Wouldn't you consider the difference between a 180-pound English Mastiff...
(Clicky for piccy!)...and the two-pound Chihuahua...
(Clicky for piccy!)... an example of how we have already altered the course of one species' evolution?
And since you're a fan of Malthusianism, what do you think about Genetically Modified crops?
Thomas Malthus doesn't need fans - he's long dead.
Ah, I see your problem! All domesticated dogs are modified wolves and back crossing any of the breeds (not species, note) would give us back the wild type wolf without too much trouble. The wolf type gene pool is in there somewhere.
Same goes for lots of human modified creatures: Darwin's favourite was the Rock Dove from which all the domesticated pigeons were developed. As with all domesticated livestock, near family members are bred together to get the traits you want, but when they escape and go flyabout you soon get a feral pigeon that is indistinguishable from the original rock dove. The reason they like city life so much nowadays are down to the roosting and nesting opportunities presented by those man made cliffs called high rise buildings, waste heat to keep warm by in winter and all the seed you can eat in the form of discarded burgers. How the chips/fries habit developed I don't know but if you have the enzymes to digest them, you're on to a winner.
We've been g-modifying crops since we first started burning the ground and scattering gluts of stripped grass seed and then coming back to (literally) reap the rewards at some later date. Those crops, like everything else we transmogrify, have genes from their own pool and would go back to wild type pretty quickly without our continuing intervention. So we select for grain size and number, stalk length and thickness, flavour, cookability, disease resistance, storage quality and so on.
There are slight problems in that as grain size increases the proportion of carbohydrate to protein (germ) increases so we have to adjust our diet to balance it by adding , say, fish or some other first class protein; or if you're a veggie, beans and so forth to get all the amino acid combinations you need to stay healthy.
The problem with the type of gene manipulation in GM crops is that genes from other species can be inserted - plant genes into animals/ animal genes into plants.
No one knows what may happen when these mutants get loose in the environment. For instance, if rogue mutants back-cross with the wild type, say in rice , wheat, barley, etc; will the insert invade the wild type and knacker up the original genome from which we've derived so much? Can we risk it?
Again, I say, fuck the quote function!