In a paper over at BMC Biology, the authors give us some evidence that parasitic worms may have been a factor in human evolution.
In fact they go so far as to call it a “major selective factor in humans.”
More than 2 billion individuals worldwide suffer from helminth infections. The highest parasite burdens occur in children and helminth infection during pregnancy is a risk factor for preterm delivery and reduced birth weight. Therefore, helminth infections can be regarded as a strong selective pressure.
They go on to tell us that parasitic worms have shaped our genes:
In summary, our data are consistent with the notion whereby parasitic worms have acted as a powerful selective force on human populations and have contributed to shape nucleotide variability at a number of genes involved in immune responses. We also show that several genes associated with helminth diversity are involved in the pathogenesis of atopic conditions or in airway hyperresponsiveness.