In a lovely little example of human intervention becoming a factor in evolution I read about today, it appears the bollworm moth has developed a resistance to Bacillus thuringiensis (Bt). "WTF?" you might say - well, Bt is a common soil bacterium that is well known for its insecticidal properties, especially against moths and butterflies. We have used it in many genetically modified plants to stop pests, such as the Bollworm Moth (cotton plant eater) and the Tuber Moth (muncher of potatoes), from destroying our lovely plants and veges.
I think its important to say a little bit about GE here, and say that I support GE, but I also support the requirement for strict controls. We need to balance the need for the advancement of genetic based science and safety of the general populous. Some people advocate a wholesale ban on GE food, and others say we should just go for it - I reckon neither position is correct, but there should be a happy middle ground.
Anyway, it has become apparent that the Bollworm moth has produced a new population that is slowly increasing in size, that is resistant to the effects of BT. Although its interesting how fast this happened since the wholesale adoption of the GE cotton plants, its not surprising in the least. A simple fact of evolution is if you put some kind of life and death pressure on a population, it will likely adapt to avoid that pressure. In this case, the Bollworm moth population was originally dominated by individuals who were not resistant to BT, as it was not a major pressure on their environment. With mans intervention, and the massive introduction of GE crops using the BT gene, that pressure became critical to their survival. As the non-resistant bugs died out, they left the individuals who were resistant to BT and they mated, were more successful in their environment, and are now dominating the Bollworm moth gene pool.
What's that got to do with elephants you ask? Well, a similar thing seems to have happened there too. With the mass killings by ivory hunters, elephants with large tusks were no longer successful in the elephant population (cause they were being shot). Tuskless elephants were not targeted, so they became more dominant in their population. This is a lot slower than the moths as their life cycle is slower, so new generations take longer to produce offspring which carry the selected genes.
"African ivory hunters, by killing only tusked elephants, have given a much larger chance of mating to elephants with small tusks or no tusks at all. The propagation of the absent-tusk gene has resulted in the birth of large numbers of tuskless elephants, now approaching 30% in some populations (compare with a rate of about 1% in 1930). Tusklessness, once a very rare genetic abnormality, has become a widespread hereditary trait." (Wikipedia)
Again, when you line up the facts this is not surprising. We see it every day in all organisms on earth from bacteria (MRSA) to shellfish (mussels) - sometimes fast, sometimes slow depending on the pressures on the population. This is why its a never ending battle against pests and diseases, and why we need to make sure we dont stop investigating genetics. If we are to stay ahead in the genetic arms race, we need to know everything we can about the mechanism's and triggers for evolution. Yay for GE and Genetic research.