I can’t explain how I just came across this article posted on the CBC website in February, but I’m glad I did.
The title and tag-line are evocative : ‘Cities causing genetic changes in plants, animals. Wild things may be changing at a genetic level to survive in modern cities.’ Genetic changes, but not necessarily mutations due to environmental mutagens, or changes engineered by man1. The changes discussed may be old-fashion advantages brought out by the selective pressures of the environment. They could be traits that have existed in a population for generations but are now more prevalent because they confer an advantage. I think this is exciting – a real life example of adaptive evolution. Not just some stuffy theory with no relevance to real life. It’s also exciting to me because it means life will go on. Not that I had any doubt it would, but having evidence of adaptation in several species is great.
Two examples provided in the article are:
- a variant gene in fish that makes PCBs less toxic to them and
- shorter wing span in swallows that likely allows them to be more nimble and dodge traffic.
Hooray – the birds and fish are surviving. Perhaps there shouldn’t be PCBs or traffic in their environment in the first place, but, well, there are. We are working on decreasing both of these things, but meanwhile, the birds and fish are doing okay.
One of the scientists interviewed for the CBC article disagrees, and is quoted as saying he thinks it might be a bad thing, because selected new phenotypes are often associated with other changes, such as decreased life span, sensitivity to other stressors or less reproductive capacity. I can see that’s a possibility. As an example, consider primate evolution from quadrupedal to bipedal.
This whole walking upright thing has its drawbacks. Sure, we can now reach to put things in the overhead bin in the airplane, but we might have fewer back problems if we’d stayed walking on all fours. That of course would put many chiropractors and massage therapists out of work and might endanger their offspring’s chances of going to university. But that might allow them to explore career options at the local college and, after one thing leads to another, decrease poor indoor ventilation conditions in many homes and workplaces, thereby lowering the incidence of asthma complications and increasing the prevalence of asthma (by increasing survival of those with it).2
My point? Yes, adaptation, by selected trait, is likely to have associated consequences. I can’t think of a reason they are more likely to be a liability, like decreased life span or reproductive power, than an asset. There are observations that certain drug-resistant bacteria are less reproductively fit than their non-resistant cousins, but I can’t find any reason to believe this is a universal phenomena. The only fundamental reason I can think of for decreased reproductive capacity in multi-cellular organisms is that most creatures are more interested in mating with another creature that is the same as they are, so if the new variant appears different, it may have a problem getting a date.
Overall, the article described great science and made interesting observations on the interaction of species with the environment. But it makes me optimistic, not pessimistic. Don’t get me wrong, these observations in no way justify polluting the environment. However, they do suggest we will survive our errors long enough to right them.
1. It might interest that this is the same kind of genetic change that proponents of genetically modified organisms claim we have been doing for centuries with our crops and domestic animals. Selection of a naturally occurring variant with a desirable trait.
2. Have I mentioned that I believe in the fundamental interconnectedness of all things?