Today, someone posed an interesting question in r/DebateAnAtheist on Reddit: As an atheist, how can one be morally good? And why be morally good?

Here is my answer, edited and drawn out a bit. (Check out the original thread for many more good responses—there are many voices of sensibility to be found there.)

Short answer: Evolution.

Long answer:

First, let’s dispense with the notion that atheists are less “morally good” than believers. A look at the violent crime rates in religious vs. secular countries and US states shows that simply isn’t the case.

The original question says, “A theist cannot commit an evil without fear of punishment since God is all-knowing.” Strictly speaking, this isn’t precisely true; as I understand Christianity, admission to heaven is based on belief, not deeds. still, what is implied here is that if theists realized there was no god — someone found a tomb containing Jesus’ bones, let’s say — they’d start stealing and killing with reckless abandon. That’s a pretty low opinion of believers!

Clearly, there is something that keeps us all, religious or not, on the straight and narrow — the conscience, if you will. So where did it come from?

A lot of apologist speakers, having given up on saying “You need God to be good” owing to the aforementioned evidence of crime rates, now say “God wrote morality on our hearts.” (Silly place; the brain would be better.) Okay, but if that were the case, wouldn’t morality be universal across humankind? I’m not talking about everyone being good, but I’m talking about broad agreement on things like the morality of same-gender relationships, capital punishment, punitive amputation, women’s rights, etc., never mind the bits of the Bible that most people now consider immoral (more on which in a moment).

If morality really is God-given, it would seem to me there must either be multiple gods issuing multiple versions of morality, or one god who can’t keep his business straight.

The way I see it, a much more plausible explanation for morality is that evolution favors altruism — concern for the survival of the group and protection of its most vulnerable members. We see this elsewhere in the animal kingdom, not just in humans. (Keep in mind that ideas and methods can be subject to natural selection as well as physical traits.)

The idea that we humans are in total control of our faculties is an illusion. We are very much herd animals, like horses and dogs, and a lot of things run on automatic pilot. (I like to say we are “hard-wired” to act certain ways, though not everyone sees the irony of an atheist saying this.) Altruism isn’t something we just choose. It is, for lack of a better term, hard-wired into most of us. Some people don’t have that wiring — sociopaths, for example — but most do.

So that is how and why atheists can be morally good.

And not just atheists — theists as well. You don’t see many devout Jews stoning gay people to death (Leviticus 20:13) or punishing rapists by forcing them to marry their victims and pay off her father (Deuteronomy 22:28-29), or Christians who hate their families because Jesus told them to (Luke 14:26), even though the Bible commands this.

Why? My guess: Deep down, they know their own human morality is superior to (supposedly) God-given morality.

If you’re a believer who thinks morality must come from God, ask yourself: If you came to the conclusion that God did not exist, would you really act less morally than you do now? I’m not suggesting you’d go out on a killing spree, because you could still get caught and thrown in prison. But would you lie more? Would you be more likely to shoplift if you thought you wouldn’t get caught? (You might have more or more creative premarital sex, but I don’t think that’s immoral—in fact I think it’s healthy.)

I can only speak from my own experience: When I gave up belief in God, it had no effect on what I do or don’t do. My morals and ethics did not change. Actually, if anything, I’d say I’m a bit more honest—because atheism forces one to realize we are responsible to our fellow humans, and when we wrong them, only we can make up the damage. There is no spirit in the sky to do it for us.

I might be tempted to argue that a theist’s reason for being good (for eternal reward or to avoid punishment) is morally superior to the atheist’s reason (being good for goodness’ sake). But I can’t, because I believe all of our morality comes from the same place: It comes from us.

Isn’t that good to know?