Or worse. If it is so easy to activate, there must be an evolutionary reason why we don’t have it.

I think you have evolution backwards. There only needs to not be a reason we need it to survive long enough to reproduce. Or more probabilistically, there needs to not be a significant reproductive benefit to it.

And bear in mind that most people don't have a problem surviving colds and the like long enough to reproduce even with no vaccines at all, and that was probably more true for much of our evolutionary history when we were living much more isolated lives, and not cohabiting with chickens and pigs.

	▲	ivan_gammel 11 minutes ago \| parent [-]
		>There only needs to not be a reason we need it to survive long enough to reproduce. Humans had life expectancy even shorter than our fertility period until recently and they developed as social species hundreds of thousands years ago, for which living beyond fertility period is beneficial (grandparents were invented by evolution too). > And bear in mind that most people don't have a problem surviving colds That’s modern people with access to antibiotics etc. > that was probably more true for much of our evolutionary history when we were living much more isolated lives, and not cohabiting with chickens and pigs For much of our evolutionary history people were eating animals, getting viruses with them.

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tshaddox an hour ago | parent | prev | next [-]

There doesn’t need to be an evolutionary reason why we don’t have something. That’s the default!

	▲	ivan_gammel 7 minutes ago \| parent [-]
		If something clearly helps survival and not an improbable thing to develop, the chances are high we would already have it. But we don’t and most species don’t. It is not the default, there likely exists a reason why.

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MarkusQ 4 hours ago | parent | prev | next [-]

Systemic cost.

We could have paper shredders, blenders, toasters, water taps, and so on that just ran all the time, but our utility bills would be ginormous. Same thing for our bodies.

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lokar 4 hours ago | parent [-]

Or the risk of autoimmune disease?

	▲	MarkusQ 29 minutes ago \| parent \| next [-]
		Yep. And probably increased allergies. Possibly decreased fertility. And who knows what else.
	▲	ekianjo 2 hours ago \| parent \| prev [-]
		Yes that's the obvious one

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Rexxar 3 hours ago | parent | prev [-]

Maybe it would made the immune system age faster if it is "used" too much.

	▲	ekianjo 2 hours ago \| parent [-]
		Inflammation is certainly not "free". It causes systemic damage.