Whale color vision gene remnants point to ancestral terrestrial life

Humans are extremely visual creatures. We ask, “How do I look?” before we go on a date. We don’t usually ask, “How do I sound?” or  “How do I taste?”

If a loved one goes blind, most people would consider it a tragedy. If a loved one loses their sense of smell, we may think it unfortunate, but we’re less likely to worry about their quality of life.

Not all animals are as visually oriented as humans are, though, and many see the world in very different ways than we do. One way that our vision is different from many other animals is through the number of colors we can perceive.

Our eyes have two kinds of cells that allow us to see: rods are used in dim light and only allow for black and white vision, whereas cones are used in bright light and allow for color discrimination.

Rods and cones
Rods (beige) and cones (green)

At the most fundamental level, the reason cones allows us to perceive colors is that different cones have different kinds of pigments, known as opsins, that absorb different wavelengths of light. Human cones can have a ‘red’, ‘green’ or a ‘blue’ opsin, and as these pigments absorb different wavelengths (colors) of light, our brains compare and contrast the relative intensities of these signals to discern color. Rods, on the other hand, only have a single pigment, so no compare and contrast is possible.

Opsin absorbances
Relative absorbances of different opsin pigments

Most mammals, such as dogs and cats, only have two kinds of cone opsins. As such, though your pets are ‘colorblind’, they do see colors; just not as much as you. If you have ever known somebody to be red-green colorblind (e.g., Protanopia), this is similar to how most mammals see the world, as shown in the image below.

Protanopia-Color-Spectrum

Finally, some mammals, such as most whales, only have one kind of cone opsin, a ‘red’ opsin, which leads their vision to be completely black and white. Others lack cones altogether, relying completely on their rods for vision.

So what does this have to do with evolution? As discussed previously, the fossil record and genetic evidence suggest that whales are descended from hoofed mammals, and are therefore related to camels, pigs and deers. Notably, all of these mammals have two cone opsins: a ‘red’ opsin and a ‘blue’ opsin. What’s interesting is that whales have genetic remnants of a ‘blue’ opsin [1], suggesting that they lost it as they adapted to an aquatic lifestyle.

Additionally, the whales that lack cones and only use their rods for vision have genetic remnants of both cone opsins as well as various genes involved in translating the light signal absorbed by the pigments into an electrical neural signal (phototransduction genes) [2].

Whale cone pseudogenes
SWS1 and LWS are cone opsin genes. Others are cone phototransduction genes. Red, blue and green indicate inactivating mutations. Choeropsis and Bos represent functional hippo and cow genes for comparison.

Whereas whales’ ancestors likely lived on land and benefitted from perceiving distinct colors, most whales live in a relatively colorless environments in oceans and rivers. Scientists think that perceiving colors was no longer important in these situations, so these genes decayed to the point of becoming functionless pseudogenes.

As such, the genetic remnants of a former life, full of color, further point to the evolution of whales from terrestrial ancestors.

Questions for Creationists

Why would the Creator create whales with nonfunctional cone genes? Would it not have been simpler Create whales without these genes entirely? Is it just a coincidence that the fossil record and genetic analyses suggest that whales descended from land-dwelling ancestors that would have benefited from color vision?

References

1. Meredith, R. W., Gatesy, J., Emerling, C. A., York, V. M., & Springer, M. S. (2013). Rod monochromacy and the coevolution of cetacean retinal opsins.PLoS genetics9(4), e1003432.

2. Springer, M. S., Emerling, C. A., Fugate, N., Patel, R., Starrett, J., Morin, P. A., … & Gatesy, J. (2016). Inactivation of cone-specific phototransduction genes in rod monochromatic cetaceans. Frontiers in Ecology and Evolution, 4, 61.

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