By a trait being "beneficial" you mean that it prolongs the existence of some gene specifically, right? My understanding of evolution is that traits aren't necessarily beneficial to those who posses it in the colloquial sense. For example, animals that perish due to reproduction.

Also, isn't saying a trait exists so it must be beneficial a bit of an over simplification? Couldn't a relatively useless trait hypothetically exist due to genes that are also related to some other relatively useful trait? It seems like a stretch to say any lasting trait must be beneficial, unless you can isolate it from other traits on the genetic level or otherwise through analysis. Traits can also cease being beneficial as we can see from the countless species that have gone extinct.

Sorry if this seems like I'm ranting, but I just need more convincing that this rule of thumb makes sense, and would appreciate being pointed in the right direction if I'm off-base.

I mostly agree with your point however IMO the psychopath thing is not a great example because it could be explained as the incomplete or nonexistent development of something that is complex that is beneficial. I think the error is that we can’t necessarily know what the cost was. And the benefit doesnt necessarily have to be that big relative to the cost. I mean I’m replying to you and that me costs something, and what’s the benefit?

While the sounds don’t make themselves, they could be a side effect of something else… instabilities in the structural tissue, the plant straining to increase the movement internal fluids… who knows?

That said, I personally think there is communication between plants, or that at the very least it’s something like trying to mimic predator insect sounds. But could be that the vibrations themselves help move fluids around (as opposed to being a byproduct of something else that does)

Only applies to genetic traits though. If psychopathy, for example, turned out to be epigenetic, environmental, or entirely psychological, it would potentially defy that pattern.

Unempathic people can make hard decisions; Such as choosing between spending a hospital budget on fuel for the generators, building upkeep, restocking, and employee wages –v.s. the life of one child. A lot of people can't make such a decision.

I wouldn't want such people unchecked though.

The argument is flawed. You defend. "if it has a cost and lasts through evolutionary time, it is beneficial."

But to conclude your conclusion, you must also show that:

- emitting noise has cost (fairly believable)

- and that something listening to it is the only way to make it beneficial, which is far from obvious. (Could just be a way to dissipate energy, or to send signal within the plant, or to get rid of some chemicals, or many other beneficial things that doesn't involve something listening)

> A small percentage of the population is psychopaths, this has an obvious cost to communities, but the pattern has lasted through time, therefore has a benefit.

It has a benefit to individuals. A benefit to the community is not necessary.

> Likely it's for war/fighting/hunting.

This is a non sequitur.

Nothing is all cost and no benefit, and nothing is all benefit and no cost either. You don't see people arguing that vulnerability to cuckoos is beneficial to the birds they parasitize. The benefit is real (you don't need to bother recognizing your offspring, because recognizing your nest is sufficient) but the cost is so much larger (your children all die) that it's obvious the birds would be better off with the ability to recognize their own young (and/or eggs). They don't have that ability... yet.