How does selection produce speciation?

[TheAskerMan]

I understand that things like geographical barriers can separate groups of a species and cause the groups to develop different dominant traits. But I don't see how this could cause a change in species. Pigs stranded on an island might develop a tendency to be tall so as to reach certain vegetation, but this is a change in dominant trait, not in genetic structure. How would the DNA and number of chromosomes of these pigs change?

[Mr Skeptic]

Selection doesn't produce speciation, anymore than deciding produces choices. Selection is a process that eliminates maladaptive information. New genetic information is produced via mutations, and in some cases (especially with an accumulation of mutations) this can result in enough differences as to make interbreeding impossible.

[dr.syntax]

I understand that things like geographical barriers can separate groups of a species and cause the groups to develop different dominant traits. But I don't see how this could cause a change in species. Pigs stranded on an island might develop a tendency to be tall so as to reach certain vegetation, but this is a change in dominant trait, not in genetic structure. How would the DNA and number of chromosomes of these pigs change?

 

mutation among the many other ways an organism has of changing it`s genetic structure. Most of the genes that make up your DNA are dormant or event junk genes that never actually expressed themselves. One factor that causes a rapid change in species is when a catastrophic event such as that metiorite strike on Earth 65 million years ago. It killed off the dynosaurs clearing the planet for the emergence of larger mammals. Small mice had an oppurtunity to evolve into such organisms as bears, wolves, humans. A huge array of new species. The basic body structure is there in mice. A genetic tweak or so and you have a rat a few more tweaks and a badger, few more and a bear or wolve emerges. Natural selection has many new traits to select amongst without all that many genetic changes. One well known example of this is the fact that human beings share 98% of our genetic makeup with chimpanzees. ...Dr.Syntax

Edited October 1, 2009 by dr.syntax

[Mokele]

There's selection and then there's genetic drift, a neutral, random process which can, over time, render two species unable to mate due to changes in gamete chemistry or mating displays.

[TheAskerMan]

Ok, so genetic mutation is what causes a new species to emerge. But wouldn't a male and female have to be born at the same time with the same mutation for a new species to begin? Are there any documented instances of this happening or is it just assumed based on comparisons of DNA in different species?

[dr.syntax]

Ok, so genetic mutation is what causes a new species to emerge. But wouldn't a male and female have to be born at the same time with the same mutation for a new species to begin? Are there any documented instances of this happening or is it just assumed based on comparisons of DNA in different species?

 

REPLY: no one said genetic mutation is what causes a new species to emerge. Almost all mutations are either harmful or simply junk,not harmful or helpful and don`t express themselves. They are inactive genes. The genes alread exist within a species to produce another species. When for some reason the members of a species are kept appart and no longer exchange genes amongst themselves, create two seperate gene pools, given enough time two different species might emerge. This usually takes many generations. For slowly maturing species like whales,or deer,lions, it could take a very long time. Humans have lived in seperated gene pools for tens of thousands of years at a time and yet are still the same species. They can still breed with each other. Certain insects have been known to generate new species within much shorter time spands. As far as a woman and a man developing the same mutation and mating with each other ,the chances of such an event are so remote. It would also have to be a mutation that expresed itself and most do not. It seems it may have have happened with some bacteria over the billions of years. Whatever, ...Dr.Syntax

[Mr Skeptic]

Ok, so genetic mutation is what causes a new species to emerge.

 

Yes, though there has to be enough of them or of the right type.

 

But wouldn't a male and female have to be born at the same time with the same mutation for a new species to begin?

 

No. You think species are distinct, but they are not. They are a continuum, and we arbitrarily choose a boundary and call them separate species. There is no sudden appearance of a species, just that differences accumulate until they are different enough to call different species, which often also is when they cannot interbreed.

 

On the other hand, a certain type of mutation results in doubling of the chromosomes. This makes them infertile with respect to their parent, but is a common enough mutation that you could get several individuals with that mutation so they could breed together. This happens quite frequently in plants. However, despite being unable to interbreed with the parent population, many do not consider these a different species.

 

Think of it this way, if you arranged everyone in the world by height, you wouldn't be able to tell the difference between two who are close together, but you would be able to tell if the difference was larger.

 

Are there any documented instances of this happening or is it just assumed based on comparisons of DNA in different species?

 

Both.

[JillSwift]

Ok, so genetic mutation is what causes a new species to emerge. But wouldn't a male and female have to be born at the same time with the same mutation for a new species to begin? Are there any documented instances of this happening or is it just assumed based on comparisons of DNA in different species?

Don't think of species as being a line of absolute demarcation. Taxonomy is a far fuzzier business than most people think.

 

As the two groups of animals diverge, in the given example, they will eventually reach the point where they can no longer mate and can be considered separate species by that criteria.

 

This conclusion has been reached by way of the fossil record as well as broad documentation of genomes. I believe there is another class of evidence as well but it escapes me at the moment.

[UC]

REPLY: no one said genetic mutation is what causes a new species to emerge. Almost all mutations are either harmful or simply junk,not harmful or helpful and don`t express themselves. They are inactive genes. The genes alread exist within a species to produce another species. When for some reason the members of a species are kept appart and no longer exchange genes amongst themselves, create two seperate gene pools, given enough time two different species might emerge. This usually takes many generations. For slowly maturing species like whales,or deer,lions, it could take a very long time. Humans have lived in seperated gene pools for tens of thousands of years at a time and yet are still the same species. They can still breed with each other. Certain insects have been known to generate new species within much shorter time spands. As far as a woman and a man developing the same mutation and mating with each other ,the chances of such an event are so remote. It would also have to be a mutation that expresed itself and most do not. It seems it may have have happened with some bacteria over the billions of years. Whatever, ...Dr.Syntax

 

Mutations are the ONLY source of new genetic material.

 

Mutations are heritable, even though they may not be expressed. If the DNA being transferred to the offspring has a miscopied base pair, it doesn't vanish because the other parent didn't have it. It's still there. Very few features have "Mendelian expression" that you seem to be stuck on. Cumulative mutations over very long periods of time can result in the formation of entirely new structures, proteins, etc. Most mutations will be deleterious, and if natural selection is allowed to function, they will be "weeded out." Those that do not give an advantage are passed on at an average rate, where they can compound with future mutations. Those that convey a distinct advantage to reproductive fitness are passed on readily.

 

Smaller numbers of mutations are unlikely to accomplish the formation of new structures, but can easily turn off normally expressed genes, or set them into "overdrive." Cancer relies on combinations of both, but these mutations (just based on probability) are often not in the reproductive cells, and many occur after childbearing years. In this case, they are not heritable.

[dr.syntax]

"mutations are the ONLY source of source of new genitic material". What does that have to do with what you quoted me on. You seem to be correcting me about some mistaken notion I proposed BUT I never said anything about it. Whatever, Dr.Syntax

Edited October 2, 2009 by dr.syntax
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[Mr Skeptic]

Are there any genetic changes that are not, by definition, mutation? I think sexual recombination might be one.

[TheAskerMan]

Ok. So here's what I'm gathering. I always viewed a species as having a unique set of genetic possibilities that allows variation in traits, but not entirely new traits. For example, a whale can vary in size and color, but it cannot spout legs. Nor can traits vary beyond a limit. For example, a mouse can vary in size, but it cannot grow too big (like the size of a rat). For a mouse to be able to grow that big or for a whale to start developing legs would need genetic mutation because the current genes just don't have that capability in them; they don't have a "develop legs" command or combination.

 

That's what I thought. But you're saying there doesn't have to be genetic mutation for such a change to occur? It is within the mouse's genetic ability to gradually adapt through selection to become a rat without changes in genetic structure? Or am I way off in my understanding of genetics?? If species are a continuum, then when does sperm stop being able to fertilize an egg? When does that incompatibility occur?

 

I'm sorry. I haven't taken biology since high school. I'm just trying to get a layman's understanding of how the process works.

[dr.syntax]

Ok. So here's what I'm gathering. I always viewed a species as having a unique set of genetic possibilities that allows variation in traits, but not entirely new traits. For example, a whale can vary in size and color, but it cannot spout legs. Nor can traits vary beyond a limit. For example, a mouse can vary in size, but it cannot grow too big (like the size of a rat). For a mouse to be able to grow that big or for a whale to start developing legs would need genetic mutation because the current genes just don't have that capability in them; they don't have a "develop legs" command or combination.

 

That's what I thought. But you're saying there doesn't have to be genetic mutation for such a change to occur? It is within the mouse's genetic ability to gradually adapt through selection to become a rat without changes in genetic structure? Or am I way off in my understanding of genetics?? If species are a continuum, then when does sperm stop being able to fertilize an egg? When does that incompatibility occur?

 

I'm sorry. I haven't taken biology since high school. I'm just trying to get a layman's understanding of how the process works.

 

REPLY: You`re going to get different answers from different sources. I don`t think any of them have all the answers with any certainty though they may pretend they do and seem convincing until you read what the next one has to say. I`d be trying sources like http://absoluteastronomy.com for one. There is a lot more to evoltion than most scientists think there is. Here`s a fact to make you wonder. An AMOEBA DUBIA, a certain species of one celled animals has over 200 times as much DNA as a human being. An onion 4 to 10 times as much. That`s called the C-value enigma or paradox. Things like that. ...Dr.Syntax

[Mr Skeptic]

Ok. So here's what I'm gathering. I always viewed a species as having a unique set of genetic possibilities that allows variation in traits, but not entirely new traits.

 

This is called the gene pool.

 

For example, a whale can vary in size and color, but it cannot spout legs. Nor can traits vary beyond a limit. For example, a mouse can vary in size, but it cannot grow too big (like the size of a rat). For a mouse to be able to grow that big or for a whale to start developing legs would need genetic mutation because the current genes just don't have that capability in them; they don't have a "develop legs" command or combination.

 

Right, a gene not in the gene pool would have to be formed by a mutation of a gene that is in the gene pool, for an animal to have it.

 

That's what I thought. But you're saying there doesn't have to be genetic mutation for such a change to occur?

 

Huh?

 

It is within the mouse's genetic ability to gradually adapt through selection to become a rat without changes in genetic structure? Or am I way off in my understanding of genetics??

 

We already answered this, but perhaps it is better for you to answer it yourself. If you can correctly define selection, you will have your answer.

 

If species are a continuum, then when does sperm stop being able to fertilize an egg? When does that incompatibility occur?

 

That's kind of the trouble. For example, horses and donkeys can produce offspring (though the mules are infertile). Mating incompatibility is just one aspect of the differences between species, though it is a biggie. It doesn't have to be a genetic incompatibility, for example they could have different mating rituals and so not be interested in each other.

[Mythranil]

I always viewed a species as having a unique set of genetic possibilities that allows variation in traits, but not entirely new traits. For example, a whale can vary in size and color, but it cannot spout legs.

 

It's besides the point, but whales actually descended from land-based creatures of the ungulate family (that family also gave rise to most of the modern-day hooved mammals). Whales still have some vestigial anatomical features hinting at their quadrupedal history. So - as I said, it's still besides the point, but should the whale's environment become unlivable for whatever reason, they may end up sprouting legs once more and return to land.

[CharonY]

Right, a gene not in the gene pool would have to be formed by a mutation of a gene that is in the gene pool, for an animal to have it.

 

Or moved into a given gene pool by horizontal gene transfer.

[GDG]

Mutations are the ONLY source of new genetic material.

 

As long as we understand that "mutations" are not limited to single base changes. Let's not forget retroviruses and transposons, gene duplication, and chromosomal translocation...