We've had a hand in our own although it is almost never wittingly. Whenever it was wittingly, it has usually been a failure. We long ago discovered how to use the tools of natural selection and use it to our own advantage with domesticated plants and animals. However trying the same tricks on ourselves has led...
Best answer: We've had a hand in our own although it is almost never wittingly. Whenever it was wittingly, it has usually been a failure. We long ago discovered how to use the tools of natural selection and use it to our own advantage with domesticated plants and animals. However trying the same tricks on ourselves has led to awful conditions like haemophilia and cretinism. Later it's led to groundless pseudo-sciences like Eugeneics which doesn't work. It's adherents did not understand that in evolution variety is fitness and tried to make Humans better by reducing variety.
The trouble with Humans is that we're already nearly identical at the genetic level. Unlike other species that have a naturally wide range of variants, Humans have so little variety that were we some unknown samples being looked at in a lab, many biologists would conclude we were essentially clones. The reason for this is at some point early in Homo-Sapiens history we were bottlenecked by some cataclysm meaning everyone alive today is descended from a few thousand individuals. No matter what continent you live on, what skin colour you have or language you speak, we're all from a single group of people who'd barely fill out a school prom. This means that we're quite brittle in terms of illness and are extra sensitive to inbreeding. It also means we can't be husbanded into unique forms like some sort of prize pig.
There's quite a few evolutionary traits Humans have been responsible for but I'm going to stick to a couple of examples.
Over the past 150,000 years our teeth have been getting gradually smaller. The reason it is thought to be because of our habit of mashing, tenderising and then cooking our food does much of the breaking down of materials that would otherwise have to be done in the mouth and gut. We're now so accustomed to the habit that our ability to function on raw flesh and raw vegetable matter is massively reduced. As has been shown in studies of physical anthropology If you give a modern Human a diet of raw unheated and unprocessed vegetables, no matter how much you eat of them you actually begin to slowly die of malnutrition as the body struggles too much with digestion process.
Another observed feature of self-inflicted evolution is persistent lactose tolerance. The gene that allows infants to digest milk is normally meant to switch off in adulthood but at some point in the last several thousand years those few with mutated genes that did not switch off found themselves able to drink the milk of other animals and make storable dairy products. As a result they, and their offspring were at a massive survival advantage in times of hardship and the corrupt gene has become widespread in many populations, predominantly in Europe and western Asia.
Most of evolution is so gradual that we are not societally aware of it. Even the relatively rapid appearance of lactose tolerance above is older than the recorded history of our species. We are now aware that our rate of evolutionary change is likely to be very slow. Humans have very few selection pressures as nearly all of us survive long enough to breed. The downside of that is that we're especially prone to genetic and hereditary diseases which would have killed many before the advent of modern medicine, but the upside is that we may now be savvy enough to weed out these diseases via genetic engineering rather than letting nature do it via suffering and death.
Wherever we go we take a little bubble of our preferred tropical habitat with us. We use clothing, central heating and air conditioning to forever perpetuate our comfort zone. With no need to adapt to hostile conditions that is another inactive pressure. We are always evolving as mutations occur naturally with every replication and over time there will be a background genetic drift. But it's possible we could maintain a similar morphology for millions of years. Why would evolution ever fix it if nothing acts as if it's broken?
The big questions for us in the future regarding evolution is just how much role we decide deliberate manipulation of our genes is going to play. The technology is just starting to become a reality and that ability is only going to improve with time. Whether we want to turn ourselves into ultra-smart ultra-beautiful super-strong augmented beings is a question that is eventually going to need to be addressed. This is no longer the realm of natural selection, this is taking that same scalpel of artificial selection we have used on the animal and plant kingdom and will be turning it on ourselves. I only hope our descendants know what they're doing because the thought of any of this terrifies the wits out of me.