This is publication was a tough one to write and a little bit terrifying, if I am honest. Fortunately, it is fully open access, so all can read and critique.
In sum, I propose the physiology that fuels our unique endurance capacities as humans is an exaptation of underlying pregnancy physiology. To be completely transparent, this paper presents an idea and not a formal test of that idea. A ton of work is going to need doing to test this hypothesis, and my hope is that this paper will inspire people across disciplines to pursue this intriguing line of inquiry.
In the paper I walk the reader through the key physiological changes associated with endurance training as well as those associated with pregnancy – highlighting the many similarities. For example, there is a similar increase in maximal oxygen consumption capacity (VO2 max) during both pregnancy and endurance training. There is also a metabolic shift towards burning fatty acids.
I then move to how this may have come about evolutionarily. In short, the development of striding bipedalism lead to pregnancy-related physiological processes being co-opted for endurance capacities. I also lay out why this would be true for females and males even if the origin of our endurance physiology comes from pregnancy.
Finally, I present how this idea could be tested and some of the potentially more fruitful routes for inquiry. For example, it is fairly well established, though it could be more thorough, that cardiac, respiratory, and metabolic changes associated with pregnancy are rather consistent across mammals. However, what is less well knows is what genes and subsequent physiological pathways/regulation are similar between pregnancy and endurance. There should also be a comparative examination across endurance mammals and endurance birds.
Why am I a bit terrified sharing this? Well, it seems anytime females are centered as a driving force in human evolution there is a vehement backlash.