>Well no, because selection operates at the level of the individual, not the species. A "defector" mutant squirrel without the instinct to cry out when it sees a predator would have an advantage over the regular squirrel.

Evolution is a statistical macro process aggregating individual selection events. Thus the "defector" mutant squirrel have higher chances to survive, yet the (sub)species consisting of only such "defector" squirrels will lose to the (sub)species where statistically significant share of specimen demonstrate altruistic behavior.

People discussing evolution usually make 2 major mistakes :

- assigning explicit "species evolution/survival" level motivation to specific action of specific specimen

- directly extrapolating individual specimen events to the level of species, not paying attention to emergent higher-order system behavior

>Some folks have done those complicated statistical calculations,

such calculations is like law logic - can be bent both ways. Have any idea about chaotic dynamical systems and the effect even small perturbation can cause?

>Does anyone have experience with screaming squirrels?

if you hike in the SF Bay Area hills, you'll see the high social organization they exhibit, including "watch duty".

Edit: for illustration, as somewhat related in principle - recently "Schneier on security" posted http://www.schneier.com/blog/archives/2011/05/status_report_... about "dishonest minority" - their individual situation is better, yet the species consisting entirely of the "dishonest minority" type specimen would obviously lose.

Do those models account for the fact that selfish individuals might get punished by the group? What if silent squirrels get systematically excluded from the screaming squirrels group? Wouldn't the loners have a lower life expectancy?