That's not how evolution works... random variation, sometimes detrimental, will sometimes lead to advantage

Sometimes both. Sickle cell anemia gives you slightly better odds of surviving malaria for instance.

It's not anemia that gives you advantage, but the gene that gives you anemia. People who carry one copy of the gene (who are heterozygous), don't have anemia but have the advantage, while people who carry two copies (are homozygous) are at a huge disadvantage due to anemia. This is a classic example of heterozygosity advantage.

Sickle cell anemia is Mendelian and recessive. So if 2 carriers (Rr and Rr) have kids, 50% of the children will be strictly superior (carriers), 25% will be normal, and 25% will die young. Not a bad outcome, especially if you have a lot of kids to reduce the variance.

> 50% of the children will be strictly superior (carriers)

Is that domain nomenclature? Because I wouldn't call having to be careful who procreate with otherwise risk losing 25% of my children from that relationship as "strictly superior"...

2/4 resistant to malaria with no side effects and 1/4 dying is much much better than 4/4 dying from malaria

pretty good considering something like half of all human beings who ever lived died of Malaria!

I am mildly disappointed to learn that this is probably an overestimate, although it is pretty significant http://factmyth.com/factoids/malaria-killed-half-the-people-...

Thanks for calling it out! I think I first heard this from Plasmodium researchers, and in my mind the claim has strengthen over time. A better statement would be: "“Malaria could have potentially killed nearly to half the people who ever lived, predominantly children”."

And this is based off the idea that for most of human history people have lived in Sub-Saharan Africa, where the majority of people who lived died as children, and the predominate cause of death was Malaria.

According to the article, the evolutionary choice at work here was isolation-induced. It was each blue family member choosing to reproduce with another blue individual that propagated the recessive gene.

Why are y’all downvoting someone for asking a genuine question they didn’t know the answer to?

This is a joke right? Evolution doesn't choose anything.

In this case, the family had a hemoglobin variation, that resulted in a different kind of non-functional hemoglobin being produced. This hemoglobin has a blue tint. This, combined with their pale coloration, meant they had a blue tint.

This is not too dissimilar to how other hemoglobinopathies come about in nature. For example, the thallassemias and sickle cell anemia are two common hemoglobinopathies. Unlike the Fugate family's hemoglobinopathy, which likely did not provide any benefit, these two do provide some benefit to heterozygotes, and thus end up existing at a steady state in the population. The Fugate family's would likely disappear if it caused any issue in reproductive fitness (even a minor one), and the family reproduced among a sufficiently large population. However inbreeding combined with genetic drift means that there simply does not end up being a large enough population for the law of large numbers to take effect.

On the other hand, if the condition causes no reproductive fitness deficiency or increased reproductive ability, then the gene could potentially continue to exist in some very small number of the population. It could die out due to the simple fact of not having many affected people able to reproduce enough to make statistics matter.

>This is a joke right?

That's a really insulting way to answer a question.