Asian Homo erectus died without issue and does not enter our immediate ancestry (for we evolved from African populations); Neanderthal people were collateral cousins, perhaps already living in Europe while we emerged in Africa... In other words, we are an improbable and fragile entity, fortunately successful after precarious beginnings as a small population in Africa, not the predictable end result of a global tendency. We are a thing, an item of history, not an embodiment of general principles.

Every breath you draw, every accelerated beat of your heart in the emotional periods of your oratory depend upon highly elaborated physical and chemical reactions and mechanisms which nature has been building up through a million centuries. If one of these mechanisms, which you owe entirely to your animal ancestry, were to be stopped for a single instant, you would fall lifeless on the stage. Not only this, but some of your highest ideals of human fellowship and comradeship were not created in a moment, but represent the work of ages.

Every living being is also a fossil. Within it, all the way down to the microscopic structure of its proteins, it bears the traces if not the stigmata of its ancestry.

How I hate the man who talks about the “brute creation”, with an ugly emphasis on Brute. Only Christians are capable of it. As for me, I am proud of my close kinship with other animals. I take a jealous pride in my Simian ancestry. I like to think that I was once a magnificent hairy fellow living in the trees and that my frame has come down through geological time via sea jelly and worms and Amphioxus, Fish, Dinosaurs, and Apes. Who would exchange these for the pallid couple in the Garden of Eden?

It appears, nevertheless, that all such simple solutions of the problem of vertebrate ancestry are without warrant. They arise from a very common tendency of the mind, against which the naturalist has to guard himself,—a tendency which finds expression in the very widespread notion that the existing anthropoid apes, and more especially the gorilla, must be looked upon as the ancestors of mankind, if once the doctrine of the descent of man from ape-like forefathers is admitted. A little reflexion suffices to show that any given living form, such as the gorilla, cannot possibly be the ancestral form from which man was derived, since ex-hypothesi that ancestral form underwent modification and development, and in so doing, ceased to exist.

It would be our worst enemy who would wish us to live only on the glories of the past and die off from the face of the earth in sheer passivity. By continuous achievement alone we can justify our great ancestry. We do not honour our ancestors by the false claim that they are omniscient and had nothing more to learn.

No self is of itself alone. It has a long chain of intellectual ancestors. The ‘I’ is chained to ancestry by many factors ... This is not mere allegory, but an eternal memory.

Perhaps the majority of paleontologists of the present time, who believe in orthogenesis, the irreversibility of evolution and the polyphyletic origin families, will assume that a short molar must keep on getting shorter, that it can never get longer and then again grow relatively shorter and therefore that Propliopithecus with its extremely short third molar and Dryopithecus its long m3 are alike excluded from ancestry of the Gorilla, in which the is a slight retrogression in length of m3. After many years reflection and constant study of the evolution of the vertebrates however, I conclude that 'orthogenesis' should mean solely that structures and races evolve in a certain direction, or toward a certain goal, only until the direction of evolution shifts toward some other goal. I believe that the 'irreversibility of evolution' means only that past changes irreversibly limit and condition future possibilities, and that, as a matter of experience, if an organ is once lost the same (homogenous) organ can be regained, although nature is fertile in substituting imitations. But this not mean, in my judgement, that if one tooth is smaller than its fellows it will in all cases continue to grow smaller.

Quite recently the human descent theory has been stigmatized as the “gorilla theory of human ancestry.” All this despite the fact that Darwin himself, in the days when not a single bit of evidence regarding the fossil ancestors of man was recognized, distinctly stated that none of the known anthropoid apes, much less any of the known monkeys, should be considered in any way as ancestral to the human stock.

The cooperative forces are biologically the more important and vital. The balance between the cooperative and altruistic tendencies and those which are disoperative and egoistic is relatively close. Under many conditions the cooperative forces lose. In the long run, however, the group centered, more altruistic drives are slightly stronger. … human altruistic drives are as firmly based on an animal ancestry as is man himself. Our tendencies toward goodness, such as they are, are as innate as our tendencies toward intelligence; we could do well with more of both.

The picture of the natural world we all take for granted today, has one remarkable feature, which cannot be ignored in any study of the ancestry of science: it is a historical picture.
[Co-author with June Coodfield]

We do not draw conclusions with our eyes, but with our reasoning powers, and if the whole of the rest of living nature proclaims with one accord from all sides the evolution of the world of organisms, we cannot assume that the process stopped short of Man. But it follows also that the factors which brought about the development of Man from his Simian ancestry must be the same as those which have brought about the whole of evolution.

With a single exception, it may be affirmed that units of volume now [1893] in use were originally in no way related to units of length, most of them being of accidental and now unknown origin. That a legal bushel in the United States must contain 2150.42 cubic inches is convincing evidence that the foot or the yard has no place in its ancestry.