Selection by groups seems to have helped develop the ethical values that are also tied to religion. Ethics which encouraged mutual respect and self-sacrifice by individuals for the group enhanced the group’s survival success. Societies with low ethical standards tended to collapse.
Decline is influenced by luxury, pluralistic ethics and egoistic individualism. American Conservatism struggles against these things but at the same time addresses the danger of sameness. Big bureaucratic states and global business often hurt competition and variation.
The disappearance of all groups but one would be catastrophic. Men like Stalin and Hitler damage the survival and variation of smaller groups by seeking world domination, more or less. Cooperative competition among separate state powers is the essence of Federalism. War is a breakdown of competition, it tends to lose the physically and mentally fit, and the most patriotic among us.
Conservatism and Federalism, as well as religions that affirm subsidiarity and traditional ethics, work in harmony with human nature and evolution. When we sink to imperialism or universalist ambitions we move away from the mutual love and self-sacrifice that has always worked best in smaller communities.
I see these developments in sociobiology and evolutionary psychology as renewing traditional American Conservatism.