Why are most leaves green?

[Maundy]

Why are a majority of plant leaves green, when they would absorb more of the sunlight's energy if they were black, thus absorbing all of the light spectrum and giving the plant more energy?

Surely for this reason and through Darwin's theory of natural selection, plants would all be black as they would grow better and grow in places with less light and consequently prevailing all the other species of plant?

Thanks

[Phi for All]

Do plants need the entire spectrum? Perhaps the black leafed plants that have evolved all overheated and didn't survive to spread seeds.

[StringJunky]

We had a discussion about this recently. The possibilities are many, including what Phi suggests, but the reasons could be condensed down to because green is a 'good fit', on the whole, for plants to do what they need to do given the conditions on terrestrial Earth..

 

Evolution is not about producing the optimum characteristics but the fittest in any given environment...it's a relative thing not an absolute. The earliest photosynthetic organisms that used green and evolved to plants were evolutionarily favoured....at some pivotal period in the history of chlorophyll-utilising organisms, conditions on early Earth facilitated their reproduction and subsequent domination.

 

To reiterate more generally, Evolution is not some hidden embedded code or algorithm driving things to evolve to some state of ultimate perfection but a mix of random mutation and prevailing circumstance that allows some characteristics to multiply over time...pot luck basically.

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Edited November 10, 2011 by StringJunky

[PhDwannabe]

Surely for this reason and through Darwin's theory of natural selection

I'm not sure how seriously you meant this, but this exact quote is actually a nicely illustrative example of the presentistic, teleological lens people often view evolution through. I think we underestimate the extent to which people are suspicious of evolution as a result of this. "If natural selection perfects everything, how come I don't have wings, because that would be awesome and confer a survival advantage because I'd be able to escape predators and go cool places. Surely I'd have that if evolution were real." Only, it doesn't work that way--it's not pointed in any direction, because there's nobody directing it. StringJunky's points are important ones that a lot of people don't seem to get.

 

(For the record, I'm not suggesting that the OP is a dirty evolution denialist--it could also be an honest, curious, hypothetical inquiry.)

[Phi for All]

(For the record, I'm not suggesting that the OP is a dirty evolution denialist--it could also be an honest, curious, hypothetical inquiry.)

Unfortunately, it's easy to jump to a conclusion like this when someone brings up Darwin in a question about modern evolutionary theory. You don't see many people questioning the timing of next month's total lunar eclipse by criticizing the work of Ptolemy.

[jimmydasaint]

Why are a majority of plant leaves green, when they would absorb more of the sunlight's energy if they were black, thus absorbing all of the light spectrum and giving the plant more energy?

Surely for this reason and through Darwin's theory of natural selection, plants would all be black as they would grow better and grow in places with less light and consequently prevailing all the other species of plant?

Thanks

 

Great question Maundy. I think you got the black leaves thing from Lovelock and Watson's hypothetical 'Daisyworld'.

Daisyworld I wonder if it is possible that aquatic plants had chlorophyll and then, as some moved on to the land, the colour green was preserved in the chlorophyll? Long wavelengths (blue light etc...) are better asorbed in the water at reasonable depths, e.g. 1.0 m, at which about 45% of the available light will get through. How Light Penetrates Water

It may be possible that this colour did not require further random selection.