TLDR: The genes of whoever reproduces get passed on.
Assuming evolution is real and natural selection rewards beings that survive and reproduce, why do I want to maximize my immediate happiness?
Am I even right that I want to maximize my immediate happiness? That seems unlikely to be true for everyone. Do single-celled organisms experience happiness? Maybe. They seem to react to their environment and make decisions on some level. But couldn’t someone say that about a computer program too? I presume the average single-celled organism or computer program is capable of experiencing astronomically less pleasure and pain than the average human.
But I’m not a single-celled organism. I’d guess I’ve evolved to seek immediate happiness. Happiness seems to be evolutionarily beneficial. Experiencing happiness motivates me to live.
However, types of sadness (i.e., unhappiness) are probably evolutionarily beneficial too. About 400 people have been identified with Urbach-Wiethe disease, which seems to prevent people from feeling fear. One woman who essentially doesn’t feel fear has been held twice at both knife-point and gun-point. Some people don’t feel pain too. They apparently tend to die because illnesses and injuries go unnoticed. Plus, Tim Urban theorizes we have our “social survival mammoth” because fitting in with our tribe was essential to human survival during the hunter-gatherer periods.
Not that every mildly common trait is or was inherently evolutionarily advantageous. It’s theorized that natural selection hasn’t eliminated gay people because homosexuality is caused by many genes. Those genes are presumably evolutionarily advantageous overall and don’t always lead to homosexuality. Being gay could also partially be due to epigenetics?
Similarly, maybe suicide rates haven’t declined (since 1950) because the possibility of suicide comes with the evolutionarily helpful traits of sadness and intelligence.
I’ll be more careful before saying anything is true about everyone. Every human’s DNA may be 99.9% identical, but even identical twins tend to not be genetically equivalent. A mutation could change anyone.
I also have a greater appreciation for my good fortune to not be a single-celled organism or one of the many beings that didn’t adapt to their environment. I have more appreciation for the unhappy feelings I’ve had too. If they’ve helped me survive, they’ve possibly led me to be happier overall.
Though I’d still like to live blissfully forever.
To clarify, I’d still prefer to be a being based on the net happiness they experience. I’d just never thought about being a single-celled organism or a member of a species on the verge of extinction before.