A lot of research into the origin of homosexuality has been concentrated on twins. There is one set of twins – James and Daniel Kelly – who may be unique in the
. One is gay, one is straight, but also one is black, and one is white. AND both of their parents have a set of twins by former partners! UK
Most studies have looked at homosexuality which appears in both identical and non-identical siblings. Having identical
DNA, the result of one fertilised egg dividing into 2 early in development, should give each identical twin the same personal and physical traits – they are clones, after all. Non-identical twins, being the result of 2 separate eggs being fertilised at the same time, don’t have identical DNA and are genetically like any other pair of siblings.
Having one black twin and one white twin isn’t as unusual as you might think. In fact, the
BBC found 5 sets of black/white twins, including the Kellys, for a programmes called “Twincredibles” in 2011. The Kelly twins are a good example of just how complicated inheritance and genetics can be, but when you get down to it, the colour of a person’s skin is inherited in the same manner as the shape of that person’s nose. How many times have you looked at a baby and said “He’s got her mothers nose” or “she’s got her father’s ears”? Skin colour is produced in the same genetic manner.
Out of the 7 children Erroll and Alyson Kelly have between them only one, Katie, isn’t a twin or a boy. The only identical twins are the middle pair, Charles and Jordan.
Even though some inherited traits, like eye colour, are determined by parts of the
DNA called alleles, skin colour seems to be one of those traits which are generated “randomly”. I say randomly because skin colour is affected by more than one gene (unlike eye colour) and a combination of all of these skin colour genes produces a wide range of tones. It’s not like mixing paint, where every drop of the paint effects the final mix. DNA doesn’t work like that. There are other genetic factors, such as the allelles, dominant and regressive genes, and epi-marks.
With non-identical siblings, like James and Daniel Kelly, each gene is slightly altered in each of them. James Kelly just happens to have inherited more dark skin genes from his father than light colour genes from his mother. The reverse is the case with Patrick. Both of their parents pass on the same amount of skin colour genes, but the other genetic factors determine how many will be part of the children’s DNA so that he/she will have the same number of skin colour genes and not double.
The lives of many mixed-race children is still dominated by prejudice. This raised it’s head for the Kelly twins when their mother placed them in a nursery school. Because their father was black, and James was black, the school insisted on having Daniel registered as black too. Even though Daniel was quite obviously not dark-skinned and his mother was white the nursery still insisted Daniel be registered as black. Since then Daniel has always refused to tick any of those “ethnic origin” boxes you see on official forms (you can hear what he puts instead in the video below).
The question of James’ homosexuality is one which, again, highlights the question of whether it is Nature or Nurture. Recent research has suggested that homosexuality may be the result of yet a third part of
DNA – the epi-mark. To remind you about epi-marks – these are kinds of switches on DNA that determine the development of various genes.
During development the foetus will detect which gender the embryo has determined to follow (in my article on gender testing at the Olympics I explained how gender is formed in more detail) and the sex-specific epi-marks switch on to ensure that the female foetus does not become affected by high levels of male hormones that may sometimes occur. They ensure the reverse for the male foetus, ensuring high female hormones don’t affect it. Epi-marks are not usually passed from parent to child because new ones are created for each generation. Sometimes epi-marks survive to be passed only from father to daughter or mother to son. In these cases, for example, a woman who inherits the sex-specific epi-marks from her father is more susceptible to the influence of male hormones during foetal development, because her own new epi-marks won’t be created in their place. And since some epi-marks can influence sexual preference this may also (but not necessarily always) mean that the women grows up a lesbian. With men, of course, the epi-marks passed from their mother will tend to make them gay. However, this epi-mark evidence doesn’t explain bisexuality or an other sexualities.
I think more research into identical twins in particular will one day make everything clearer. Until then, we still have to look at twins like James and Daniel Kelly and say “One twin in gay, the other isn’t, is it nature or nurture?”
Here is the
BBC documentary about the Kelly twins. It can explain their situation and the problems they encounter in life much better than I can.