Is it just me, or did that last post read like complete bollocks? 
Yes and no. Although it does seem rather arm-wavy, it seems to allude to the punctuated equilibrium model of evolution, where species remain relatively stable in a niche until their environment (the evolutionary, not climatic meaning) changes, at which point they either suffer a decrease in their range, go extinct or undergo a period of realitively rapid evolutionary development as they hill-climb to a new local optima. 'Rapid' in this context can mean 10K -100K years for the spread of a single beneficial gene through >90% of the population, for a long-lived and scarce (for most of our history) population like humans (for bacteria, this could occur in 10 hours or less, and does).
If you examine gene allele-frequencies for grain-eating adaptations, 70-90% of the population in the middle east, where grain cultivation has been of great importance for 10K years, carry specific genes for the metabolisation of grains, which historically grain-naiive people such as Eskimos almost entirely lack (and thus are succeptable to diabetes and heart disease when introduced to these foods).
evolution would dictate that the overpopulation concern will correct itself; more people being born without the ability to reproduce, for example.
This is pretty bull-shitty however. Evolution dictates no such thing, and when the conditions are right, any species will undergo a population explosion (except giant pandas, who'd whine that it wasn't the right type of bamboo, fuck each other in the ass trying to breed and then keel over from a slight draft), followed by a population crash as they exhaust a critical resource. Evolution will actually favour the *most* reproductively successful individuals in such a situation, as their offspring will compose a higher proportion of the survivors than their less promiscuous rivals (all other things being equal).
To say that evolution will solve overpopulation is to engage in the same magical thinking that leads people to believe that global warming is Gaia trying to rid itself of humanity, or that 9/11 is God telling the US to pray more. Evolution is a blind, statistical force that drives a huge number of species up evolutionary dead ends and on to extinction because it lacks the slightest bit of foresight. It can't prepare in advance for a population crash, beyond what it's furnished us with already in our ability to make war, survive famine and generally be more adaptable and harder to kill than cockroaches.
"Is she gone yet?"