Twins: And What They Tell Us About Who We Are by Lawrence Wright

They seem to tell us that we're almost entirely genetics, not very much environment. Separated at birth twins end up the same, and more so, the older they get. For that matter adopted children end up like their biological parents and not like their adoptive parents, and again, more so, the older they get. This is concerning personality, IQ, crmininality, etc. African Americans that are adopted by white familes end up with the same IQ as other African Americans (which is markedly lower than the average, thanks to hundreds of years of slavery natural selection.)

IQ and personality are almost entirely the result of genetics. Short of horrific abuse/neglect it just doesn't matter how you're brought up. Religion is genetic. Although the particular dogma you choose depends on which dogma you were indoctrinated into. Sexual preference is at least somewhat genetic. Although there is for this (and all others) the question of differences in the womb environment.
Divorce is largely genetic. Racism. Closemindedness. Musical talent.

Who you marry isn't. That's mostly just chance. At least to the extent they've studied it. Because we all can really get it on with a ton of very different people you know.

But what if twins aren't actually a good experiment for nature versus nuture? What if they're telepathic with each other and that's the real reason separated twins are still so much alike? CIA experiment. Close open eyes on command. See if other twins alpha wave rhythms also changed. 2 out of 13 twin sets showed "the results they were looking for". No unrelated subjects did.

But what about adopted children still eventually ending up like their biological parents? (Did they also have a telepathic link? What if you killed the parents........)

These are mostly awful results. They suggest eugenics, racism, etc. And so they have been attacked. The scientists have been attacked. Cyril Burt had his reputation destroyed after he died. He had concluded IQ was almost entirely genetic based on decades of twin data. Eventually his work was completely discounted. Later Minnesota studies that haven't been discounted at all ended up with almost the exact same conclusion on IQ/genetics.

Schizophrenia is only half genetic, as is alcoholism. Respiratory diseases and some cancers are almost entirely environmental. Smoking, insomnia, career, hobbies, coffee consumption and suicide are all highly genetic. (But if smoking is genetic... than you've just made your environment...) Criminality is more than twice as much the result of genetics than of environment.

There are plenty criticizing these conclusions but they're not convincing. Apparently liberals can be dishonest too. On the bright side, if you've had some awful things in your life, or your parents were kind of duds, perhaps you're mistaken in thinking it really mattered. Perhaps with better parents you still would be a nobody and you should just not worry about it, about any of it.

This book was written more than ten years ago. I'm not aware of any eugenics programs starting up since. We seem to still be well on our way to an idiocracy. Because you know this is the end of mankind. Before reading this book I vaguely thought we're 75% genetics for most things. It was a conservative estimate on my part based on my own observations/anecdotal evidence. Safe now to ramp that up quite a bit. I won't bother trying to get my dumbass 8 year old nephew to play music or read a book. By now he would already have been doing so if he had it in him at all. You can give people nudges, and make things available to them, but if they don't got it, there's no point in going on about it.