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Line 53: − − ==Non-biological natural selection== − The term natural selection is usually used with regard to the evolution of life, however natural selection also applies to none living matter: all planets are round because a cubical planet will eventually be rounded by gravitational and centrifugal forces, and we only find rounds rocks in riverbeds because erosion rounds them.
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==='''Sickle cell anemia'''===
==='''Sickle cell anemia'''===
This is a condition where red blood blood cells have a sickle shape caused by faulty hemoglobin genes. Suffers with full sickle cell anemia have two alleles for the condition and none of their red blood cells are formed correctly. These cells get stuck in blood capillaries and cannot carry oxygen properly. This is clearly not advantageous and many sufferers die early in life. Even though death occurs in some parts of East Africa up to 50% of babies carry the genes for sickle cell anemia and 14% have anemia<ref>Biology 2, Jones M. & Gregory J., 2001, Cambridge University Press, ISBN 0-521-79714-4</ref>. This can be explained as an individual with one normal allele and one sickle cell allele will have mostly normal red blood cells and a few sickle red blood cells. This condition is not harmful and the carriers can live a normal life. However, the protoctist ''plasmodium'' that causes malaria cannot survive in sickle red blood cells, thus giving an advantage to carriers in a high-risk malaria area.
This is a condition where red blood blood cells have a sickle shape caused by faulty hemoglobin genes. Suffers with full sickle cell anemia have two alleles for the condition and none of their red blood cells are formed correctly. These cells get stuck in blood capillaries and cannot carry oxygen properly. This is clearly not advantageous and many sufferers die early in life. Even though death occurs in some parts of East Africa up to 50% of babies carry the genes for sickle cell anemia and 14% have anemia<ref>Biology 2, Jones M. & Gregory J., 2001, Cambridge University Press, ISBN 0-521-79714-4</ref>. This can be explained as an individual with one normal allele and one sickle cell allele will have mostly normal red blood cells and a few sickle red blood cells. This condition is not harmful and the carriers can live a normal life. However, the protoctist ''plasmodium'' that causes malaria cannot survive in sickle red blood cells, thus giving an advantage to carriers in a high-risk malaria area.
==Common misunderstandings about natural selection==
==Common misunderstandings about natural selection==