Wednesday, January 21, 2009

Introduction and Chapters I-II notations

Some of a host of random notations and questions I had while reading through the first ~60 pages of OTOOS

p3) Naturalists continually refer to external conditions ... as the only possible cause of variation

Is this statement true? Did no one before Darwin publish an explanation for variation that relied on factors intrinsic to organisms?

p6) Furthermore, I am convinced that Natural Selection has been the main but not exclusive means of modification.

From the get-go, Darwin is making it clear that he thinks NS works in concert with other natural phenomena to modify the species of the world. It takes a while to get out of him what he thinks these other natural phenomena are but eventually he talks about them.

p8) But I am strongly inclined to suspect that the most frequent cause of variability may be attributed to the male and female reproductive elements having been affected prior to the act of conception.

Okay, in Chapter I he starts laying down the framework for how he thinks variability in organisms occurs. The problem is that ...this is massively generalistic and begs big questions. The (to use the modern terminology) gametes are affected? By what? By ...the organism's thoughts? By actions of the environment? By use and disuse? The answer here can't be NS because that's not going to affect reproductive elements, NS is only acting on whole organisms, not parts of them.

p11) Nevertheless some slight amount of change may, I think, be attributed to the direct action of the conditions of life -- as, in some cases, increased size from amount of food ...

So the conditions of life cause variation in organisms. Is this limited to that one individual in its life or is this something that becomes inheritable, e.g., an acquired characteristic? I'd say it's not but then a few sentences later...

The great and inherited development of the udders in cows and goats in countries where they are habitually milked ... is another instance of the effect of use. Not a single domestic animal can be named which has not in some country drooping ears; and the view suggested by some authors, that the drooping is due to the disuse of the muscles of the ear ... seems probable.

This is the beginning of a book full of comments that show that Darwin did not have a scientific problem with acquired characteristics; he just didn't think that they alone explained variation. If promoting acquired characteristics makes one a Lamarckist than Darwin is being a Lamarckist in OTOOS. (and I use the term Lamarckist in its general sorta pop-sci understanding of the term. Even wikipedia tells me that's too simplistic but ...just go with it)

p20-29 I won't quote but basically Darwin gives a great litany of well thought-out reasons why domesticated pigeons, even though they show amazing amounts of variation, must be descended from one ancestral species. It's weird reading this in a book full of Darwin deferring to popular opinion at the time that domesticated dogs must have descended from several ancestral species.

p32-42 Darwin is doing the best job he can at explaining out artificial selection as the driving force behind variation in domesticated species. And it's a great job: he establishes that breeders are picking up tiny, minute differences in their animals. He establishes that not all of these animals breed. He makes it certain to explain that breeders don't aim to make a new variety of, say, dog. No one sat down and decided to make a Dalmatian. But breeders picking small changes in generation after generation will eventually produce a new breed of dog. Artificial selection may be intelligently-driven but it does not have directionality, since breeders can't control what the next generation of bred organism will look like. Or, more to the point, breeders can't create novel features, they can merely select for them.

All Darwin has to do now is replace the word "artificial" with "natural" and "breeders" with "nature" and he can convince the reader that NS occurs.

p43) No one supposes that all the individuals of the same species are cast in the very same mould.

This became part of discussion today because the Mayr introduction to this OTOOS publication mentions how Darwin took species away from typological understanding into a population-level understanding. There was a lot said today about this and ...a lot more can easily be said about it. I don't have much to add.

p46) I am inclined to suspect that we see in these polymorphic genera variations in points of structure which are of no service or disservice to the species, and which consequently have not been seized on and rendered definite by natural selection.

Later in the text Darwin will come back to this with his commentary on how one should make phylogenetic trees (although, of course, he doesn't use that terminology.) But, when I read this, I fail to see how Kimuran neutral theory (or at least the first assertation of it) is in anyway contradictory to natural selection. DNA and RNA aren't organismal structures (they literally build strucutres) but if they're not under selection than they can be as neutral as they want to be.

Chapter II is generally a long discussion on how the "What is a species?" discussion will never have any definite winner. To cut to the chase...

p52) From these remarks it will be seen that I look at the term species, as one arbitrarily given for the sake of convenience to a set of individuals closely resembling each other, and that it does not essentially differ from the term variety, which is given to less distinct and more fluctuating forms.

In our modern biological world we could probably argue that species have definite molecular markers and that we could use those to define a "species", but even in that case there might be more unsampled populations out there which actually show a marker that is 'partway' between one defined species and another.

Embracing Darwin's worldview partially means embracing the idea that species are abstracts. In a Darwinian world, species barriers "break down" as we take modern-day populations of organisms and expose them to the fourth dimension. In so doing we see that somewhere the species we are tracing back in time start off as a 'variety' of another species, and that species the same, and so on and so on etc.

four-dimensional populations of organisms that are all more re n


Dr. Fox said...

I appreciate this close reading of the text, Josh. A few remarks:

Re: your notes on p. 6 and 11. As Mayr notes in his introduction, Darwin has a tendency to hedge his bets, which got worse in later editions. It's clear he thinks natural selection is more important than other factors that might drive evolution, but he's not prepared to rule anything out entirely. Probably a variety of reasons for this. It'd take a lot of confidence/arrogance to conclusively rule out the ideas of other well-regarded experts on the basis of the available evidence, and Darwin was cautious by nature. He was also an unstoppable fact-gatherer, and determined not to draw conclusions until he had all the facts (which you never do...) Plus, if you're already worried about the reception you're going to get, best not to needlessly annoy your professional colleagues. Modern scientists still hedge their bets in the same way, but often only in passing, so you're often not sure if they really mean it.

Your notes highlight that even Darwin's tentative remarks on the causes of variation seem confused and difficult to interpret, especially to modern readers. Remember that, despite Darwin's undoubted rejection of typological thinking, the only language or terminology available to him to describe his ideas about variation was typological language. In this language, species or varieties are viewed as having some kind of ideal 'type', and deviations from this type are unusual events. The attempt to express population thoughts in typological language is necessarily confused and confusing. For instance, Darwin's remarks about variable characters occasionally reverting to the ancestral type sound odd to readers who know their Mendel. But if you think of deviations from 'type' as unusual events that must have some specific cause, it's natural to expect organisms to sometimes revert back to the way they 'should' be or 'want' to be.

Didn't quite follow your comments on p. 46 re: Darwin's intuitive grasp of what we'd now call neutral drift. Darwin's comments look prescient to my modern eyes. If selection doesn't favor a particular trait value or state, then we would indeed expect to see a larger range of standing variation in trait values/states, due to what we'd now call mutation and drift. I don't think that Darwin sees what we would now call drift and mutation as contradictory or mutually exclusive of natural selection.

Also not sure that artificial selection can't have 'directionality', or that breeders don't set out to make a 'Dalmatian' (i.e. a new breed with certain desired features). It seems to me that's exactly what breeders do. For instance, Darwin cites the remarks of a pigeon breeder as to the number of years it would take him to breed a pigeon with a desired beak shape or plumage. Surely it's precisely by imposing artificial selection that breeders impose 'directionality' to evolution. As to whether breeders can 'create' features, I'd say yes, absolutely. Obviously they don't create and can't control the small random variations that are provided to them each generation. But they can control which variations are accumulated, and that seems to me to be as 'creative' as one could ask. Have a look at Chapter 3 of Dawkins' The Blind Watchmaker for more on this.

Tonya said...

I'm glad you mentioned the quotes on p11. I was a little surprised to see Darwin discussing acquired characteristics. It's so interesting to know that he believed? in it. Or as Fox mentioned, maybe he didn't and he was just hedging his bets. Nonetheless he still wrote about it in the first chapter.

If, as you say, embracing Darwin's worldview means embracing that species are abstracts than I do not embrace his view. It seems that your 'fourth dimension' explanation is describing the evolutionary species concept, would I be correct in saying that? My view is that species are real, not abstract but that are boundaries are abstract. My adviser has a wonderful analogy in that species are like mountains. We are quite certain where the peak is, but where does one mountain become another? We would not call mountains abstracts even though they came from the same ground. I personally adhere to de Queiroz's (2007) unifying species concept which states that species are separately evolving metapopulation lineages and all other 'species concepts' are actually different properties that can be falsified. I'm actually kind of sick of everyone quoting Darwin that a species is what a good naturalist says it is but that is just my opinion :)

The comments on Dalmations brings me to another quote from Darwin (p8): "No case is on record of a variable being ceasing to be variable under cultivation". I think Dalmations are pretty much at their capacity to have anything bred out of them, as sickly a breed as they are.

Good comments Josh!