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Laws of Variation

Narrated by Professor Terrie Moffitt

Twins Early Development Study - Environment

Institute of Psychiatry, London


We need to know that every human being is unique, and individual. And some piece of evidence that that's not true always surprises us, over and over again.

I think twins have got to look around them and see that most other people are not twins and so from a very early age they realise their specialness. Particularly twins that are dressed alike must grasp onto that at a very early age that they and their twin are looking just alike whereas other people are not.

We only ever see ourselves in a mirror image and therefore we see ourselves flipped about, and since our faces aren't symmetrical we see ourselves incorrectly really when we look in the mirror so that you're, the kind of part of your smile that pokes up is actually the part that pokes down, whereas with twins they actually can see themselves correctly in their twin, so that has to be different from what the rest of us get... the visual input has to be different.

And yet it must be very interesting to see your twin, who looks just like yourself, both of you reacting to some... something, seeing a bird fly by or your friend approaching or something and, and realising that you're not showing the same facial expression, although you have the same face. So that would almost send a message of greater feeling of individually I would think, realising that you look just like this person but your feelings are quite different or your thoughts are quite different. Now I do know that all the times we've interviewed these twin pairs, 11,000 twin pairs, interviewed over and over again, year after year, never once has any twin said to us, You don't have to interview my twin because I can tell you what they think. They've never, any of them, presumed that they can stand in for each other, or that they know what their twin will say in answer to a question.

We interview the twins as well about their experiences of symptoms of depersonalisation, and de-realisation and... So we interview the twins and ask them questions about do they think that someone else has ever been able to read their thoughts, not just from knowing them well, but actually read their thoughts? Have they been able to read someone else's thoughts? Has someone been able to insert ideas in their mind that they didn't have before? Has someone else been able to take ideas out of their mind and take information out of their brain away from them? But what's surprising in the study of twins is that, so far, none of them have said, Yes my twin can read my thoughts. Yes my twin can put thoughts in my head or take thoughts out of my head, so they respond to the questions just the way that singletons do, thinking only of their own brain and how their own brain works, and their own subjective experience of their thought processes, but they... each of them responds as an individual just the way a none twin would respond to that set of questions about bizarre mental experiences.

Why are humans altruistic?   You know if Darwin was right and it's survival of the fittest why would humans ever help each other, they should just compete with each other, and their theory is that you only help people who share a lot of your genes. And according to their theory if you have an identical twin you would really want to help that twin because that's the same as helping yourself. But if you have a twin who is not identical you'd be less interested in helping and more interested in competing against them. Evolutionary theorists would pit twins in games against each other predicting that the monozygotic twins who are identical would not complete and would help each other, and that is indeed what happens.

There's huge amounts of serious violence that children are exposed to and even victims of. One thing that we are able to do by interviewing people over and over and over again, year after year, is build their confidence so they will then tell us about things like child harm or violence between the mother and her partner that the children might get exposed to, neglect of children's basic needs. Often the children that we visit are cold and hungry and are in poor physical health, and we come upon a lot of heartbreaking human tragedy. I just don't think I would have thought before, that this was so common, that there is so many people in the world, in the first world, in an affluent place like England or New Zealand, where we do our research, who are living a day-to-day life of quiet desperation, so that's been an eye-opener for me, and one of the ways I can tell how common it is, is when we interview people about things like domestic violence and symptoms of mental illness, and child neglect and child harm, they're not shy about talking with us about it. And that tells me that they've lived with it so long it seems normal to them. As long as you kind of assume that that's how the world works and that everybody lives with, you know, terrible violence in their home all of the time, there's no real reason to try to get out of that so there is a, it's a um... disturbing thing that I've learned but also a err... a thing that sometimes fills me with despair, about how many people out there, living with tragedy don't see it as unusual and don't even see it as something that they deserve to have a better live, they just think that's how life is. I think that's really tragic.

The most inspiring thing that I've learned from my studies of twins, has been watching, pairs of twins develop over the years where one of the twins has been left with a handicap from the birth process, so it's not so unusual for twins, one or both twins, to have cerebral palsy following the birth and be left with quite a severe physical handicap and sometimes not be able to talk very well, whereas the other twin might develop in a normal healthy way.

Seeing those, the courage of the handicapped twin to have self-esteem and happiness, when confronted on a daily basis with the healthy version of herself is, pretty amazing. So just being able to... everything that she can't do, such as feed herself or go to school, her twin can do, must be staggering for a small child who's growing up, and yet somehow, these children develop a good, healthy, strong self-concept, and they do what they can do.

The most valuable thing any of us can have, is an appreciation of how wildly different people are, the huge amount of variation there is out there in the human world. The tendency that we have is to arrange our lives so that we can surround ourselves with people like ourselves, that's much more comfortable, but it's also false and so trying to break out of that sit, endure a little bit of challenge and discomfort, to appreciate how different people can be behaviourally, I think has got to be enriching.