Is there a reason why human eyesight and plants make use of the same wavelength of light?

Question

The accepted range for the wavelengths of light that the human eye can detect is roughly between 400nm and 700nm. Is it a co-incidence that these wavelengths are identical to those in the Photosynthetically Active Radiation (PAR) range (the wavelength of light used for normal photosynthesis)?

Alternatively is there something special about photons with those energy levels that is leading to stabilising selection in multiple species as diverse as humans and plants?

Answer 1

Good question.

If you look at the spectral energy distribution in the accepted answer here, we see that photons with wavelengths less than ~300 nm are absorbed by species such as ozone. Much beyond 750 infrared radiation is largely absorbed by species such as water and carbon dioxide. Therefore the vast majority of solar photons reaching the surface have wavelengths that lie between these two extremes.

Therefore, I would suggest that surface organisms will have adapted to use these wavelengths of light whether it be used in photoreceptors or in photosynthesis since these are the wavelengths available; i.e., organisms have adapted to use these wavelengths of light, rather than these wavelengths being special per se (although in the specific case of photosynthesis there is a photon energy sweet spot).

For example this study suggests that some fungi might actually be able to utilize ionizing radiation in metabolism. This suggests that organisms on a hypothetical world bathed in ionizing radiation may evolve mechanisms to utilize this energy.

Answer 2

The human species (and presumptive many of our close ancestors) have an extraordinary ability to detect shades of green and red. there is a theory behind this saying that we evolved this ability to better distinguish ripe fruits and thus optimizing the foraging. Most other mammals do not in fact have the ability to detect color.

P.S. I have no direct reference to this theory, but I have most likely read about it in Campbell & Reece's biology textbook. D.S.

Answer 3

The selection you refer in multiple species could be due to a mutual advantage. If fruits absorb visible wavelengths, they can be spotted by other animals and eaten together with the seeds. Seeds can then mature inside the host and, once eliminated with the feces, grow up a new plant in a different place.

This is not only valid for light absorption, but for light emission also: for some fruits, the ripening causes a blue-UV luminescence that can be spotted by some insects.