A recent FB post from Stuff discussed the rising concerns around the evolution of antibiotic-resistant bacteria. (This is something that Siouxsie Wiles has often written about: here and here, for example; her excellent book on the subject is reviewed here.)
Fairly predictably, it didn't take long for the proponents of essential oils to turn up, soon to be joined by the usual antivax folks and those arguing that an 'alkaline' diet is the best cure-all. (They also believe that drinking lemon juice – an acid – is the best way to achieve thisA. It's not, and alkalosis is not a healthy state of being.) However, someone also commented that we should basically allow natural selection to take its course, by removing the "weak and feeble". It's not the first time I've seen this said, but it annoys me every time.
Firstly, because many diseases don't give a damn whether you're fit & healthy, or not. Smallpox was no respecter of health (or social status), for example; nor was the "Spanish flu"B that caused the pandemic towards the end of World War I. In fact, that particular form of influenza had a more severe effect on the young & the healthy. As this article in the Smithsonian says:
The 1918 pandemic was unusual in that it killed many healthy 20- to 40-year-olds, including millions of World War I soldiers. In contrast, people who die of the flu [these days] are usually under five years old or over 75.
This article on the Stanford University site adds further, chilling, information:
The effect of the influenza epidemic was so severe that the average life span in the US was depressed by 10 years. The influenza virus had a profound virulence, with a mortality rate at 2.5% compared to the previous influenza epidemics, which were less than 0.1%. The death rate for 15 to 34-year-olds of influenza and pneumonia were 20 times higher in 1918 than in previous years.
In some ways, one of the worst aspects of this pandemic is the way that – in the US at least – truth also became a casualty, with public health officials initially lying about its severity and spread. They were supported in this by newspaper editors, who refused to print letters from doctors that warned of the danger.
What was it that killed so many healthy young people, in particular? The general consensus seems to be that their deaths were largely due to the impact of their own immune systems, which mounted such a strong response that they severely damaged the patients' lungs (which also made it much easier for secondary bacterial infections, such as pneumonia, to take hold). For these people, "weak & feeble" didn't come into it.
The other reason that attitude annoys me is that it betrays a deep misunderstanding of how natural selection operates. This is because the process isn't future-focused. A population under the influence of natural selection may well become better-adapted to its current environment, but what works now may not work so well if the environment should change.
And some genetic traits of which that original commenter might be dismissive, could turn out to be beneficial. After all, the reason that the sickle-cell allele is retained in many African countries is that it offers some protection against malaria (the same is true for thalassaemia in Mediterranean lands), despite the fact that having two copies of this allele (ie being homozygous for it) confers significant, life-threatening disadvantages.
Then there's cystic fibrosis (CF) – again, in individuals homozygous for the allele, this disorder is life-threatening. But the allele is relatively common: among newborns in Europe, 1 in 2,500 will have CF. It's hypothesised that this is because an individual with a single copy of the allele (a carrier) may be protected from the worst effects of cholera. This is because cholera results in very large amounts of watery diarrhoea, and the same cell-membrane chloride pumps that are implicated in producing all that watery efflux don't work properly in CF individuals. (There's also a suggestion that the allele may have conferred an advantage to some people early in the development of dairying, when lactase persistence was not widespread.)
I guess I shouldn't really read the comments sections!
A In fact, there are an awful lot of totally incorrect claims made for the benefits of drinking lemon juice.
B While it's generally been thought that this pandemic strain originated in China, a second Smithsonian story suggests that it may actually have begun in the US, in Kansas, where the virus may have jumped from pigs (possibly pigs already infected with an avian influenza virus).