The evolution of life on earth has largely progressed through one simple natural process :

A species that adapts well to the environment prevailing at the time flourishes and develops. A species that struggles gradually declines and disappears. This rule also applies within a single species itself. The stronger members will dominate and set the trend for future growth, weaker members decline and die off.

With the emergence of us, the human species, on earth (and our increasing awareness of the world and wider environment around us), this basic but rather ruthless rule of survival does not quite agree with our dawning and gradually increasing humane inclination.
It has therefore been (and still is) in our nature to somewhat modify it, soften its edges so to speak - primarily within our species, but increasingly towards other species (like animals, plants, trees) as well - through our notions of compassion and morality (ethics).

Here is how the philosopher Jean-Jacques Rousseau has defined these :

These are concepts which by no means have been fully realised by us in this world. But it are goals to strive for, for this how we ultimately will define ourselves as true human beings.
Many philosophers (as well as others) have pointed out that Religion is not the foundation of ethics, morality. It is rather the other way around : ethics provide the foundation for Religion. Religion of course has been a successful vehicle spreading morality over time and through large region of the world to a wide audience. But (in due course) it has also started to misuse and corrupt the very principle of morality by giving it a selfish slant and using it as an instrument of crowd control :

"We know you are suffering and have a miserable life,
"but be good in this life and you will go to Heaven, (be reborn in a higher class, a higher human being)"

"on the other hand if you do not behave you will go the Hell, (be reborn in a lower class , or as a monkey)"

A believer who respects ethics merely in the hope of Heaven or fear of Hell is not virtuous, but simply selfish and prudent. As Immanuel Kant has expressed it :

I personally believe that most members of a formal religion these days are so to speak "in good faith". But those carrot and stick are inevitably always in one's mind.
In this regard the conscious atheist has an undeniable advantage. He does not believe in a hereafter or in any reward or punishment for his actions. When he does good he is therefore more likely to do it in the right spirit as defined by Kant.

PS
The various quotes included in this section are derived from The Little Book of Philosophy by André Comte-Sponville. As I have mentioned earlier in this Blog it is a delightful book which I wholeheartedly recommend to you.