Dr John Peet investigates claims that the Y chromosome is degenerating
I was recently asked an alarming question.
‘Is it true that the Y chromosome of men is degenerating to such an extent that they will eventually become extinct or, at least, unnecessary?’ The question resulted from claims by some researchers reported in the press. This is another example of a problem that often annoys scientists: the press reports an apparently outstanding new discovery but goes silent when the establishment shows that the claim is unwarranted. So, what is this about?
Humans have 23 pairs of chromosomes. 22 of them are common to males and females, but the 23rd pair, known as the sex chromosomes, differ. The female has a pair of X chromosomes and the male has one X and one Y chromosome.
What is the Y for? or Y for art thou?
It is the Y chromosome that controls the development of the embryo into a male infant, if it is present. A gene (SRY) on this chromosome triggers the sequence of events to this end, initiating, for example, the production of the hormone testosterone.
When a man and woman have intercourse, the male sperm carries either his X or the Y chromosome to the egg, which, in turn, has the mother’s X chromosome. The fertilised egg then develops very quickly so that, after three weeks, the embryo has a heart with its own blood system, and the spinal column and the nervous system are beginning to form. By six to seven weeks, most organs are in place. At eight weeks, if the Y chromosome is present, the SRY gene ‘kicks in’ and sexual differentiation occurs. A boy is on the way.
However, various researchers1 have claimed that the gene is degenerating due to accumulating mutations and so will become ineffective. They compared the X and Y chromosomes. In the former, there are 1376 genes present, but only 284 on the Y chromosome (other references quote various figures such as around 2,000 and 78 genes respectively!). The other genes have, they claim, been destroyed over a long period of time in our evolution from an ape-like ancestor. Indeed, Bryan Sykes described it as a ‘graveyard of rotting genes’.
The problem is supposedly accentuated as men produce sperm throughout their lives, and so the older the man, the more the mutations that affect his sperm. Other workers have more recently claimed that, in mice, the gene pool on the Y chromosome can be reduced to two specific genes and still produce males! However, the process is only possible by artificial insemination and not by natural reproduction. Other scientists are cautious on how far this can be applied to humans.
Conflicting figures
The sceptics reckon we have lost many of these genes on the Y chromosome over the last 100 million years and so have only 100,000 to 5 million years left. Others have pointed out that even on this time scale, the Y chromosome has been virtually unchanged for the last 6 million years2, so our survival would be very much longer. More recently, two groups of researchers3 have confirmed that the genetic content of the Y chromosome is stable and ‘not a single gene has been lost … in the past 44 million years’. A reading of a summary article in the popular journal, New Scientist 4, makes it clear that these ages (and the reasoning) are based on evolutionary assumptions, but the principle confirms what we would expect from a biblical standpoint.
The presumed problem relates to the fact that all other chromosomes exist as pairs, so, if a mutation occurs on one of the pair, then the unaffected one can compensate. The Y chromosome does not have that protection as it is singular in this respect.
However, this is where we see a sign of the good hand of the creator. The Y chromosome has no problem on this front as it has unique checking and repairing mechanisms. The Y chromosome has a mirror image of its gene distribution5 , the top sequence being repeated in the bottom end (often described as a palindrome). So, it folds up on itself to pursue this backup process!
For those who see the origin of humans as a result of special creation as recorded in Genesis 1-2, the presence of such design aspects is no surprise. Jennifer Hughes says that human and chimpanzee Y chromosomes differ ‘radically in sequence and gene content’6 , which seems to make a poor case for a common ancestry.
Those who hold to the argument of the degeneration of the Y chromosome and its inevitable consequences actually resort to an approach to evolution that is in conflict with the usual claim that ‘natural selection’ favours improvement over time. Others would point out that the evidence accumulated, for example in the Human Gene Mutation Database, favours the argument that mutations are almost, if not entirely, degenerative.
However, don’t worry, ladies; your men will be around until the Lord returns – that’s his promise (Luke 17.34)!
Some biblical issues arising
There are two unusual examples in the Scriptures which concern the role of the Y chromosome, each of which I have had raised at some time. The first concerns the origin of Eve. The biblical account is plain. She was created by the direct and specific action of God himself. ‘Male and female he created them’ (Genesis 1.27, ESV), and, more specifically, ‘The rib that the LORD God had taken from the man he made into a woman’, (Genesis 2.22, ESV).
At first glance that sounds like a cloning of Adam, but it clearly was not. If Eve had been a clone, she would be a man with Adam’s Y chromosome. But she was a true, a perfect woman. That this was an exceptional act is clear from the apostle’s comment, ‘For man was not made from woman, but woman from man’ (1 Corinthians 11.8, ESV). The cells from Adam’s bone would have contained X and Y chromosomes, but Eve clearly didn’t inherit the Y chromosome. The Bible does not tell us the detail, but God clearly only transferred the X chromosome to Eve.
Then we have the miraculous conception of our Lord and Saviour. Mary, being a woman, had only X chromosomes, but our Lord was a perfect man and would have had a Y chromosome. Again, it is clear that God controlled this and created a Y chromosome in the fertilised egg. As the Scriptures say, ‘The Holy Spirit will come upon you [Mary] and the power of the Most High will overshadow you, therefore the child to be born will be called holy – the Son of God’ (Luke 1.35).
For those who accept the biblical account of the creation of man and woman, we recognise that the creation of humans was a miracle, along with the rest of creation, so these two miracles (origin of Eve and conception of our Lord) do not raise any difficulty. We have no difficulty in believing that the LORD God did these things too.
