[mattmanser]

I don't think it works like that, from my recollection of the uni courses I did 20 years ago.

Even a small advantage like 1% will quickly propagate in a population, because it's about advantage over 1,000s of generations.

That this disease defence CAN be turned on, means some people would have at some point had a genetic mutation to turn it on.

As the GP pointed out, therefore it must be a net negative from an evolutionary stand point.

I also suspect it would be calorific consumption, as someone else said, so it might be ok.

However, there are plausible other explanations. For example there are medical conditions that result from a too aggressive immune system and it could instead be reducing the chance of that occuring.

[gignico]

The problem is implying that “if evolution did not do it there must be a reason”, because 1) it makes evolution look like an engineer evaluating trade offs, which is not and 2) it considers the current state of affairs the final “product”, which is not. For example, flowers did not exist in the Cretaceous, so somebody looking at what evolution did until then would say “if evolution did not invent flowers, then we’d better not do it”. But of course that’s absurd.

Also as I said evolution is not a process towards a goal. There are 8 billion people around the world which proves Homo sapiens is quite fit for its environment so the pressure to evolve further features is quite low.

[mattmanser]

pressure to evolve further features is quite low

I'm really sorry, but you're really misunderstanding how evolution works.

Worth reading something like the Selfish Gene if you want to understand it a bit better.

There are always reproductive pressures and there are always genetic variations.

Modern civilization and medicine has simply changed what the pressures are.

As an example if a genetic variation occured tomorrow which gave resistance to spermicide, within 100 generations that variant would probably be quite successful and prevalent in the human population.

[gignico]

I know about reproductive pressure and I’ve read The Selfish Gene. What you say is correct but does not explain that “if evolution did not, better not do it” attitude of the original comment, which I think is wrong for many reasons as I’ve wrote.

[Escapado]

I would say you are both right in that if you have two competing variables (on-time for the defence vs calorie consumption), when the main causes of death before procreating were infectious disease and malnutrition before modern times, I would expect some equilibrium to be reached and we have not had that much time to evolve since caloric scarcity in the western world was a solved problem for large swaths of the population.

If in the future we could trade a few hundred extra calories per day for a great immune system (without auto-immune side effects) we would have found a nice cheat code!

[awakeasleep]

Thinking about your point- I bet we do not know if some people have it on or not. It feels like something that would have to be specifically investigated.