscis monkey, which stands very readily, lives in mangrove swamps. The habitat of the bonobo, which, like dolphins, beavers, sea otters and humans, mates face to face, includes a seasonally flooded forest. Then there is our nakedness. In all the other apes it points downward.
Humans are the fattest primate.
We have 10 times as many fat cells in our body as any other animal of similar size. Unlike other primates, our children are born fat with a large proportion of white fat which is good for insulation and buoyancy but not for energy. Morgan thinks it is an adaptation that protected babies that had fallen out of trees. As with most aquatic animals, but unlike other primates, our fat is present all year and is stored, not deep within the body, but under the skin where it serves as an insulative layer. The only other mammals that store fat in this way are aquatic, like dolphins, seals and hippos.