You sir, are a complete moron. Your timeline is all fucked up.
Polygamy, whatever your feelings on the subject, is basically as old as marriage in general, and is included as a feature in "biblical" marriage.
Of course, an inclination for a heterosexual man to fuck more than one woman isn't a "difference in the brain" because that's all heterosexual men. That's the standard model. Humans: They want to fuck around.
Gay rights, that's a later concept. The modern gay rights movement began in 1969 at the Stonewall Inn, a gay bar in NYC. And yes, studies of gay and straight brains show evidence of differences.
Beastiality is gross. But it's older than the modern gay rights movement, as there are records of people caught with their pants down in the barnyard long before Stonewall. The nature of the act being private, it's a hard concept to date, but, hey, it's included in Greek mythology, so we know it's fucking old.
NAMBLA isn't a functioning organization right now, as I understand it, it's like 2 guys with a copying machine. Yes, I know, it's gross, but please, let's not overestimate the threat. The way people act, you'd think it was NRA or AARP sized, at least.
I don't know what causes pedophilia, but, brain scans have found that pedos tend to lack impulse control. Seems plausible to me.
Serial killing is older than gay rights and older than NAMBLA, asshole. Ever heard of "Jack the Ripper?" He was, after all, killing women in Victorian England, not exactly a modern setting. Before him, there was, for example, Elizabeth Bathory, who murdered young women to bathe in their blood.
Serial killing is probably sexual in nature for the people who do it. They almost always kill exclusively the sex to which they are attracted. Straight men kill women, gay men kill men. I've never heard about MRIs of serial killers, but it's not unbelievable for some of that shit to show up on a brain scan.
Psychology all depends on brain functions. Explaining why people do things has nothing to do with making the thing "ok" to do, we can simultaneously view pedophilia as a mental illness AND believe children ought to be protected.
Don't be such a dumbass.