Complexity not so costly after all, analysis shows

Sep 27, 2010

The more complex a plant or animal, the more difficulty it should have adapting to changes in the environment. That's been a maxim of evolutionary theory since biologist Ronald Fisher put forth the idea in 1930.

But if that tenet is true, how do you explain all the well-adapted, complex organisms---from orchids to bower birds to humans---in this world?

This "cost of complexity" conundrum puzzles biologists and offers ammunition to proponents of intelligent design, who hold that such intricacy could arise only through the efforts of a divine designer, not through natural selection.

A new analysis by Jianzhi "George" Zhang and coworkers at the University of Michigan and Taiwan's National Health Research Institutes reveals flaws in the models from which the cost of complexity idea arose and shows that complexity can, indeed, develop through evolutionary processes. In fact, a moderate amount of complexity best equips organisms to adapt to environmental change, the research suggests. The findings will be published online in the during the week of Sept. 27.

The study focused on a genetic phenomenon called pleiotropy, in which a single gene affects more than one trait. Examples of pleiotropy are well known in certain human diseases, and the effect also has been documented in experimental animals such as . Biologists also recognize its importance in development, aging and many . However, pleiotropy is difficult to measure, and its general patterns are poorly understood, said Zhang, a professor of ecology and .

Even so, scientists have developed mathematical models of the phenomenon, based on certain assumptions, and have made predictions from the results of the models. Zhang and coworkers decided to test the assumptions against real-life observations by analyzing several large databases that catalog the effects of specific on traits in model organisms (yeast, roundworms and mice). Each data set included hundreds to thousands of genes and tens to hundreds of traits.

For simplicity, mathematical models of pleiotropy have assumed that all genes in an organism affect all of its traits to some extent. But Zhang's group found that most genes affect only a small number of traits, while relatively few genes affect large numbers of traits.

What's more, they found a "modular" pattern of organization, with genes and traits grouped into sets. Genes in a particular set affect a particular group of traits, but not traits in other groups.

In addition, the researchers learned that the more traits a gene affects, the stronger its effect on each trait.

All of these findings challenge the assumptions underlying the classic mathematical models that suggest complexity is prohibitively costly.

When Fisher first wrote about the cost of complexity, he argued that random mutations---which, along with natural selection, drive evolution---are more likely to benefit simple organisms than complex organisms.

"Think of a hammer and a microscope," Zhang said. "One is complex, one is simple. If you change the length of an arbitrary component of the system by an inch, for example, you're more likely to break the microscope than the hammer."

In a paper published in 2000, evolutionary geneticist H. Allen Orr of Rochester came up with additional reasons for the cost of complexity. According to his model, even if a mutation benefits a complex organism, it's unlikely to spread throughout the whole population and become "fixed." And even if it does that, the advantage of the mutation is likely to be small.

By incorporating a more realistic representation of pleiotropy, Zhang's analysis found the reverse of Orr's arguments to be true. Although Fisher's observation still holds, reversing Orr's assertions minimizes its impact, thus reducing the cost of complexity.

Further, the analysis showed that the ability of organisms to adapt is highest at intermediate levels of complexity. "This means a simple organism is not best, and a very organism is not best; some intermediate level of complexity is best in terms of the adaptation rate," Zhang said.

The new findings help buffer evolutionary biology against the criticisms of intelligent design proponents, Zhang said. "The evolution of complexity is one thing that they often target. Admittedly, there were some theoretical difficulties in explaining the evolution of complexity because of the notion of the cost of complexity, but with our findings these difficulties are now removed."

Explore further: Evolutionary study aids battle against parasitic diseases

More information: Proceedings of the National Academy of Sciences: www.pnas.org/

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User comments : 5

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Eikka
not rated yet Sep 28, 2010
Why would you need to defend evolution against religious sophism?

No matter what or how you explain, the believers are not going to change their minds because the point of faith is to blindly believe in what you want to be true, so you can justify your actions accordingly.

The whole point of ID is to ask questions and make statements in a way that makes the scientist go "Hmm... I don't know how to answer to that", so they in turn can go "A HA! So God did it! I mean... a Designer did it."
Donutz
not rated yet Sep 28, 2010
The whole point of ID is to ask questions and make statements in a way that makes the scientist go "Hmm... I don't know how to answer to that"


except that scientists have this nasty habit of going off and trying to actually resolve the question. Then they come back with a reasonable answer and the IDer says "Look! they keep changing their minds! It's all crap!". This is possibly the biggest criticism of theists is that they look upon the idea of modifying theories to fit facts and to answer criticisms with what can only be described as contempt.

bfast
not rated yet Sep 28, 2010
Eikka, Donutz, Let me suggest that you have IDers in a box that is much too small to fit the real world of IDers.

It may be true that the dozen or so public ID proponents are unlikely to be swayed by facts. There are, however, many IDers, such as myself, who weigh every new piece of data in light of the data that has gone before. It is for people like me that the science needs to be done, and the science needs to be published in the public forum.

If Darwinism is correct, and if the challenges raised by IDers are seriously met, it won't cause the Dembskis and Behes of the world to abandon their position, but it will give them a smaller audience.

If y'all would quit disrespectfully dismissing IDers, and give us the benefit of genuine discussion, you may be shocked to find that you will join the ID camp. After all, maybe it is you that has the head in the sand.
Eikka
5 / 5 (1) Sep 28, 2010
you may be shocked to find that you will join the ID camp


What sort of ID are you talking about? The kind that claims that complexity can't be brought about by simpler things, so complex things like life must have a designer?

Then who designed the designer's designer's designer? (And other ontological problems of ID)

Seadiver
not rated yet Oct 16, 2010
To Eikka, He means like the information-carrying molecule DNA, because its purpose is to carry the structural plan for the whole organism so reproduction can happen, but it couldn't exist independent of the organism (needs the support hardware). [An even stronger point, to me, is the source of the information itself.]

As to where the designer came from, that's really a question about the meaning of time. Being a creature bound by time it is hard for me to think out of that box: we think in terms of a previous cause for a thing (previous in time).

But if there is a non-material creator of matter, then that creator would exist before the creation of matter, and therefore before (outside of) time, because time is a function of the movement of matter. So time would begin when the creator made matter and started it moving.

But before time there could be no meaningful sequence, at least as far as we can understand, so there would not need to be a predecessor of the designer.