I have a question about sexual selection. In Charles Darwin's book The Origin of Species, he talks about natural selection and sexual selection (and a bunch of other things, of course). However, all I ever hear about is "natural selection." So has sexual selection been found to not have an effect in evolution? Or do people simply not like talking about it?
Sexual Selection
Darwin did cover this concept in his book "The Descent of Man and Selection in Relation to Sex". If you read Darwin, you should remember that he did not understand Mendelian genetics, he believed in Lamark's ideas. Basically, Lamark believed that structures were inherited if you used them, and atrophied if you did not use them. Thus a fiddler crab had a large claw because it was used so often, but the small claw atrophied through the generations because it was not used often.
| Voodoocat wrote: |
| If you read Darwin, you should remember that he did not understand Mendelian genetics, he believed in Lamark's ideas. |
That's totally false. Darwin realized that some of the similarities between parents and children were heritable, though he didn't have a proposed mechanism for that heritability. Darwin knew that you could alter a parent without affecting the way its offspring looked -- that organisms carried some information that laid the foundation for their development, and that the effects of the environment built upon that foundation.
To answer aface's question, sexual selection is a really huge topic in biology, and it has been for a while. It doesn't get popularized as much as natural selection because it can be a little more complicated, but it's definitely not a subject that is avoided by scientists.
Darwin introduced the idea of sexual selection because he realized that it would be an important process if traits were heritable. His point in bringing it up is that sexual selection can cause traits to evolve that hurt the individuals chance of surviving (and are therefore acted against by natural selection). A good example is elk horns. They need the horns to secure mates (sexual selection) but large horns cost energy to produce, and can cause higher rates of mortality in the winter (natural selection). People are thinking a lot these days about how conflicting selective forces act on traits, and how sexual selection and other evolutionary forces interact.
Gagnar pretty much covered it.
Natural selection is the process by which traits evolve based on their ability to help an organism survive to be able to mate; those better able to survive (escape predators, acquire resources, fight off disease, etc etc) are more likely to pass on their genes than those less capable of surviving (given that those traits are heritable). This is your standard model of evolution.
Sexual selection, by contrast, is the process by which traits develop that have no effect upon survivorship, or even hinder it, but increase the chances of attracting a mate when they do survive. This form that hinders survivorship, but enhances their competitiveness in mating is generally driven by mate choice (usually the females selecting for more attractive males, but there are examples of the opposite) rather than by the ability to compete for survival.
Many great examples of this are found in many species of birds, some reptiles, mammals, insects, and of course, many other groups. Peafowl are a classic example; the females (peahens) are basically your standard chicken-like bird, mottled brown without superflously long feathers, very well camouflaged in their forest habitat and capable fliers; males (peacocks) by contrast are bright blue and green, with extremely long, decorative tail coverts (the fan)... the decoration means they cannot hide from predators as well as females, the extremely long and heavy fan hinders their ability to fly (and escape predation), and the complex structures of the long feathers, pigments and physical microstructure of the feathers to create the bright colours are very costly to produce... but those males that are more brightly coloured with larger, more impressive fans are more likely to mate with females, passing on their genes with more frequency than drabber males that may be able to compete better for survival, but not as well in the all important mating stage.
So really, there is evolutionary selection, which may be driven by a number of factors: natural selection is driven by organism vs. environment+competition for resources+predator avoidance; sexual selection is driven by the ability to compete with conspecifics in mating. There are a few other forms of selection that may come in to play, but these are the most common, with the least debate as to their validity; you may also encounter the concept of kin selection, in which related individuals help one another survive based on how closely related they are... but there's a lot of controversy over that. Social selection is a system by which social factors influence selection, which is only really a factor in species (such as ours) with complex social structures and factors like class determine which individuals are capable of mating, rather than more "natural" factors. There are a couple others as well.
Evolution is a fascinating subject
Natural selection is the process by which traits evolve based on their ability to help an organism survive to be able to mate; those better able to survive (escape predators, acquire resources, fight off disease, etc etc) are more likely to pass on their genes than those less capable of surviving (given that those traits are heritable). This is your standard model of evolution.
Sexual selection, by contrast, is the process by which traits develop that have no effect upon survivorship, or even hinder it, but increase the chances of attracting a mate when they do survive. This form that hinders survivorship, but enhances their competitiveness in mating is generally driven by mate choice (usually the females selecting for more attractive males, but there are examples of the opposite) rather than by the ability to compete for survival.
Many great examples of this are found in many species of birds, some reptiles, mammals, insects, and of course, many other groups. Peafowl are a classic example; the females (peahens) are basically your standard chicken-like bird, mottled brown without superflously long feathers, very well camouflaged in their forest habitat and capable fliers; males (peacocks) by contrast are bright blue and green, with extremely long, decorative tail coverts (the fan)... the decoration means they cannot hide from predators as well as females, the extremely long and heavy fan hinders their ability to fly (and escape predation), and the complex structures of the long feathers, pigments and physical microstructure of the feathers to create the bright colours are very costly to produce... but those males that are more brightly coloured with larger, more impressive fans are more likely to mate with females, passing on their genes with more frequency than drabber males that may be able to compete better for survival, but not as well in the all important mating stage.
So really, there is evolutionary selection, which may be driven by a number of factors: natural selection is driven by organism vs. environment+competition for resources+predator avoidance; sexual selection is driven by the ability to compete with conspecifics in mating. There are a few other forms of selection that may come in to play, but these are the most common, with the least debate as to their validity; you may also encounter the concept of kin selection, in which related individuals help one another survive based on how closely related they are... but there's a lot of controversy over that. Social selection is a system by which social factors influence selection, which is only really a factor in species (such as ours) with complex social structures and factors like class determine which individuals are capable of mating, rather than more "natural" factors. There are a couple others as well.
Evolution is a fascinating subject
| Gagnar The Unruly wrote: | ||
That's totally false. Darwin realized that some of the similarities between parents and children were heritable, though he didn't have a proposed mechanism for that heritability. Darwin knew that you could alter a parent without affecting the way its offspring looked -- that organisms carried some information that laid the foundation for their development, and that the effects of the environment built upon that foundation. To answer aface's question, sexual selection is a really huge topic in biology, and it has been for a while. It doesn't get popularized as much as natural selection because it can be a little more complicated, but it's definitely not a subject that is avoided by scientists. Darwin introduced the idea of sexual selection because he realized that it would be an important process if traits were heritable. His point in bringing it up is that sexual selection can cause traits to evolve that hurt the individuals chance of surviving (and are therefore acted against by natural selection). A good example is elk horns. They need the horns to secure mates (sexual selection) but large horns cost energy to produce, and can cause higher rates of mortality in the winter (natural selection). People are thinking a lot these days about how conflicting selective forces act on traits, and how sexual selection and other evolutionary forces interact. |
Thank your for the answer. I already completely understood sexual selection, I just didn't understand why I never heard anyone talk about it. I think that your answer is correct, it can get a lot more complicated than natural selection which is why it's not talked about as much (I never even learned about it in my introductory biology class that I took - I just learned about natural selection).
Well, sexual selection is a 'special case' of natural selection.
There is a nice section on the Berkeley Uni website which might be worth a read;
http://evolution.berkeley.edu/evosite/evo101/IIIE3Sexualselection.shtml
There is a nice section on the Berkeley Uni website which might be worth a read;
http://evolution.berkeley.edu/evosite/evo101/IIIE3Sexualselection.shtml
maybe sexual selection is just one of the effects of natural selection.
from a web,
from a web,
| Quote: |
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Natural selection is the process by which favorable heritable traits become more common in successive generations of a population of reproducing organisms, and unfavorable heritable traits become less common, due to differential reproduction of genotypes. Natural selection acts on the phenotype, or the observable characteristics of an organism, such that individuals with favorable phenotypes are more likely to survive and reproduce than those with less favorable phenotypes. The phenotype's genetic basis, genotype associated with the favorable phenotype, will increase in frequency over the following generations. Over time, this process may result in adaptations that specialize organisms for particular ecological niches and may eventually result in the emergence of new species. In other words, natural selection is the mechanism by which evolution may take place in a population of a specific organism. Natural selection is one of the cornerstones of modern biology. The term was introduced by Charles Darwin in his groundbreaking 1859 book The Origin of Species[1] in which natural selection was described by analogy to artificial selection, a process by which animals with traits considered desirable by human breeders are systematically favored for reproduction. The concept of natural selection was originally developed in the absence of a valid theory of inheritance; at the time of Darwin's writing, nothing was known of modern genetics. Although Gregor Mendel, the father of modern genetics, was a contemporary of Darwin's, his work would lie in obscurity until the early 20th century. The union of traditional Darwinian evolution with subsequent discoveries in classical and molecular genetics is termed the modern evolutionary synthesis. Although other mechanisms of molecular evolution, such as the neutral theory advanced by Motoo Kimura, have been identified as important causes of genetic diversity, natural selection remains the single primary explanation for adaptive evolution. |
| Afaceinthematrix wrote: |
| Thank your for the answer. I already completely understood sexual selection, I just didn't understand why I never heard anyone talk about it. I think that your answer is correct, it can get a lot more complicated than natural selection which is why it's not talked about as much (I never even learned about it in my introductory biology class that I took - I just learned about natural selection). |
i avoid biology like it had the plague. But if you want to see sexual selection concepts tossed about in daily conversation, the psychology department is a good place to hang around. Sexual selection is a huge topic in evolutionary psychology. It's pretty much the whole field.
| knight_frost wrote: |
| maybe sexual selection is just one of the effects of natural selection. |
It's not an effect, it's a mechanism. Natural selection doesn't cause sexual selection, but sexual selection is one of the ways natural selection works.
It's kind of a fuzzy semantics issue, because even though sexual selection really is just a mode of natural selection, most biologists tend to talk about them as though they are two different things, for ease of communication. There's no good phrase for "anything that is natural selection other than sexual selection." Since scientists often explicitly compare the effects of sexual selection and "every other kind of natural selection," they tend to refer to "every other kind of natural selection" as "natural selection" for simplicity. The tendency I've observed is that people refer to "natural selection" + sexual selection as just "selection."
I did a little looking around, and there's a simple reason Darwin didn't say much about sexual selection:
1: His society at the time was very squeamish about any subject having to do with sex.
2: His work was very controversial already, so he didn't want to rock the boat more than he had to.
1: His society at the time was very squeamish about any subject having to do with sex.
2: His work was very controversial already, so he didn't want to rock the boat more than he had to.
Darwin actually wrote a lot about sexual selection. He needed to, because some traits that biologists knew about at the time couldn't be explained without it (like peacocks). If Darwin hadn't brought up sexual selection, his detractors could've used animals like peacocks against him and discredited his theory.
Yep, The Origin of Species is full of sexual selection, and uses artificial selection extensively as well as a vehicle explain the grander concepts of natural selection.
You are definitely correct in the fact that he didn't want to rock the boat more than necessary... in fact, if it weren't for Alfred Russel Wallace he quite probably never would have published "his theory". As it was, he revised The Origin after its initial publication to make it less controversial, going back on many (correct-ish) things he said in the original publication to appease the masses.
You are definitely correct in the fact that he didn't want to rock the boat more than necessary... in fact, if it weren't for Alfred Russel Wallace he quite probably never would have published "his theory". As it was, he revised The Origin after its initial publication to make it less controversial, going back on many (correct-ish) things he said in the original publication to appease the masses.
Mendel performed his experiments between 1856 and 1863. He read his paper in 1865 then published his findings in 1866; Darwin published On the Origin of Species in 1859. Since Darwin started working on his book in 1856 (and thought about it for many years before) then published it three years later Mendel did not influence Darwin.
Here is an interesting link from PBS: http://www.pbs.org/wgbh/evolution/library/06/1/l_061_01.html
Here is an interesting link from PBS: http://www.pbs.org/wgbh/evolution/library/06/1/l_061_01.html
Darwin's grand idea of evolution by natural selection is relatively simple but often misunderstood. To find out how it works, imagine a population of beetles:
1. There is variation in traits.
For example, some beetles are green and some are brown
2. There is differential reproduction.
Since the environment can't support unlimited population growth, not all individuals get to reproduce to their full potential. In this example, green beetles tend to get eaten by birds and survive to reproduce less often than brown beetles do.
3.There is heredity.
The surviving brown beetles have brown baby beetles because this trait has a genetic basis.
End result:
The more advantageous trait, brown coloration, which allows the beetle to have more offspring, becomes more common in the population. If this process continues, eventually, all individuals in the population will be brown.
1. There is variation in traits.
For example, some beetles are green and some are brown
2. There is differential reproduction.
Since the environment can't support unlimited population growth, not all individuals get to reproduce to their full potential. In this example, green beetles tend to get eaten by birds and survive to reproduce less often than brown beetles do.
3.There is heredity.
The surviving brown beetles have brown baby beetles because this trait has a genetic basis.
End result:
The more advantageous trait, brown coloration, which allows the beetle to have more offspring, becomes more common in the population. If this process continues, eventually, all individuals in the population will be brown.
Actually I would want all of you here to read this link
http://en.wikipedia.org/wiki/Assortative_mating
it is about
There are a lot of review on this and it almost the same as sexual selection in lay man terms
although I must say that is not exactly the same
I will continue on the topic if some one is interested
http://en.wikipedia.org/wiki/Assortative_mating
it is about
| Quote: |
| Assortative mating (also called assortative pairing) takes place when sexually reproducing organisms tend to mate with individuals that are like themselves in some respect (positive assortative mating) or dissimilar (negative assortative mating). In evolution, these two types of assortative mating have the effect, respectively, of reducing and increasing the range of variation, or trait variance, when the assorting is cued on heritable traits. |
There are a lot of review on this and it almost the same as sexual selection in lay man terms
although I must say that is not exactly the same
I will continue on the topic if some one is interested
| mshafiq wrote: |
| Darwin's grand idea of evolution by natural selection is relatively simple but often misunderstood. To find out how it works, imagine a population of beetles:
1. There is variation in traits. For example, some beetles are green and some are brown 2. There is differential reproduction. Since the environment can't support unlimited population growth, not all individuals get to reproduce to their full potential. In this example, green beetles tend to get eaten by birds and survive to reproduce less often than brown beetles do. 3.There is heredity. The surviving brown beetles have brown baby beetles because this trait has a genetic basis. End result: The more advantageous trait, brown coloration, which allows the beetle to have more offspring, becomes more common in the population. If this process continues, eventually, all individuals in the population will be brown. |
The creationist objection to this, however, is that the brown and green traits had to be there beforehand. They will accept this as "microevolution", but will continue to reject "macroevolution" using the (flawed) argument that with this model, there will never be a pink beetle, because the pool of traits has only green and brown beetles.
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