This awful disease called bipolar disorder, this disease that can make people take their own lives, that can make living life hell, why does it stay in our gene pool? Why hasn’t evolution routed out this disease so that it simply doesn’t exist anymore?
Well there are theories about why. And one of them is that relatives of the proband (the person with disease, in this case bipolar d/o) are very productive, very intelligent, very artistic, are the CEO’s, the Prime Ministers, the Presidents of companies, countries, of the world.
What this means is that the genes that may cause bipolar d/o in large numbers, in smaller numbers will not cause the disease, but will enable someone to be extremely productive and successful.
Lets say that there are genes X, Y, and Z. They have alleles (forms of genes) x1, x2, y1, y2, z1, z2. Now a person will get bipolar disorder only if they have x1, y1, and z1 and they are homozygous for these alleles, which means both copies of the chromosome that houses these genes have x1, y1, and z1 alleles. So individuals homozygous for x1, y1, z1 have bipolar disorder. However their relatives who have for example, x1, y2, z2 will not have bipolar disorder, but may well be very intelligent, driven and hard working. Therefore, any other combination of these alleles except x1, y1, z1, will confer advantages to an individual.
Therefore, evolution “lets” this awful disease remain in the gene pool because the same genes confer advantages to the non diseased, related individual. So we bipolar people are the sacrifice that evolution makes so that these genes can remain in our gene pool, so that relatives of bipolar people who are not ill, can get the benefit of these genes that allow them to be hardworking, driven, intelligent CEO’s, leaders, movers and shakers of society and the world.
the same thing happens in Sickle Cell anemia. This involves one of the hemoglobin genes. If you inherit two recessive copies, you have sickle cell anemia (SCA). If you inherit one recessive copy and one dominant copy, you not only don’t have SCA, you are protected from getting malaria, as the malarial parasite cannot grow well in blood cells that have hemoglobin from the recessive gene. So in this case, two recessive genes give you the disease, while one gives you protection from a bad disease such as malaria.
Quite similar to what’s been hypothesized about bipolar disorder. That perhaps recessive alleles of a certain type mean you get bipolar d/o, while either dominant or other combinations of the same genes/ alleles confer advantages.
So, sorry if you have bipolar d/o. Evolutionarily you may have been sacrificed for the greater good! And that’s the way it is…