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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?

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4 Answers 4

up vote 52 down vote accepted

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 hypothetical organisms on a world bathed in ionizing radiation may evolve mechanisms to utilize this energy.

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For further reading, this review by Dartnell in 2011 discusses multiple roles cosmic and planetary ionizing radiation may have played in the origin of life. online.liebertpub.com/doi/abs/10.1089/ast.2010.0528 –  Ben Haley Dec 18 '12 at 14:58

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.

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If they absorb visible light, they don't reflect it, which would make them harder to see. –  Lee Louviere Feb 15 '12 at 14:56
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They preferentially absorb one or more colors, rendering the others easy to see. For instance, chlorophyl absorb more blue and red light, so you see leaves as green. –  Gianpaolo R Feb 15 '12 at 20:22

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.

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It is outright false that mammals cannot perceive color. Non-primate mammals are usually dichromats (lacking one cone type), leaving them red-green colorblind. –  Alexander D. Scouras Apr 28 '13 at 10:29
    
Yes indeed, I believe I was thinking of other mammals failing to detect different tones in this red-green spectrum. But I wrote it very missleading. Thanks for commenting =) –  Zewz May 16 '13 at 13:36
    
Didn't mean to be so assertive up there. But I've run across far too many people who think dogs and cats literally only perceive shades of gray. Science education levels are frustrating, to say the least. –  Alexander D. Scouras May 17 '13 at 5:41

A rule of thumb in optics is that light interacts with materials that have features with dimensions similar to the wavelength of light. For example, radio waves with large wavelengths interact with large objects like airplanes ,as in the case of radars, and really small wavelengths (x-rays & gamma rays) interact with really small objects like nuclei of atoms. If you take the visible spectrum, light interacts with materials with similar dimensions and/or energies like the C-C, C=O etc that constitute most of the organic compounds. Heck, light with the appropriate wavelength may even interact (or get diffracted in this case) with an organic material that possess many C=O-OH groups spaced with distances similar to the wavelength of light that is shone on it (provided they are regularly spaced and there are lots of them to produce an observable result). Since all organisms are carbon-based the C-C, C=O, C-O, C=_N etc dominate the constituents of the living matter from retina of the human eye to the photosensitive compounds in plants. Hence from the light-matter-interaction perspective all living beings are made up of more or less same materials and this is the reason why plants use the similar wavelength the human eye can detect for photosynthetic processes.

Source: just my intuition

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