Tuesday, 28 February 2012

Evolving Simple Complexity.

Airbus A320
Sitting inside a plane a few months ago I was struck by the similarity between aeroplanes and segmented animals. On a typical short-haul plane, once you're inside and looking down the plane you see a central aisle with rows of three seats on either side. Overhead is a row of lockers. There are rows of windows spaced evenly along the sides, with a few modified as emergency exits, etc.

If we could see the wiring for lights, in-flight entertainment, pipes for fresh air supply, emergency oxygen and so on, we would see this segmentation repeated. No doubt the same basic segmentation is repeated in the construction of the body of the plane itself, with superstructure, panels, etc. Running the length of the plane will be cables and wire for flight control, warning lights, etc, etc.

Compare this with an internal view of the skeleton of a python. See the basic similarity?

Python skeleton from the inside
The reason for this similarity is not a coincidence. It is easier to construct a series of identical or slightly modified modules and join them together to make a larger structure. In python embryology, where this process happens, the same genes with the same set of controls in the form of hox genes only needs to be repeated at each segment; to make a plane you only need to design a single row of seats, one set of overhead lockers, one window pane, one unit of lighting, fresh air supply, emergency oxygen, etc, then make a lot of them and fit them together.

So, this brings me in a roundabout way to the idea of complexity. Very generally speaking, as the so-called 'higher' animals evolved and more functionality was added so they apparently became more complex. But, this is largely illusory and in many cases actually false.

For example, does it add complexity to add an addition body segment to a python? One might as well argue that two pythons are more complex than one. Would it be a more complex aeroplane if an additional row of seats were to be added to the body, complete with all the accessory structures, leaving aside that it might need bigger wings or more powerful engines? Are two Airbus A320s more complex than one?

So, it should be fairly easy to see that, apart from a more complex (or is it just larger?) brain, there is no increase in complexity as humans evolved from the early hominids to modern Homo sapiens. There is no additional complexity to explain and certainly our DNA is no more complex and has no more information in it that that of Pan troglodytes (common chimpanzee), with whom we share 98.5% of our DNA anyway.

But, there are many examples of evolution evolving a loss of complexity. Indeed, the python itself lost complexity when it's ancestors lost their legs and shoulder and pelvic girdles with them.

Very many parasites have lost complexity during their evolution, especially parasitic worms, some of which have even lost their digestive systems and have become little more than machines for making more worms. See my blog "Intelligently Designed By A Loving God?" for examples of parasites.

And now here comes a bit that will really annoy creationists: humans, and all warm-blooded animals, are less complex than many cold-blooded animals. For example, some salamanders have vastly more DNA than we do. Some up to 30 times as much per cell.

The reasons for this are disputed, but one explanation, I think, makes a great deal of sense. A salamander needs its body to function over a wide range of ambient temperatures; warm-bodied creature have no such problem. All metabolic processes are essentially enzyme-controlled chemical reactions. It's a characteristic of enzyme-controlled reactions that they are optimal only over a very narrow temperature range, so salamanders need several different enzyme systems for the same basic process where mammals and birds only need one. So, salamanders need lots more DNA to produce all those different sets of enzymes.

Once our early ancestor, probably a small mammal-like reptile living between 30 and 70 million years ago, had evolved the ability to regulate their body temperature they could dispense with all those unnecessary enzyme systems which were now free to evolve into other systems or atrophy and the DNA could be lost or co-opted or become just junk, free to mutate away with no loss of function. But the main thing was that, with warm-bloodedness, our ancestors had become genetically less complex.

Here's an interesting database with comparative genome sizes for all sorts of animals. As you can see, in terms of genome size, the human genome at just over 3 million base pairs (Mbp) is nothing out of the ordinary for a mammal so, on the basis so beloved of information theorist creationists of 'increasing DNA complexity' being synonymous with evolution, humans are far from being the most complex and mammals are less evolved than many other orders.

Would an information theorist creationist care to explain how the second law of thermodynamics renders this evolution impossible, please? Preferably one who hasn't taken the Creationist Oath and so may not be trying to mislead us for money or political power.

Of course, this isn't a problem for the Theory of Evolution which is the scientific model for explaining the fact of evolution, because increasing complexity and relative genome size are not and never were part of the theory. Genes, and with them the species which carries them, evolve by differences in them carrying differential advantages in the given environment. Evolution by natural selection can explain the differences in the genome without resorting to magic. By contrast, creationists are left once again attacking a straw man which has only a tangential bearing on evolution and which is based, through ignorance or by deliberation, on a fundamental misunderstanding of the subject they are purporting to refute.





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3 comments :

  1. Hi Rosa,
    Interesting point that in some cases what passes for complexity is simply an increase in network size , more neurons , more genes, etc. I being an amateur enthusiast on evolution, complexity is one of the issues I day dream about. I realize that there is no goal to natural selection, and an animal is atleast as likely to decrease in complexity as increase it. But when there is genuine increase in incremental complexity ; is that just another variation within the population like the beak size of a finch. Or is that more rare , maybe mutation within the hox genes ?

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    Replies
    1. There are no rules. If increased complexity, or reduced complexity, however you measure it, gives more surviving genes in the gene pool then the population will have evolved, by definition. However, most evolution is about variations on a basic theme with no change in complexity.

      Delete
  2. Hi rosa, thank you for your great post

    ReplyDelete

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