In a few passages of his book, Altman identifies the secret teaching as an affirmation of Darwinian evolution and the public teaching as an affirmation of Platonic eternity. That public teaching of Strauss is what Altman embraces as true. By contrast, I find the Platonic teaching of eternal cosmic standards implausible, and I embrace the Darwinian teaching of enduring but not eternal standards as true. This Darwinian teaching is not nihilistic, as Altman believes it is, unless one agrees with the early and late Nietzsche that Darwinism is a "deadly truth" because it frustrates our longing for eternal standards.
Strauss seems to be favorable to the "young nihilists" when he writes:
"I have tried to circumscribe the intellectual and moral situation in which a nihilism emerged which was not in all cases base in its origin. Moreover, I take it for granted that not everything to which the young nihilists objected was unobjectionable, and that not every writer or speaker whom they despised, was respectable. . . . Let us then not hesitate to look for one moment at the phenomenon which I called nihilism, from the point of view of the nihilists. . . . A new reality is in the making; it is transforming the whole world; in the meantime there is: nothing, but--a fertile nothing." (363)But then Strauss pulls back and suggests a criticism of nihilist historicism:
"I frankly confess, I do not see how those can resist the voice of that siren who expect the answer to the first and the last question from 'History,' from the as such, who mistake analysis of the present or past or future for philosophy, who believe in a progress toward a goal which is itself progressive and therefore indefinable; who are not guided by a known and stable standard: by a standard which is stable and not changeable, and which is known and not merely believed." (364)Altman reads this as Strauss's effort to reassure the reader that he is not attracted to nihilism. "This has been Strauss's point all along, he now reassuringly suggests. Moreover, it is only by embracing a timeless, absolute, and unchanging standard that the nihilist can be refuted. Strauss now seems to be calling for a revival of traditional Platonism ('the Ancients') or even possibly actual knowledge--rather than mere belief--in the Living God ('Jerusalem')" (327). Altman then proclaims his own belief in this "exoteric teaching" of Strauss.
But according to Altman, Strauss's secret teaching denies that there is any "timeless, absolute, and unchanging standard," and thus Strauss is a Darwinian. "LS [Leo Strauss] generally ignores Darwin, but in his immorality, his atheism, his historicism, and in his revival of 'natural right' (as opposed to rights), LS is neo-Darwinian" (382).
Altman offers no proof that Darwinism must promote immorality, atheism, and historicism. But in a footnote, he suggests that he accepts the argument of Richard Weikart's book From Darwin to Hitler: Evolutionary Ethics, Eugenics, and Racism in Germany (416, n. 85). I have written some posts on Weikart's books, who argues that Darwin was responsible for Hitler, and that the only alternative to Darwinian Nazism is intelligent design theory.
One oddity here is that the arguments for intelligent design were originally invented by the Athenian Stranger in Book 10 of Plato's Laws. So while Altman generally scorns the Athenian Stranger, here he seems to agree with him about the need for persuading people to believe in intelligent design, because any natural evolutionary explanation for human nature within the cosmos will promote immorality, atheism, and historicism. But the Athenian Stranger's arguments are not very plausible. And it's not even clear that he believes them himself.
Strauss and the Straussians are ambivalent about this. (One can see this, for example, in Catherine Zuckert's Plato's Philosophers.) On the one hand, they suggest that the only alternative to historicist relativism is a Platonic cosmology of eternal standards for human life. On the other hand, they suggest that Socrates never clearly endorses this cosmology, and that he implies that the ultimate standards for human life must be drawn from human nature, from natural needs and desires, as arising from human biological nature.
My argument is that the Platonic dialogues give us reasons to believe that conceptions of cosmic teleology and the eternity of species are implausible because they contradict what we know by experience. More plausible, I suggest would be Aristotelian and Darwinian conceptions of immanent teleology and the natural history of the human species that would support standards of moral and intellectual excellence grounded in natural human desires.
These points are elaborated in various posts that can be found here, here, here, here, here, here, and here.