Speciation questions

[davidneff]

Hello guys,

Forgive me. I am new to the forum and relatively new to studying evolution (I'm an apostate of Christianity and YEC so I'm relatively new to learning about stuff like this) and I have a few questions about how speciation works and how it is detected.

1. What is the best definition for speciation?
2. Has speciation ever been observed?
   1. If yes, can you cite me some good examples?
   2. If yes, can you prove that this was a case of speciation?
   3. How do you falsify a supposed speciation event?

According to the Talk.Origins archive (one of my favourite resources):

Biological classification is hierarchical; when a new species evolves, it branches at the very lowermost level, and it remains part of all groups it is already in. Anything that evolves from a fruit fly, no matter how much it diverges, would still be classified as a fruit fly, a dipteran, an insect, an arthropod, an animal, and so forth.

¹

How then can there be changes in the upper levels of the taxonomy?

One of my creationists friends asked me how and at what point, does a dog become/gives birth to a non-dog.

Thank you for taking time to read (and hopefully answer) these questions. Once again, I'm new to the study of evolution. Hopefully, I will take biology courses in college.

References

1. http://www.talkorigins.org/indexcc/CB/CB910_1.html

[Moontanman]

What you ask has been done so many times on this forum I suggest you search the forum for threads like that that have been hashed out over and over.

 

Barring that I suggest you watch this video, it explains the things you ask easily and concisely.

 

 

This is one of an entire series that makes science easy to understand...

[CharonY]

1. It depends a little bit on the definition of species. I will use a fairly accepted, though in some cases outdated: the one of reproductive isolation. Species is then defined as a population of organisms that can interbreed and is isolated from other such groups. In order to explain how speciation may occur I will give the example of the so-called allopatric speciation.

Imagine a species (i.e. group of interbreeding individuals). Now for some reasons a subgroup gets isolated and they stop interbreeding. Over time these groups may diverge so much that they cannot successfully interbreed , even if they are not isolated anymore. It is therefore to understand that speciation is a population event, not an individual one. Also it generally occurs over longer time-frames (for both reasons the example with the dog does not make sense).

Also I just realized that there is quite a nice wiki page to this topic My link. I think I will leave it there for the moment and you may want to read up on it and maybe you can ask more questions, if you think that the article(s) need clarification?

 

 

How then can there be changes in the upper levels of the taxonomy?

At higher taxa there is only reclassification if one realizes that the evolutionary history of organisms need re-arrangement, i.e. to conform with new genetic data. There will be no biological changes as all the taxonomy is only a way for us to order and categorize things. In nature only species exist (and even that is tricky, especially when go to prokaryotes) and it does not particularly care about hierarchies.

[akh]

I will start by saying that concepts of evolution and speciation are fairly advanced topics. Its very important to have a strong command of the principles of genetics to be able to understand many of the concepts of evolution and speciation. With that said, it is not impossible to have some basic understanding.

 

1. What is the best definition for speciation

 

 

The best definition; the processes by which an organism becomes genetically isolated from a common ancestor. Over time, due to the genetic isolation, the two separate lineages become unable to reproduce or produce viable offspring through interbreeding. Genetic isolation can occur through many processes. Obviously, there is a lot of grey area during the process. When it comes to actually defining what makes a species, you maybe disappointed to know that there isn't a "best" definition. There is some disagreement among biologists in this area. In many cases, it really depends on what is being studied.

 

Speciation processes:

 

Allopatric speciation

Parapatric speciation

Sympathic specaition

Peripatric speciation

 

 

One of my creationists friends asked me how and at what point, does a dog become/gives birth to a non-dog

 

 

This is a fallacious inquiry. The answer; there isn't a specific point, and never. But this does not mean that speciation does not occur. I suggest that you look into speciation processes I listed above. I will try to find links to the processes later, or better yet, look them up yourself.

Edited August 4, 2012 by akh

[davidneff]

What you ask has been done so many times on this forum I suggest you search the forum for threads like that that have been hashed out over and over.

 

Barring that I suggest you watch this video, it explains the things you ask easily and concisely.

 

 

This is one of an entire series that makes science easy to understand...

 

Thanks for that video. LOL @ Ken Ham and the Creationists. Taking scientific advice from them is akin to taking historical advice from a holocaust denier.

 

And thanks to anyone else that replied.

Edited August 4, 2012 by davidneff

[ronians1]

davidneff, on 3 August 2012 - 11:45 PM, said:

 

One of my creationists friends asked me how and at what point, does a dog become/gives birth to a non-dog

 

I should imagine this happens when a significant chromosome mutation occurs

which stops the species from interbreeding. Normal point mutations don't usually stop sub-species from interbreeding.

[Delta1212]

Regarding a dog becoming a non-dog:

 

Let's use the definition of species that states two populations are separate species when they cannot interbreed.

 

 

To simplify things, we'll use individual dogs that represent ideal members of their populations because narratively I think it's easier to wrap your mind around individuals than populations. Each dog referenced in this example will be considered capable of reproducing with any healthy member of their concurrent population, and anything a member of their population can successfully reproduce with, they can, too. Basically, every dog will be representative of a whole generation of dogs.

 

 

So, we start with Fido. Fido will be our original generation. Fido has a puppy named Fido 2, who is a lot like Fido, but not exactly since children are never exactly like their parents. Many generations pass, various small genetic mutations build up in the population, and eventually Fido 10,000 would no longer be capable of breeding with Fido if he were still alive. Well, they must be separate species!

 

But wait, Fido 10,000 is the first dog incapable of reproducing with Fido because of genetic incompatibility. That means that Fido 9,999 could still have viable children with Fido, so Fido 9,999 must still be a dog.

 

Hey, hold on, Fido 10,000 is almost exactly like Fido 9,999. They wouldn't have any trouble reproducing. If Fido 9,999 is a dog, and Fido 10,000 can reproduce with Fido 9,999, then they must be the same species and Fido 10,000 must still be a dog.

 

So we move on to Fido 20,000. Fido 20,000 is the first to be incapable of reproducing with Fido 10,000. Finally, we have something that isn't a dog!

 

Or wait, Fido 19,999 was still capable of reproducing with Fido 10,000, and since we determined that since Fido 10,000 could still reproduce with a dog, he must also be a dog, and therefore Fido 19,999 is a dog as well. Fido 20,000 is very similar to Fido 19,999, so Fido 20,000 must be a dog, too!

 

 

I could keep chaining it like this all the way to Fido 100,000,000, which looks absolutely nothing like anything we'd think of as a dog and would be completely incapable of reproducing with one. There is no actually point where an animal gives birth to a different species. They sort of bleed into each other and we make up arbitrary demarcation points to make it easier to classify things.

 

After all, since we can trace ancestry back pretty far, we could use the chaining method I described to claim all animals are the same species because they'd be capable of mating with some ancestor that could mate with some ancestor that could mate with some ancestor, etc until all the chains converged to one population of proto-animals.

 

It's an interesting thought experiment but it also renders us incapable of categorizing the diversity of life as it currently exists. The important point to take away from this is that species don't really exist in nature.

 

The more "real" way of grouping things from an evolutionary perspective is by population, which is a group of individuals capable of interbreeding. Dogs now, and dogs 100 years ago are defined as being members of the same species, but they are not members of the same population, because dogs that are currently alive are incapable of breeding with dogs 100 years ago.

 

We find it useul to categorize them all as dogs because it would be rather ridiculous to have to come up with a new name for things every generation, but in terms of evolution, once something is dead, it's pretty much irrelevant and can't be counted as a part of anything. So Fido 10,000 may or may not make the cutoff for being of the same species as Fido based on where someone wants to draw the line, but they aren't part of the same population so it doesn't matter whether you categorize Fido or Fido 10,000 or both or neither as being a dog.

 

Dog is not an objectively real category. The only categories that evolution actually concerns itself with are alleles, individuals and populations. Dog is a label that can be applied to individuals or populations, but there is no individual or population that encompasses all dogs. If you want to talk about the effect of evolution on a dog, you have to specify an individual or population that you are applying the label to, and you cannot conflate the properties of the two just because they share a label. A good rule of thumb is that each category is capable of producing a separate entity at the same level of itself, but not higher. An allele can be replicated to create a distinct copy of the allele, it cannot create a whole new individual by itself. An individual can reproduce and produce a distinct individual, but it cannot create a whole new population by itself. A population can give rise to a distinct population separated from the original by space or time.

 

When saying that a dog gives birth to a non-dog, you would be describing a population level occurrence happening on the level of the individual, which doesn't happen, but which people have trouble with sometimes because we are so used to thinking of dogs as all being one "kind" of thing even though they really aren't.