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There is no purpose or planning behind evolution, so blood types could just be a random genetic mutation that does not reduce the chances for individuals of hav

There is no purpose or planning behind evolution, so blood types could just be a random genetic mutation that does not reduce the chances for individuals of having offspring that survives long enough to have children. Just like curly vs flat hair or blue vs green eyes. I'm not a biologist so I might very well be wrong about that, but it seems that one possible explanation is that the question has no meaningful answer.

refurb 10y ago
This is accurate. Evolution doesn't drive change. Change happens automatically and evolution just selects for certain changes (sometimes). It is clearly possible that random genetic changes happen with no impact on fitness at all. They just are.
- ChemicalWarfare 10y ago
  if a random mutation in a given specimen doesn't give them an immediate "evolutionary advantage" - what is the fixation mechanism then?
  - drcross 10y ago
    What's a fixation mechanism?
    - ChemicalWarfare 10y ago
      https://en.wikipedia.org/wiki/Fixation_(population_genetics) https://en.wikipedia.org/wiki/Fixation_(population_genetics)
  - sleepychu 10y ago
    Chance? Colocation with another mutation?
kmm 10y ago
I don't think blood types are a neutral mutation. For starters proteins are not free to make and blood cells make up 5% of our total body weight. But also incompatibility between blood types between a mother and child can lead to hemolytic disease[0] (which is mostly a problem with the rhesus factor). Being rhesus positive in a mostly rhesus negative population is a very strong disadvantage (and vice versa) so I'm not sure the initial mutation would proliferate. Secondly, one would expect a neutral mutation to eventually be present in 50% of the population and homozygous in 25%. Or for three variations, we'd expect 1/9th of people to be O, 1/3rd A, 1/3rd B en 2/9ths AB. We've had blood types for millions of years, and no population has anything close to the distribution, which makes me believe there is some kind of evolutionary pressure. 0: https://en.wikipedia.org/wiki/Hemolytic_disease_of_the_newborn https://en.wikipedia.org/wiki/Hemolytic_disease_of_the_newbo...
- Someone 10y ago
  Is this a three-way choice? I though it is two two-way choices, and I would expect 50% to have A, 50% not-A, similarly 50% to have B, 50% not-B, and hence, assuming zero correlation between them, 25% not-A-and-not-B (= O), 25% A-and-B (= AB), 25% A-but-not-B (= A) and 25% B-but-not-A (= B)? Also, if there is evolutionary pressure, given that we know blood groups of millions, it shouldn't be that hard to find some correlation between blood group and life expectancy, number of kids, etc. Are you aware of any?
  - logfromblammo 10y ago
    In general, gene variants start out with > 99% the original variant and < 1% the new variant. So at some point, most people were probably OO, and a baby was born with mutant AO genotype. Then A spreads from the mutant. For modeling purposes, I'll start with 50000 people, set the generation span at 20 years, and on average, each female will have 2.004 surviving children. Well, then the mutant population grows at the same rate as the general population, so remains at a tiny fraction. So I update the model to provide a tiny advantage to the mutant by giving the mutant phenotype more surviving children per generation. If I set up the model to start with 49998 OO, 1 AO, and 1 BO, set type O reproductive success at 2.004, type A at 2.013, type B at 2.012, and type AB at 2.013, and let it go for 2500 generations (50k years), the ending population is about 20M total, 41% O, 42% A, 11% B, and 4% AB. That amounts to a relative advantage of only 0.45%. Obviously, the A and B mutations are very unlikely to have occurred at the same time, but it looks like both may have occurred after humans had already migrated from Asia to North and South America, as natives of South America are almost entirely type-O, and the presence of type A in North America may be explainable by Clovis migrants from Europe. So a 50ky timespan is actually a bit too long. It seems as though there must be a selective advantage to A and B antigens, or that they be linked with an advantage, otherwise, they would not be observable as a significant population now. [Edit:] Note that this only applies to pre-medicine. Blood type compatibility for the purposes of transfusions is definitely a survival advantage now. If current technology and politics were fixed for the next 50ky, it is likely that the "O" gene variant would become rare, and AA, BB, and AB genotypes would dominate.
folli 10y ago
Given your hypothesis you also need an explanation why there aren't thousands of blood types.
- ivanhoe 10y ago
  Actually there's quite a few, if you count all the subtypes and antigens https://en.wikipedia.org/wiki/Human_blood_group_systems https://en.wikipedia.org/wiki/Human_blood_group_systems
- lightqa 10y ago
  I always thought that everything happens/happened , all the possibilities were tried by nature and 99% of those possibilities couldnt produce furthur (got killed diseases/stability) .
finid 10y ago
There is no purpose or planning behind evolution... To me, that's a shocking statement. So you're here by accident?
SilasX 10y ago
I would definitely consider it a meaningful answer to say, "There is no selection pressure in favor of that one gene vs its subsitute(s), so both/all kinds of antigens [expressed by those genes] persist with equal regularity in successive generations [modulo the effects of recessiveness/dominance]."

refurb 10y ago

This is accurate. Evolution doesn't drive change. Change happens automatically and evolution just selects for certain changes (sometimes). It is clearly possible that random genetic changes happen with no impact on fitness at all. They just are.

ChemicalWarfare 10y ago
if a random mutation in a given specimen doesn't give them an immediate "evolutionary advantage" - what is the fixation mechanism then?
- drcross 10y ago
  What's a fixation mechanism?
  - ChemicalWarfare 10y ago
    https://en.wikipedia.org/wiki/Fixation_(population_genetics) https://en.wikipedia.org/wiki/Fixation_(population_genetics)
- sleepychu 10y ago
  Chance? Colocation with another mutation?

kmm 10y ago

I don't think blood types are a neutral mutation. For starters proteins are not free to make and blood cells make up 5% of our total body weight. But also incompatibility between blood types between a mother and child can lead to hemolytic disease[0] (which is mostly a problem with the rhesus factor). Being rhesus positive in a mostly rhesus negative population is a very strong disadvantage (and vice versa) so I'm not sure the initial mutation would proliferate. Secondly, one would expect a neutral mutation to eventually be present in 50% of the population and homozygous in 25%. Or for three variations, we'd expect 1/9th of people to be O, 1/3rd A, 1/3rd B en 2/9ths AB. We've had blood types for millions of years, and no population has anything close to the distribution, which makes me believe there is some kind of evolutionary pressure. 0: https://en.wikipedia.org/wiki/Hemolytic_disease_of_the_newborn https://en.wikipedia.org/wiki/Hemolytic_disease_of_the_newbo...

Someone 10y ago
Is this a three-way choice? I though it is two two-way choices, and I would expect 50% to have A, 50% not-A, similarly 50% to have B, 50% not-B, and hence, assuming zero correlation between them, 25% not-A-and-not-B (= O), 25% A-and-B (= AB), 25% A-but-not-B (= A) and 25% B-but-not-A (= B)? Also, if there is evolutionary pressure, given that we know blood groups of millions, it shouldn't be that hard to find some correlation between blood group and life expectancy, number of kids, etc. Are you aware of any?
- logfromblammo 10y ago
  In general, gene variants start out with > 99% the original variant and < 1% the new variant. So at some point, most people were probably OO, and a baby was born with mutant AO genotype. Then A spreads from the mutant. For modeling purposes, I'll start with 50000 people, set the generation span at 20 years, and on average, each female will have 2.004 surviving children. Well, then the mutant population grows at the same rate as the general population, so remains at a tiny fraction. So I update the model to provide a tiny advantage to the mutant by giving the mutant phenotype more surviving children per generation. If I set up the model to start with 49998 OO, 1 AO, and 1 BO, set type O reproductive success at 2.004, type A at 2.013, type B at 2.012, and type AB at 2.013, and let it go for 2500 generations (50k years), the ending population is about 20M total, 41% O, 42% A, 11% B, and 4% AB. That amounts to a relative advantage of only 0.45%. Obviously, the A and B mutations are very unlikely to have occurred at the same time, but it looks like both may have occurred after humans had already migrated from Asia to North and South America, as natives of South America are almost entirely type-O, and the presence of type A in North America may be explainable by Clovis migrants from Europe. So a 50ky timespan is actually a bit too long. It seems as though there must be a selective advantage to A and B antigens, or that they be linked with an advantage, otherwise, they would not be observable as a significant population now. [Edit:] Note that this only applies to pre-medicine. Blood type compatibility for the purposes of transfusions is definitely a survival advantage now. If current technology and politics were fixed for the next 50ky, it is likely that the "O" gene variant would become rare, and AA, BB, and AB genotypes would dominate.

folli 10y ago

Given your hypothesis you also need an explanation why there aren't thousands of blood types.

ivanhoe 10y ago
Actually there's quite a few, if you count all the subtypes and antigens https://en.wikipedia.org/wiki/Human_blood_group_systems https://en.wikipedia.org/wiki/Human_blood_group_systems
lightqa 10y ago
I always thought that everything happens/happened , all the possibilities were tried by nature and 99% of those possibilities couldnt produce furthur (got killed diseases/stability) .

finid 10y ago

There is no purpose or planning behind evolution... To me, that's a shocking statement. So you're here by accident?

SilasX 10y ago

I would definitely consider it a meaningful answer to say, "There is no selection pressure in favor of that one gene vs its subsitute(s), so both/all kinds of antigens [expressed by those genes] persist with equal regularity in successive generations [modulo the effects of recessiveness/dominance]."