Humans1 are animals and have evolved from ancestors that were not human. But our “bodily frame,” as well as the capacities that stem from it, show also that we are a unique kind of animal, a unique kind of ape, with distinctive features, of which the moral sense is one and, if we are to agree with Darwin, the most important one (Darwin, 1871b, p. 67). As Steven Pinker has written, “Morality is not just any old topic in psychology but close to our conception of the meaning of life. Moral goodness is what gives each of us the sense that we are worthy human beings” (Pinker, 2008, p. 34). In this essay, I will examine morality as a consequential attribute among those that determine “the difference of being human.” At issue, of course, stands the evolutionary origin of morality.
Two conspicuous human anatomical traits are erect posture and large brain. We are the only vertebrate species with a bipedal gait and erect posture; birds are bipedal, but their backbone stands horizontal rather than vertical (penguins are a trivial exception) and the bipedalism of kangaroos lacks erect posture and is drastically different from our own. Erect posture and bipedal gait entail other morphological changes in the backbone, hipbone, and feet and others.
Brain size in mammals is generally proportional to body size. Relative to body mass, humans have the largest brain. The chimpanzee brain has an approximate volume of 300 cm3; a gorilla’s is slightly larger. The human adult brain is more than three times larger, typically between 1,300 cm3 and 1,400 cm3. The brain is not only larger in humans than in apes but also much more complex. The cerebral cortex, where the higher cognitive functions are processed, is in humans proportionally much greater than the rest of the brain when compared with apes.
Erect posture and large brain are not the only anatomical features that distinguish us from nonhuman primates, even if they may be the most obvious. Other notable anatomical differences include the reduction of the size of the jaws and teeth and the remodeling of the face; reduction of body hair and changes in the skin and skin glands; modification of the vocal tract and larynx, with important implications for spoken language; opposing thumbs that allow precise manipulation of objects; and cryptic ovulation, which may have been associated with the evolution of the nuclear family, consisting of one mother and one father with their children.
Humans are notably different from the apes and all other animals in anatomy, but also and no less importantly in their functional capacities