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.
Alternatively:
Everyone will change the world whether they like it or not. It's usually in small ways and it's not always good, but you will have an impact and you are important.
Everything you do makes a difference, even if it's unclear how.
You're in a desert, walking along when you look down and see a tortoise. It's crawling toward you. You reach down and flip it over on its back, its belly baking in the hot sun, beating its legs trying to turn itself over. But it can't. Not with out your help. But you're not helping. Why is that?
I have no illusions about me being a "good" person, but I never leave any creature in need to suffer if I can help it, and that includes everything, even insects.
This has resulted in us adopting quite a few "rescue" animals and to be honest, the love and loyalty you get from them is on a completely other level still. They KNOW.