Human Errors #5: Sickle Cells and Goldilocks
We know that evolution eliminates harmful genes; and yet we find some of those disease-causing genes continue in the gene pool. The easy answer in some cases is that the disease in question occurs after the individual has already had babies, which means the genes were transmitted before they did the harm. In others, the answer is that it’s a combination of genes that causes the problem, so there’s no easy way to eliminate all the genes in question. But that still leaves a few single gene-based diseases that act (and kill) young. Like the (in)famous Sickle Cell Disease (SCD), writes Nathan Lent in Human Errors . It results in “mutant versions of haemoglobin”, the molecule that carries oxygen in our blood. A fatal drawback, obviously, if your blood can’t get enough oxygen around. Surely such a gene should have been eliminated long back. “Yet this mutant coding that causes SCD is hundreds of thousands of years old, and it has appeared and spread – spread! – in many differen...