Colored Vision and Low-Light Levels
Abstract
Given the public discussion about the importance of low-light environmental conditions as an important driving factor in the evolution of the optics of the human eye, this project will measure orbit size and cranial vault to determine the correlation, if any, between these two. I will also measure light levels at times of peak food-collecting and preparing activities for the San people as well as measure the prevalence of colored-vision deficiencies to compare to their northern hemisphere counterparts in Reimchen’s data.
Project Summary
Pearce and Dunbar (2011) suggest a very close correlation in scaling between the size of human orbitals and thus, the volume of a human eyeball, and the size of the human visual cortex. This, they state, follows a predictable pattern that can be mapped according to differences in latitudes of residence which they conclude is due to an overall decrease in available photopic light. However, in 2014, Meyer et al. revised the 2011 study’s methods and claimed to have found a weak correlation between latitude and orbit size and, that once body size was controlled for by examining foramen magnum size (a correlation they claim remains unfounded and yet was used in the 2011 publication), orbit size appears to in fact decrease with latitude.
In a 1987 publication, Reimchen explored red-green color deficiencies and their prevalence by latitude and searched for its value as an evolutionary advantage rather than an unhelpful mutation in the human eye. His findings indicated that individuals who suffer from red-green “color blindness” are able to detect smaller differences in the brightness of colors especially when in low-light conditions.
With the many implications that light conditions seem to have in the modification and evolution of the human eye, this project will measure prevailing light conditions during peak hours of San activity as not many populations below the equator have been studied. It will also conduct measurements of skull size and orbital size and estimate visual cortex size in order to determine whether scaling of these are in fact closely intertwined along the course of human evolution. Additionally, because a large brain is one of the most energetically expensive feats of the modern human body, I propose that there is a more complex mechanism for the selection of larger brains in these higher latitude, low-light environments. These environments are not known to be as species-diverse and are known to be hostile places to survive in. For these reasons, selecting for larger brains would indicate some sort of food security amidst harsh environmental conditions and perhaps not simply space for the integration of more visual input.
If possible, I would further like to determine how prevalent red-green color insensitivity is in the San people in hopes of adding to the data collected in Reimchen’s publication and confirming that the same insensitivity pattern is exhibited by populations in the southern hemisphere. Furthermore, the administration of a brightness sensitivity threshold test across this population in normal and color-blind individuals would be a great project to undertake because of Reimchen’s claim of its importance as an evolutionary adaptation.
Statement of Significance
By determining the prevalence of color-blindness in populations across the world as well as the effects that light conditions have on the anatomy of the human eye and brain, we would have a much better understanding in the type of vision necessary for the survival of ancient humans. We would also then be better equipped to make informed decisions about ancient environmental conditions in which the human eye was refined as well as factors that lead to the increase, peak, and eventual decline of brain size in ancient human relatives
We would also be better informed about our sensitivity to external pressures and perhaps how that has changed beginning with the use of controlled fire for evening activities and the now widespread use of electricity. The revolutionary use of electricity could perhaps have unknown negative impacts on the subsequent evolution of our eyes as a species contrary to the prevailing view of electricity as a resource to be prized because of how it revolutionized productivity and the perception of time.
Budget/Resources
This project will require a trip to South Africa where I will attempt to gain access to many ancient remains of modern and ancient human relatives. It will also require trips to visit the San in their places of residence as well as to the places they have inhabited along the course of their history to understand the environmental conditions they were exposed to as they were displaced or chose to move to.
Additionally, I am still working on the equipment necessary to collect and how to best record such data.