Evolution Through the Looking Glass

01 March 2011
Posted by Anders Aufderho....

Darwin's theory of evolution by natural selection is one of the most well known theories in science and in the 150 years it has explained not only the fundamentals of genetics but also many of the nuances of human behaviour.

However despite its ubiquity, there are still all sorts of unresolved issues that evolutionary biologists have encountered when interpreting the theory. One of these issues concerns itself with how life adapts to its environment. A quick look at the world's ecosystems seems to tell us that wildlife is well adapted to everything around it with animals and plants each having their own evolutionary niche. However, this view presents a bit of a problem when it is combined with evolution. For example, if species are really so well adapted to their environment then what is the point of natural selection?

On the other hand, if species are constantly evolving, does that mean that they are not really adapted to their environments at all? The answer to this little conundrum has been linked with a passage from Lewis Carrol's "Through the Looking-Glass" when Alice, the protagonist meets the character of the Red Queen:

"Well, in our country," said Alice, still panting a little, "you'd generally get to somewhere else -- if you run very fast for a long time, as we've been doing." "A slow sort of country!" said the Queen. "Now, here, you see, it takes all the running you can do, to keep in the same place. If you want to get somewhere else, you must run at least twice as fast as that!"

Alice discovers that she needs to run as fast as she possibly can just to stay in the same place. It seems a bit nonsensical to link this strange story to natural selection but the evolutionary biologist, Leigh Van Valen did just this, coining the term "red queen theory" to explain that all species exist in an environment that is constantly changing and that in order to survive they need to adapt with it.

A good way to think about this is by considering the relationship between prey and predator. As the gazelle evolves to become better at avoiding lions, the lions get better at catching them. This leads to what Richard Dawkins has called the "evolutionary arms race". Just like in a military arms race where nations build greater and more terrible bombs, missiles, helicopters and submarines, species are forced to constantly better themselves to survive a changing hostile environment. What this tells us is that a species that adapts faster is more likely to survive.

The Red Queen Theory also surprisingly answers some other questions, such as why species have sex. To most of us this seems like a rather strange question to ask but in many ways, sexual reproduction is not the obvious way to do things. Only the female of the species is able to reproduce while the males really tend to be rather useless as they don't reproduce and don't tend to contribute much to the offsprings' upbringing (I say this without reference to any gender stereotypes that might come to mind - its just a observation of nature). Furthermore in many species such as lions, the males are a direct threat to live young as they are known to kill offspring that aren't their own. So from a theoretical perspective, reproduction without sex, by multiplying like bacteria for example might seem a more attractive idea.

However sex does give us one positive advantage. When faced with constantly changing threats such as parasites, we need to adapt much faster. Sex allows us to do this because by mixing our genes we become more genetically diverse. If our genes serve us well in this generation against one parasite, its all the more likely that a new parasite will evolve to deal with this in the next generation.

We're forced to adapt to constantly changing threats and it's only by having the genetic diversity that sex gives that allows us to constantly improve our defences. This might seem like a very speculative theory but it would be wrong to say that it can't be demonstrated. In fact, in 1990, a team from Rutgers University tested the theory by observing groups of fish known as Topminnow. Topminnow are a curious type of fish because some populations reproduce asexually and others produce sexually, providing a perfect opportunity to test these ideas. Topminnows are known to be under constant attack by a parasitic worm that causes a condition called black spot disease. The study showed that black spot disease was significantly more common in the populations which didn't reproduce sexually, a finding which seems to confirm the Red Queen hypothesis.

As well as explaining adaption and sexual reproduction, Red Queen Theory has also often been thought to explain the emergence of new species. Just like the military arms race in the cold war ended with the collapse of the Soviet Union and the emergence of new republics, it has often been thought that the evolutionary arms race will continue until a species is unable to keep up and new species start to emerge. This seems like a perfectly simple idea so far, but to paraphrase the satirist H. L. Mencken "there is always a well-known solution to every problem; neat, plausible, and wrong."

The problem here is when comparing this idea to the evidence in the fossil record; we don't come anywhere near to predicting the rate at which new species should appear. A study in January 2010 by a team at the University of Reading may well have provided an alternative solution. By running mathematical models on data of around 100 genetic groups of animals, they showed that new species are more likely to emerge because of random events, ranging from the rather subtle changes, such as genetic alterations in a species' mating patterns to the more profound, such as the appearance of mountain ranges, rivers and islands. So rather than thinking of species as running out of energy in a Red Queen race or indeed, failing to keep up with Dawkins' arms race, it seems like it might be more of a case of happy accidents.

Natural selection has always been seen as the main reason behind why new species arise and this recent research is likely to ruffle a few feathers in the evolutionary biology community. Of course, just one paper isn't enough to completely reshape a theory. However if further studies do show that the emergence of new species is simply down to localised random events it will truly be a paradigm-shifting discovery that opens up all sorts of new questions. If natural selection isn't the reason for the emergence of new species then what kind of role does it have to play in evolution? Time will tell but if these recent results are shown to be solid, it will mark a significant milestone in how we understand the origin of species.

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