2.3 Through evolution
One of the great ethical achievements of early Christianity and some of the other religions was a recognition in principle of the brotherhood of man. The first grand lesson learned from evolution was that of the unity of life. Not only are all men brothers; all living things are brothers in the very real, material sense that all have arisen from one source and been developed within one process. 
We are part of nature and we are related to every other organism that has existed, or that does or will exist on the earth.  But we are more nearly related to some than to others. It is obvious that man is an animal and not a plant, which is a taxonomic way of saying that he is more closely related to all animals than to any plant.  Among the animals it is equally obvious that, in the same sense, man is a vertebrate and not an invertebrate. Among vertebrates he is a mammal, not one of the various sorts of "fishes," an amphibian, a reptile, or a bird. Among mammals he is a primate, a member of the Order Primates and of no other of the numerous mammalian orders.
As the degrees of relationship are narrowed, the distinctions become less and their significance becomes less obvious. The general position of Homo sapiens within the animal kingdom, within the vertebrate subphylum, and within the mammalian class is absolutely established and beyond any doubt.The exact position within the primate order and the detailed relationship to each of the other primates, living and fossil, are not yet known with complete precision. Such questions as whether the gorilla, the tarsier, or some other living primate is the closest surviving branch from the human ancestry have no essential bearing on the nature of man or on man's place in nature.
Man's intellectual, social, and spiritual natures are altogether exceptional among animals in degree, but they arose by organic evolution.  It has also been shown that purpose and plan are not characteristic of organic evolution and are not a key to any of its operations. Man was certainly not the goal of evolution, which evidently had no goal. He was not planned, in an operation wholly planless. He is not the ultimate in a single constant trend toward higher things, in a history of life with innumerable trends, none of them constant, and some toward the lower rather than the higher. Is his place in nature, then, that of a mere accident, without significance? The affirmative answer that some have felt constrained to give is another example of the "nothing but" fallacy. The situation is as badly misrepresented and the lesson as poorly learned when man is considered nothing but an accident as when he is considered as the destined crown of creation. His rise was neither insignificant nor inevitable. Man did originate after a tremendously long sequence of events in which both chance and orientation played a part. Not all the chance favored his appearance, none might have, but enough did. Not all the orientation was in his direction, it did not lead unerringly human- ward, but some of it came this way. The result is the most highly endowed organization of matter that has yet appeared on the earth—and we certainly have no good reason to believe there is any higher in the universe. To think that this result is insignificant would be unworthy of that high endowment, which includes among its riches a sense of values.