The bittersweet reunion of abducted girl Jaycee Lee Dugard with her family touches on the worst fears of a parent and leaves us all shaking our heads as to how someone could commit such an act. Social psychologists have some answers.

Dugard, now 29, was reportedly abducted in 1991 when walking to her school bus stop in South Lake Tahoe, Calif. For 18 years, her alleged abductor Phillip Garrido, 58, and his wife Nancy, 54, kept Dugard isolated in a backyard encampment of tents and sheds, where her two daughters, allegedly fathered by Garrido and now 11 and 15, also lived. Known as "Creepy Phil" in his neighborhood, Garrido said God spoke to him through a box, according to news reports.

Garrido may have been sort of wired to commit these acts of kidnapping and rape, say psychologists, who are quick to note that even if the behavior can be partially explained, it doesn't justify such acts.

Twisted building blocks

To make sense of a seemingly non-sensical event, social and evolutionary psychologist Daniel Kruger, of the University of Michigan's School of Public Health, looks to our ancestors.

"It's kind of like you have all these building blocks that make sense given our ancestral contacts, and once in a while you'll find these building blocks put together and twisted in a way that doesn't seem to make sense to us as outsiders looking in," Kruger said during a telephone interview.

The bottom line, which may seem out of touch with modern society, is the innate desire to  pass along genes.

"This relates to a long, long human history of women basically being reproductive assets and being seen as resources that are taken in conflicts both within groups and between groups," Kruger said.

And while abducting and raping a young girl is "not justifiable," Kruger said, guys do prefer younger women.

"This is something that could be the extreme end of a continuum," Kruger said. "Men in general do have a preference for younger women and seem to be most attracted to women who are either at their peak reproductive potential or even younger than that." At that age, he said, a woman is less likely to already have offspring from other mates.

As horrid as it seems, rape could serve as a last-resort mating strategy. "I think that there's flexibility in mating strategies," Kruger said. "And one of the things some evolutionists have suggested is that rape is about sex with powerless men." (Kruger notes that feminists and others consider rape an act of power not sex.)

He added, "Usually rapists are guys who can't get sex through normal means of attracting a women and getting her to get into a romantic relationship with you. These aren't guys who other women would find highly attractive. This could be a high-risk strategy for people who find themselves not succeeding through normal means."

He recalls warlords like Genghis Khan who supposedly raped and imprisoned women and ended up fathering lots of children (and passing along their genes far and wide). Genetic-testing suggests Khan has about 16 million male descendants living today, he said.

"Not that this justifies what he was doing. [Garrido] did have two daughters through Jaycee," Kruger said.

Unscrewed mentally

Even if evolution can rationally explain a behavior, how could someone like Garrido take such actions toward a young girl? Perhaps a mental illness pushed him toward sex offending; some news reports have suggested Garrido suffers from schizophrenia.

Jack Levin, a social psychologist at Northeastern University in Boston, doesn't think Garrido is schizophrenic, but rather is a sociopath.

"I doubt he is psychotic or legally insane. I don't think he hallucinates or talks to dogs or hears voices," Levin said. "A really effective sociopath will say anything. He'll feign mental illness. He'll become born again or find religion."

Psychopaths (also called sociopaths) share typical traits, scientists are finding. These include: lack of empathy and guilt; impulsivity; shallow experiences of emotions; a grandiose sense of self-worth; and failure to accept responsibility for their actions. And while the roots of this mental disorder still elude psychologists, research is showing some people have a genetic predisposition toward psychopathy, and their brains are even wired a little differently from others.

Such individuals also have a need for control, power and dominance over others. "He has an excessive need to be in charge," Levin said. "And he can exercise that need by taking someone else's life, determining how much someone else suffers, or determining in general the fate of another human being. That's exactly what Garrido did in this case." Levin is referring to the "complete control" Garrido supposedly had over the then 11-year-old Jaycee.

Baboons do it

Humans aren't the only animals to kidnap and commit sex acts against females.

"Hamadryas baboon males are harem-holders. When they reach adolescence they sometimes kidnap a juvenile female and keep her close until she grows up, a few years later, when both he and she are old enough to start reproducing," said Frans de Waal of Emory University and the Yerkes Primate Center, where he studies the evolution of human behaviors through primate research.

"Usually more females are being added the stronger the male grows. But the harem-holding of these primates is special: few species do this," he added.

Males chimpanzees (one of our closest relatives) sometimes take a female "on safari," de Waal said. "What this means is that the male forces a female to travel with him to areas outside the competition with other males so that he mates with her undisturbed for one or two cycles until they return to the group," de Waal told LiveScience. "This is usually done by high-ranking males, and requires female cooperation."

And like prisoners, "females sometimes 'bolt' and try to get away from the male," he said.

Asked if such primates could shed light on the human parallel, de Waal said, "Yes, in the sense that male primates like to monopolize females."

Red flags

Could anything be done to change the behavior of people long before they become sex offenders or kidnappers? Tagging someone a sociopath or a future sex offender when he or she is just a kid is daunting at best. One of the problems has to do with false positives, Levin said.

"There are millions of American men who are sociopaths — they may lie, they may cheat, they may sell you a bad used car, but they don't abduct anyone," Levin said. "So how do you identify the relatively few guys out there, or boys, who will grow up to become sexually dangerous adults?"

If one were to weed out all the boys who showed a sense of powerlessness, you'd be casting a too-wide net. "There are lots of youngsters who feel powerless, and have an excessive need for power and control and dominance. And somehow they get over it, and they grow out of it and grow up and become decent, moral human beings. But a few don't. The problem is how do you tell the few that don't from the large number that do.

Another warning sign would be social isolation at an early age, though this factor isn't foolproof either. "It may be also that for some reason during early childhood a youngster is unable to bond with other human beings and grows up absent any meaningful relationships with adults or other children," Levin said.

Again, while most of these children will grow up to become "decent human beings," some don't, Levin said.

Animal abuse as a clue

One possible red flag could involve a person's violent acts toward dogs or cats, Levin said. "There's a certain kind of animal abuse that does seem to be predictive and that is the sadistic and cruel abuse of dogs or cats in a hands-on, up close and personal manner in order to maximize pain and suffering," Levin said.

His research suggests more than half of all serial killers have abused dogs and cats in a sadistic, cruel manner. And such killers often use the same method on humans that they had used decades ago on animals. "If they beat dogs, they'll beat women. If they practice bestiality on animals, they'll rape women," Levin said. 

While he said scientists are continuing to look for warning signs of those who will commit future violent acts, Levin recommends a helping-hand approach to troubled kids in general.

"We shouldn't just look to punish children," Levin said. "If we see a child who is abusive to dogs and cats and has a sadistic streak, we should reach out to that child."

He mentions that children who are bullied every day for years fall into this category of troubled child who needs help.