Selfish Acts, and the mystery of why, defying reason

What seed is planted in humans that establishes selfish people? Was it some depravation of childhood, was it always apparent? Was it a gene? A horrible childhood? Why would you nuture it, condone it? Why would you tolerate it's constant demand to be fed? Why does it grow? Why does it thrive on demeaning others? Why would it begin to look normal to anyone? My friend of many years husband lands in the hospital for several weeks, he has multiple serious problems, artery surgery needed again in another leg, yet addiction to painkillers to be weaned off of first, that reared it ugly head after the first leg was done. Amazing she still drives, but not liking winter she has not made an attempt to go see him, nor has she talked to any of doctors. We're talking husband and wife here, 50% = the other 50%. Her sister and kids tell her off about this, and implore her to go see him. Nada. She pleads her case of she might fall and get hurt going to see him..... I am amazed, I have seen so many sides to the "human" element, the selfish side, that I have no doubts why my Mom preferred dogs to most people, it brings back my humor. I've known her for years, I was business partners with her once, but still I am amazed that the seed of self preservation is so very deep. If my spouse ever needed me I would be there, and even if he was pissed at me, I'd stay very near....whether he knew it or not...and I'd be right up those doctors asses, too. Most of all I'd want to assess how I thought it was shaping up for someone I say I love.