Study reveals why humans have difficulty in having babies

Researchers at the Milner Centre for Evolution at the University of Bath recently in a study said “selfish chromosomes” are to be blamed for early death of majority of human embryos. Before even a mother realises, she is pregnant, over half of fertilised eggs experience a very early death. The research published in the journal PLoS Biology, explains why fish embryos usually do not have an impact on the treatment of infertility while human embryos don’t survive. And if by chance, those who survive are aborted after few weeks, reported by ANI.

Professor Laurence Hurst, Director of the Milner Centre for Evolution’s looked into why, despite thousands of years of evolution, it’s difficult for human to have a baby. As the embryos contain incorrect number of chromosomes many deaths are caused directly because of this. The fertilised eggs should have 46 chromosomes, 23 each from mother and father.

Professor Hurst said, “Very many embryos have the wrong number of chromosomes, often 45 or 47, and nearly all of these die in the womb. Even in cases like Down syndrome with three copies of chromosome 21, about 80 per cent sadly will not make it to term." The professor explains, “This first step of making eggs is odd. One chromosome of a pair will go to the egg the other will be destroyed. But if a chromosome `knows` it is going to be destroyed it has nothing to lose, so to speak. Remarkable recent molecular evidence has found that when some chromosomes detect that they are about to be destroyed during this first step, they change what they do to prevent being destroyed, potentially causing chromosome loss or gain, and the death of the embryo." If the death of an embryo would benefit the other children of that mother, as the selfish chromosomes will frequently be in the siblings and will get extra nourishment.

The researcher further added that amphibians and fish don’t have this problem. He said, “In over 2000 fish embryos not one was found with chromosomal errors from mum.” Birds likewise have a very low rate- roughly 1/25th of what all mammals experience and the probable reason Hurst pointed is nestling competition that occurs only when they have hatched.

Humans also only have one child at a time and the death of an early embryo allows the mother to quickly begin another pregnancy- having no idea her egg has been fertilised.

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(With inputs from agencies)