Hookworms are longer-lived than viruses and bacteria; they could have had a more significant effect on human evolution.
Humans live in all sorts of places---high deserts, tropical lowlands, frigid tundra. Over the millennia, you'd expect each population's assortment of genes to evolve to reflect the demands and dangers of its home environment: those who live in the deserts would possess genes for extra skin pigments to help keep their tender integument from burning (like African peoples), and those who live in sub-zero climes much of the year would have genes that keep them well-insulated in fat (like the Inuit). But what if factors other than climate, like the food available nearby or the viruses, bacteria, and parasites native to the area, also had an effect on various human populations' genetic toolkits? It's a fascinating question, but, given that we have to reconstruct all this supposed evolution from the current state ...
