In Homer’s The Iliad, the seas were the color of wine and honey was described as green, but what did the world look like for early humans—or even early primates?
By comparing photoreceptor genes of different primate species, Dartmouth scientists were able to determine that our primate ancestors could sense UV light, but ancient species that were diurnal had the increased ability to sense blue-spectra light. Not only was the team able to describe what early primates might be able to see, but they suggest that the ecological pressure to determine foods by color and see fast moving predators could influence the evolution of the visual system.
The team was focused on genes that encode opsins, which are light sensitive proteins found in our retina which send signals to the brain to determine color, brightness and can even aid in circadian rhythm mechanisms. Our eyes now have about 6 million cone cells, helping us to see color, and 120 million rod cells, which help us determine grayscale light.
By evaluating the differences in opsins between nocturnal and diurnal primates, the team could determine the selection patterns on genes that require and don’t require light. To do so, they specifically looked at the opossum (nocturnal) and a tree shrew species (diurnal). They discovered that the opsin-1 gene, which is important for “short wavelength detection” such as blues and purples were found in diurnal primates but were absent from nocturnal primates; however they also found that there were less mutations found in diurnal primates compared to the nocturnal species for another opsin-1 gene, encoding for “long wavelength detection” such as reds and yellows.
Since these two genes differ across the order of primates, it shows that these genes could be good for estimating ancestral divergence time between species to help us learn more about the evolution of humankind.
The ability to see a beautiful world is something that people do not appreciate on a day to day basis; over just a few millennia our kind developed a dramatic change in perception and consciousness, rooted in just shifts in DNA, a change greater than most seen before. Imagine what further advancements could be made were humans to persist on Earth a millennium more.
Sources:
Melin, A (2016)Eurachontan Opsin Variation Brings New Focus to Primate Origins. Mol Biol Evol. (33)2
doi: 10.1093
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