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  Topic: Probably a dumb question, but..., From [i]The Ancestor's Tale[/i].< Next Oldest | Next Newest >  
Stephen Elliott



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(Permalink) Posted: Mar. 04 2007,05:39   

ATM I reading Richard Dawkins "The Ancestor's Tale" and have hit a puzzle (for me). It is in the chapter The howler monkey's tale. In this chapter Richard is telling about the development of trichromatic vision.
   
Quote
 
Why would good colour vision be so important that trichromacy evolved independantly in New and Old World monkeys? A favoured suggestion is that it has to do with eating fruit. In a predominantly green forest, fruits stand out by their colours. This in turn, is no accident. Fruits have probably evolved bright colours to atract frugivores, such as monkeys, who play a vital role of spreading and manuring their seeds.
(bottom of page 152 in my copy)

My confusion is that Dawkins apears (to me), to be saying. "Fruits evolved colour to atract colour sighted creatures and colour vision evolved in some creatures to find fruit". It just doesn't sound right. Or could this be an example of co-evolution that may result in co-dependent systems?

I realise that Dawkins site would be a more apropriate place to post this question but I have only just registered there (specifically to ask this) and haven't received my confirmation e-mail yet. Yes I am impatient. OTOH it might induce some interesting replies here.

  
k.e



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Joined: Mar. 2006

(Permalink) Posted: Mar. 04 2007,07:12   

Quote (Stephen Elliott @ Mar. 04 2007,13:39)
ATM I reading Richard Dawkins "The Ancestor's Tale" and have hit a puzzle (for me). It is in the chapter The howler monkey's tale. In this chapter Richard is telling about the development of trichromatic vision.
   
Quote
 
Why would good colour vision be so important that trichromacy evolved independantly in New and Old World monkeys? A favoured suggestion is that it has to do with eating fruit. In a predominantly green forest, fruits stand out by their colours. This in turn, is no accident. Fruits have probably evolved bright colours to atract frugivores, such as monkeys, who play a vital role of spreading and manuring their seeds.
(bottom of page 152 in my copy)

My confusion is that Dawkins apears (to me), to be saying. "Fruits evolved colour to atract colour sighted creatures and colour vision evolved in some creatures to find fruit". It just doesn't sound right. Or could this be an example of co-evolution that may result in co-dependent systems?

I realise that Dawkins site would be a more apropriate place to post this question but I have only just registered there (specifically to ask this) and haven't received my confirmation e-mail yet. Yes I am impatient. OTOH it might induce some interesting replies here.

It seems a tautology I know but there is an alternative suggestion.

Fuit evolved so talking snakes could tempt Eve and it follows, so all women could tempt men to start another little human. Which thus provided an interesting Myth.  As to why the only animal on earth to be aware of its own mortality could reason away the fact that its self designed grandfather of all things and creator of life and therefore an afterlife, since it follows by magical logic, that that proto father could not possibly love something he caused to die by giving them the gift of life on the one hand and by fiat cruelly take it away with the other; except to justify all manner of evil, particularly by self righteous idolators of said creation myth

So much easier than figuring out which came first, the chicken or the egg.

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The conservative has but little to fear from the man whose reason is the servant of his passions, but let him beware of him in whom reason has become the greatest and most terrible of the passions.These are the wreckers of outworn empires and civilisations, doubters, disintegrators, deicides.Haldane

   
Stephen Elliott



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(Permalink) Posted: Mar. 04 2007,08:41   

Quote (k.e @ Mar. 04 2007,07:12)
 
Quote (Stephen Elliott @ Mar. 04 2007,13:39)
ATM I reading Richard Dawkins "The Ancestor's Tale" and have hit a puzzle (for me). It is in the chapter The howler monkey's tale. In this chapter Richard is telling about the development of trichromatic vision.
       
Quote
 
Why would good colour vision be so important that trichromacy evolved independantly in New and Old World monkeys? A favoured suggestion is that it has to do with eating fruit. In a predominantly green forest, fruits stand out by their colours. This in turn, is no accident. Fruits have probably evolved bright colours to atract frugivores, such as monkeys, who play a vital role of spreading and manuring their seeds.
(bottom of page 152 in my copy)

My confusion is that Dawkins apears (to me), to be saying. "Fruits evolved colour to atract colour sighted creatures and colour vision evolved in some creatures to find fruit". It just doesn't sound right. Or could this be an example of co-evolution that may result in co-dependent systems?

I realise that Dawkins site would be a more apropriate place to post this question but I have only just registered there (specifically to ask this) and haven't received my confirmation e-mail yet. Yes I am impatient. OTOH it might induce some interesting replies here.

It seems a tautology I know but there is an alternative suggestion.

Fuit evolved so talking snakes could tempt Eve and it follows, ...

I hope you don't think I was trying to do an ID type tactic here. It just seems like a strange explanation to me. After thinking about it some more it seems even stranger. Surely if the evolutionary pathway of selection by being noticed was "encouraging" fruit to develop colour then why wouldn't white be the most likely development? That would stand out to even colour blind frugivores would it not?

  
qetzal



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(Permalink) Posted: Mar. 04 2007,10:20   

Quote (Stephen Elliott @ Mar. 04 2007,05:39)
Or could this be an example of co-evolution that may result in co-dependent systems?

That seems reasonable to me. Presumably the monkeys were frugivores while they still had dichromatic vision. Monkeys with better color vision (i.e. trichromacy) would presumably be more efficient in finding fruit, giving them a survival advantage over other monkeys.

At the same time, fruits that are more brightly colored are more likely to have their seeds widely dispersed. That should give them a survival advantage over other fruit plants.

I'm just speculating though. As a lowly molecular biologist, I don't have advanced expertise in evolutionary biology.

  
Stephen Elliott



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(Permalink) Posted: Mar. 04 2007,11:54   

Quote (qetzal @ Mar. 04 2007,10:20)
...
I'm just speculating though. As a lowly molecular biologist, I don't have advanced expertise in evolutionary biology.

I am just speculating too and my expertise in evolution is way below yours.
The dichromatic monkeys is a given in the scenario presented as it about how trichromatic arose seperately on two continents.
But in the scenario given, why don't we see many white fruits? They would be easier to spot by both dichromatic and trichromatic (probably even tetrachromatic) frugivores.

EDIT: Could it be that to become white (would that be colourless?) requires far more dramatic changes in the fruit DNA than other colours? Assuming that white fruit would require a complete loss of the coding used for colour.

  
qetzal



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(Permalink) Posted: Mar. 04 2007,12:21   

Quote (Stephen Elliott @ Mar. 04 2007,11:54)
But in the scenario given, why don't we see many white fruits? They would be easier to spot by both dichromatic and trichromatic (probably even tetrachromatic) frugivores.

Good question. I don't have any good answers. There are naturally occuring white flowers, so obviously it isn't because plants somehow can't make white organs.

Maybe an all white fruit is actually disadvantageous? Maybe it would tend to get overlooked because it looks like a patch of bright light?

It might be interesting to try to simulate what white vs. brightly colored fruits in a forest would look like to an animal with dichromatic & trichromatic vision. Maybe the intuition that white would stand out better is incorrect.

IIRC, there are flowers that look white to us, but are multi-colored in the UV wavelengths that their pollinators (e.g. bees) can see.

That's the best I can come up with off the top of my head. Maybe someone who actually knows what they're talking about will chime in with a better answer.

;-)

  
Stephen Elliott



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(Permalink) Posted: Mar. 04 2007,13:20   

Quote (qetzal @ Mar. 04 2007,12:21)
... Maybe someone who actually knows what they're talking about will chime in with a better answer.

;-)

Hehe,
Yeh, that is what I was hoping for. I consider it quite fascinating. Still waiting for my account activation e-mail, then I can try Richard Dawkins site.

Alternatively, while I am waiting maybe somebody else could ask this over there and post a link. :D

Quote
There are naturally occuring white flowers, so obviously it isn't because plants somehow can't make white organs.
Good point.

  
Mike PSS



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Joined: Sep. 2006

(Permalink) Posted: Mar. 04 2007,14:50   

I think you are committing a sin of ommision here.  Fruiting plants had already developed before howler monkeys "regained" trichromatic vision.

p.146 (First Mariner Books edition 2005) states (continuation of first paragraph):
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"To this day most mammals, even those who have returned to live in the daylight, have rather poor colour (sic) vision, with only a two-colour system ('dichromatic').
...
We catarrhine apes and Old World monkeys have three: red, green and blue, and are therefore trichromatic, but the evidence suggests that we regained a third class of cone, after our nocturnal ancestors lost it.  Most other vertabrates, such as fish and reptiles but not mammals, have three-cone ('trichromatic') or four-cone ('tetrachromatic') vision, and birds and turtles can be even more sophisticated."

Although Dawkins carries on to state the seemingly tautological statement related fruit development to howler monkies, the fruits came before the monkies in this case and the statement, I think, should read more like...
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"Fruits have probably evolved bright colours to attract frugivores, such as monkeys birds, ...


Does that help?

  
Stephen Elliott



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(Permalink) Posted: Mar. 04 2007,15:33   

Quote (Mike PSS @ Mar. 04 2007,14:50)
...Does that help?

A little but not much. Hasn't it just moved the idea further back in time? Unless of course there is another reason why colour vision would be an advantage to frugivores (and there may very well be, I don't know).

From my POV (and it is only a POV). The explanation seems to be stating that frugivores evolved colour vision because it was an advantage in seeing coloured fruit and fruit developed colour because it was an advantage to be seen by colour vision capable frugivores. It just sounds wrong (or unlikely).

Now if colour vision had other advantages that selected for it and therfore also made it easier to spot fruit, that would be easier to understand. Or, if having colours made fruit easier to spot by dichromatic eyes, selected fruit to gain colour, that would have the same result.

I am not disputing that this evolved, just why.

My only experience of vision is my own (surprise surprise). A regular human eye can only see colour in fairly bright light. Night vision relies almost entirely (if not exclusively) upon rods. At night we have a blindspot where we normally focus (right in the centre of our vision). The blindspot is where the cones are concentrated. From that I would reckon that our night vision is pretty much dichromatic. Now I know that white objects are easier to spot at night (by humans) than colours. So under those conditions why is it that more/most fruits are not white?

This may be a damned silly question with an obvious answer. But right now I can't figure it out and was hoping that somebody here would know (not too daft considering the expertise of regular posters here).

Oh BTW, yes it was an ommision on my part. Sorry. Not a "sin" though but rather an "error".

EDIT: Thanks for the answer MikePSS. I am sure that I sound ignorant (I am). Biology stopped being a part of my formal education from around age 13, so I am on catch-up here.

  
Henry J



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(Permalink) Posted: Mar. 04 2007,18:44   

Re "then why wouldn't white be the most likely development? That would stand out to even colour blind frugivores would it not?  "

I wonder if there aren't a whole lot of other things in jungles that might appear white to eyes that don't see in color?

Another thought, since birds were mentioned, maybe the colorful fruits attracted them first, and monkeys later took advantage of that when their color vision evolved?

Henry

  
ericmurphy



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(Permalink) Posted: Mar. 05 2007,01:14   

Another thing to consider. Plants did not evolve colored fruits "so that color-vision organisms could find them." Animals did not evolve color vision "so that they could find fruit." This is in inappropriately teleological way of looking at the issue. I believe it is likely that plants evolved colored fruits entirely accidentally, as animals evolved color vision entirely accidentally. However, since the two properties are mutually reinforcing, there's a feedback loop, where plants with more brightly-colored fruits have an adaptive advantage, and animals with more accurate color vision also have an adaptive advantage. Check this out: coevolution.

And always remember—things don't evolve in a particular direction for any particular reason.

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2006 MVD award for most dogged defense of scientific sanity

"Atheism is a religion the same way NOT collecting stamps is a hobby." —Scott Adams

  
MidnightVoice



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(Permalink) Posted: Mar. 05 2007,07:41   

Do we need to develop a new field - culinary evolution?   :p

--------------
If I fly the coop some time
And take nothing but a grip
With the few good books that really count
It's a necessary trip

I'll be gone with the girl in the gold silk jacket
The girl with the pearl-driller's hands

  
Mike PSS



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(Permalink) Posted: Mar. 05 2007,08:04   

Quote (Stephen Elliott @ Mar. 04 2007,16:33)
A little but not much. Hasn't it just moved the idea further back in time? Unless of course there is another reason why colour vision would be an advantage to frugivores (and there may very well be, I don't know).

From my POV (and it is only a POV). The explanation seems to be stating that frugivores evolved colour vision because it was an advantage in seeing coloured fruit and fruit developed colour because it was an advantage to be seen by colour vision capable frugivores. It just sounds wrong (or unlikely).



KNOWLEDGE WARNING.  THIS ISN'T MY FIELD BUT I CAN STICK MY NECK OUT A LITTLE.  JUST WAITING FOR A BLACK-CAPED PROFESSIONAL TO COME ALONG AND GIVE IT A CHOP.
****************
That being said I think ericmurphy has one option covered in convergent evolution.

Another angle could be that fruiting plants appeared after color (colour for you upper-class twits... and Canadians... and Aussies... and... well... the rest of the english-speaking world I guess) vision was already present in reptiles, birds, turtles, etc.  The actual size of the fruit was probably small (just like wild fruit compared to domesticated/cultivated plants) so that the plant offerred a treat without a large input of energy.  The plants DIDN'T want to attract animals that would fully digest the seed (ruminants, etc.) but those who would eat the fruit whole and pass the seeds in a little package with fertilizer as a bonus.

I can take this analogy further, but this makes the point generally.  Basically the fruit offers a quick recognition to any color vision creature to immediately take advantage of the offerring before a clumsy ruminent comes along and munches the entire bush/tree/cactus/fern.  So I say the chicken (color vision) was around before the egg (fruit).  Howler Monkeys redeveloped trichromatic vision to take advantage of existing opportunities within their local environment.
Quote
EDIT: Thanks for the answer MikePSS. I am sure that I sound ignorant (I am). Biology stopped being a part of my formal education from around age 13, so I am on catch-up here.

I'm sure that I sound ignorant to others more learned in the field too.  I'm trying to catch-up on a lot of subjects as much as you are.  The fact that I had to refer back to Dawkins book (I read it 6 months ago) reinforced some aspects of the ToE I hadn't thought about before.

  
The Ghost of Paley



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(Permalink) Posted: Mar. 05 2007,09:34   

Keep in mind that alot of these scenarios are very speculative, and that fossil and genetic research will often refute them while suggesting alternatives that weren't on the table at the time. Fish/amphibian intermediates like Acanthostega come to mind. It appears that most of the fin-to-leg modifications occured before the fish hit land, not after. The selective landscape is a lot more complex and unpredictable than many scientists had assumed. So some of these paradoxes might be a twinkle in Dawkins's eye.  :)

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Dey can't 'andle my riddim.

  
Stephen Elliott



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(Permalink) Posted: Mar. 05 2007,09:37   

So from the posts so far would people agree that evolution is seldom an isolated event (in the long term)? ie: If anything that is part of a larger eco-system evolves a new trait then it is likely that something else may evolve that exploits that trait?

Henry J           
Quote

Another thought,since birds were mentioned, maybe the colorful fruits attracted them first, and monkeys later took advantage of that when their color vision evolved?


I think that is probably close/correct. Sounds pretty sensible anyway.

ericmurphy      
Quote

Another thing to consider. Plants did not evolve colored fruits "so that color-vision organisms could find them." Animals did not evolve color vision "so that they could find fruit." This is in inappropriately teleological way of looking at the issue.


Agreed. But that is how I read the passage from The Ancestor's Tale which I quoted in the OP. I like the book so far but that particular claim threw me somewhat.

Still not sure why we don't get more white fruits though. Although the mention of ruminants (from Mike PSS) that maybe white would atract them and possibly white fruit would be selected against for that reason. Does that sound feasible? It does to me.

  
qetzal



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(Permalink) Posted: Mar. 05 2007,11:27   

What about bioluminescent fruits? Or bioluminescent plants in general. Are there any (not counting the man-made ones)?

If animals can harbor bioluminescent bacteria in light emitting organs, why couldn't plants do the same? If they can why don't they?

Sorry for going off on a tangent, but the question of 'why aren't there any white fruits' has tweaked my imagination.

  
Glen Davidson



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(Permalink) Posted: Mar. 05 2007,11:28   

Red fruits (well, most fruits in fact) are generally small (including the ancestors of apples) and seem mostly to appeal to birds, who are good at not crushing (no teeth) or digesting the seeds.  Doesn't mean that it wouldn't be good for primates to evolve to eat the birds' food.

However, within the past two or three years there was an article in, as I recall, Nature, which suggested that in fact trichromatic vision evolved in at least some of the primates in order to eat the reddish young leaves of plants.  I forget what the whole reasoning was, but it seems to me that they thought that red fruits were not actually invisible to primates (we can distinguish greens better than any other color), while the young leaves were a red that couldn't be seen via our vision of "green".

It seems inevitable that red vision does enhance our capacity to see red fruit in any case.  I think that one of their points was that young reddish leaves were important sources of food when other sources weren't available, so whatever the effect seeing red fruit had wasn't as important as seeing young reddish leaves when so little else was available to eat.  

Why not white fruits?  Because at a distance they'd probably look more like open spaces among the leaves, dappling of light, the sky, etc.  Perhaps it has also to do with cognitive faculties, as white does not have a strong effect on us, while colors like red act more like signals and produce a strong response (probably somewhat muted by the many colors in today's society).

Glen D

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Nothing in biology makes sense except in the light of coincidence---ID philosophy

   
JohnW



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(Permalink) Posted: Mar. 05 2007,11:36   

Quote (MidnightVoice @ Mar. 05 2007,07:41)
Do we need to develop a new field - culinary evolution?   :p

Primordial soup?

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Math is just a language of reality. Its a waste of time to know it. - Robert Byers

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Glen Davidson



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(Permalink) Posted: Mar. 05 2007,12:47   

Remember also the peppered moth, that it was whitish in the pre-industrial environment as camouflage.  Fruits are more commonly camouflaged as green until they are ripe, but white also is a reasonable camouflage due to  lichens, dead leaves, bleached wood, etc. (in addition to sky, dappled light, open areas that I mentioned before).  White is one of the default colors in the environment, not at all a striking signal.

Some flowers are white, but they are usually, if not always, scented, and attractive to moths, not to bees and vertebrates.  Hummingbirds are attracted to red flowers above all.  One might ask why moth flowers are white, though, instead of green or some such color, and probably it has to do with a slight (and not costly) signal against the green leaves.  In edit ,I'm adding that they may also be white in order not to be pollinated by birds and bees, but to be pollinated by the "right insects".

Do most moths see colors?  I'd guess that most don't see them well in the evening, when they tend to do their pollinating.  There has been a report of one insect, I believe it was a moth, that can see colors in the dark, yet I have no idea if this means that color vision is common in moths, let alone at twilight.  It may not matter anyhow, since white flowers are very visible close-up (and have no pigment costs), while it is the scent that draws moths in from a distance.

White fruits are not unknown, indeed the standard warning to boy scouts, etc., is that white berries are to be considered always poisonous.  Poison ivy berries are white--what eats them (of course animals are typically not affected by poison ivy--I've seen bees pollinating poison ivy, making me wonder what sort of honey that produces)?  

I just googled "white berries" and "sumac", and it turns out that poison sumac berries are also white.  Redosier dogwood berries are also white, says my google, and are eaten by at least 18 species of birds, including quails.  Why white?  I don't really know.  Maybe the white berries on redosiers contrast nicely with the red bark when the leaves fall off, or maybe the berries are "meant" not to be too striking so that the right birds find them after everything else is gone, and thus might distribute the seeds better than a more indiscriminate selection of feeders would.  One thing I'm saying is that not all fruits are "vying for" maximum exposure, having evolved simply to be "visible enough" to the "right organisms".

Bioluminescence in fruit?  It would be fairly expensive, and would probably appeal more to nocturnal seed eaters than to diurnal birds.  Fruit bats in the tropics might be signaled by bioluminescence, but as I understand it they already have a keen sense of smell and further signals would cost more than they were worth, probably.  Bioluminescence evolving now would probably just attract unwanted feeders.

Glen D

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Nothing in biology makes sense except in the light of coincidence---ID philosophy

   
Henry J



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(Permalink) Posted: Mar. 05 2007,22:26   

Re "Do we need to develop a new field - culinary evolution?"

Wouldn't that have something to do with why so many land vertebrates taste like chicken? ;)

Re "Primordial soup?"

Which would of course use the proverbial warm pond to maintain its temperature. :)

Henry

  
skeptic



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(Permalink) Posted: Mar. 05 2007,23:44   

My first instinct was that it had to do primarily with the chemistry of the colors, based on the compounds.  This seemed interesting but since I've forgotten quite a bit of organic chemistry over the years, I thought I'd do some research.  I came upon this and I thought I'd post it as you may or may not find it useful:

Fruit Color Polymorphisms

  
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