LIMITS TO EVOLUTION
My first fiction-adjacent publication was in Analog Science Fiction and Fact when I was in graduate school. The article was published in the October 2000 issue and was nominated for the Best Fact Article that year. This article describes several categories of evolutionary constraints.
- Developmental constraints arise because of the way the developmental process works. For example, because fingers develop from the middle outwards in the embryo horses run around on their middle fingers instead of their index fingers or thumbs.
- Selective constraints arise when selection at one level opposes the evolution of a trait at another. For example, reproducing asexually is advantageous for many females individuals, but species that reproduce this way often go extinct because they lack the ability to remove bad genes from the population which sexual reproduction provides.
- Functional constraints are imposed by the laws of physics. For example, warm-blooded animals can't evolve gills because that would cool their blood too quickly and they would die.
- Pleiotropic constraints are when the changes in the genes that provide an advantage create a negative side-effect. For example, a mutation in hemoglobin provides resistance to malaria, but that same change causes sickle cell anemia which is even worse.
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