Do species actively evolve toward a certain outcome...

[Blackfin]

Or are the characteristics of a species merely a coincidence of circumstances like natural selection and environment?

 

I'm in AP right now, and in a lot of texts I've noticed the implication that species are actively evolving towards a certain end, usually in sentences like, "Despite a harsh environment, Species B has evolved a trait that allows it to combat it quite effectively..."

 

This implies a direct action by the species that's evolving - or, if you take a religious bent on it, a big metaphysical hand pulling the puppet strings of evolution. I like to think that species are merely the passive product of natural selection, and do not consciously evolve towards a certain end except through instinctive selection of mates. However, I have a feeling most species mate with another member of they're species because they think 'They're hot' (or the organism's equivalent), NOT because they're thinking 'This will make my species more genetically resistant to extinction.'

 

I know this is definitely splitting hairs in a gray area of biology, but it's only by splitting hairs and arguing over fine points any progress has ever been made in science. It's not just about the big concepts, it's also about the finer details.

 

So, ideas? I could very well be wrong.

[Mokele]

You are, at least to the best of my knowledge, correct. I suspect that the problem with such phrases is simply the limitations of the English language; to say that a particular adaptation was 'designed' to do something is simply the most natural way to talk about it, from a grammatic and linguistic POV. Obviously, we know that it wasn't *consciously* designed, but that's just the word that fits. It's even more confusing when it's talking about species, rather than individuals, and as such almost personifying the entire group of organisms as a whole (rather than an aggregate of individuals).

 

Mokele

[Blackfin]

Well, you know that and I know that, but who says the average biology student does? I know I actually had to ponder the meaning of some texts before getting the actual meaning between the lines. It seems pointless to debate, yes, but I just wanted confirmation from other individuals.

[Deified]

Yes we often speak of mutations being "intended" for this or that. In fact they just happen to work well toward this goal or that goal (even here, I'm using the word goal. There is no goal, survival is the positive outcome, but you can't even say that it is the goal)

[Ophiolite]

I think the root of the problem may be that evolution is a two part process, one part chance, mixed with one part controlled. The opportunity to change is created by random mutations, but the success of that change, and hence, overall, its direction is determined by environmental controls. (And before any one starts to nitpick I include the internal setting of the organism amongst the environmental factors.)

And there you have that dreaded word direction, which resonates with others, such as design and goal and purpose. Suddenly creationists have sprung, apparently ex nihilo, from the margins of the argument. Blackfin reminds us we have to use words carefully. (I now gleefully await someone as pedantic as myself to point out where I have abused usage in this post. I tried very carefully to be accurate. Honest.)

[Hellbender]

I like to think that species are merely the passive product of natural selection, and do not consciously evolve towards a certain end except through instinctive selection of mates.

 

I don't really have much more to say than this is what is accepted as true.

[Sayonara]

I'm in AP right now, and in a lot of texts I've noticed the implication that species are actively evolving towards a certain end, usually in sentences like, "Despite a harsh environment, Species B has evolved a trait that allows it to combat it quite effectively..."

I think that's just woefully bad phrasing. It should be "because of", not "despite".

 

Burn the book.

[coquina]

I think that's just woefully bad phrasing. It should be "because of"' date=' not "despite".

 

Burn the book.[/quote']

 

That's still putting the cart before the horse. The harsh enviroment didn't cause the mutations. As I understand evolution, the mutations would have happened randomly anyway, but there had to be a niche open that they fit, and the mutations had to occur often enough to produce a viable population.

 

Unfortunately, there is just no concise way to state what happens.

 

Even though I stated above what I was taught - I'm not sure that it is absolutely true. When I was reading about the human genome project, I read that there was a lot of "junk DNA" that didn't seem to "do" anything. Maybe it just appears to be useless because the organism is not currently living in a niche where it would be useful. Maybe a harsh environment somehow triggers it to become useful. However, I will not go so far as to say that there were "long neck junk genes" lurking in the giraffe's DNA to get turned on when all the low growing leaves had been eaten.

[Sayonara]

You're right, the harsh environment doesn't cause the mutations. But it does cause them to mean something.

[kotake]

However, I have a feeling most species mate with another member of they're species because they think 'They're hot' (or the organism's equivalent), NOT because they're thinking 'This will make my species more genetically resistant to extinction.'

I have always imagined that individuals find certain members of their species attractive, or "hot", because they unconsciously see in them genetical values; values to make their species more resistant from extinction.

[-Demosthenes-]

I think that's just woefully bad phrasing. It should be "because of"' date=' not "despite".

 

Burn the book.[/quote']

My AP bio book is very clear about the subject. I didn't know that evolution was such a big part of biology until AP, now its obvious.

[Deathby]

Evolution says that we do not move towards a "goal" but apologist creationists might argue that the hand of God is in all things, so it is God who determines if a "random" mutation exists that allows a species to survive a new environment. In either case there is no real way to tell, even if humanity lives for a million years, which is true. But from a secular POV, species do not evolve towards a goal.

 

You're right many people get confused and its natural for them to just say towards a goal, since it is part of our language, it sounds very roundabout to say stuff like this trait happened to be a minority in the gene pool, but became larger when the environment just so happened to change into a position where that trait was more advantageous. It's much easier to say this trait evolved to suit the new environment.

 

And what you say about the "they're hot" line of thought is true, but they can't be hot if they're already dead since they cannot compete. Success of a mate is as much a factor in determining the concept of beauty as any other. Eg. Big strong muscles in a human is a sexy, for obvious reasons.

[Hellbender]

And what you say about the "they're hot" line of thought is true, but they can't be hot if they're already dead since they cannot compete. Success of a mate is as much a factor in determining the concept of beauty as any other. Eg. Big strong muscles in a human is a sexy, for obvious reasons.

 

exactly. But in with human culture basic traits that enhance survival, etc. can be sometimes overshadowed by traits that are "culturally selected" for. For example there is a south american tribe where all the males have (please, I am not trying to be gross or offensive here, this is the best example I can think of) blue penises. In their culture, having a blue penis means the man is better, or magical, and the trait is selected for.

[Sayonara]

Evolution says that we do not move towards a "goal" but apologist creationists might argue that the hand of God is in all things, so it is God who determines if a "random" mutation exists that allows a species to survive a new environment. In either case there is no real way to tell, even if humanity lives for a million years, which is true. But from a secular POV, species do not evolve towards a goal.

Apologist creationists aren't responsible for evolutionary theory though - so if we're talking about evolutionary theory, who cares what they argue?

[blike]

I find that many highschool text books have sloppy wording. Nonetheless, I've heard phrases like "x has come up with a novel solution for y by chaning z trait" a million times in college. It's just assumed you understand evolutionary theory and that you can place phrases like that in the proper context.

[Gnieus]

Adaptive Dynamics.

 

It's all flowing ...

Adaptive Dynamics is a theoretical framework for bridging the scales between micro- and macro-evolution. It is based on two main simplifying assumptions: a separation between the population dynamical and mutational time scales, and clonal genetics. These simplifications allow rapid scientific progress, while the analyses of special cases suggests that the predictions obtained usually aggree with those from more sophisticated models.

 

Evolution proceeds by the continual replacement of resident types by novel mutants. The latter originate by chance but their evolutionary fate depends on their fitness, i.e. on their capacity to increase in numbers. This fitness necessarily depends the current environment E which is set by the composition of the resident population. By eliminating E we get the invasion function, i.e. the fitness of potential mutants as a function of the type of the mutant and of the types constituting the resident population. In order to calculate this function we start with describing the dependence of individual population-dynamical behaviour on supposedly heriditary traits. From this we obtain the initial exponential growth rate of a mutant population in the ergodic environment set by the resident population-dynamical attractor. Once this invasion fitness is known, it provides a summary of the underlying processes necessary and sufficient to make the step to macro-evolutionary considerations.

 

The research on the foundation of Adaptive Dynamics deals with (1) justifying and/or modifying the various theoretical steps sketched above in order to delimit as well as enlarge the domain of applicability of the theory, and (2) deducing consequences of the resulting framework in combination with developing tools for dealing with the large range of specific ecological-evolutionary models that fall under the general realm of adaptive dynamics.

[Gnieus]

exactly. But in with human culture basic traits that enhance survival, etc. can be sometimes overshadowed by traits that are "culturally selected" for.[/b'] For example there is a south american tribe where all the males have (please, I am not trying to be gross or offensive here, this is the best example I can think of) blue penises. In their culture, having a blue penis means the man is better, or magical, and the trait is selected for.

 

Peacock decorative feathers aren't necessarily helpful in direct survival. ... If having a blue penis is correlated with a direct genetic line to the one who guy who was so cool and had a blue penis it might well be some indicator for genetic fitness ... Like in our society slim is in, while if you have nothing fat is in. When everyone was tanned through hard labour outside white was in as display of riches. Today that can afford the most holidays and is tanned is supposed to be healthy then the fakers aka tan studio come in and that is then frowned upon. All moving ... Then you forget the psychological stabilsation factor of rituals which can increase survival etc etc.

 

So cultural evolution is pretty much the same as "normal" evolution where uses might be obvious.

[coquina]

For example there is a south american tribe where all the males have (please, I am not trying to be gross or offensive here, this is the best example I can think of) blue penises. In their culture, having a blue penis means the man is better, or magical, and the trait is selected for.

 

But maybe having a blue penis is linked to another gene that is not obvious, for instance, maybe men with a case of the blues have a higher sperm count. This could not be observed, but "blue penis = more babies" could be.

 

There are a couple of adaptations which have always baffled me. One of them is protective coloration. Here is a study that was done to determine that birds do indeed avoid contact with the colorful coral snake, as opposed to plain brown snakes.

http://www.utm.edu/staff/rirwin/391Brodie.htm

 

How is it that the birds avoid coral snakes? Since the bite would certainly be fatal, it couldn't be something that has been passed on in the genes. It has to be that other birds observed the catastrophic results of attacking a coral snake and "taught" their offspring to avoid them.

 

Here is a page about mimicry and protective coloration:

http://cgee.hamline.edu/see/questions/dp_transformation/dp_trans_adapt_mimic.htm

 

It makes a little more sense in the coral snake - maybe its bite killed the bird before it killed him, but what about the smaller insects, like the butterfly and the poison dart frogs? They may kill their prey, but they are still dead and can't reproduce.

 

The only way this makes sense is that the predator has to be smart enough to pass the knowledge that is has observed on to its offspring ...

 

I would like to see results of the same experiment done with birds that do not have coral snakes in their environment, and also with species of birds raised in captivity, to see if the avoidance is learned or inherited.

[blike]

Coquina, here's a study that might interest you:

 

Reactions of hand-reared and wild-caught predators toward warningly colored, gregarious, and conspicuous prey

 

Access to the study is limited, but the abstract contains a good deal of information about their results:

 

"The results confirm previous results regarding the innate avoidance of color. Naive predators seemed to have a genetically or culturally transmitted avoidance of yellow and black prey compared to brown prey. Surprisingly, yearling wild-caught great tits were more selective than adults, which did not show as strong avoidance of yellow and black prey. More importantly, birds did not find gregarious prey more aversive than single prey, which indicates that grouping alone does not serve as an innate avoidance signal. Conspicuousness itself was not aversive to the predators. Our results suggest that the avoidance against a particular color pattern probably has an inherited basis, whereas gregarious and conspicuous characters of prey presumably aid the avoidance learning."

 

http://beheco.oupjournals.org/cgi/content/abstract/10/3/317

[coquina]

Coquina' date=' here's a study that might interest you:

 

[b'] Reactions of hand-reared and wild-caught predators toward warningly colored, gregarious, and conspicuous prey[/b]

 

Access to the study is limited, but the abstract contains a good deal of information about their results:

 

"The results confirm previous results regarding the innate avoidance of color. Naive predators seemed to have a genetically or culturally transmitted avoidance of yellow and black prey compared to brown prey. Surprisingly, yearling wild-caught great tits were more selective than adults, which did not show as strong avoidance of yellow and black prey. More importantly, birds did not find gregarious prey more aversive than single prey, which indicates that grouping alone does not serve as an innate avoidance signal. Conspicuousness itself was not aversive to the predators. Our results suggest that the avoidance against a particular color pattern probably has an inherited basis, whereas gregarious and conspicuous characters of prey presumably aid the avoidance learning."

 

http://beheco.oupjournals.org/cgi/content/abstract/10/3/317

 

Thanks for the link. That is really interesting. One would think that it would be a big disadvantage for the snake to be so colorful - although maybe some of the critters it eats can't see colors. In that case, it might blend in pretty well on a forest floor littered with leaves and splattered with sunlight.

 

Maybe Mokele can shed some light - he's the resident Herp guy, isn't he?

[Mokele]

Well, most brightly colored snakes (like coral snakes) typically spend their time burrowing in the leaf-litter, are nocturnal, or both. Even crypticly colored snakes usually hunt in the dark, in enclosed areas (they *love* rodent burrows, yummy baby rodents).

 

In fact, a suprising number of such brightly-colored snakes are snake-eaters, and prey on slow-moving species, so avoidance isn't an option for their prey.

 

There is also the confusion factor. South American coral snakes (which are substantially larger than their northern cousins, often over 6 feet) will form a ball of coils when threatened, and then "writhe". This creates a confusing panoply of colors, along with a difficulty in keeping track of the highly venomous head. They can actually move while doing this, eventually escaping from their assailant.

 

Oh, as for the lethality, venomous snakes *can* refrain from injecting venom, and often will in the case of attackers. It'll usually kill the attacker too late for the snake, so why waste the metabolicly expensive venom? In fact, up to 40% of bites are "dry bites" (though I'd advise against playing those odds).

 

But, even with a dry bite, snakebites hurt. Elapids (corals, cobras and the like) have short, fixed fangs that will increase the pain somewhat, but vipers...well, how many predators will mess with something after they've been stabbed with a pair of 1-inch needles repeatedly? And some of the larger vipers of genus Bitis can have 2-inch fangs.

 

Mokele

[coquina]

Do reptiles see in color?

 

Incidentally - we have large canebrake rattlers around here. And the Dismal Swamp - just south of here, has cottonmouth moccasins. People have told me that the latter are territorial and well attack if they think their space has been invaded, even if they are not in immediate danger. Is this true?

[Skye]

Reptiles can see colours.

[Mokele]

Skye is right, reptiles have color vision, and many can see into the UV spectrum. Snakes are a bit more complex, because they have very peculiar rods and cones (possibly due to burrowing ancestry for snakes as a whole), but they can still see colors, even if they see them differently than us. On top of that, in those species with heat-sensitive pits (pythons, boas, and pit-vipers), the nerves from ther pits feed into the visual center of their brains, meaning they can effectively see in IR as well.

 

Cottonmouths are territorial (several other species are as well), and are also, well, ballsy. They're suprisingly smart animals when in captivity, and I suspect they're just used to things backing down from their threat displays (not many things wouldn't) and assume that includes humans.

 

Mokele

[KholdStunner]

evolution is going to one certain place and ONE place only...

 

-SURVIVAL-