By Elizabeth Preston
Mar 2, 2011 4:04 PMNov 5, 2019 12:22 AM


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Do you ever find yourself squinting into the glare of your computer screen around 4 PM and thinking that your eyes aren't built for this? You're right, of course. The human eye evolved on the African savanna. This is what it's built to see:

Scientists from the University of Pennsylvania and elsewhere took about 5,000 digital photos in a Botswana savanna. They captured natural scenes at various times of day, from sun-baked vistas to up-close tree bark to fresh elephant dung, and compiled the images into a publicly available database.

Clicking through the albums may make you feel overheated, but it also simulates a pleasant stroll through the savanna. (Spoiler alert: baby baboons!)

The researchers used this database to investigate the evolution of the human eye. Specifically, they wanted to find the logic behind how our color-sensing machinery is set up.

Our eyes detect color using cone cells, which come in three types: one that detects light at short wavelengths (blue), one for medium wavelengths (green), and one for longer wavelengths (red). The three types of cones aren't distributed evenly across the retina, though. The blue-detecting cones are rare, and mostly exist around the outer edges of the retina. The red and green cones are much more common, but the ratio between them varies widely from person to person.

For each of the scenes in the Botswana photo database, scientists calculated how much light of different wavelengths would be reaching the viewer's eye. Based on those numbers, they mathematically determined the most efficient distribution of cone cells in the retina. They found that blue-detecting cones couldn't pick up as much information as the red or green cones (which explains why we don't make very many of these cells) but were most useful at the periphery of the eye. The red and green cone cells, though, would be about equally useful at picking up information from these scenes. That explains why humans can have widely varying ratios of red to green cone cells without an effect on their vision.

Though they may seem disorganized, our retinas have evolved to efficiently gather information from our environment--or our ancestral savanna, anyway. Future research might address how our eyes handle other environments. Additionally, the authors say that knowing how to build eyes efficiently might help us create better robots. Not having had the benefit of evolution, today's robots can't see nearly as well as we can.

Photos: University of Pennsylvania.

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