Fiendish wheat genome reveals grain's history : Nature News & CommentIt's been another bad week for the Intelligent Design industry. No wonder their secretive five year 'Wedge Strategy' is now well into it's sixteenth year, during which the number of non-believers in the USA has gone up from about 4% to about 20%, conservative Christianity has become the preserve of the white right fringe and court after court has thrown out their attempts to subvert the Constitution and smuggle fundamentalist Christian extremism into the US public school system disguised as science.
As I explained in a recent blog about the genome of the Norwegian spruce (Christmas tree), one of their lines of attack on Darwinian Evolution is that it always moves from the simple to the more complex - something they imagine they can prove to be impossible with a misrepresentation of the Laws of Thermodynamics. They also habitually misrepresent evolution theory as a theory about the origin of humans. This parody puts humans at the top of some notional 'ladder of evolution' with lesser species arranged on the rungs below and making it look like the TOE says one species (represented by a single animal) spontaneously mutated into another in a single act of speciation (curiously, whilst leaving obligatory fossilised examples of 'transitional forms' as it did so).
So, taking these two together, creationist pseudo-scientists are in effect arguing the the TOE claims that humans are the most complex of all species being the most highly evolved. Evolution theory says nothing of the sort, of course. It's simply that creationists have constructed a ludicrous straw man to attack rather than deal with the real Theory of Evolution. More to the point, the idea that an increasingly complex genome means an increasingly complex organism is nonsensical.
Now, following on from the revelation that the Norwegian spruce has a genome seven times larger than that of humans and a functional (i.e. protein-coding) genome almost twice the size of our 17,000 functional genes, we have news that bread wheat (Triticum aestivum) has a genome more than five times as large as the human one.
Wheat got its large genome by a different route to that of the Christmas tree where the cause was a normally-corrected mistake in the DNA copying mechanism common to most species but in which the error-correction mechanism is broken too. So, over about 120 million years the Christmas tree has been accumulating an ever-expanding genome all to no discernible purpose. Not only would a hypothetical designer have made a fundamental error in the DNA copying mechanism but it would also have designed a broken mechanism for correcting its earlier error. In the case of wheat, the genome came about by a doubling of the number of chromosomes to give a tetraploid form (i.e., one with four copies of each chromosome instead of the normal two) when two related normal diploid species hybridized to give a new species. This form then hybridized in another rare example of spontaneous speciation by hybridization when the tetraploid form again hybridized with another related diploid form to give a hexaploid genome containing six copies of each of seven chromosomes, giving 42 chromosomes in all divided into six sub-genomes.
This is believed to have happened somewhere in the Tigris-Euphrates valley and was the environmental change which probably enabled wheat-based agriculture and urbanization to occur. Bread wheat now feeds 30% of the worlds people and provides 20% of our calories. I've already blogged about this rare example of evolution by hybridization so I'll resist the temptation to upset creationists with is again.
I'll simply point out how the example of bread wheat with its hugely complex genome not only represents all the problems for creationism that I outlined with the Christmas tree example but also gives the lie to another of their lines of attack - the idiotic claim that mutations are always harmful and so Natural Selection will never have an advantageous mutation to 'favour'. Given that bread wheat has six copies of every gene without even considering any gene duplication within each sub-genome, all these spare copies are free to mutate without having any detrimental effect whatsoever. If, however, one of these mutations gives a significant advantage, Natural Selection will ensure it spreads throughout the genepool.
Yes, it's been another bad week for creationism. They must pray for the day when scientists stop producing all this evidence against their daft notion.
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I'm so glad, Rosa, that you have a pedagogic talent coupled with the abilities of well-written conciseness and a high readability factor. I learn a lot by following your blog. It's a pity that creationists because of confirmation bias and the like seemingly are unable to learn from your lessons of evolution and mutations.
ReplyDeleteYou're so right, Rosa, when you conclude that creationists against their better judgement continue to make "the idiotic claim that mutations are always harmful and so Natural Selection will never have an advantageous mutation to 'favour'."
Talking of mutations I can highly recommend this article: http://rstb.royalsocietypublishing.org/content/365/1544/1153.full
It's a very long article and not easy to understand if you,re not a geneticist specialized in the field of mutation. None the less I hope many of your followers will read it.
Hera are nine appetizers (I hope) from the article, chosen by me since the facts presented are relatively easy to understand:
1) [M]utations are essential raw materials for evolution.
2) We review work that (...) predict how mutations interfere with each other.
3) Based on their effects on fitness, mutations can be divided into three broad categories: the ‘good’ or advantageous that increase fitness, the ‘bad’ or deleterious that decrease it and the ‘indifferent’ or neutral that are not affected by selection because their effects are too small.
4) While this simplistic view serves well as a first rule of thumb for understanding the fate of mutations, research in recent decades has uncovered a complex web of interactions.
5) For example, (i) the effects of mutations often depend on the presence or absence of other mutations, (ii) their effects can also depend on the environment, (iii) the fate of mutations may depend on the size and structure of the population, which can severely limit the ability of selection to discriminate among the three types (making all seem nearly ‘indifferent’), and (iv) mutations' fate can also depend on the fate of others that have more pronounced effects and are in close proximity on the same chromosome.
6) The dynamics of mutations are dominated by chance, yet we search for general principles that are independent of particular random events.
7) Mechanisms exist to control the frequency of transposition events to limit the damage from resulting deleterious mutations.
8 ) Of course not all mutations are harmful, and the occasional fitness increasing mutations drive adaptive evolution.
9) [Examples of how mutations can drive adaptive evolution:] [C]ompensatory mutations that at least partially repair some harmful effects at the molecular level (...) [R]esistance mutations that are part of biological arms races between hosts and parasites. (...) [M]utations that enable a species to start expanding into a new ecological niche.
Thanks again, Helmer.
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