Evolution of a peeve

I am often peeved at the way evolution is presented and explained. It is bad enough when lay people get it wrong, but it is intolerable when science commentators and scientists explain it sloppily.

First things first, the term evolution comes from the Latin evolutio meaning unrolling. In modern English vernacular is has the generally understood meaning of a progressive change in a particular direction - the general direction being understood as being better or more advanced from the previous form.

This is a horrible term to use for the process Darwin described because it comes with preconceptions that are simply untrue - namely that of a progressive change in a particular direction for good (as opposed to its antonym, devolution).

It also does not help that so many science commentators (all I would say) and scientists (most, I would say) continue to perpetuate this inaccuracy. The say things like, "Plants evolved colourful flowers to attract insects," or "Organisms evolved camouflage to evade predators," or "The species evolved to adapt to its environment."

All three of those statements are totally and completely false and dangerous because they put the cart before the horse and presume some sort of deliberate and intentional progressive development. Using the terms evolution and adaptation are, in my opinion, wrong and dangerous. We should instead be using an expression like, "propagation of advantageous survivability traits", which is a far more accurate description of the process going on.

Every organism has genetic variations from its predecessors, some are simply the result of mixing characteristics (we get half our DNS from our mother and half from our father), there are transcription errors (when a piece of DNA is not properly copied - commonly called a mutation), and finally there are transpositions (this is when a piece of DNA from one strand is grafted onto another. Our DNA contains, not necessarily identical, copies of genes on both strands, but sometimes during the transcription process, a copy of a gene may be moved from one strand to another, thus introducing a change). Most changes are harmless or provide no survival benefit - i.e. there is no reproductive benefit for you to passing on your genes and so those changes simply get lost in the wash of genetic information out there. Some changes are not harmless and severely curtail your survivability - these usually are quickly eliminated from the gene pool. However, there is an interesting class of traits that are fatal (for example sickle cell anemia), which have not been excised from the gene pool. Why? Because having one defective gene and one good gene confers a survivability advantage. People with a single sickle cell anemia gene are more resistant to malaria than people without it.- consequently, they get to live to sexual maturity and reproduce.

Plants did not evolve colourful flowers to attract insects. Plants which had a mutation which gave them colourful flowers attracted more insects. Consequently, the insects preferred to visit the colourful flowers, thus pollinating them, this allowing them to propagate. The plants with dull drab coloured flowers, being ignored by the insects, died out.

Organisms did not evolve camouflage to evade predators. Organisms which were harder for predators to find, had a higher survival rate, consequently they passed their characteristics on to their descendents. Those that did not hide well from predators where soon gobbled up and their genes removed from the gene pool. A rather recent example of camouflage evolution was in Great Britain, where a species of moth came in two colours: grey and black. Before the industrial revolution, the grey moths were the dominant ones, since they blended nicely into the bark of trees as they rested, the black ones stood out and got eaten up. When lots of coal was being burnt and everything was covered in soot, the black ones had the advantage and the grey ones became rare.

A species does not evolve to adapt to its environment. Either the species, or some members of the species are able to survive in the new environment or not. If not, the species dies. Suppose there is an earthquake and a river is diverted as a consequence. All the mice living downstream suddenly find themselves scarce of water. They do not suddenly start changing and learning to live with less water (which would be adaptation). Those who can't live with less water die. Those, assuming there are some, who, perhaps owing to a small genetic variation which permits them to survive with less water, may continue to survive. When water was plentiful, they had no survival advantage over the other mice. Now that water is scarce, they do. The mice did not adapt, those that were able to survive and pass on their genes survived, the others died. Genetic variation and mutation are rarely isolated to a single effect. Typically there is a cascade effect which may include morphological changes as well - for example, Down's Syndrome results when there is excess (duplicated) genetic material on chromosome 21. This results in the over expression of certain genes, resulting in morphological, as well as other consequences.

This is not to say that there are no unanswered questions with evolution, there are plenty, but as a mechanism which describes the transmission of common traits to descendents which confer the ability to survive it works very well.

Darwin's vision of a slow and steady progressive evolution is archaic and is better replaced with Niles Eldrege's and Stephen J. Gould's notion of punctuated equilibrium: for large periods of time, there is little or no change in organisms, however, during times of great environmental or ecological stress, evolution occurs quickly as those who cannot survive die and those that can pass on survivability traits to descendants. Add in some mutations and you have a recipe for rapid change. Which organisms are least likely to survive? Ones which reproduce slowly, they cannot introduce genetic diversity fast enough for natural selection to take place. That is why dinosaurs are extinct. This is why large mammals are dying off, they cannot cope with rapid changes. There is probably some upper limit on how fast change can occur before an organism is unable to cope with the necessary changes and dies off. Also, even if an organism reproduces quickly (say mice), it may still die out if the change is too rapid (for example, if the aforementioned river increased its flow toward the mice and flooded them, I would expect them to drown and not adapt - since I consider it unlikely that there are any mice capable of underwater respiration).

As for unanswered problems? Consider what good a quarter trunk or half trunk is for an elephant. An elephant's trunk is very complex. How it could evolve slowly or in fits and starts is a mystery. Of course, we could always consider the tapir and its elongated snout as a starting point for our question.

The next time someone tells you, "Abc evolved xyz in response to ijk", tell them they are wrong. Tell them that "The selection pressure introduced by ijk caused those abc organisms with the characteristic xyz to survive. Those that did not have characteristic xyz died out."

Image nabbed from here.

[Updated 06-Septemeber-2006 to correct typos (including one caught by Nathalie).]