"Evolvability" and "Evolution" are two different things.
Pretty much all dogs on the planet belong to the same technical species. A Shitzu can breed with a Bulldog for perfectly viable (at least in terms of genetics) offspring. Now... anatomical differences can be to such a degree that human intervention is necessary for an entire breed to survive (they would perish in the wild) - but the point here is to compare our concept of a species ("us") to the reality we seem to overlook.
Humans have an exceptionally narrow range of genetic diversity within the animal kingdom. Studies into our mitochondrial DNA show that there are periods of time (within the past ten to fifteen thousand years, if I remember correctly) where our species numbered no more than a thousand individuals on the whole planet. We've been dangerously close to extinction many times over.
Which is probably why most ancient cultures have tales of global destruction at the hands of a wrathful deity. Regardless of the cause - if you grew up and watched all the civilizations you knew of get effectively snuffed out ... you'd take some time to wonder if your species had pissed something off.
Anyway - even within this very small window, there was considerable genetic change and adaptation. As people migrated north out of Africa, the heavy melanin content in their skin began to become something of a detriment, as melanin prevents the skin from using sunlight to generate Vitamin D. Trivial, by today's standards - but hardly so when you're a hunter-gatherer. Even then, a fact that is often overlooked in today's "politically correct, everyone is the same" environment is that blacks living in the more extreme latitudes (closer to the poles) and during winter months should be conscious of their Vitamin D intake. It's not a bad idea for everyone (who spends much time with their skin exposed when it's 15 below zero?) ... but the fact of the matter is that there's a functional difference there that people should be prepared to address.
There's also the fact that most asians are lactose intolerant because they never developed dairy industry like the western and persian cultures did. Though their intake of very high-octane alcohol has led them to develop an enzyme that specializes in the break down and neutralization of alcohol. It gives asians a more pronounced blush than other races.
Of course... humanity's affair with alcohol is mostly to do with the fact that it served the purpose of chlorine in today's water systems... exccept that water systems of the day often had to contend with open and unregulated sewer systems (where they were present, at all). The west developed beers, lagers, and wines based on their agriculture. The east largely developed rice whiskeys that one consumed separately from water, but were concentrated enough to nip Montezuma in the bud.
Which is the leading cause of death in the world, even still. Diarhea-induced dehydration beats out starvation (the ones lucky enough to not get so sick that they shit their very soul out die of starvation). Just in case anyone wonders -how- alcohol became such a central fixture of our culture. Though most people, now, only insult its history through their abusive intake of it - but many of the creatures calling themselves humans, these days, insult the long legacy that spawned them.
Which... is a considerable deviation from where this conversation with myself started.
Comparing dogs to humans... if humans were to suddenly disappear from the picture - a lot of dog breeds would find themselves in trouble. Some dogs, you'd expect would be very survivable and capable - but the reality is that they have been bred to have heads that are too wide for normal birth - and would be unable to properly reproduce (at least with their own breed). Others would do okay - but their breeds would all rapidly collapse and lose distinction after several generations.... spare for, perhaps, some of the more 'natural' canine breeds - the Shepherds and Huskies.
The fact is that any population is under -some- selective pressure. Any organism is going to develop genetic diversity allowable within the selective pressures acting upon them. In many cases - these selective pressures are endemic to the very species involved. Humans, for example, are genetically disposed to having a 1:1 ratio of males to females and frequently bare only one child per maternity cycle. Humans are a prime example of self-imposed Red Queen Evolution (see signature) - the rate at which our species developed and the extremes to which it developed make no rational sense. Sure - the benefits of our intelligence make sense -now- ... but when you look at the sprawling gulf we had to cross between chimps and us.... it makes no sense. Was a super-smart chimpanzee so radically survivable even though its brain was consuming 10% more calories per day than the others, that its children would barely fit down the birth canal - forcing a considerable widening of the hip of the opposite ***?
It's like saying a peacock's feathers make it more survivable. Other factors drive evolution... one of the most powerful being fetishism. One of our female ancestors thought a clever chimp was attractive. Her offspring were more likely to be both clever and have a bias towards clever mates... and the race began as substantial portions of the poulation began to adopt the same fetish. 'Survival' wasn't the name of the game. Getting a mate who would produce attractive kids (to everyone else) was. This is enough to drive certain traits into extremes well beyond what would have developed if environmental survival was the key factor.
But that's not exactly what this study is saying... it's simply saying that the genetic diversity of a reproductively compatible population increases in relation to its size. Though, currently, a lot of traits are likely 'dormant' or only mildly expressed. If selective factors were suddenly imposed upon the global population (in such a way as to not instantly collapse global travel) - then considerable change in the human species could be seen within only a few generations.
Though, at this point, it's difficult to envision environmental changes that would be enough to act as a strong-enough selective bias. The strongest biases in our population are likely going to be rooted in mating preferences - which, at this point, are likely to lead to sub-speciation as opposed to global population changes. After all... a species doesn't necessarily evolve. Individuals within it do. The individuals with the best traits are the most successful - those individuals that do not are less successful (and in some cases - perish or leave no legacy). The people born alongside those individuals dont inherit their traits. If they are lucky - their kids or grandkids will by recognizing the importance of those traits and making a conscious effort to seek them..... otherwise - they keep on trucking with the genes they have and that were part of the species, beforehand.
And I'm kind of talking in circles, right now. Just taking a break from reading/writing fan-fiction and yard work and decided one of my publicized ramblings would fit here.