Looking back on why we look forward: A special research series by Adam Glover, Part 6

Research Conclusions

The evolution of anteriorly directed eyes and orbital convergence thus has been hypothesized to have been functionally related to locomotion, feeding behavior, and the detection/avoidance of predators, and many of these arguments continue to this day. The three are not necessarily mutually exclusive, however, and each hypothesis proposes certain fitness benefits that orbital convergence could have provided in combination with others in a certain ecological context. For example, the occupation of an arboreal niche which provided fruits, nectar, and insects may have been a preadaptation for the selection of orbital convergence; if snakes emerged as predators to early primates within this ecological context, it is very reasonable to propose that orbital convergence would be strongly selected for to provide an enhanced ability to move, obtain food, and detect predators within the environment.

That said, it seems that two different conceptual camps exist when considering theories of why certain traits may or may not have been selected for; one believes that selection pressures cannot be disentangled from one another in a way that allows for the identification of any one as the primary selective pressure, and the other believes that for any trait there had to be a primary selective pressure (Isbell, 2009). The studies of the evolution of convergent orbits in primates is no different, and future studies must continue to work to either identify a single primary selection pressure for convergent orbits or a cohesive suite of them. Further investigation of the Snake Detection hypothesis could be a good place to start, as some of its core predictions are still novel and yet to be confirmed or refuted. For example, the prediction that if snakes acted as the primary selective pressure in the development of convergent orbits in primates, catarrhine primates (which, being native to Africa and Asia, would have encountered snakes earlier than the platyrrhine primates of the New World) should detect snakes faster or more reliably or from a greater distance than platyrrhine primates needs to be confirmed in order to support the Snake Detection hypothesis (Isbell, 2009).

BroaderImplications

In studying the selection pressures that operated on early primates, we are truly studying that which made us human (the environmental pressures which eventually led to the speciation of Homosapiens) as well as studying that which makes us humans- our strengths and our flaws, our desires and our fears; as this review has just shown, the study of selection pressures could eventually explain our fear of snakes (Snake Detection hypothesis), can explain why we have a blind spot in our field of vision (evolution results in fitness trade-offs, not perfect structures), and hopes to someday even explain why we are able to so accurately reconstruct the three-dimensional world around us (Arboreal hypothesis, Visual Predation hypothesis). The study of selection pressures and their effects thus has incredible biological significance and personal significance in the way that it helps tell the story of our identity.