The idea that religion is the only source of ethics is based on the idea that "God" (and I don't believe in him/her/it) dispenses laws or moral codes for humans to obey, and rewards those who obey and punishes those who disobey.
Anyone who does a good thing because they expect a reward for it from (or avoids a bad thing because they expect to be punished by) some cosmic lawgiver is clearly immoral. In Matthew 6, Yeshua is reported as talking about getting rewards in heaven for doing good on earth (or at least, that is the way that the passage is often interpreted). Eeeeeuuuuuwwwwwww!!!! Wrong wrong wrong.
I do what I believe to be right and good (the pursuit of justice and the comforting of the afflicted and oppressed, donating to charity, participating in campaigns for social & environmental justice) because I believe it to be right and good, and I hope that it will increase the sum of happiness, not because I expect a pat on the head from a non-existent person in the sky.
OK so I get satisfaction from seeing people looking & feeling better after I have helped them - but the amount of effort involved probably outweighs the reward. And OK so I also get satisfaction from doing what is good and right, cos it makes me feel as though I am making a difference, and it makes me feel better about myself, but I don't see why I shouldn't. Self-esteem is good, isn't it?
And anyway, empirical evidence in the form of numerous morally upright atheists (though not all atheists), and millions of bigoted religionists (though not all religionists), make it obvious that the sort of religions that have prescriptive moral codes are not a good place to get your ethics from. The sort of religion that is inclusive and tolerant and rational would be a better place to get your values from, but you should still check them against your own conscience, reason and experience.
There's an excellent book by Richard Holloway called Godless Morality which explains exactly why God being the source of moral commandments can't possibly work even if you actually believe in God (which Holloway doesn't, though he says he isn't exactly an atheist or an agnostic either). The reason is this: because we cannot be sure what "God" wants, or even if s/he exists, we cannot claim in our moral pronouncements to speak for God. If two people both claim to be doing what God wants, but do exactly the opposite, how do we decide between them? By using ordinary evidence, reason and compassion to decide.
I tend to use the word ethics to mean a set of best practices that have evolved or emerged from a group ethos (though that is not the etymology of ethics), and I use the word morals to mean a set of practices imposed by a moral code. In this sense, ethics are clearly more pragmatic and flexible and humane, whereas moral codes, because they are usually arbitrary and invented, are usually cruel and inhumane.
Ethics and altruism are clearly evolved characteristics — but that doesn't make them any less beautiful, especially as we usually have a choice about whether to do the ethical or altruistic thing. It's amazing and wonderful that both people and animals will help the injured and dying, often at considerable cost or risk to themselves — and people often help others who are clearly not genetically related to them, including other species.