Born on Krypton, raised in Kansas

Last week I created pages for PW on Twin Studies and Adoption Studies and made a few easy Harry Potter references, but I've been thinking more about nature and nurture since then. For people like me, Adoption Study finds no finer expression than the case of Kal-El aka Clark Kent aka Superman, a Kryptonian alien raised by Kansas farmers Jonathan and Martha Kent.

Superman Arrives, 1978-style

Superman is a great example of an Adoption Study because he shares his biology with his Kryptonian parents (and so he can fly, is really strong, indestructible, etc) but had his values shaped by his human parents. That's why he fights for "Truth, Justice and the American Way".

In the 1950s, Superman was straightforwardly linked to American values. But in the 1978 film, Superman's farmboy idealism is laughable to city girl Lois Lane.

One of the interesting things the TV series Smallville did with Superman was increase the difference between his Kryptonian father Jor-El and human father Jonathan Kent. In the TV show, Jor-El is unemotional and merciless but Superman/Clark learns compassion (rather than "the American way") from his human father.

The idea of adopted children inheriting great power from their biological parent but learning moral values from their adoptive parent is a popular one in legend and literature. King Arthur is the biological son of the violent and lustful King Uther Pendragon, but he is raised by the humble knight Sir Ector and his honest foster-brother Sir Kay, where he learns the humility that Uther Pendragon lacked.

Look closely. That's Sir Patrick Stewart on a horse, looking tough-as-nails. The music is Wagner - awesome!

The author T.H. White took this idea further. In The Sword In The Stone, Merlin is Arthur's tutor and lets the boy experience life as different types of animals so that the future king can learn imagination, intelligence and empathy.

Not one of my favourite Disney adaptations, but the book and its sequels are excellent

The Merlin/Arthur story was re-played in Star Wars, with Luke Skywalker as the farmboy raised by his none-more-ordinary aunt and uncle, but tutored by the wizard/Jedi Knight Obi-Wan Kenobi. Star Wars very much takes the view that biology is destiny. No matter how narrow his upbringing, nothing can stop Luke from fulfilling his biological fate to learn the ways of the Force, like his biological father before him. Except (SPOILERS)... Darth Vader is his biological father!

Still gets me, every time

Interestingly, Star Wars is a Twin Study as well as an Adoption Study. Not only is Luke concordant with his biological father in terms of being a Force-user, he is concordant with his (DZ) twin sister too.

It's not Wagner, but John Williams' emotional score lifts this scene

All of these stories propose the idea that biology is fairly amoral: it gives children powers and potential, but not values. Values have to be learned and come from upbringing and education, hence the importance of loving parents or wise teachers like Merlin or Obi-Wan Kenobi. Without these influences, Kal-El would have grown up like Zod, Arthur like Uther Pendragon, Luke like Darth Vader.

However, that's not the only way of looking at it.

In the Harry Potter books and films, Harry Potter endures a terrible upbringing from un-loving parents. The Dursleys are not just neglectful and cruel, they're also snobbish and small-minded and oppose anything magical or romantic. But Harry is concordant with his biological parents, James and Lily, not just in being a wizard, but in being honourable and adventurous.

This is a common idea in fairytales, where the hero is born a prince or princess but abducted or exchanged at birth and is raised by a horrible witch or troll instead. Nevertheless, the hero keeps the dignity and decency of their royal birth and doesn't learn their adoptive parent's wicked ways. You can see this in Disney's Entangled and in Wagner's opera Siegfried, where the human boy Siegfried is raised by the dwarf Mime, who he believes to be his true father.

The most heated debate in nature/nurture is not about princes or princesses, however. It's about sexual orientation. Is sexual preference a matter of upbringing, or are people "born that way"?

There are huge implication for deciding this one way or the other. For example, if people learn their sexual orientation from childhood experiences and how they were treated by their parents, it follows they may be able to "un-learn" it later in life. After all, if you can have therapy to help you overcome your smoking habit, why not therapy to make you straight?

On the other hand, if sexual orientation is fixed at birth, no amount of therapy will change it and will only mess you up. Moreover, since people cannot help the things they have been born with (like their sex or the colour of their skin), then it's wrong for other people to discriminate against them. This makes homophobia the same sort of thing as racism.

Examining the whole nature/nurture debate about sexuality will take another blog, but it's worth noting that Twin Studies have been used extensively here in the past. For example, Bailey & Pillard (1991) found a concordance rate of 52% for homosexuality in MZ twins, but only 22% in DZ twins. This suggests a big genetic component in sexuality, since both types of twins had been brought up the same way.

Bailey & Pillard were criticised for their small sample (59) which was recruited through the readership of gay lifestyle magazines. Twin studies involving larger samples recruited from Twin Registers in Australia and Sweden have found much lower concordance rates, closer to 11% for male MZ twins and 14% for female MZ twins.

These studies still suggest there is a genetic influence in sexuality - but it's not the only factor and upbringing and personal experiences play a large part too. Because of this, research into the biology of sexual orientation has moved on from classic Twin Studies and now focuses instead on brain imaging and epigenetics (how genetic changes happen in the womb or after birth).

The nature/nurture debate is a hot topic. It's tied in with religious beliefs and with civil rights. It's fun to explore its implications through fairy tales and superheroes, but the psychological research into it needs to be evaluated much more carefully.

It has, however, been treated light-heartedly, in The Simpsons (where else?!?) where MZ twins Patty and Selma have different sexual orientations despite their shared genes; Patty came out as a lesbian in the 2005 episode There's Something About Marrying.