Wortfish wrote:

NineBerry wrote:
The threshold moves as well. Say we have 1000 generations numbered from 1 to 1000. 2 are the children of 1. 3 are the children of 2 and so on.

Generation 50 may be able to procreate with generation 1 (except all from 1 would already be dead). Generation 100 would be able to procreate with generation 50, but not any longer with generation 1. Generation 150 would be able to procreate with generation 100 but nit with generation 50. And so on.

It's a bit like a program written for Windows 95 may still run on Windows 98, but not on Windows XP. but another program written for Windows 98 still runs on XP but doesn't run under 95.

I get what you are saying about generational time. But the versions of windows are more like new species, rather than generations. The basic problem is if Species A only produces Species A offspring, then there is no generation in which Species B can appear. There has to be a tipping point where even a tiny change, building on previous changes, means that parents give birth to offspring that they cannot interbreed with (if they wanted to). Of course, they would still see the offpsring as their own species.

That is a misunderstanding of evolution. As has already been said, most speciations are very gradual, not over-night!
(Unless, of course, you consider that most animal species are beetles!)

DavidMcC wrote:
It wouldn't be a whole generation at once, Wortfish, because the changed genes do not suddenly pop up in an entire generation. Physical or reproductive separation is required, otherwise the genetic change in one individual or family gets swamped by the rest of the population. This is how non-isolated populations remain one species, even over evolutionarily long periods. (Having said that, isolation does not have to be geographical, it can be by mate preference.)

True. It may just be a single individual since variations happen in individuals rather than entire populations. The chromosome 2 fusion event probably happened in just one individual who, through isolation, founded our own lineage. But he/she would have been different enough from its parents to be a new species even if, anatomically, there was no real physical difference.

Wortfish wrote:

DavidMcC wrote:
It wouldn't be a whole generation at once, Wortfish, because the changed genes do not suddenly pop up in an entire generation. Physical or reproductive separation is required, otherwise the genetic change in one individual or family gets swamped by the rest of the population. This is how non-isolated populations remain one species, even over evolutionarily long periods. (Having said that, isolation does not have to be geographical, it can be by mate preference.)

True. It may just be a single individual since variations happen in individuals rather than entire populations. The chromosome 2 fusion event probably happened in just one individual who, through isolation, founded our own lineage. But he/she would have been different enough from its parents to be a new species even if, anatomically, there was no real physical difference.

Yes, but you said nothing previously to suggest that reproductive isolation of the different individual was necessary for speciation by that route.

Look. Species are an after-the-fact classification. When a population of species A is separated into two populations that cease to exchange genes, they at first belong to the same species A.

But then those two new populations evolve into different directions. After some time, the two populations are different. At this point, we call them two different species: A1 and A2.

To try to find the point when individuals stopped to belong to A but instead started to belong to either A1 or A2 is not something that can be done precisely. This is a process. There is no clear point in time to find.

There is some point when you could take the two sub-populations and make them mate with each other and one would observe that some individuals could still produce offspring with each other while others couldn't while for some individuals, they could only procreate sometimes but not always. At this point of time, it is not absolutely clear whether we have two different species or not.

Wortfish wrote:

Shrunk wrote:
If you don't understand this, you really have no business trying to discuss evolution with grown ups. Did you just hear about evolution for the first time five minutes before you decided to post in this thread? You can't have actually been thinking of the topic much longer than that without understanding this basic concept.

Follow the logic. A member of a species can only have offpsring that are of the same species. That is what both Dawkins and the creationists believe. The problem for Dawkins is that, if it is true, then no species can transition to become a new species.If erectus only produces erectus offspring, then sapiens can never emerge.

"Logic." It seems you do not understand the meaning of that word. Let's go back to that colour graph:



If we are talking about a speciation event that occurred over the course 250,000 years in an organism with a generation time of 20 years, that would be about 12,500 generations. So divide that colour graph into 12,500 evenly spaced horizontal segments, each representing a generation. Would there be a discernible difference in colour between any two adjacent segments, such that they could be identified as a different "species"? No. Yet, there is enough of a difference that, between the top and the bottom of the diagram the colour has changed from completely red to completely blue.

Call this scenario A.

Now, look at the diagram below:



Again, divide this up into 12,500 sections (this time left to right). All the sections will be blue, and then suddenly they will all be orange.

This is scenario B, which you creationists think is what must happen.

Dawkins is explaining that scenario A is what occurs.

Your response is that, if scenario A is what occurs, then scenario B should occur.

This is absolutely idiotic, and is a violation of the most basic rule of logic, the law of non-contradiction. This is why it is pointless to try discuss science with creationists, because they are incapable of following even the most simple principles of rational thought.

DavidMcC wrote:
That is a misunderstanding of evolution. As has already been said, most speciations are very gradual, not over-night!
(Unless, of course, you consider that most animal species are beetles!)

What I am saying is that the transition between two species may be very gradual and protracted, but there must come a tipping point when all those small changes finally result in a member of the next generation becoming a new species in the usual definition of the term. If this didn't happen, then speciation would be impossible.

DavidMcC wrote:
Yes, but you said nothing previously to suggest that reproductive isolation of the different individual was necessary for speciation by that route.

It may or may not be necessary. However, it doesn't change the fact that the offspring must be a different species to its parents for speciation to occur.

Wortfish wrote:

DavidMcC wrote:
It wouldn't be a whole generation at once, Wortfish, because the changed genes do not suddenly pop up in an entire generation. Physical or reproductive separation is required, otherwise the genetic change in one individual or family gets swamped by the rest of the population. This is how non-isolated populations remain one species, even over evolutionarily long periods. (Having said that, isolation does not have to be geographical, it can be by mate preference.)

True. It may just be a single individual since variations happen in individuals rather than entire populations. The chromosome 2 fusion event probably happened in just one individual who, through isolation, founded our own lineage. But he/she would have been different enough from its parents to be a new species even if, anatomically, there was no real physical difference.

No. For example, people with Downs syndrome can have children. They can also have children who do not have Downs syndrome. In the same way, a fusion of two chromosomes does not prevent procreation with other people without the fused chromosome unless there are more changes over time...

People are born as babies, then become children, then adolescents, then adults and then old fucks. However, there is not a single night that someone goes to bed as baby and wakes up as a child or when someone goes to bed as an adult and wakes up as an old fuck. The classification is just not clear enough that there is not a phase where a classification is not possible 100%.

NineBerry wrote:Look. Species are an after-the-fact classification. When a population of species A is separated into two populations that cease to exchange genes, they at first belong to the same species A.

But then those two new populations evolve into different directions. After some time, the two populations are different. At this point, we call them two different species: A1 and A2.

To try to find the point when individuals stopped to belong to A but instead started to belong to either A1 or A2 is not something that can be done precisely. This is a process. There is no clear point in time to find.

There is some point when you could take the two sub-populations and make them mate with each other and one would observe that some individuals could still produce offspring with each other while others couldn't while for some individuals, they could only procreate sometimes but not always. At this point of time, it is not absolutely clear whether we have two different species or not.

None of what you say makes the term "species" a meaningless artifact of human language. It is more-or-less corrrect, IMO, for most cases. So-called inter-species hybrids only mean that we do not have enough information about what are and are not separate species, plus, as has already been mentioned, the gradualness of reproductive isolation in large animals (ie, not beetles!).

Wortfish wrote:

DavidMcC wrote:
Yes, but you said nothing previously to suggest that reproductive isolation of the different individual was necessary for speciation by that route.

It may or may not be necessary. However, it doesn't change the fact that the offspring must be a different species to its parents for speciation to occur.

That's not a fact.

NineBerry wrote:People are born as babies, then become children, then adolescents, then adults and then old fucks. However, there is not a single night that someone goes to bed as baby and wakes up as a child or when someone goes to bed as an adult and wakes up as an old fuck. The classification is just not clear enough that there is not a phase where a classification is not possible 100%.

Be that as it may, the term none-the-less has some use (especially for beetles, although this thread is not about them). The main problem is that we don't know enough about which "species" really are 100% separate from which other "species". Historically, this has brought the term into disrepute in some people's minds. Genuinely separate species do exist, but there aren't as many of them as we think. (Exceptions to that are in the insect world, where there are, eg, more species of large blue than we thought, because they look simlilar, but behave differently.)

Shrunk wrote:

Again, divide this up into 12,500 sections (this time left to right). All the sections will be blue, and then suddenly they will all be orange.

This is scenario B, which you creationists think is what must happen.

Dawkins is explaining that scenario A is what occurs.

Your response is that, if scenario A is what occurs, then scenario B should occur.

This is absolutely idiotic, and is a violation of the most basic rule of logic, the law of non-contradiction. This is why it is pointless to try discuss science with creationists, because they are incapable of following even the most simple principles of rational thought.

You're missing the point entirely. Both Dawkins and the creationists agree on two fundamental points:

1. Change occurs within a species over time.
2. Parents can only produce offspring of the same species.

It may well be that offspring are slightly different to their parents - a lighter shade of red if you insist - but they are still of the same species. But according to Dawkins, however much change occurs over the generations, there is never a point at which parents ever give birth to offspring that are of a different species to themselves, let alone genus. This makes speciation impossible. What I am saying is that for speciation to occur there must be gradual change within the species leading to a point where any further change, however minor, leads to member(s) of the new generation being a different species to their parents n matter how we decide to define what a species actually is.

Here's a (very simple) example how speciation can occur without violating parent-child interfertility.

Suppose a species is a population of organisms which are interfertile. Suppose some species is geographically divided by a mountain so that it has three subpopulations

(i) lives in the forest to the West of the mountain, there are about a million of these individuals, they can all reproduce with one another (allowing for opposite sex) or with any individual of type (ii) (of the opposite sex).
(ii) lives on the mountain that separates the habitats of (i) and (iii). Individuals from this population can reproduce with any individual of type (i), (ii) or (iii) (of the opposite sex).
(iii) lives in the forest to the East of the mountain, there are about a million of these individuals, they can all reproduce with one another (allowing for opposite sex) or with any individual of type (ii) (of the opposite sex).

Now, one day, the following things happen: 10 individuals of type (i) are born that are all interfertile with the type (i) population. 10 individuals of type (iii) are born that are all interfertile with the type (iii) population. It turns out that the mountain was a volcano and it erupts. All individuals of type (ii) are incinerated or choke to death.

What remains? We now have two populations which cannot interbreed and are thus different species yet we have not violated the parent-child interfertility condition.

Thommo wrote:

Wortfish wrote:

DavidMcC wrote:
Yes, but you said nothing previously to suggest that reproductive isolation of the different individual was necessary for speciation by that route.

It may or may not be necessary. However, it doesn't change the fact that the offspring must be a different species to its parents for speciation to occur.

That's not a fact.

Indeed, inter-species hybrids can occur, but, as I said before, that is only a reflection of our lack of information about which of the presently defined species really are 100% separate, and which are just variants.

No, that's not what I meant.

DavidMcC wrote:
Indeed, inter-species hybrids can occur, but, as I said before, that is only a reflection of our lack of information about which of the presently defined species really are 100% separate, and which are just variants.

I think interbreeding between species may only be possible in one direction. Neanderthal men may have successfully mated with Sapiens women, but not the other way round.

Thommo wrote:No, that's not what I meant.

Maybe not, but it's what I meant!

Just don't talk to me. Don't quote my posts and say "indeed" if it has nothing to do with me. Easy.

Thommo wrote:
What remains? We now have two populations which cannot interbreed and are thus different species yet we have not violated the parent-child interfertility condition.

Yep, understood. But looking at our own lineage, we know that we have ancestors that were not members of our species. How did these ancestors produce direct descendants that are not of their own species if Dawkins is to be believed?