Our moral sense is a product of evolutionary pressures that favored cooperation and kin protection, so morality is a biological adaptation, not evidence of a transcendent moral lawgiver.

Why people find it persuasive

Evolutionary biologists and psychologists have documented cross-species precursors to human morality — reciprocal altruism in primates, kin selection, reputation-based cooperation — that plausibly account for why creatures like us feel that fairness, loyalty, and harm-avoidance matter. If a purely naturalistic process can produce moral feelings and behaviors, there is no need to posit God to explain why we have a conscience at all.

Important distinctions

• • Explaining the origin of moral feelings/psychology versus explaining the existence of objective moral facts or obligations
• • Descriptive claims about what moral beliefs evolved versus normative claims about what actually is right or wrong
• • Evolution explaining why creatures like us would believe certain things are moral versus evolution explaining why those beliefs would be true
• • Moral psychology (the feeling of obligation) versus moral ontology (whether obligation is real and binding independent of feeling)
• • Evolutionary debunking arguments applied selectively to religious moral belief versus applied consistently to all belief-forming processes including reason itself

Christian response

• • Evolutionary accounts of moral psychology are well evidenced and are not in tension with theism as such; many theists, including Francis Collins and philosopher Robert C. Roberts, accept that evolution shaped our capacity for moral feeling and reasoning while still holding that morality itself is objectively grounded beyond biology. The real philosophical question the objection needs to answer is not why we have moral feelings, but whether there are objective moral facts (that torturing children for fun is actually wrong, not merely that most humans evolved an aversion to it), and evolutionary psychology by itself is silent on that ontological question.
• • Philosopher Sharon Street's evolutionary debunking argument (A Darwinian Dilemma for Realist Theories of Value, 2006) actually cuts in an interesting direction here: she argues that if our moral beliefs were shaped by processes selected for reproductive fitness rather than for tracking objective moral truth, we have no particular reason to trust that they track truth at all, which is a genuine problem for confident secular moral realism, not merely for theism. If evolution explains away moral knowledge, it does so for everyone's moral beliefs, secular and religious alike, undermining the objection's implicit assumption that only religiously-grounded morality is undercut by an evolutionary account.
• • C.S. Lewis's argument in Mere Christianity (1952) and later developed by philosophers like J.P. Moreland is that the reality of a binding moral law which we regularly experience as obligating us even against our evolved self-interest (choosing not to abandon a drowning stranger at personal cost, honoring commitments when cheating would be undetected and advantageous) sits oddly with a purely fitness-based origin story, since natural selection would be expected to favor genuinely selfish behavior wherever it goes undetected, not a felt sense of binding obligation that persists even then.
• • Theistic accounts, defended by philosophers like Robert Adams (Finite and Infinite Goods, 1999) and William Lane Craig, hold that God's own nature, rather than evolutionary programming, grounds objective moral values, while allowing that evolution (or general revelation, as in Romans 1:19-20 and 2:14-15) is simply the mechanism by which humans come to perceive and internalize those independently real moral facts, similar to how evolution shaped our sensory organs to perceive an independently real physical world without evolution being what makes the physical world real.
• • This does not disprove naturalistic moral realism, which some secular philosophers like Erik Wielenberg (Robust Ethics, 2014) defend by arguing objective moral facts can simply be brute, non-natural facts requiring no further explanation, analogous to logical or mathematical truths; the dispute at this point becomes a genuinely difficult metaethical debate about whether unexplained brute moral facts are more or less parsimonious than a theistic ground for morality, rather than a debate evolutionary biology alone can settle.

Christian counterresponse

The divine grounding claim is not meant to do causal-mechanistic work alongside evolution but metaphysical work: it addresses why there are truths about value there at all for any perceptual mechanism, evolved or otherwise, to track, which is a different explanatory question from the biological one, comparable to how positing mathematical Platonism does not compete with, but rather stands alongside, an account of how human brains evolved the capacity to do mathematics.