Map of evolution in action:Global Map of the Sickle Cell Gene Supports 'Malaria Hypothesis'

[TZ]

ScienceDaily (Nov. 2, 2010) — At a global scale, the sickle cell gene is most commonly found in areas with historically high levels of malaria, adding geographical support to the hypothesis that the gene, while potentially deadly, avoids disappearing through natural selection by providing protection against malaria.


In a study funded by the Wellcome Trust, geographers, biologists and statisticians at the University of Oxford, together with colleagues from the KEMRI-Wellcome Trust Programme in Kenya, have produced the first detailed global map showing the distribution of the sickle cell gene. The results are published in the journal Nature Communications.

Haemoglobin S (HbS) is known to cause sickle cell disease, which is usually fatal if untreated. Natural selection suggests that such a disadvantageous gene should not survive, yet it is common in people of African, Mediterranean and Indian origin.

http://www.sciencedaily.com/releases/2010/11/101102130133.htm
While this connection has been known for years, this is a really wonderful visual map of this connection. To those who don't "believe" in evolution--> this pretty much trumps anything you can say. Darwinian natural selection in the human genome.

[Jim__]

1. I wish the maps were larger and the legends clearer.

Is the bottom map (the one with the green) showing the endemicity of malaria? The correlation for India and Africa is clear. But, based on my reading of these maps (I'm guessing because I can't actually read the legends) I would expect to see the sickle cell gene in South America. Or, did the gene originate in the African population after the South American population had already emigrated? Or, has control of malaria in South America suppressed this gene in that area?

[TZ]

2. Malaria, while fairly common in SA

Is not nearly as epidemic as it is in West Africa and South Asia. I suspect the evolutionary pressures there were much weaker than Africa. Also- interesting that the fequency of malaria in the Southern US is starting to be equivalent to parts of SA. That's pretty nice visual evidence of climate change.

[mysuzuki2]

3. There was no malaria in the New World until

European contact. There was also no sickle cell. A similar condition, thalassemia, is common in malarial areas of the mediterranean. It is, like sickle cell, a balanced polymorphism in which the heterozygous condition confers a degree of protection against malaria. The thalassemia gene was also absent from precontact america.

[Jim__]

5. Interesting. Was the mosquito (the one that transmits malaria) already here?

And so, once the disease was here it would remain because it had a method of transmission.

[Chulanowa]

4. Malaria is not indigenous to the Americas

Much like influenza, yellow fever, and tuberculosis, it arrived after Columbus. In the case of malaria and yellow fever, the disease came with slaves brought from Africa.

[Jim__]

6. Thanks. That's the part I was not getting from the map. - n/t