[ultramundane8]

I don't completely follow this line of reasoning. Something like "a minor enhancement like this would have been selected for by now, so it not being selected means it has a drawback?"

I'm no evolutionary biologist, but it seems like the increased intelligence (or more accurately, cognitive performance) may not have had all that practical a benefit until just recently in our history anyway.

I accept that the verdict is still out on tDCS, but am clamoring to reach that verdict.

[keenerd]

It is a rephrasing of "There ain't no such thing as a free lunch". It is safe to assume that everything has side effects and the side effects are going to be roughly proportionate to the primary effects. If you think there are no side effects, then you have not looked hard enough.

This is a fairly cynical point of view. But safe. We are not talking about medicine, we are talking about messing with otherwise perfectly healthy people.

Off the top of my head, vitamins and vaccines are the only side-effect free wonder drugs for healthy people. Similarly, clothing is the only body augment to fit this category. (And even then we get it wrong sometimes. Lots of examples from women's fashion in the past and currently the debate about shoes's effects on the knees/back.)

[gwern]

> Off the top of my head, vitamins and vaccines are the only side-effect free wonder drugs for healthy people.

Vaccines have well-characterized death rates and is why things like the smallpox vaccine stopped being administered as soon as possible even though it'd be comforting to have built-in immunity against that nasty biowarfare possibility; and some vitamins have been shown to increase mortality in RCTs.

[gwern]

> I'm no evolutionary biologist, but it seems like the increased intelligence (or more accurately, cognitive performance) may not have had all that practical a benefit until just recently in our history anyway.

That's obviously wrong, because the brain is so metabolically expensive that if it was not pulling its weight, it would long ago have shrunk considerably. More intelligence is always better - if the intelligence is not too expensive. (I cover this in the link.)