Scientists at Duke University just released a fascinating study examining the visual acuity of thousands of species, including humans. According to this research, humans see the world in greater detail than most other animals.
In this massive study, researchers collected and compared the visual sharpness of well over 600 species of animals. In addition to mammals, scientists also examined the eyes of various insects, fish, and birds.
Investigators first looked into the structure of each species’ eyes and then ran a few behavioral tests. With this data in hand, scientists charted the animals’ visual acuity using the standardized measure of cycles per degree, which refers to how many black and white parallel lines a patient can see before the lines become blurry.
In their study, researchers found that the average human eye can see 60 cycles per degree. Unsurprisingly, chimpanzees have a similar rate of visual acuity.
The only animals that saw in greater detail than humans were birds of prey. One of the best performing birds was the Australian wedge-tailed eagle, which can see an incredible 140 cycles per degree.
Insects, on the other hand, had the lowest visual acuity scores with many not close to one cycle per degree. Just for reference, a person is considered legally blind when s/he can’t see more than 10 cycles per degree.
Previous studies on this topic have shown that humans aren’t able to see at nighttime or tell the differences between colors as well as most other animals. The relative strength of human visual acuity, therefore, comes as a bit of a shock.
Besides giving scientists a better insight into the strengths of human vision, this study could help biologists settle a few long standing debates. For instance, entomologists have wondered for years what evolutionary purpose butterfly’s wings could serve. Some experts argue that these wings developed as a mechanism to ward off birds. Other scientists suggest these butterfly wings are intended to attract mates.
With this visual acuity data in mind, study authors suggest the bird thesis is more plausible. Butterflies simply wouldn’t be able to make out the detail of each other’s wings as birds could.
Graduate student Eleanor M. Caves, the winner of Duke’s 2017 Dean’s Award for Excellence in Mentoring, was the lead author on this study. The two other biologists involved in this project include Drs. Nicholas C. Brandley and Sönke Johnsen.
Anyone interested in learning more about this research should check out the latest edition of Trends in Ecology & Evolution. Study authors published this report under the title, “Visual Acuity and the Evolution of Signals.”