Atheists, is morality really subjective?

Then why do all human cultures, as well as monkeys and apes, share the same basic moral codes? The evidence is encyclopaedic that basic morality (do not harm others; help others; abhorrence of lies and cheating; value of charity, honesty, good parenting, etc.) is hard wired into our genes, to strengthen social bonds to increase our chance of survival and reproduction. How can anyone possibly say that morality is subjective? Note, I'm talking about moral behavior, not social conventions such as ual expression, dietary regime or worshiping fantasy beings.