GENOMEThe different kind blood group you have determines your susceptibility to certain diseases. For example, people with A blood are less likely to get diarrhoea than people with B blood. People with O blood are more susceptible to getting diarrhoea than anybody else. People with AB blood are virtually immune to diarrhoea because of their resistance. Nobody really yet knows how AB genotype protects them from this disease. "Since people with the O blood are the most susceptible to the disease, shouldn't they die out according to natural selection?' you are probably asking. That is true but there are a couple of things that keep the O group alive and one of them is malaria. People with O blood are more resistant to malaria than other groups. Another thing is that the O group is less likely to get certain cancers. These benefits cancel out the negative effect that the O blood group has on the diarrhoea disease so, this balance has kept the group from disappearing.
the autobiography of
a species in 23 chapters
by Matt Ridley
(from chap 9)
