Dear Alistair, thank you for your response. I shall do my best to clarify, although I must say, the question itself is murky to me:


>>Darwinism is not really a term most biologists use - or at least not evolutionary biologists. Darwin's great insight was really in recognising the mechanism of natural selection and how this leads to modification with descent.

Apologies for my words, I'm aware that "Darwinism" is a colloquialism. I understand Darwin's incredible achivements (I hope?), i.e. that nature propogates species (and more succinctly, individuals) by way of natural selection, which is random 'trait' changes that leave a creature more or less fit to survive in its' surroundings and carry on its seed. As those environments and requirements change (forest to savannah over a decent period of time)  those changes in traits will accumulate, and cause species to diverge especially after physical and/or behavioural separation.

>>Since he knew nothing of genetics (let alone genetics) it would be fair to say evolutionary biology hasn't really been "Darwinian" for a long time.

Thank you. That is exactly what I'm trying to clarify. When Mendel and Watson/Crick entered the picture, I believe it was fair to still see the world in strictly the terms Darwin envisioned. Genes and DNA did nothing, in the beginning, to alter the strictly non-network, tree-like vision Darwin had; genes and DNA, for many years, merely showed the underlying structure to Darwin's morphologically variable traits (i.e. a big hand or a small one) and how such traits were transmitted from parent to offspring. A single common answer was still assumed to be at the root of things, so to speak. Am I correct here?


>>Your comments re convergence are perhaps conflating two phenomena - one being convergent evolution of traits or structures that show similarity in form or function without a common evolutionary origin. So classic examples of these would be wings of bats vs birds (note in fact that forlimb skeletal structures are "homologous" while the way in which the wing is supported are not).

I humbly admit my understanding of convergence comes largely from Conway Morris. However, my deeper, if non-understanding EXPERIENCE of convergence, ranges my entire life wondering how, with all of these very similar structures, how the idea of randomness can be so paramount in how life evolves. Clearly there are limitations, and I've often thought to myself that those limitations must be addressable by scientists at some point. Physics, chemistry, and some form of ecology, biology, and population science...I won't pretend to know what I'm asking here. But there seem to be only so many ways to evolve. I'm not saying that number is exceedingly finite, but it is clearly not infinite, otherwise convergence would happen much less often. The reason I struggle so hard to understand this, is because I want to understand the order I see in a way which is not teleological or purposeful. When I speak of numbers, I am hoping that there are numbers which do not require forethought on the part of an organism, but merely mechanical necessity. Not to drift into philosophy, but a sort of "metabiology" which is strictly material while accounting for bird, bat, and pterosaur wings; or octupus and possum arms. The various internal regulatory systems. Live birth. 

This is not the same thing as "reticulate evolution" in which previous divergent lineages partially merge (e.g. through hybridisation between species) which has led to sugegstions that netwworks rather than trees might best describe relationships among taxa.

My understanding of hybridization is, of course, limited. On the level of large metazoans (say cats) it seems that MANY extant cats (Pantherinae, Felinae) are capable of creating viable offspring, even between subfamilies (leopards and cheetahs and kitties oh my!). But my understanding is also such that, in nature, this would be incredible rare, probably even more rare than a Denisovian or Neandertal mating with a "man" because of geographical and behavioural differences. Nonetheless, is it valid to view hybrids as part of a tree, or part of a web/network?

>>So in general terms  - yes - we attach a lot of numbers, and we use a lot of theoretical models (which are described using the albebraic language of maths).

I understand that biologists attach a lot of math to their work. I suppose I'm ultimately, regrettably, asking a question that makes no sense yet. I can't even articulate the question myself.

How is a bat wing related to a bird wing in a manner analogous to Einstein asking how is one force related to another? No need to answer that, I think I just spoke rubbish, to be honest.

This is what happens when you have a curious but not particularly gifted student...

Shawn

Some more slightly disconnected thoughts on your comments above from me...

>A single common answer was still assumed to be at the root of things, so to speak. Am I correct here?

Yes that is correct

>When I speak of numbers, I am hoping that there are numbers which do not require forethought on the part of an organism, but merely mechanical necessity. Not to drift into philosophy, but a sort of "metabiology" which is strictly material while accounting for bird, bat, and pterosaur wings; or octupus and possum arms. The various internal regulatory systems. Live birth.


What you are alluding to sounds much like the concept of "mechanical constraint", which is basically to say that physics imposes limitations on the set of evolutionary outcomes that might occur. For instance some wing morphologies will not provide enough lift for a particular body size or shape to get off the ground. Clearly there is fundamental physics involved here, but bear in mind that - smaller wings are still biologically possible, and evolution may go there if losing flight ability does not impose a huge cost on fitness (so we have flightless birds with small wings). Similar constraints are imposed by (bio)chemistry of course and ultimately fundamental evolutionary processes (e.g. rate of mutation) are governed by chemical and physical processes.   

>On the level of large metazoans (say cats) it seems that MANY extant cats (Pantherinae, Felinae) are capable of creating viable offspring, even between subfamilies (leopards and cheetahs and kitties oh my!). But my understanding is also such that, in nature, this would be incredible rare, probably even more rare than a Denisovian or Neandertal mating with a "man" because of geographical and behavioural differences. Nonetheless, is it valid to view hybrids as part of a tree, or part of a web/network?

I don't think there's much evidence of hybrids between big (Panthera) and small (Felidae) cats but I take your point. Many closely related species can hybridise. Often the examples we give involve geographically distinct animals with a recent common ancestor - so in effect we can see the process of speciation as being "incomplete". The populations are diverging and it may be reasonable to hypothesise that in future generations the hybrids will no longer be viable. Of couse something could happen  - e.g. range expansion resulting in "secondary contact" that results in more frequent hybridisation and ultimately coalescence into what might be best viewed as a single species again. I'm not an expert on this but my understanding is that hybridisation as a route to speciation (i.e. 2 distinct species "giving birth" to a new one) is well supported by molecular evidence in a lot of plant groups (but rather less so in animals).