For example: Sickle Cell Anemia
and Evolution
Your name
Brief introduction of the disease
• What is it?
• Where is it?
• How much of a problem is it?
Proximate Causation
• The proximate cause of this disease is:
Evolutionary Question
• For example:
• Why are genes for sickle cell so common, since
they cause sickle cell anemia, a devastating
disease?
• Shouldn’t natural selection have removed the
sickle cell allele from human populations?
Evolutionary Hypothesis
• One possible answer to those questions:
• Heterozygote advantage of the sickle cell allele
in areas with malaria.
Explanation of Evolutionary
Hypothesis
• Heterozygote advantage in sickle cell might
work like this…
• This is an example of ______(for example,
“Balancing Selection”, one of the categories of
evolutionary medicine hypotheses from the
class)
Predictions and evidence for this
hypothesis
• If the sickle cell trait provides a benefit in
malaria, we should see higher numbers of
people with the trait in places with malaria.
• Evidence for sickle cell trait matches the
distribution of malaria.
Alternative Hypotheses
• Sickle cell is not adaptive – it has no benefit
– This is not supported by evidence for survival of sickle cell
heterozygotes in Africa.
• Sickle cell is a sporadic mutation
– This idea is not supported by the high frequency in the
population, way higher than what is expected for sporadic
mutation rates.
Significance
• This hypothesis explains the epidemiology of
this disease
• Other gene polymorphisms that affect the red
blood cell might also provide benefit in
malaria.
Summary and Conclusions
References