Evolutionary biologists often talk about selection pressures:
Any cause that reduces or increases reproductive success in a portion of a population potentially exerts evolutionary pressure, selective pressure or selection pressure, driving natural selection.[1] It is a quantitative description of the amount of change occurring in processes investigated by evolutionary biology, but the formal concept is often extended to other areas of research.
Think of it this way: in a mixed population, genetically speaking, if a new environmental pressure is brought to bear on a portion of the population vulnerable to it, other less vulnerable portions of the population will flourish, relative to the oppressed, and this may lead to evolution of the sub-population to become less and less vulnerable to that environmental pressure.
I’m beginning to wonder if this is what we’re seeing with the delta variant of Covid-19:
“The mask was off only momentarily, not an entire day or hours. We want to make the point that this is not the teacher’s fault — everyone lets their guard down — but the thing is delta takes advantage of slippage from any kind of protective measures,” Tracy Lam-Hine, an epidemiologist for the county, said in an interview.
The case study, published by the Centers for Disease Control and Prevention and highlighted by CDC director Rochelle Walensky during a briefing on Friday, highlights the potential danger for children under the age of 12 — the only group in the United States ineligible for coronavirus vaccines as a hyper-infectious variant tears across the country. [WaPo]
The tendency for bacteria to become immune to targeted antibiotics is an example of the problems associated with evolutionary pressures. The antibiotic destroys most of the bacteria, but if some are resistant, but not otherwise superior to their brethren, they remain hidden until the antibiotic strips away their cousins. Once they are no longer suppressed by those cousins, they can run rampant in the patient. A lack of antibiotic specific to them, or a lack of recognition of the problem, can lead to long-term damage or death.
The evolutionary pressure may be the masks, which have kept a lot of people from being infected. Until now. Now the delta variant may have changed to make it through masks, or it’s simply more efficient at infection so that a single mistake is more expensive.
It’s a real medical conundrum that infectious disease docs must face quite often.
