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Evolutionary trade-offs



Evolutionary trade-offs have occurred on many levels throughout evolutionary history. There are many functional and genetic trade-offs that have taken place throughout human evolutionary history.

Human ancestors, such as the neanderthals, had stronger, thicker bones than Homo sapiens today. Thicker, stronger bones were much less likely to break and were therefore beneficial to neanderthals, who lived in harsh conditions. Humans today do not have such thick, strong bones, because, although stronger bones would eliminate the worry of breaking a bone, they would require humans to increase their calcium intake substantially. In the trade-off between the benefits of stronger bones and the detriment of needing more calcium, the negative effects of thicker bones outweighs the positive effects.

In many ways, having more sensitive ears could be beneficial to humans, allowing for improved hearing. However, improved hearing would allow humans to hear air molecules moving around, thus providing a constant distraction. With a less heightened ability to hear, humans do not have this distraction.

Mutations that confer a reproductive advantage often increase in frequency within a population, despite rendering individuals more vulnerable to a particular disease.

Individuals that carry two copies of the sickle cell gene suffer immensely and die at a young age. Those with two copies of the "normal" gene, rather than the mutated form that confers sickle cell anemia, are at a much higher risk for malaria. However, individuals that are heterozygous at this locus (one normal copy, one mutated copy) are protected from both malaria and sickle cell disease. Despite the negative effects of the sickle cell gene, it persists in populations in areas where malaria persists.

Similarly, Cystic Fibrosis is caused by a genetic mutation in the CFTR gene. Because Cystic Fibrosis leads to early death and reduced reproductive fitness in many cases, one would expect the mutated version of the gene to be eliminated from the gene pool. However, Gerald B. Pier of Harvard Medical School recently conducted a study supporting the idea that individuals who are heterozygous at this locus (one normal copy of CFTR, one mutated copy, conferring CF) are better able to evade the acquisition of typhoid fever, a disease that was once very prevalent and deadly, particularly in Europe. Therefore, in areas where typhoid fever exists, individuals that are heterozygous for the CFTR gene are most fit, allowing for the mutated CFTR allele to persist in the human population.


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Wikipedia

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