Thursday, February 09, 2006

My critique of Darwin's Origin of Species, p.5

As part of writing the first draft of Chapter 4, "History ... Darwin," of my book, "Problems of Evolution," I have decided to skim through Darwin's Origin of Species (6th edition, 1872) noting problems in it. I considered saving these problems to a file or web page, but then I thought of posting these pages to my blog. This way it could be useful to others and might generate some constructive feedback (although as usual I won't have the time to debate at any length comments received). I will use the British Library's webbed version, which preserves the pagination of the original.

Here is my critique of the first page (page 5), ignoring Darwin's Historical Sketch and Introduction, since I want to concentrate on Darwin's actual theory. My comments are bold and in square brackets. They will usually be brief and unreferenced, and will serve as points to address in more detail in my book (although the sheer number of them will mean I can only include the most significant).


Causes of Variability.

WHEN we compare the individuals of the same variety or sub-variety of our older cultivated plants and animals, one of the first points which strikes us is, that they generally differ more from each other than do the individuals of any one species or variety in a state of nature. [Is this true? What detailed comparisons did Darwin make? What criteria did he use? Since "cultivated plants and animals" are a tiny subset of "species ... in a state of nature," how statistically valid is the comparison? Also, since most cultivated plants are polyploids, which have little (if anything) to do with the Darwinian natural selection of random micromutations (NSRM). So how relevant is this to Darwin's argument, given that Neo-Darwinists (like botanist Stebbins, a co-founder of the Neo-Darwinian modern synthesis) have rightly tended to downplay the evolutionary importance of polyploidy:

"Polyploidy is a very common method of evolution in higher plants. Between one-fourth and one-third of the species of flowering plants are polyploid with reference to their nearest relatives. Familiar examples among crop plants are wheat, oats, potato, tobacco, cotton, alfalfa, and most species of pasture grasses. Familiar weeds and wild flowers which are polyploid are the eastern blue flag (Iris versicolor), meadow rue (Thalictrum spp.), some species of wild rose, chickweed (Stellaria media), miner's lettuce (Montia perfoliata), yarrow (Achillea spp.), and various species of violets and asters. Furthermore, there is evidence that polyploidy in the remote past has given rise to many genera and groups of genera such as the apples, olives, willows, poplars, and many genera of ferns. Nevertheless, polyploidy has contributed little to progressive evolution. In genera which contain both diploids and polyploids, the major trends of evolution are all represented by diploid species, and the polyploids serve merely to multiply the variations on certain particular adaptive `themes.' This is probably because the large amount of gene duplication dilutes the effects of new mutations and gene combinations to such an extent that polyploids have great difficulty evolving truly new adaptive gene complexes." (Stebbins G.L., "Processes of Organic Evolution," Prentice-Hall: Englewood Cliffs NJ, 1966, Second printing, p.129)]

And if we reflect on the vast diversity of the plants and animals which have been cultivated, and which have varied during all ages under the most different climates and treatment, [How could Darwin know this? Is it even true? The range of "plants and animals" humans cultivate is actually quite narrow.] we are driven to conclude that this great variability is due to our domestic productions having been raised under conditions of life not so uniform as, and somewhat different from, those to which the parent species had been exposed under nature. [Again, is this true? Tropical fruit is usually cultivated in the tropics, unless grown in glasshouses, etc.]

There is, also, some probability in the view propounded by Andrew Knight, that this variability may be partly connected with excess of food. It seems clear that organic beings must be exposed during several generations to new conditions to cause any great amount of variation; [Is this true?] and that, when the organisation has once begun to vary, it generally continues varying for many generations. [In what sense does it vary? Is the variation cyclical or linear? How long is "many generations"? For what is supposed to be a major scientific theory, Darwin's argument here has a vague, unfalsifiable, `how long is a piece of string?', quality!] No case is on record of a variable organism ceasing to vary under cultivation. [Is this true? Or if it is true, do not the variations tend to become increasingly minor and then oscillate around a mean? What about the leading plant breeder Luther Burbank's "law ... of the Reversion to the Average"?:

"There is a law ... of the Reversion to the Average. I know from my experience that I can develop a plum half an inch long or one 2 ½ inches long, with every possible length in between, but I am willing to admit that it is hopeless to try to get a plum the size of a small pea, or one as big as a grapefruit. I have daisies on my farms little larger than my fingernail and some that measure six inches across, but I have none as big as a sunflower, and never expect to have. I have roses that bloom pretty steadily for six months in the year, but I have none that will bloom twelve, and I will not have. In short, there are limits to the development possible, and these limits follow a law. But what law, and why? It is the law that I have referred to above. Experiments carried on extensively have given us scientific proof of what we had already guessed by observation; namely, that plants and animals all tend to revert, in successive generations, toward a given mean or average. Men grow to be seven feet tall, and over, but never to ten; there are dwarfs not higher than 24 inches, but none that you can carry in your hand. ... In short, there is undoubtedly a pull toward the mean which keeps all living things within some more or less fixed limitations." (Burbank L., in Hall W., ed., "Partner of Nature," AppletonCentury, 1939, pp.98-99, in Macbeth N., "Darwin Retried: An Appeal to Reason," Gambit: Boston MA, 1971, p.36. Ellipses Macbeth's)]

Our oldest cultivated plants, such as wheat, still yield new varieties: [Wheat is another polyploid, in fact a hexaploid , i.e. the result of a hybridisation between two ancestral grass species (2n=14), then doubling of the hybrid's entire genome (2n=28), then a further hybridisation with another species (n=14 + n=7 = 2n=21), and then another genome doubling (2n=42), so it is not an example of the selection (leaving aside for the moment the difference between selection by an intelligent human designer and selection by a `blind watchmaker') of micromutations.] our oldest domesticated animals are still capable of rapid improvement or modification. [Again, is this true? If they were "capable of rapid improvement or modification" then it would have happened already in the thousands of years that humans have been selectively breeding "our oldest domesticated animals"! The very fact that modern science has had to employ not only intelligent design, in the form of selective breeding, but advanced intelligent design, in the form of genetic and cellular modifications, using the knowledge and techniques of modern molecular biology to obtain further "improvement or modification," also argues against Darwin's claim.]

[Continued at pp.5-6]

This critique of just one page of Darwin's Origin of Species has taken me longer than I expected. I only hope Darwin did not have so many questionable claims in the subsequent 423 (pages 6-429) pages! Because even at a page a day, this could take over a year, I will continue through the rest of my book's first draft and catch up with the section on Darwin's Origin of Species later.

Stephen E. Jones, BSc (Biol).
"Problems of Evolution"


Anonymous said...

It is true that historically polyploidy, though common, was not thought to be an important evolutionary force. However, in the past thirty years, we have learned a lot more about polyploidy, both at the cellular level and population level. It is now thought that polyploidy is a very important source of variation in natural populations on which evolution by natural selection can act. Additionally, our increasing knowledge and understanding of the variety of mechanisms that contribute to variation in nature only help clarify evolution and don't refute Darwin's observations. It is in fact quite amazing that Darwin got so much right given how litle was known at the time about genetics. I would recommend reading more current reviews and research, such as Nuismer SL, Cunningham BM. Selection for phenotypic divergence between diploid and autotetraploid Heuchera grossulariifolia EVOLUTION 59 (9): 1928-1935 SEP 2005; Rapp RA, Wendel JF
Epigenetics and plant evolution
NEW PHYTOLOGIST 168 (1): 81-91 OCT 2005 Ryan FP, Genomic creativity and natural selection: a modern synthesis BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY 88 (4): 655-672 AUG 2006

Stephen E. Jones said...


Thanks for your comment.

However, I regard it as a red herring since it does not address *my* comments on Darwin's claims about "cultivated plants and animals" that "they generally differ more from each other than do the individuals of any one species or variety in a state of nature" that:

"... most cultivated plants are polyploids, which have little (if anything) to do with the Darwinian natural selection of random *micromutations* (NSRM)" (my emphasis)


"Wheat is another polyploid ... [a] *doubling of the hybrid's entire genome* ... and then *another genome doubling* so it is not an example of the selection ... of *micromutations*" (my emphasis).

Stephen E. Jones