According to Becker, the Declaration assumes a transcendentalist view of human beings as created in God's image and thus endowed with the moral dignity that justifies their special claim to "unalienable rights"--a teaching that Becker traced back to John Locke. But Becker thought this Lockean philosophy of natural rights was denied by the Darwinian view of evolution.
When so much the greater part of the universe showed itself amenable to the reign of a purely material natural law, it was difficult to suppose that man (a creature in many respects astonishingly like the higher forms of apes) could have been permitted to live under a special dispensation. It was much simpler to assume one origin for all life and one law for all growth; simpler to assume that man was only the most highly organized of the creatures (the missing link would doubtless shortly be found), and to think of his history accordingly, as only a more subtly negotiated struggle for existence and survival. (274-75)
According to Becker, this supported a Machiavellian view of politics.
In a universe in which man seemed only a chance deposit on the surface of the world, and the social process no more than a resolution of blind force, the 'right' and the 'fact' were indeed indistinguishable; in such a universe the rights which nature gave to man were easily thought of as measured by the power he could exert. (276)
If this were true, then we would have to say that Darwinian science subverts any belief in natural rights, and thus denies the fundamental principles of the American political tradition as well as the modern tradition of human rights. In fact, some of the critics of Darwinian science have drawn this conclusion in arguing that Darwinism is morally and politically dangerous.
Against this, I argue that Darwinian science actually supports Locke's understanding of natural rights as rooted in human biological nature.
In his Two Treatises of Government, Locke justifies natural rights as rooted in the natural desires and natural reason of human beings as animals endowed by God with "sense and reason," as opposed to the "inferior animals" that are moved by "sense and instinct." The natural desires become natural rights when human beings as rational animals reflect on the social conditions for satisfying their desires (FT, #86-92). Because of their strong desire for self-preservation, human beings can recognize the right to life as a natural right. Because of their strong desires for sexual mating and parental care, human beings can recognize the rights of parents to rear their offspring. Because of their strong desire for property, human beings can recognize the rights of property. Murder and theft violate the laws of nature and God, because murder and theft are contrary to "the principles of human nature," which are also contrary to God's law insofar as God's will is evident in the way He has "ordered the course of nature" (FT, #89; ST, #10, 67).
Critical to this reasoning is the thought that human beings as rational animals can understand that to satisfy their desire to receive good from others, they must satisfy the like desire in others as "being of the same nature" (ST, #5).
Human beings are naturally equal, because as members of the same human species, they are born to the same general capacities for reasoning about the satisfaction of their desires. They are naturally free, because they naturally resist being attacked or exploited by those who would rule over them by force rather than consent.
When Locke thus speaks about the law of nature as implanted or written into human nature, some readers see this as contradicting Locke's denial of innate ideas in his Essay Concerning Human Understanding. There he is famous for arguing that the human mind should be conceived as an "empty cabinet" or "white paper" that receives any content coming from experience (I.1.15; I.2.22; II.1.2).
His argument in the Essay assumes, however, a very narrow kind of "innateness"--an invariant trait that appears immediately at birth fully formed without any need for experience. This leaves open the possibility of another kind of innateness--natural propensities or inclinations that develop in response to experience. The first kind of innateness assumes an absolute dichotomy between nature and nurture or instinct and learning. The second kind of innateness allows for the interaction of nature and nurture or instinct and learning. For this second kind of innateness, nature can be nurtured, and we can have instincts for learning.
It is this second kind of innateness that runs through the Two Treatises. So, for example, Locke argues: "we are born free, as we are born rational; not that we have actually the exercise of either: age that brings one, brings with it the other too. And thus we see how natural freedom and subjection to parents may consist together, and are both founded on the same principle" (ST, #61).
Moreover, this natural propensity for human beings to develop into fully rational animals through their rearing by parents is open to "defects that may happen out of the ordinary course of nature," when mental disorders impede the full development of normal human rationality (#60). And, even within the normal range of human rationality, there is variation, in that intelligence is variable across individuals (#54).
This is the kind of innateness that one finds in Darwinian biology. Although Darwin sees human traits as products of an evolutionary ancestry linked to other animals, he recognizes the uniqueness of human beings in their natural capacities for reason, morality, and language. Those capacities are not rigidly fixed instincts that arise automatically and necessarily at birth fully formed. Rather, they belong to our evolved human nature as natural propensities that develop over the life of each human individual in response to cultural experience.
Recent research on how the human brain has evolved for social intelligence and cultural learning confirms this Darwinian understanding in a way that also confirms Locke's argument.
Human beings are unique in their capacity for social reasoning. Other primates might show some ability for "mind-reading" or "theory of mind"--being able to probe the mental point of view of other individuals. But human beings are unique in the extent to which they can infer the desires and beliefs of others as they negotiate the terms of social cooperation as based on a social contract constituted by collective agreement to serve the common good.
Evolutionary psychologists like Michael Tomasello and Robin Dunbar have shown how human infants in their first few years show a capacity for "joint attention"--following the gaze of adults to direct their attention to the same object being attended to by the adults. Subsequently, they learn how to direct the attention of adults to objects the infants are looking at. Other primates don't show this ability for sharing attention, and thus they lack the capacity for language and culture that is built on this shared attention.
This evolved human capacity for shared attention--for getting into the minds of others and reaching agreement on the socially constructed norms of cultural life--is the fundamental presupposition of Locke's understanding of natural rights. How this evolved social psychology allows us to agree on our natural rights and duties is well stated in a passage from Richard Hooker's Laws of Ecclesiastical Polity (I.8.7) that is quoted by Locke (ST, #5):
The like natural inducement hath brought men to know, that it is their duty no less to love others than themselves. For seeing those things which are equal, must needs all have one measure; if I cannot but wish to receive all good, even as much at every man's hand as any man can wish unto his own soul: how should I look to have any part of my desire herein satisfied, unless myself be careful to satisfy the like desire, which is undoubtedly in other men, we all being of one, and the same nature? To have anything offered them repugnant to this desire must needs in all respects grieve them as much as me, so that if I do harm, I must look to suffer; there being no reason that others should show greater measure of love to me, than they have by me showed unto them. My desire therefore to be loved of my equals in nature as much as possibly may be, imposeth upon me a natural duty of being to them-ward fully the like affection. From which relation of equality between ourselves and them that are as ourselves, what several rules and canons natural reason hath drawn for direction of life, no man is ignorant.
Chimpanzees don't have the natural cognitive ability for such social reasoning that leads to the understanding of justice as reciprocity, or the Golden Rule. Only human beings have this ability by virtue of their evolved nature, which supports the historical experience that has brought about our modern Lockean understanding of natural rights and natural duties.
Some related posts can be found here, here, and here.