The Greatest Show On Earth - A Book Summary In Many Parts

by cofty 81 Replies latest watchtower beliefs

  • cofty

    Part 10

    Chapter 5 –Before Our Very Eyes... continued

    Evolution works by the non-random selection of random mutations of genes. The work that has been done by Dr Lenski and his team is surely one of the clearest demonstrations of the power of this process. E.Coli is one of the commonest bacterium on earth, there is around 100 billion billion of them in the world at any given time and around 1 billion of them in your gut right now. Most of the time they cause no problem, until a new strain wreaks havoc on its hosts digestive system. If we assume the the probability of a particular gene mutating to be 1 in a billion the size of the population is so high that just about every gene in the E.coli genome will hav emutated somewhere in the world every day.These bacteria reproduce asexually through simple cell division so Lensky began by cloning a population of genetically identical individuals. Next he divided them equally into 12 identical flasks each of which contained the same nutrient broth to produce 12 tribes of E.Coli, which have remained totally separate for 21 years and counting.

    Every day 12 new flasks are prepared with the very same broth consisting of a mixture that contains glucose that they feed on, and citrate, which they are not able to eat, but more on that in a minute. Exactly 1% of the population of each flask is removed daily and put into the new flasks. That means that there are now 12 lines of 7000 flasks each stretching way back the beginning if the experiment. The 12 tribes were sampled at intervals to see how they were changing and, at strategic points, samples were frozen to provide living “fossils” that could be resuscitated for comparison with later generations.

    E.Coli don’t waste any time in reproducing, averaging between 6 and 7 generations per day. That means that Lenski has bred 45,000 generations of bacteria. If we were to scale that up to human generations it would take us back a relatively modest (in evolutionary terms) 1 million years.

    Every day the same pattern was observed, the population of the lucky 1% would initially soar, then as the food began to run out, it would level off as starvation set in: Boom and bust, day after day for 45,000 generations. The question to be answered was whether or not the bacteria would evolve, and if so would they change in similar or different ways?

    The expectation was that if a bacterium underwent a mutation that allowed it to make better use of the limited food supply then it would be favoured by natural selection and in time the mutant would take over the tribe. Well this is exactly what happened in all 12 tribes, every one got better than their ancestors at exploiting the available glucose. What was really amazing was that they all got better in different ways; they each discovered their own novel mutations to improve their fitness.

    In each case populations began to grow faster and the average body size of the bacteria grew. Most of this growth happened over the first 2000 generations after which it began to plateau. The graphs of their growth all fit a hyperbolic curve beautifully, but each curve follows a slightly different path as different mutations occur at different times in each tribe.

    The graphs also show an exception to this rule of diversity however. Two tribes appeared to follow identical rates of growth over 20,000 generations. Lenski and a team of scientists investigated by studying the DNA of the populations concerned. The astonishing result they discovered was that the same 59 genes had undergone the same changes in both tribes. This is truly staggering!

    The genome of the E.Coli bacterium contains 4,403 genes made up from 4,639,221 base pairs. So what are the chances of the same mutation happening independently in 2 populations? Fairly low but not unreasonable? So what if we find 2, 3 or 4 mutations the same? Now it’s getting remarkable. But 59 changes in the same genes in both populations? That is the kind of incredible odds that creationists get so excited about. How many analogies are there – too many to count! Monkeys writing Shakespeare, jumbo jets in scrapyards, the list is endless. But here is an event or series of events with odds against that are stupefyingly large, odds that would beggar belief if it were not for the fact that it actually happened in the lab and the evidence is there for any competent scientist to examine.

    This is the whole point about the power of natural selection, it achieves things that appear impossible through the step by step accumulation of favourable changes. Both tribes had independently discovered the same 59 mutations out of all the millions of possible changes.

    At generation 33,000 something else happened that was utterly remarkable, something that strikes at the very heart of the “intelligent design” movement. As the population of bacteria in a flask grows the liquid becomes increasingly cloudy. Each day the “cloudiness” or optical density (OD) is carefully measured and recorded. The OD of one particular tribe, named Ara-3, had been coasting along at a level of 0.04 similar to the other 11, when it suddenly it went into vertical take-off growing six fold to an OD level of 0.25 After a few days the population level stabilized and all future generations of this tribe, and this tribe alone, achieved the same results.

    So what was going on? Remember I mentioned earlier that the broth contained citrate? Well it turned out that Ara-3 had worked out how to metabolise citrate and therefore had loads more food to eat than the other 11 tribes. So when the other tribes were beginning to starve after the glucose ran out this tribe was still enjoying a bonanza.

    Lenski worked out that this change was not likely to be the result of a single mutation, as it should have been discovered by other tribes as well. Neither was it a series of mutations of the sort where each change builds on the previous. That would not be rare enough to account for the dramatic uniqueness of Ara-3. What was needed was a combination of mutations of the kind that creationists call “irreducible complexity” where 2 or more mutations are required before there is any improvement whatsoever.

    One of Lenski’s students, Zachary Blount, ran a gruelling set of experiments involving 40 trillion E.Coli cells from across the generations to discover what had actually happened. The magic moment turned out to be around generation 20,000. Thawed out clones dating from before that point never discovered how to use citrate, they were just like the other 11 tribes. Those that dated from after that generation showed increased probability of subsequently evolving citrate capability. A mutation had occurred that conferred no advantage the bacterium but it primed it to take advantage of a later mutation. Not only does this show new information entering genomes - something the likes of John Mackay endlessly asserts is impossible - not only does it demonstrate the power of natural selection to put together combinations of genes that, by the naïve calculations so beloved of creationists, should be tantamount to impossible; it also undermines their central dogma of “irreducible complexity”.

    Lenski's research shows, in microcosm and in the lab, massively speeded up so that it happened before our very eyes, many of the essential components of evolution by natural selection: random mutation followed by non-random natural selection; adaptation to the same environment by separate routes independently; the way successive mutations build on their predecessors to produce evolutionary change; the way some genes rely, for their effects, on the presence of other genes. Yet it all happened in a tiny fraction of the time evolution normally takes.

    In 2006 Lenski was rewarded for his outstanding work with his election to the United Sates National Academy of Sciences.

  • cofty

    Part 11

    Chapter 5 –Before Our Very Eyes... continued

    I want to deal with a common misunderstanding of evolution that arises from a sort of shorthand that it is often necessary to use in describing specific examples.

    In the text above regarding Lenski's E.coli I said a number of times that specific strains had "discovered" certain survival strategies. Of course bacteria don't actually discover anything. So-called superbugs like MRSA have not adapted to their environment or learned how to survive antibiotics.

    Mutations are entirely random, most are neutral and many are harmful. When a change occurs that gives an individual an advantage over its rivals it is more likely to survive and breed successfully. The mutation that gave it an advantage, however small, gets passed on and become more common in the gene pool. This is why seemingly impossible odds are defied by evolution, as small incremental steps are accumulated one at a time.

    Nothing learns how to evolve, nothing adapts to its environment - all of that is simply a quick way of describing a much more wasteful process.

    Dawkins concludes this chapter with another fascinating example - this time a more attractive one than E.coli

    In common with many creatures there are two conflicting evolutionary pressures pulling male guppies in opposite directions. On the one hand it is a big advantage to stand out from the crowd with bright and attention grabbing patterns to attract female guppies otherwise your genes will not be passed on to the next generation. On the other hand it is very advantageous to disappear into the background and avoid the attentions of predator fish that are on the prowl for a free lunch.

    Dr John Endler of Exeter University studied wild guppies living in mountain streams in Trinidad, Tobago and Venezuela. He noticed striking differences between populations depending on the existence of predators, in some the males were as bright as in any captive aquarium, in others they were only slightly less drab than the females.

    Endler decided to set up an experiment to see how much and how quickly they would adapt to varying conditions. In a large greenhouse he set up ten ponds, five of which had course, pebbly gravel and five had finer, sandy gravel. Guppies were assigned randomly to the various tanks and allowed to breed freely for the first six months. After that Endler did something very subtle. Into four tanks, two with course gravel and two with fine, he introduced a predator fish, the pike cichlid. In another four tanks he put six weak predators each, known as killifish. In the other two tanks he put no predators at all.

    After five months and again another nine months later he took a census of all the ponds and counted and measured all their spots. Even after such a short time the results were spectacular. Originally there was a large variety among the fish in the experiment. During the first six predator free months the mean number of spots shot up in response to selection by females. Then when the predators were introduced there was a dramatic change. In the four tanks with the cichlids the number of spots plummeted. In the tanks with the weak predators and the tanks with no predators the number of spots continued to increase, it reached a plateau by five months and stayed high.

    Spot size told an interesting story. In the tanks with predators, whether weak or strong, the fish in the ponds with coarse gravel developed big spots and vice-versa. However in the tanks with no predators the opposite was observed, fine gravel resulted in male guppies with big spots and coarse gravel tanks became populated by fish with small spots. In this way they were even more conspicuous to the females by standing out from the background.

    Endler then attempted to repeat a similar experiment in the wild. He went to a stream that contained the dangerous cichlids and removed the guppies, which were predictably drab, to a safe part of the river and left them to get on with living and breeding. Twenty-three months later he visited them again and found his lab experiment had been successfully repeated in the wild, the males had become more brightly coloured.

    Nine years later David Reznick of the University of California went back to Endler’s stream to see what the longer-term results would be. The males were now very brightly coloured but that was not all. Remember the foxes of chapter three and how artificial selection for tameness pulled in it’s wake a whole cluster of other changes, well a similar thing happened with the guppies under natural selection. Colour difference was only the tip of the iceberg. With low-predation guppies also reached sexual maturity later, they were larger, the produced litters of young less frequently and their litters were smaller with larger offspring. All of these changes had taken place at a spectacular pace and demonstrate evolution before our very eyes.

    So maybe you are thinking that the kind of changes we have been talking about so far are not a problem to creationism, after all guppies with big spots and guppies with small spots are still guppies right? Well in chapter 6 Dawkins begins to take bigger steps as we look at the much misunderstood topic of missing links...

  • ammo

    Thank you for taking the time to put all this down.

    It makes lot of sense.

    I will be ordering a copy of The Ancestors Tale, the way you have put all this together is not only easy to grasp (well kind of) it makes me want to explore the whole evolutionary process..... very very interesting.

  • botchtowersociety

    Oh cool. I love Bible Study classes delivered with evangelical zeal, especially when they are rehashed from defunct jwsupportforum threads. You can get the book, by the way, for a ten spot. The real thing, by God! Awesome as a guppy's tail, and you don't have to wade through maggots to get to the flies.

  • cofty

    Thanks Ammo that makes it worthwhile.

    The Ancestor's Tale is Dawkins Magnum Opus - if you can find (and afford) the big hardback version its fantastic. I settled for the paperback but I borrowed the big version once from the library.

    Reading science and evolution/genetics is the most interesting thing I have ever done.

    BTS - I explained my reason for doing this in my OP. There are plenty lurking JWs who couldn't dare buy a book on evolution. JWS is gone for good and I decided it was worthwhile doing it again.

  • Hortensia

    It is worthwhile! People who aren't interested don't have to read the thread.

    One of the hardest things for me to get when I first looked at evolution was the complete randomness of it. I think it was because the way people talk about evolution makes it sound as though there is some kind of direction driving evolution. Recently, for instance, articles on the bbc said that some ancient animal (can't remember which) developed feathers for sexual display rather than flight. The truth is that feathers developed, kind of randomly, but they turned out to be useful for sexual display. Big difference.

  • botchtowersociety
  • cofty

    Thanks BTS but I'm guessing more lurking JWs and ex-JWs who hang on to creationism will be made to think by this thread than by posting a link to an off-site summary.

    My summary has pretty pictures.

  • botchtowersociety

    The format is tolerable, and the full book is available here (including pretty pictures):

  • still thinking
    still thinking

    I'm keeping this thread to read alongside the book (which my partner has now pinched off me so I have to wait to get it back)

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