Blogging Dawkins, Chapters Three and Four

Posted by jrosenhouse on October 29, 2009
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What with all the general business and the ample supply of recent blog fodder, I seem to have gotten away from my Blogging Dawkins project. That state of affairs ends now.

In Chapter Two Dawkins laid out the case that artificial selection can and has caused enormous changes in the physical features of organisms in a relatively short amount of time. In terms of the broader case for evolution, this can be viewed as a plausibility argument. If random variations sifted through selection can craft both chihuahuas and Great Danes from a common wolf-like ancestor in a relatively short amount of time, a lot of humility is in order when asserting what can and can not happen over the course of geological time.

In Chapter Three Dawkins turns from artificial selection to natural selection. Can nature play the role of the human breeder? What, in nature, takes the place of the human eye in making selections?

Dawkins serves a number of biological curiosities to show that nature can serve as a selective agent. Based on these examples he describes the following four-step progression:

  1. Humans deliberately choose attractive roses, sunflowers etc. for breeding, thereby preserving the genes that produce the attractive features. This is called artificial selection, it’s something humans have known about since long before Darwin, and everybody understands that it is powerful enough to turn wolves into chihuahuas and to stretch maize cobs from inches to ffet.
  2. Peahens (we don’t know whether consciously or deliberately, but let’s guess not) choose attractive peacocks for breeding, again thereby preserving attractive genes. This is called sexual selection, and Darwin discovered it, or at least clearly recognized it and named it
  3. Small prey fish (definitely not deliberately) choose attractive angler fish for survivial, by feeding the most attractive ones with their own bodies, thereby inadvertently choosing them for breeding and passing on, and therefore preserving, the genes that produce the attractive features. This is called — yes, we’ve finally got there — natural selection, and it was Darwin’s greatest discovery.
  4. Without any kind of choosing agent, those individuals that are `chosen’ by the fact that they happen to possess superior equipment to survive are the most likely to reproduce, and therefore to pass on the genes for possessing superior equipment. Therefore every gene pool, in every species, tends to become filled with genes for making superior equipment for survival and reproduction.

Near the end of Chapter Three Dawkins writes:

Bear in mind this order of evolutionary change [to produce a peke and a pye-dog from a common ancestor] , and then extrapolate backwards twenty thousand times as far into the past. It becomes rather easy to accept that evolution could accomplish the amount of change that it took to transform a fish into human.

Creationists have a standard answer to this sort of thing. The differences between chihuahuas and Great Danes are, indeed, impressive, but both are still dogs. This is microevolution, and does not involve one sort of life changing into a different sort of life. While there can be extensive changes within a “kind,” there are fundamental barriers preventing evolution beyond this point. Turning one kind of dog into another kind of dog does not show that a fish can transform into a human.

At this stage of the case this argument has a certain plausibility. It becomes increasingly difficult to maintain, however, as you learn more about the anatomy and genetics of modern organisms, and sift through the fossil record for clues as to the sorts of creatures that existed long ago. We have impressive transitional fossils to show how certain, seemingly very difficult, transitions were accomplished. That reptilian jaw bones can transform into mammalian ear bones becomes much easier to believe when you can effectively watch them do so through a series of fossils. A study of anatomy and genetics makes it clear that modern structures are the modified descendants of precursor structures. This, I suspect, will be fodder for later chapters.

I will not say much about Chapter Four, except that it is excellent. Dawkins provides an impressively lucid explanation of radiometric dating and its role in establishing the age of the Earth. I have seen many explanations of these ideas, but still found myself enjoying Dawkins’ lucidity.

In terms of the broader case for evolution this is another “setting the stage” chapter. It addresses the age of the Earth question, but mostly it is preparing a discussion of the fossil record. It’s great stuff, but I am now just over one hundred pages into the book and the case is still in a rudimentary state. I suspect that will change in the next chapter. Stay tuned!

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Comments

  1. #1 Mike Haubrich, FCD
    October 30, 2009

    Jason, I am at about the same place in the book as you are. I have been greatly enjoying it, too.

    While it may not likely convince committed creationists (of whatever stripe) those who pick it up to get more detail on why there is a “controversy” will certainly gain a great deal of appreciation for how the sciences have demonstrated the facts of evolution.

  2. #2 eric
    October 30, 2009

    Without any kind of choosing agent, those individuals that are `chosen’ by the fact that they happen to possess superior equipment to survive are the most likely to reproduce…

    Darwin considered competition to be a much stronger selective force than the general environment. I.e. your #1-3 stronger than #4. I’m thinking this was another thing Darwin got right, but does Dawkins say anything about it?

  3. #3 Bill Shipley
    October 30, 2009

    There were a few less than stellar examples that, with a little bit more work, could have been done much better. For instance, Dawkins uses the example of decreasing tusk size in elephants,due *presumably* by hunters, as an example of real-time evolution. However, there are much better examples. One is the decrease in body size in many commercial fishes due to overfishing with fixed-size nets. An even better recent example is the careful work documenting selection against horn size in BigHorn Sheep due to trophy hunting.

  4. #4 Ritchie Annand
    October 31, 2009

    I’m enjoying his book as well, but I must say that despite its lucidity, it lacks a great deal of spit and polish. There were numerous points throughout the book where I just found myself asking “why does he come up with this weird theoretical example? Why doesn’t he just ask around for a real example?” It would make his point more forcefully if he did so.

    It has the feel of a long series of interesting blog posts where he didn’t want to take too much of a break. A lot of potshots in there, too, some fully justified, some… belabored ;)

    I was hoping it would be more like the first hardcover edition of Ancestor’s Tale, but I’m still enjoying it :)

  5. #5 Andrew
    October 31, 2009

    I don’t know why we still refer to Darwin as if he is the ‘God’of evolution; His sketches clearly indicates that He was just thinking, not coherently but did a good attempt to think through how life could have started: Indeed evolution is like a tree but Darwin forgot the roots;
    Looking at a tree, it begins with the roots in a messy cob-web like structure so difficult to comprehend and unravel;
    It should now common knowledge that life could not have easily come from the unicellular organism.
    A prominent journal devoted an cover article on how darwin was wrong;The article was in newscientist dubbed’Uprooting Darwin’s tree’ Infact darwin’s tree did not have roots. It started from the trunk;
    The artclce is another demonstration of how complex the life is.
    see the article on http://www.newscientist.com/article/mg20126923.000-editorial-uprooting-darwins-tree.html

    AS a summary:
    New Scientist looks at how advances in molecular biology are turning the tree of life into a web of life.
    As researchers began comparing genes between species, especially among microbial species such as bacteria, amoebas, and archaea, they found that these creatures promiscuously engage in horizontal gene transfer (HGT). As the New Scientist reports:
    The true extent of HGT in bacteria and archaea (collectively known as prokaryotes) has now been firmly established. Last year, [researchers] examined more than half a million genes from 181 prokaryotes and found that 80 per cent of them showed signs of horizontal transfer.
    So the bottom of the tree of life is a messy web of life. But HGT doesn’t end with single cell microbes. As more and more plant and animal genomes have been sequenced, researchers have discovered that multicellular creatures also experience horizontal gene transfer. It turns out the hybridization, cross-breeding between species, is a major force driving evolution. For instance, wheat is the result of the combination of the genomes of three different ancestral grass species. And our species may be the result of interbreeding between the ancestors of chimpanzees and earlier human species.
    Viruses also carry genes between multicellular species. As the New Scientist notes:
    Other cases of HGT in multicellular organisms are coming in thick and fast. HGT has been documented in insects, fish and plants, and a few years ago a piece of snake DNA was found in cows. The most likely agents of this genetic shuffling are viruses, which constantly cut and paste DNA from one genome into another, often across great taxonomic distances. In fact, by some reckonings, 40 to 50 per cent of the human genome consists of DNA imported horizontally by viruses, some of which has taken on vital biological functions.
    Nevertheless, Darwin’s central insight regarding natural selection and descent with modification as being the origin of species remains firmly grounded. The New Scientist article concludes:
    …the tree concept could become biology’s equivalent of Newtonian mechanics: revolutionary and hugely successful in its time, but ultimately too simplistic to deal with the messy real world.

  6. #6 tyaddow
    November 2, 2009

    Thanks for blogging this. I’ve been doing more of a summary of it (I’m only up to chapter 5) since I have a lot of creationist family members who will never read the actual book. I’ve almost finished the book and I must say, it’s as enjoyable as many of his books. I look forward to the rest of your review…

  7. #7 Sigmund
    November 3, 2009

    Its a pity that Dawkins hasn’t kept up to date with modern molecular genetics. He occasionally comes out with examples or statements that sound ridiculous in the light of information we have learned in the past decade or two.
    For instance Dawkins uses DNA hybridization temperatures – essentially the zoo-blot principle, as an example of how to gauge the relatedness of different species. While factually correct it is not something that has been used in major laboratories for at least a decade, if not longer. There are far better modern techniques in use that he fails to mention.
    Two other points he uses tend to get on my nerves. First he used an example of a brachiopod that looks morphologically similar to a fossil species from tens, if not hundreds, of millions of years ago and states that they could probably interbreed if it were possible to introduce the two to each other.
    We know from molecular evolution that the differences accumulated would almost certainly make such matings unsuccessful (there will be too much accumulated differences in their DNA to successfully combine into a fertile or even viable progeny).
    The final disagreement is in his insistence that all change is simple microevolutionary discrete changes such that each species would find it easy to interbreed with its immediate ancestral type. Its become clear that this is not the case and that occasionally there are molecular barriers to this process – mainly in the form of chromosomal alterations. This is the reason why humans cant interbreed with chimpanzees. At some point in the evolution of many if not most species a chromosomal alteration would make interbreeding with the proceeding stage very difficult (although not completely impossible). Dawkins doesnt mention this point – and since he made the same mistake in ‘The Ancestors Tale’ I wonder if he has thought it through properly (or alternatively whether he thinks its too complicated for the public to follow).

  8. #8 Gerdien
    November 4, 2009

    It’s great stuff, but I am now just over one hundred pages into the book and the case is still in a rudimentary state. I suspect that will change in the next chapter.

    #4
    It has the feel of a long series of interesting blog posts where he didn’t want to take too much of a break.

    #7
    It’s a pity that Dawkins hasn’t kept up to date with modern molecular genetics.

    I finished the book and it never gets to the grits. Dawkins has not only not kept up to date with modern molecular genetics, but has not kept up to date – and moreover forgot some classical comparative anatomy. The total impression is of a book that has been written ‘on his brainstem’, without any thinking.

  9. #9 Jean
    January 14, 2010

    I really love your blog! I almost can not start my day without reading it. I hope you can provide resources links, etc. Thanks in advance.

  10. #10 Swiss
    January 17, 2010

    At first I admire Dawkins a lot, but not until his book was used to map the topography of intelligent design theory.

  11. #11 Glee Skin
    January 31, 2010

    I love Richard Dawkins’ RED QUEEN! Every time I share about book, it is always in my list.