One thing that has always bugged me about evolution.

[pietertje]

So we all know the fundamental thought behind the evolution theory: Random mutations occur in individuals which are then selected for or against by natural selection, mutations that result in favorable traits get passed on to the next generation. I may have formulated it a bit awkward, but you get the point.

Now what bugs me, look for example at the antlers of deer. Obviously strong/big/antler-y antlers are important for male deer and as such it is selected for by natural selection. But how did these antlers ever come to be favorable in the first place? I imagine the evolution of antlers begun with a thickening of the skull, or maybe some small stumps, the problem, in my view, however is that I can't see how these small mutations ended up getting selected for?

It could be said that it's just dumb luck that deer happened to evolve antlers, but that seems like a too simple answer to me.

Thoughts?

[Qaanol]

To make a major oversimplification, the animals that didn’t involve antlers are the ones we do not to call deer.

There’s nothing “special” about evolving antlers. It just happened at some point to some animals. Their descendants that also had antlers didn’t all go extinct, so some of them are still alive. And those are the animals we call “deer”.

[Dr.Buck]

So, in that case, what would you call a deer with no antlers?

Spoiler:

Certainly not a no-eyed deer!

I'll get my coat....

[Charlie!]

So, in that case, what would you call a deer with no antlers?

A doe?

[Bears!]

the problem, in my view, however is that I can't see how these small mutations ended up getting selected for?

Evolutionary biologists argue that these traits are selected for because they are indicative of fitness. Generally, females (the gender generally doing the selecting in most species) are not interested in a trait in and of itself; instead, females want to mate with the healthiest, strongest males of the species, ensuring the preservation and propagation of their genes.

We don't necessarily have conclusive evidence that traits which are selected for always indicate a healthier male in certain species; in fact, there are cases where it seems apparent that traits which are sexually selected for happen to mitigate the actual survivability of certain males. We might ask, "why then do these traits persist?" This is the nature of evolution: balancing adaptations to ensure survival and the propagation of genes. If costly traits guarantee a mate for a male, all that is required for sexual selection to continue within that species is that the required cost (fitness) is counterbalanced by the propagation of genes. If the trait is too costly, sexual selection will likely stop or the species will simply go extinct.

Hope that helped!

*edit* Modified in response to Qaanol's critique.

[Izawwlgood]

I'm surprised, that of all the physiological traits to look at, you contend antlers. That's like seeing a 747 and contending metallurgy.

You should also read up a bit on sexual selection works, as mentioned.

[Qaanol]

Evolutionary biologists argue that these traits are selected for because they are indicative of fitness. Generally, females (the gender generally doing the selecting in most species) are not interested in a trait in and of itself; instead, females want to mate with the healthiest, strongest males of the species, ensuring the propagation of the species.

This is not correct. An individual making a selection of mate does not weigh “the propagation of the species” at all. Individuals select on traits alone. They mate with the other individual they like best.

Traits that the opposite sex happens to like best, get propagated more than other traits, until they are found throughout the whole species. That is because the individuals without those traits were not able to attract mates as well, so over time fewer and fewer of them reproduced until eventually the lack-of-trait phenotype died off with the last remaining individual who didn’t have the trait.

[Bears!]

This is not correct. An individual making a selection of mate does not weigh “the propagation of the species” at all. Individuals select on traits alone. They mate with the other individual they like best.

You're right. I realize that what I said sounds like organisms possess a motive to propagate species, though it would more accurately be described as a motive to preserve genes.

[tooyoo]

I'm not a biologist and admittedly never cared too much about the finer points of evolution, but this might be helpful or interesting:

There's a nice essay by von Glasersfeld (again not a biologist...) giving an introduction to constructivism. What's relevant to the discussion here is that he raises the point that evolution is not a positive selection principle, but a negative one. What he means with positive/negative is the following: Among a set of possible mutations it is not the best that evolution chooses. Instead, those not fit to survive die out.

In context of the debate on antlers: If you can survive with antlers, then go for antlers.

[Dopefish]

Not a bio person: Can't some genes work double duty, so that the same gene that makes for large antlers also increases resistance to diseases X,Y,Z? This sort of thing would make make those with antlers more likely to pass on their genes, and the actual antlers themselves just a coincidence.

With regards to doe's simply finding antlers more sexually attractive and that's why those genes get passed on more often, doesn't that lead to the question of why female deer ended up hard-wired to be attracted to large antlers in the first place?

[Izawwlgood]

With regards to doe's simply finding antlers more sexually attractive and that's why those genes get passed on more often, doesn't that lead to the question of why female deer ended up hard-wired to be attracted to large antlers in the first place?

Sort of, but mostly, the traits that were selected for by females are exaggerated displays that demonstrate a males ability to survive. Ginormo antlers are indicative of a male with enough wherewithal to eat enough to grow them, and is strong enough to not get killed bearing them, etc. It'd be easy to imagine how the impetus started small, and just kept building up. It's also possible to see how the trait may have evolved out of a survival imperative that later became sexually selected for.

Also, there's no 'gene for big antlers'. There are genes that may designate 'start growing antler things here', but the traits to make them grow larger are separate. Additionally, 'grow antlers here' isn't going to also be 'recognize blood flukes'.

[Bears!]

With regards to doe's simply finding antlers more sexually attractive and that's why those genes get passed on more often, doesn't that lead to the question of why female deer ended up hard-wired to be attracted to large antlers in the first place?

This is a tricky question. There haven't really been any definitive answers regarding *why* these sexually selected traits were ever selected in the first place. Again, some traits may be intimately linked to the survivability of individuals. This may have been the case particularly early on in the evolution of sexually selected traits: members of a population may have had predecessor forms (nubs or small antlers) which demonstrated a certain virility or fitness. Females may not have initially selected for the sexually selected trait; rather, the members that possessed the predecessor forms of these sexually selected traits were already more fit than other members lacking these traits. As a result, the sexually selected trait was preserved within the gene pool, with the genes conferring this trait reaching fixation within the population (since mating occurred less frequently with those less fit members lacking the sexually selected trait). Since historically male members of a population which had these nubs or antler-predecessors tended to survive, somehow the females of the population managed to develop behavior which allowed them to determine the fitness of a potential mate (or at the very least their sexual attractiveness, reflecting an earlier connection between the presence of these nubs and increased fitness) based on these traits. There's the rub! The question of how the behavior subsequently evolved is difficult to answer; suffice it to say, we know that it evolved. The question of how any behavior actually evolves and develops is difficult, but hopefully this explanation will aid you in seeing how, given the proper circumstances, the behavior might arise. Many evolutionary biologists tend to think that sexually selected traits evolve beyond their usefulness in determining the fitness of a member of a species, as evidenced by the large plumage of peacocks, for example, which might often serve as a liability to survival rather than an aid. Such a paradox can only be explained by the "fixation" of the behavior of selecting for the "largest antlers," the "brightest feathers," and so on; this is all that is required to ensure that mating and thus gene propagation occurs, since members of a species only need the sufficient fitness to survive which counterbalances the cost of such burdensome sexually selective traits.

Hopefully my rambling was coherent and helpful. Everything I've said certainly runs the risk of being wrong - I am a molecular biologist, not an evolutionary biologist!

[Izawwlgood]

Sexual displays that are a detriment to the male serve as an indicator of the males fitness. A male peacock can't maintain that ridiculous plumage unless they're particularly good at evading predators and aren't chock full of parasites.

[Bears!]

Sexual displays that are a detriment to the male serve as an indicator of the males fitness. A male peacock can't maintain that ridiculous plumage unless they're particularly good at evading predators and aren't chock full of parasites.

A fair point, and one that is frequently mentioned in these sorts of discussions; however, some evolutionary biologists attribute the extinction of certain species (as in the case of the Irish Elk - stolen from Wikipedia) to sexually selected traits. As I mentioned previously, it's a balance between the perceived cost in fitness and the reward in terms of mating opportunities. Sometimes you win, sometimes you lose!

[ConMan]

Also, remember that while we sit here and go "Ah, natural selection has favoured antlers and coloured feathers", we're drawing up a story from the point of view of what's already happened. From the evolutionary perspective, thousands of random mutations have happened, and by a combination of factors (not least of all luck), some have lasted longer than others. So it's not like evolution was aiming for antlers, antlers just happened and the environment at the time the moose were evolving happened to favour antlers rather than, say, orange eyebrows.

[Qaanol]

This is not correct. An individual making a selection of mate does not weigh “the propagation of the species” at all. Individuals select on traits alone. They mate with the other individual they like best.

You're right. I realize that what I said sounds like organisms possess a motive to propagate species, though it would more accurately be described as a motive to preserve genes.

You’re still making the same fallacious imputation that an individual has any sort of care whatsoever about genes or the species or even having children. Okay, in a lot of “higher” species especially among mammals and birds, individuals do seem to care about having children and raising them. But for the vast majority of species, even that isn’t a concern.

An individual only “cares about” what “feels good at the time”. The individual feels a desire to get freaky, so they go find someone to mate with. There’s no “oh crap I better pass my genes along” about it. Similarly, there’s no, “oh wow I want my progeny to have his genes in them” motivation. There’s just “I am sexually attracted to him, let’s get it on”.

The result of this, is that individuals who are inherently more attractive to the opposite sex, do have more offspring. So their genes do get propagated more. And those individuals who are inherently less attractive, have fewer offspring. When a genetic variation affects how attractive an individual is, the variation that makes individuals more attractive is the one that will get passed on more and become more widespread.

In other words, genotypes that produce less-attractive phenotypes tend to see all individuals carrying that genotype die off eventually. When the more-attractive phenotype is also less able to avoid predators and find food, then it is, as mentioned, a balancing act, but it is not an act that individuals balance. Instead, it’s just a question of which group dies off first: the more attractive group because they can’t get food or dodge enemies, or the less attractive group, because they can’t woo a mate? Sometimes one group dies off, sometimes the other, sometimes both groups survive and go their separate ways, and sometimes both groups die.

It’s important to note that “natural selection” and “survival of the fittest” really mean “who died before having kids and who didn’t”.

[Izawwlgood]

however, some evolutionary biologists attribute the extinction of certain species (as in the case of the Irish Elk - stolen from Wikipedia) to sexually selected traits.

You didn't read the rest of the paragraph in that entry did you?

So it's not like evolution was aiming for antlers, antlers just happened and the environment at the time the moose were evolving happened to favour antlers rather than, say, orange eyebrows.

Right, but part of the thing to keep in mind is that sexual selection creates it's own pseudo-environment. There comes a point where plumage or loud calls or antlers aren't a survival trait, but a fitness indicator. Behaviors are even more interesting.

An individual only “cares about” what “feels good at the time”. The individual feels a desire to get freaky, so they go find someone to mate with. There’s no “oh crap I better pass my genes along” about it. Similarly, there’s no, “oh wow I want my progeny to have his genes in them” motivation. There’s just “I am sexually attracted to him, let’s get it on”.

That's not entirely true; what makes an individual 'sexy' may be that they bear fitness indicators. This sends a message to females that they possess positive traits, and will produce offspring with a high fecundity. You say just this later, but seem to be missing the connection between sexiness and fitness.

[Bears!]

however, some evolutionary biologists attribute the extinction of certain species (as in the case of the Irish Elk - stolen from Wikipedia) to sexually selected traits.

You didn't read the rest of the paragraph in that entry did you?

I did, but I guess I'm not making the connection you're intending for me to make. My point is that sometimes those detrimental sexually selected traits are just that - detrimental. So detrimental, in fact, that they can cause the extinction of a species and don't actually demonstrate fitness.

An individual only “cares about” what “feels good at the time”. The individual feels a desire to get freaky, so they go find someone to mate with. There’s no “oh crap I better pass my genes along” about it. Similarly, there’s no, “oh wow I want my progeny to have his genes in them” motivation. There’s just “I am sexually attracted to him, let’s get it on”.

To clarify, when I say that they have a "motive," I'm not talking about a motive in the human sense. I'm really saying "they're naturally driven to do x." Saying that they are motivated to propagate their genes is my shorthand for "they're naturally driven for whatever reason to have sex and produce offspring." I understand why you're criticizing my way of speaking about sexual selection. I just want you to understand that I am aware of how it can be misleading.

In addition, I think that it's equally misleading to say "I am sexually attracted to him, let's get it on." Even in this statement, it seems you're ascribing an element of intention to what organisms do when, in reality, I think we'd all agree that really it's just chemical responses that are conditioned by environmental and genetic factors. Intention, whatever that may be, isn't really a part of the equation.

[Qaanol]

An individual only “cares about” what “feels good at the time”. The individual feels a desire to get freaky, so they go find someone to mate with. There’s no “oh crap I better pass my genes along” about it. Similarly, there’s no, “oh wow I want my progeny to have his genes in them” motivation. There’s just “I am sexually attracted to him, let’s get it on”.

That's not entirely true; what makes an individual 'sexy' may be that they bear fitness indicators.

You’re getting the cause and effect backwards.

An individual with great fitness—meaning the ability to live a long time, avoid predators, and obtain lots of food—but that does not look particularly sexy, would have few or no offspring. This implies the genes that create such extraordinary fitness would not get passed on, and that genotype would go extinct.

An individual with great sex appeal—meaning the ability to win lots of mates—but that is not able to survive in dangerous conditions, would have lots of offspring, but when hard times come they would all die off. So that genotype would go extinct as well.

It is only when an individual carries both fitness and sex appeal characteristics that they can have lots of offspring, and those offspring can survive hard times.

Therefore, it is not that “looking fit” is an appealing trait because individuals “want” to mate with fit individuals. It is actually that, in species where “looking fit” is not an appealing trait, those species go extinct since the “actually fit” individuals aren’t attractive enough to get laid. So the only species that can possibly self-perpetuate in the long term are those where fitness and attractiveness are correlated.

This sends a message to females that they possess positive traits, and will produce offspring with a high fecundity. You say just this later, but seem to be missing the connection between sexiness and fitness.

In your example, the females (and males, for that matter) don’t care about the expected fecundity of offspring. It just so happens that the individuals who themselves are fecund, tend to have fecund offspring, and so forth. Individuals who are attracted to non-fecund mates will have fewer offspring, and thus their genetic lines will die off. Being attracted to non-fit or non-fecund individuals leads to extinction.

The reason we see individuals attracted to fit individuals is that species where that doesn’t happen, aren’t still alive. Well, it can happen during “good times” that every individual is “fit enough” to survive. In that case, true fitness is irrelevant to survival, and only fecundity/sexiness leads to having lots of offspring. In species living in good times, sexiness can be selected for without fitness also. But when the bad times come, the individuals that are not fit enough will all perish.

I apologize if this comes off as brusk, I just get a bit miffed when people mischaracterize the processes of evolution as somehow “conscious” on the part of the individual.

[Jplus]

Evolutionary biologist here. Listen to Qaanol!

Adding to what Qaanol said, I want to get something clear. Evolution (of a trait) is what you get when you combine the following three ingredients:

• variability (of the trait);
• inheritability (of the trait);
• selection pressure (on the trait).

Now what I see a lot in this thread is people talking about mutations in genes. It's true that those are a possible source of variability, but it's not the core of the story. There are many more ways in which variations of a trait can be added to the pool, also in inheritable ways. Some of these don't involve any genetic novelties at all (such as simple recombination or epigenetic changes).

Another thing I want to clear up is sexual selection. It's just one of the many forms of selection pressure, nothing more and nothing less. As Qaanol said, today some trait may be favoured by sexual selection while tomorrow it might be selected against by some environmental condition. An interesting thing here is that evolution seems to produce sexual preferences in which new trait variants are considered sexy. For example, male finches that got a silly ornamental feather stuck on top of their head were suddenly a lot more attractive to females, and it has been argued for that all people with blue eyes might descend from a single ancestor simply because that ancestor's peers found them so attractive. You can explain that because "attraction to novel traits" is in itself a trait with positive selection pressure on the long term.

So here's the thing: you don't need to assume that female deer estimated male deer with antlers to be more healthy or strong than deer without antlers. When the first deer with antlers was born, he might simply have been selected because he carried a new trait and the females found that sexy.

Finally, I want to remark that not all changes in traits are due to evolution. Take the branching shape of deer antlers as an example: there is probably no selection pressure on the precise shape since the antlers are functional in any branching and because the deer themselves probably don't really care what piece of antler branches off where. The only reason that antlers differ (and change slightly over the generations) is that nature can't make perfect copies.

[Izawwlgood]

You’re getting the cause and effect backwards.

No I wasn't. My point was that some traits which are found to be sexy are indicators of a males fitness, and may have arisen because of this.

In your example, the females (and males, for that matter) don’t care about the expected fecundity of offspring

You're going to have to explain how you arrived at that conclusion, considering the statement I made was about offspring fecundity. Also, see Sexy Son Hypothesis.

In species living in good times, sexiness can be selected for without fitness also

Right, which is possibly how some traits get locked into place, but out of curiosity, can you name any sexual features that don't also serve as fitness indicators? I'm not suggesting that all fitness indicators are detrimental (beyond requiring a resource investment to maintain, that is), like a peacocks feathers.

I apologize if this comes off as brusk, I just get a bit miffed when people mischaracterize the processes of evolution as somehow “conscious” on the part of the individual.

I made no such insinuation. What an individual finds sexy may be an entirely physiological imperative. This is why I mentioned that when you factor sexual behavior into this equation, things get interesting.

[radams]

Antlers are an advantage to male deer, not just because female deer find them attractive, but also because they give an advantage in the head-butting combats that deer use to establish dominance.

To the OP's question: you have to go very far back in the fossil record to find an ancestor of the deer that doesn't have horns. When the deer family split off from the other ruminants, the proto-deer certainly had horns, which developed over the generations into antlers, probably because they give an advantage in fights for dominance. This form of combat probably predates the splitting off of the deer family, as many other ruminants do the same or very similar. Giraffes compete for dominance in a very similar manner - "necking" contests - and even their short, stubby horns are an advantage to males in those contests.

[Username4242]

For those of you interested in deer evolution, the leaf deer is considered to be one of the most primitive cervids extant today. I know far too little about the cervid fossil record, but if you're looking for something that the 'ancestral cervid' likely looked like, the leaf deer is going to be pretty close.

http://www.google.com/search?gcx=c&q=le ... 82&bih=929

[ftfs]

So, in that case, what would you call a deer with no antlers?

A doe?

A deer?

[qetzal]

A couple of quibbles.

Qaanol wrote:

The reason we see individuals attracted to fit individuals is that species where that doesn’t happen, aren’t still alive. Well, it can happen during “good times” that every individual is “fit enough” to survive. In that case, true fitness is irrelevant to survival, and only fecundity/sexiness leads to having lots of offspring. In species living in good times, sexiness can be selected for without fitness also. But when the bad times come, the individuals that are not fit enough will all perish.

There's no such thing as "true fitness" as you seem to be using the term here, and fitness is never irrelevant to survival. It's just that the definition of fitness changes with the environment (where environment includes other members of your own species, as well as their preferences, etc.).

Jplus wrote:

Adding to what Qaanol said, I want to get something clear. Evolution (of a trait) is what you get when you combine the following three ingredients:
variability (of the trait);
inheritability (of the trait);
selection pressure (on the trait).

I think this is more a definition of natural selection. Evolution also includes unselected changes due to neutral drift, right?

[Username4242]

Evolution also includes unselected changes due to neutral drift, right?

Yes. Furthermore, depending on population sizes, the two (selection and genetic drift) may act counter to each other, with genetic drift being much more prominent when population sizes are low.

[Bears!]

Therefore, it is not that “looking fit” is an appealing trait because individuals “want” to mate with fit individuals. It is actually that, in species where “looking fit” is not an appealing trait, those species go extinct since the “actually fit” individuals aren’t attractive enough to get laid. So the only species that can possibly self-perpetuate in the long term are those where fitness and attractiveness are correlated.

Izawwlgood sort of responded to this point you made, and I'd like to echo his response. Are there demonstrable instances of precisely this occurring? It seems contrary to the nature of evolution for organisms to develop a behavior of selecting less fit mates, even if they had more sexual appeal. Indeed, I always had the impression that sexually selected traits and sexual appeal would usually serve as indicators of fitness (not permanently, of course - I mean at some point in the evolution of these traits). Of course, that need not be the case always in the evolution of a sexually selected trait (something I explained before), but at the very least I assumed that in order for the developing of the behavior of choosing more sexually appealing mates to occur, this trait likely must have at some point in time indicated or conferred some sort of fitness advantage. It seems strange to think that organisms would, out of the blue, develop the behavior of arbitrarily finding certain traits sexually appealing and then selecting for these traits even if they reduced fitness or reflected a lack of fitness. It seems more likely that these traits conferred or indicated a fitness advantage; the sexually selective behavior of females served as an adaptation because those females with the selection bias would choose the fittest mates, thereby producing fit offspring. Female offspring would learn/possess this (possibly innate) behavior and would continue to produce fit offspring until the only offspring remaining are those who possess the selection bias (in the case of females) or those with the sexually selected trait in its various forms (in the case of males). Please, correct me if I'm wrong.

If there were a situation where sexual selection occurred even though there weren't any strong environmental selective pressures, then this would immediately sever the connection between fitness and sexually selected traits and would likely indicate that organisms really do simply evaluate mates on the basis of "how attractive they look," whatever that means on a psychological and chemical level. Or, there may be circumstances where a behavior develops in which females of a species simply find a trait sexually appealing, but this trait does not confer or indicate fitness. This situation was previously mentioned by Qaanol:

The result of this, is that individuals who are inherently more attractive to the opposite sex, do have more offspring.

I think I finally understand your point. Now, if you could offer examples of when this actually occurred (where the traits didn't confer or indicate fitness), that would aid me enormously. (I just realized that this is what I actually said initially in my long winded post..)

I'll just leave what I've written instead of continuing to think out loud. I'm interested to see what responses I'll get; there's a lot in understanding evolution thoroughly for me, since I'm going to be teaching it to inner-city children. So please, correct me! I want to understand!

[Izawwlgood]

@Bears!
The only thing that stands out to consider, is that females may not necessarily select males with the best traits for survival, but the 'sexiest' traits. While these generally overlap, sometimes it results in things that can be detrimental to the immediate health of the female. The Sexy Son Hypothesis is that females will look for males who exhibit traits that will produce sons that will best capable of mating. For example, elephant seals practice what amounts to 'alpha male rapes the females'. While the females are put at risk due to this behavior, what it means is that any sons that they bear are more likely to in turn possess traits that might make them alpha males. Other sexual strategies in elephant seals include beta males sneakily boning the females; this is also in the females favor because sons from beta males, while not in possession of a harem of females to defend, will still sneakily mate with a handful of females.

So physical and behavioral reproductive strategies are generally, to grossly sum up, 'things that females think will produce sons that are better able to in turn successfully net females'.

[Qaanol]

It seems contrary to the nature of evolution for organisms to develop a behavior of selecting less fit mates, even if they had more sexual appeal.

This quote suggests you have a misunderstanding of “the nature of evolution”. The true nature of evolution is that the traits which become common across a population are exactly those traits which are most likely to be propagated.

What makes some traits more likely to be propagated than others? Well, there are a few major areas:

1. Does the trait make an individual more likely to survive long enough to have offspring than individuals without that trait?
2. Does the trait make an individual more likely to have more offspring than individuals without that trait?
3. Does the trait make an individual’s offspring more likely to survive long enough to have their own offspring?
4. Does the trait make an individual’s offspring more likely to have more offspring?

Traits of types 1 and 2 are “individual fitness” traits. The former has to do with surviving in the world, and the latter with finding a mate. Both of those are necessary to make babies. Traits of types 3 and 4 are “parenting” traits. They make it more likely that one’s children will have children.

The important thing is that evolution doesn’t select “for” certain traits—it selects “against” traits, by virtue of individuals that carry traits weaker in those four areas dying with few or no offspring.

Additionally, these are all statistical probabilities which are only approximated by large population sizes. It’s entirely possible for one individual to be inherently superior to all the rest of its species in every regard: faster, stronger, sexier, able to get more food, and so forth. But that individual might happen to struck by lightning and die one day, before ever passing on its traits. There is a lot of random chance that goes into evolution.

The “selection pressure” that “guides” evolution is nothing more than the statistical likelihood for individuals with one trait to have more offspring by the time they die than individuals without that trait.

Now, if you could offer examples of when this actually occurred (where the traits didn't confer or indicate fitness), that would aid me enormously.

Gladly. It’s not a fitness indicator at all. Other primates, indeed most other mammals, have enlarged mammaries only when they are nursing. This one species, however, has them all the time. It’s not any sort of indicator like “fat reserves show the ability to obtain extra food”, since in fact fatness is sexually selected against in this species. Indeed, this particular trait actually makes the individuals who carry it be more likely to develop spinal problems than they would be otherwise. But for sure this trait is preferred by almost all members of the opposite sex when selecting a mate.

So physical and behavioral reproductive strategies are generally, to grossly sum up, 'things that females think will happen to be statistically more likely to produce sons and daughters that are better able to in turn successfully net females produce offspring of their own'.

Fixed.

[iChef]

So, in that case, what would you call a deer with no antlers?

A doe?

A deer?

A female deer.

[Mr. Samsa]

With regards to doe's simply finding antlers more sexually attractive and that's why those genes get passed on more often, doesn't that lead to the question of why female deer ended up hard-wired to be attracted to large antlers in the first place?

The problem with this is that it presupposes that there is a specific, and hard-wired, attraction to a particular trait. I don't know enough about deer to say whether this attraction is innate or not, but for some selection of mates (even universal traits across individuals and cultures) the attraction is a product of learning and environmental variables. For example, it could be an incidental effect from the process of species-identification that takes place during early development, and (to put it extremely simply) the observation that the doe's father has antlers results in them being predisposed to liking them. Since antlers would be universal in this early population of deer, as a result of the success in competitive fights and defence, there would be a universal attraction to them. You would then get a superstimulus effect, where "bigger is better", which would feedback into evolutionary pressures resulting in greater selection for bigger antlers, and so on. (As I said though, I don't know enough about deer to say that "this is how it happened", but rather just trying to point out that it can be problematic to automatically assume that something is an evolutionary trait).

Jplus wrote:

Adding to what Qaanol said, I want to get something clear. Evolution (of a trait) is what you get when you combine the following three ingredients:
variability (of the trait);
inheritability (of the trait);
selection pressure (on the trait).

I think this is more a definition of natural selection. Evolution also includes unselected changes due to neutral drift, right?

Yep, Jplus is referring to Williams' (1966) criteria for identifying a trait as being an adaptation. And, as you correctly point out, not all traits come about through adaptationist processes.

[jestingrabbit]

So, in that case, what would you call a deer with no antlers?

A chevrotain, apparently (I was going to say "Horses" but these are, again apparently, more closely related).

[ftfs]

So, in that case, what would you call a deer with no antlers?

A doe?

A deer?

A female deer.

Ray, a drop of golden sun.

[Izawwlgood]

Qaanol, attractiveness to breasts would be a behavioral trait found in some primates. I already mentioned that behavioral strategies are interesting, by which I meant they were heavily based on other existing indicators, and plainly pointing to them as a non-indicator trait is a somewhat muddied endeavor. It'd be easy to draw a connection to enlarged sexual organs and sexual availability/readiness/maturity, and the behavior of finding breasts attractive to be a product of that.

But yes, attractiveness is often, even when due to behavioral queues, not a conscious endeavor on the part of the individuals involved. So sure, females don't 'think that it will' provide reproductively successful offspring, they are simply engaging in behavior that was previously advantageous to do so.

[Qaanol]

The Sexy Son Hypothesis is that females will look for males who exhibit traits that will produce sons that will best capable of mating. For example, elephant seals practice what amounts to 'alpha male rapes the females'.

I am trying really hard to not to go ad hominem here, so I want to be up-front that I am responding to this hypothesis, not to you personally. What the quoted material amounts to, is saying, “Females choose who rapes them.” There is so much wrong with that, I’m not even going to begin.

[Izawwlgood]

It's important to not extrapolate everything that you see in the animal Kingdom to the human condition. There are an enormous amount of organisms for whom reproduction is effectively 'What male can mate with a female despite all resistance, from other males and her alike'. This isn't just vertebrates either; off hand, I recall a number of insects wherein the female hatches slightly after the males, and the males swarm all over emergent females, the first there and the best able to push the other males aside, being the 'best choice for producing sons able to do the same'. Some centipedes ball up, and a successful male is one that can physically unball the female and mate with her.
So, to be crystal clear here, do you have issue with the hypothesis as it pertains to sexual selection in animals, or with how the concept of rape in the Animal Kingdom (anthropomorphism in and of itself) makes you uncomfortable because it reminds you of humans?

[gmalivuk]

Personally, the biggest objection I have to that account is on logical grounds, where you call the behaviors "rape" and "resistance" and yet also refer to females as having some "choice".

[Izawwlgood]

Yeah, I'm certainly guilty of anthropomorphizing the behaviors in this thread, as well as mincing terms like 'rape' 'resistance' and 'choice'.

These are all concepts that don't necessarily or entirely translate as we understand them, to the sexual behaviors we're discussing.

[Bears!]

It seems contrary to the nature of evolution for organisms to develop a behavior of selecting less fit mates, even if they had more sexual appeal.

This quote suggests you have a misunderstanding of “the nature of evolution”. The true nature of evolution is that the traits which become common across a population are exactly those traits which are most likely to be propagated.

What makes some traits more likely to be propagated than others? Well, there are a few major areas:

1. Does the trait make an individual more likely to survive long enough to have offspring than individuals without that trait?
2. Does the trait make an individual more likely to have more offspring than individuals without that trait?
3. Does the trait make an individual’s offspring more likely to survive long enough to have their own offspring?
4. Does the trait make an individual’s offspring more likely to have more offspring?

Traits of types 1 and 2 are “individual fitness” traits. The former has to do with surviving in the world, and the latter with finding a mate. Both of those are necessary to make babies. Traits of types 3 and 4 are “parenting” traits. They make it more likely that one’s children will have children.

The important thing is that evolution doesn’t select “for” certain traits—it selects “against” traits, by virtue of individuals that carry traits weaker in those four areas dying with few or no offspring.

Thanks. This was actually incredibly helpful in clarifying my own thoughts and getting at the heart of what we were disagreeing about. It really just came down to me being unable to separate points 3 and 4 from the question of fitness (a question which, I've realized, isn't always relevant to the evolution of certain traits). Appreciate the insights.

[tomandlu]

The Sexy Son Hypothesis is that females will look for males who exhibit traits that will produce sons that will best capable of mating. For example, elephant seals practice what amounts to 'alpha male rapes the females'.

I am trying really hard to not to go ad hominem here, so I want to be up-front that I am responding to this hypothesis, not to you personally. What the quoted material amounts to, is saying, “Females choose who rapes them.” There is so much wrong with that, I’m not even going to begin.

I think you're over-anthropomorphising here (not helped by the phrase "Sexy Son Hypothesis"). The feelings and sexual politics of both the male and female are irrelevant - the only thing that is relevant is "is the strategy helpful?" I don't think the theory is saying anything about female 'choice' (which would be an oxymoron if we're talking about rape).