All species are transitional

This, like so much else, depends on the definition. If a transitional is one which "posseses features of two currently distinct higher taxa". The an animal doesn't have to have descendant species to be this kind of transitional.At some point in time there were probably 100's or 1,000's of species that were all cousins and all part way along the path from dinosaur to bird. It may be that exactly one of these species gave raise to all modern birds or certainly only a handful of them. But I'd claim that ALL of them were transitional -- that is straddling the gap between the two higher taxa.

I don't understand how you arrive at this conclusion. Do you think that all animals should fossilize? What portion do you think should? Under what circumstances?
Do you have an explanation for the pattern in the fossils we do have? Perhaps you should define what "showing "intermediacy"" would look like and what "intermediacy" is?
Then you could show the details of the logic that you think is being followed to produce the circular reasoning you think is there.

Unfortunately, it is very messy and gene pools are not so isolated even when we call them different species.
See:
Message 132For a quote from Meyrs on this topic.

My critical comment is:It is a great representation.

whew! You had me worried for a minute too. (as in what does para know???)

Remember the speakled beasties are a contrived example. There will be many more gradiations of larger and larger speckles in most real examples.

But the heavy speakles are only isolated from the no speakles not from the lightly speakled which are not isloated from the no speakles.There is, therefore, some gene flow from heavy to no.

The point is that it isn't clear there is a really new species on the day of the first heavy. It is still not completely isolated from the gene pool. There is, in fact, still one gene pool.After that it could go on as one species with the no speakles dying out slowly or the mix of heavy, no and light continuing in the gene pool or split if something finally stops the heavies from breeding with anyone else.

Even if it isn't all that likely it depends on more details of the scenario. But it would be demonstrating a different point.I'd say that the mix of no, heavy and light speckles (I think I finally have the spelling right) isn't so likely. Rather we would get some speckling become the only coat in the population over time. Then some other mutation happens that increases it a bit more. This too becomes "fixed" (all through the population). This carries on over time. However unlikely the chain of mutations is they can arise if the population isn't too small and we allow enough generations.This isn't what we have been discussing because we were showing the "fuzziness" of speciation. The above scenario still does but it is now spread out over time so it isn't so apparent.It is, just to muddy things a bit more, entirely possible that all 3 forms of no, heavy and light speckling will stay in the population. This could occur if the environment consisted of some bush and some open savana kind of places (think lion colored coat with no marks). If one coat offered a level of advantage in part of the environment and one in another they may all be preserved in the population.In that case, over time, the no speckle form may occupy the open areas and the heavy speckles the bush and we would see the speciation without losing either one. If the climate changed back and forth we could see the population tracking it a bit too.It maybe that homo ancestors went through something like this if being aboreal was of greater and lessor advantage and moved back and forth as the climate changed.

In the contrived example we are discussing the isolation becomes complete when the mixed population dies away. So if you take this as the "speciation" you're saying that the heavy speckles are not a species at one moment and then when something over the nearby hill gets swallowed by a boa it suddenly becomes a species.That may be correct in some way, but it is a bit odd.

No we would not. That is the whole point of this recent part of the discussion.As has been noted we use multiple definitions of species. E.O. Wilson (Diversity of Life) makes it clear that no definition is totally satisfying. We are trying to attach category labels to things which refuse to always fit into nice, neat niches.Generally, the biological species definition based on gene pool isolation works fine. Obviously, a whale and an elephant are in isolated gene pools at any one moment in time. It works fine. However, as we've seen there are many examples where speciation is happening but is only "complete" to varying degrees.When we lay thing out in time as well, that blurring becomes the norm rather than the exception.Species (one of the mutiple definition) works well enough to allow it to be used as part of a method of managing the information about life. To fuss about it at the most detailed level is a waste of time. There is NO "perfect" definition. Biologists have been trying for one for decades. It ain't gonna happen.This message has been edited by NosyNed, 10-28-2005 06:09 PM

Reading E.O. Wilson's "The Diversity of Life" (around page 70 + or -) I think that we can say there are speciation events. This doesn't mean that speciation isn't also fuzzy it just means it is wrong to say an "event" never happens.He speaks of polyploidy producing a new species in a single generation. This he says accounts for something like half of living plant species and a "smaller number of animal species".

Wilson says:

quote:

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Polypoidy is virtually instantaneous in its effect, potentially isolating a group of individuals from its ancestors in one generation.

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It seems it follows the biological species concept. They can not breed with their parents species.This message has been edited by NosyNed, 11-01-2005 12:20 PM

Wilson brushes over this.I recall we discussed mice on an island somewhere. Any details? Any other examples. How do sexually reproducing mammals get around the not-having-a mate-available problem?

Gee, this reminds me we haven't seen him for ages . Message 35And from a link in
Message 42

quote:

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A recent (13 January 2000) report in Nature describes a study of house mouse populations on the island of Madeira off the Northwest coast of Africa. These workers (Janice Britton-Davidian et al) examined the karyotypes of 143 house mice (Mus musculus domesticus) from various locations along the coast of this mountainous island. Their findings:

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* There are 6 distinct populations (shown by different colors)
* Each of these has a distinct karyotype, with a diploid number less than the "normal" (2N=40).
* The reduction in chromosome number has occurred through Robertsonian fusions. Mouse chromosomes tend to be acrocentric; that is, the centromere connects one long and one very short arm. Acrocentric chromosomes are at risk of translocations that fuse the long arms of two different chromosomes with the loss of the short arms.
* The different populations are allopatric; isolated in different valleys leading down to the sea.
* The distinct and uniform karyotype found in each population probably arose from genetic drift rather than natural selection.
* The 6 different populations are technically described as races because there is no opportunity for them to attempt interbreeding.
* However, they surely meet the definition of true species. While hybrids would form easily (no prezygotic isolating mechanisms), these would probably be infertile as proper synapsis and segregation of such different chromosomes would be difficult when the hybrids attempted to form gametes by meiosis.

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