We're social creatures and our lizard brain has been programmed by natural selection to help others and be good stewards to our environment. Those feelings come from a dopamine rush as a biological reward for practicing behaviours that have lead to survival and prosperity.
The triune brain is an obsolete theory.
Natural selection also selected self-preservation, fear of the unknown and a plethora of other biases that lead to all kinds of anti-social behavior, there's not much foundation for ethics to be found in natural selection.