Friday, October 17, 2008

Evolution, it's all about the genes ... not quite.

West Nile virus is a pathogen that causes fatal encephalitis in humans. A chemokine receptor (a type of receptor found on the surface of certain cells) CCR5 is critical for protection in humans. However, in predominantly Northern European populations a defective CCR5 allele (form of the gene) has been found. This defect is known as CCR5 delta 32.

Homozygosity (i.e possession of two defective forms of the gene inherited from each parent) for CCR5 delta 32 is significantly associated with high risk and a fatal outcome when it comes West Nile Virus.

Now, HIV also uses CCR5 as a co-receptor in order to invade its target cells and homozygosity for CCR 35 delta 32 is reported to provide strong protection against HIV infection. So those Europeans who are homozygous for CCR5 delta 32 (estimated at 10% of the population) have a strong protection against HIV but a weak resistance to West Nile Virus.

In a long term scenario with the uncontrolled and unchecked spread of HIV, you might reasonably expect the population to become predominantly homozygous for CCR 35 delta 32 i.e. to be brutal, they are the ones who are more likely to survive.

However, with environmental changes we are seeing the spread of West Nile virus further North and if it is uncontrolled and unchecked then you could reasonably expect a decline in the level of homozygosity for CCR 35 delta 32. Again, for rather brutal reasons.

I mention this to illustrate one point. Evolution is not independent of the environment; it is predominantly controlled by it. In an environment which is constantly changing, where strengths can become weaknesses and vice versa, the stability of a complex system often depends upon diversity. Variability in the genetic make-up and the phenotype of a population can often save it.

In the current unstable economic climate, it is often tempting for a company to retreat to core activities and minimise diversity. This is probably the last thing you should be doing.

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