Grasse’s concept of « mother form » organisms

[Roy (34-year veteran)]

But then no species would vary much from the the ‘mother’ form, and there’d be no continued divergence.

That contradicts observations of real species.

[Faizal_Ali]

@Giltil

Maybe the best thing to do at this point is to present a specific chain of two or more connected mother forms that, according to Grasse, can be inferred from the fossil record?

As far as I can see, literally any of the lines in the tree of life below that go to the present day would fit your criteria for a “mother form” in terms of travelling thru time and having various species shoot off from it. (Note that the diagram is highly simplified and only shows a fraction of lineages that have actually existed.) The ones that don’t fit your criteria fail to do so only by virture of having gone extinct. Up to the point of extinction they, too, would have qualified as “mother forms”.

What am I getting wrong?

Evogeneao: The Tree of Life

[John_Harshman]

@Giltil

Don’t think it is a problem, for we can imagine that a given mother form can give rise at time T1 to a given species A that will last let’s say 5 millions years and then give rise again to nearly the same species at let’s say time T1 + 4 my, etc

This contradicts the evidence of both paleontology and phylogeny, notably molecular phylogeny. We would expect a star tree of all species descending from a given mother form, and yet we see a mostly bifurcating tree. You really seem to be working hard to find an untestable model, but the data keep preventing you.

[RonSewell (RonS)]

@Giltil

IOW, in this scenario, the mother form acts as a stem cell niche, periodically re-issuing derived forms as older lineages decay.

OK, then the mother forms are still around. Which of the cat family, or the carnivores, or however far back it goes, is the mother form stem cell species, and can I see one in a zoo?

@Giltil

Their genomic stability over hundreds of millions of years may partly reflect the efficiency of purifying selection in stable, large populations, rather than an intrinsic mutational rate difference.

Claude must have had a brain fart. The heart of GE meltdown is that purifying selection does not apply.

[Joe_Felsenstein]

Separating forms into “generalized” and “specialized” is dubious. If students of arthropods were watching (say 500 mya) and saw an early insect, they’d say “wow, what a weird, specialized arthropod that is”. While students of insects, finding it in the fossil record, would consider it to be very generalized.

[John_Harshman]

And consider birds, in one obvious respect perhaps the most specialized of vertebrates. Yet they have also diversified more than any other group of similar age.