and can therefore immediately dismiss a staggering number of plausible courses of action (which by definition a domain-general mechanism would have to examine one by one) for one or a few favoured alternatives. For this reason domain-specific mechanisms are faster and more effective than their domain-general counterparts and we should expect natural selection to have favoured them.
This implies that specialized mechanisms are quicker and more effective at finding the best solution compared to general-purpose ones, which must examine every possibility individually.  Natural selection would favor this specialization for its efficiency.