Why do animals evolve superficial traits?

[HydrogenBond]

Moderation Note: The first three posts of this thread were moved from the thread "The order left unmentioned: Gymnophiona (Caecilians)" as they discuss evolution rather than Caecilians.

 

What I always thought it odd, is why animals evolve so many superficial changes that have limited practical use, other than being cute. Whether a frog is green or green with a couple of yellow or orange spots, or a funny hair style, it may not affect what is under the hood. The affect is like an auto making adding a new body style to last years chassis and drive train. It may change the headlights or add some pin striping.

 

The only logic I can see, is connected to breeding differentiation. The unique visual affect sets the species apart, so unique " birds of a feather", will breed, limiting genetic variations. It may be easier to evolve using fewer variables, with each small distinction in body style, narrowing down what will be breeding. This would imply the brain limiting possible genetics variations using sensory cues. If the brain didn't care if the mating frog was green, with red, blue or orange spots or hand a funny hairdo, there would be more genetic diversity within the breeding stock. But selective advantage evolved the brain to place a limit on genetic variations.

[freeztar]

This is off-topic HB, but I feel it's important to address these misconceptions.

 

What I always thought it odd, is why animals evolve so many superficial changes that have limited practical use, other than being cute. Whether a frog is green or green with a couple of yellow or orange spots, or a funny hair style, it may not affect what is under the hood.

 

You're making the assumption that the frog is choosing to evolve these "cute" traits when in fact it is random genetics.

 

The only logic I can see, is connected to breeding differentiation.

 

It seems like you are thinking of speciation, when two groups of individuals will no longer mate with each other. For example, consider the fact that humans will mate with one another despite different eye, hair, and skin coloring.

 

If you want to discuss this further, please start a new thread.

[HydrogenBond]

Sorry, I didn't mean to highjack the thread. But I thought it interesting that the DNA might cause a random visual affect, like you pointed out. But the brain causes similar animal looks to be more attractive, causing a narrowing of further variation.

 

Relative to humans, all the allowable breeding between humans is relatively new. Even 50 years ago, races were far less likely to cross breed, even though it offers diversity advantage to the genes. Not too long ago, even ethnicities of the same race would have an irrational drive to keep the ethnicity, pure, limiting adding fresh genes. The animals appear to do this naturally until real breeding barriers appear that genetically separate. Then we have a new branch in the evolutionary tree. The superficial might help keep the critters separate long enough until genetics makes it independent in a more permanent way.

[Moontanman]

So far you have yet to mention anything that is superficial, spots can have lots of reasons for being there, camouflage, warning to predators of a bad taste, mating colors, the list goes on and on. What do you consider superficial? Human skin color is not superficial, it has a definite reason for existing and human racial interbreeding is hardly new or limited in any way. Skin color is/was reinforced by various factors. Sunlight intensity is one of them, we might see white and black in our racial mindset but in reality there is a spectrum of skin colors from the darkest at the equator to slowly lighter as we go toward the poles. Our modern ability to travel is mixing this up but before wide spread travel is was skin cancer and lack of vitamin D that kept darker people near the equator and lighter people nearer the poles.

[sman]

This thread seems to have died, but I think there may be something meaningul in here. Some traits ARE superficial, even if it's hard to think of examples. There are billions of bits of zoological documentaion that we can assume HydrogenBond has been pouring through all this time and may spend the rest of his life doing so trying to find an example of some phenotypical effect that some scholar won't be able to cry "benefit" about.

 

Maybe what his intuition is pointing out is what Ernst Mayer and others called Isolation Mechanisms, in this case Post-Zygotic Isolation Mechanisms. There are wonderful examples in insects and also in the ciclid fish of lake Victoria.

[Moontanman]

This thread seems to have died, but I think there may be something meaningul in here. Some traits ARE superficial, even if it's hard to think of examples.

 

For this thread to continue I think you need to list a few.

[sman]

 

For this thread to continue I think you need to list a few.

GREAT!

 

Ciclid fish spieces Pundamilia pundamilia and Pundamilia nycrerei, different only by an arbitrary red spot, which was manipulated by colored light in an exparament by Ole Seehousen, causing the two to interbreed.

 

Grasshoppers Chorthippus brunnus and Chorthippuys biguttulus, different only by the "songs" that they fiddle to attract females.

 

I guess the idea is that these "superficial" traits are picked out by the evolving genotype and used as indicators of gene harmony, or to put another way, to avoid sterile hybrids.

[Moontanman]

GREAT!

 

Ciclid fish spieces Pundamilia pundamilia and Pundamilia nycrerei, different only by an arbitrary red spot, which was manipulated by colored light in an exparament by Ole Seehousen, causing the two to interbreed.

 

Why would you say this spot is arbitrary? Do these fish occur in the same habitat?

 

Grasshoppers Chorthippus brunnus and Chorthippuys biguttulus, different only by the "songs" that they fiddle to attract females.

 

Again i would ask do these insects occur in the same habitat? Are they genetically different? Do they interbreed? What are the population dynamics between the two "singers" ? I ask this not be obtuse but to point out that these effects can be subtle and the dot or the song could be a sign of some genetic marker that came about for a reason we are simply unaware of. The dot could separate populations of fish from different ranges the song could be the start of speciation for some environmental pressure we are just unaware of. Saying that a "trait" is somehow superficial is one of those things that require extraordinary evidence.

 

I guess the idea is that these "superficial" traits are picked out by the evolving genotype and used as indicators of gene harmony, or to put another way, to avoid sterile hybrids.

 

Works for me but then that means they are not superficial :naughty:

[Galapagos]

What I always thought it odd, is why animals evolve so many superficial changes that have limited practical use, other than being cute

...

Orgel's Second Rule: "Evolution is cleverer than you are"- Francis Crick

...

 

In lineages subjected to artificial selection, humans can sometimes shape the morphology. If you look for it, you will notice that a common thread in all of our domestic pets is neoteny, or retention of juvenile traits. The faces of many cats and dogs approximate the dimensions of a human infant's face(big eyes, big conspicuous face/head, symmetry) because they were bred to be that way.

Artificial selection for neoteny was actually observed/documented in an experiment that lasted many generations and over 50 years involving the domestication of the silver fox:

Domesticated Silver Fox - Wikipedia, the free encyclopedia

Belyaev believed that the key factor selected for domestication of dogs was not size or reproduction, but behaviour; specifically amenability to domestication, or tameability. More than any other quality, Belyaev believed, tameability must have determined how well an animal would adapt to life among humans. Because behavior is rooted in biology, selecting for tameness and against aggression means selecting for physiological changes in the systems that govern the body's hormones and neurochemicals.

 

Belyaev decided to test his theory by domesticating foxes; in particular the Russian Silver Fox. He placed a population of them in the same process of domestication, and he decided to submit this population to a strong selection pressure for inherent tameness.

 

The result is that Russian scientists now have a number of domesticated foxes which are fundamentally different in temperament and behavior from their wild forebears. Some important changes in physiology and morphology are now visible, such as mottled or spotted colored fur. Many scientists believe that these changes related to selecting for tameness are caused by lower adrenaline production in the new breed, which causes these physiological changes in a very small number of generations, thus allowing for these new genetic offshoots not present in the original species.

 

The project also investigated breeding vicious foxes to study aggressive behavior. These foxes snap at humans and otherwise show no fear.

The neotony in morphology appear to have been a by-product of the selection for behavioral neoteny in this case.

 

In the case of sexual selection, organisms of opposite sexes can alter each others appearance based on aesthetic appeal. Natural selection is about who reproduces most. If females(females do most of the choosing, but there are cases where males do, such as in seahorses, where females are as expected more brightly colored) happen to select some arbitrary trait(the attraction may be a by-product of cognitive appeal to some color in the diet/environment), or it happens that some physical trait is an honest(or sometimes even dishonest) signal of fecundity or health, then this trait can be magnified by sexual selection. Another way sexual selection can act is through sexual competition, like in the extremely long neck of the giraffe which is believed to have evolved in response to deadly headramming competitions between males over mates. Another important thing to note is that sexual selection is also testable. Where there is sexual dimorphism, there should be heavy competition for mates. And organisms who are primarily monogomous should be less sexually dimorphic. This prediction is actually borne out in nature, and often organisms that appear monogomous but dimorphic are actually cheaters when observed more closely!

 

In case anyone didn't know, both artificial selection and sexual selection are theories first put forward by Darwin in On the Origin of Species.

http://darwin-online.org.uk/content/frameset?itemID=F373&viewtype=side&pageseq=1

 

And one more thing that might be important to note when considering "superficial"(I'm assuming this meant non-adaptive?) traits: spandrels. Not every trait is adaptive; adaptation often involves trade-offs and result in by-products. This paper by Stephen Jay Gould and Richard Lewontin is seminal:

The Spandrels of San Marco and the Panglossian Paradigm:

Their position is stated quite strongly, but there is much wisdom in that paper, and some that may elucidate some of the observed traits that inspired this thread.

[sman]

I'm new to forums and kindof inept, but I'm trying to post a link about the cichlids.

Science/AAAS | Science Magazine: Sign In

Please let me know it that worked, or if you'd have me do it a different way. Anyway, this is an article in Science about the experiment I mentioned.

 

Yes, they share territory and no, they do not interbreed. This is what makes the experiment informitive. The grasshoppers differ genetically I assume at least by the genes involved with the songing behavior but not so much that the hybrids are not viable(sterile).

I stole both examples from Dawkins, The Ancestor's Tale, but the only place I've ever read about "isolation mechanisms" is Ernst Mayr.