... I'd love to see a discussion for instance on the continual existence of evolutionary destructive traits such as homosexuality ... Parasites. Parasites freq

... I'd love to see a discussion for instance on the continual existence of evolutionary destructive traits such as homosexuality ... Parasites. Parasites frequently manipulate the host to change its behavior. Toxoplasma gondii, for example, is associated with a 6X increase in car crashes among human drivers. Parasites also cause variety to evolve in the host immune system and other body systems, resulting in a variety of oddball genetic variations and autoimmune disorders. There is also an effect called frequency-dependent selection. Some gene variants are useful if you get one copy of the variant, but harmful if you get two. Evolution multiplies the useful gene in the population to the point where the good effects on reproduction balance the bad. Examples of this include sickle cell anemia (one copy protects against malaria, two copies give crippling sickle cell attacks), and the sphingolipid storage disorders (a small influence causes higher IQ, more influence causes lethal degenerative changes of the brain).