You have no business attempting an eugenics program for one simple reason - you are too stupid. Trust me, I mean that in the kindest way possible. I'm not talking down to you, please don't look so offended. It's really nothing personal, really. Look, I don't know you but I don't really need to. If you are a human being (and I'm assuming you are) then you aren't up to the task. You may be the best and the brightest human to ever grace walk this pale blue dot but when it comes to eugenics you may as well be as smart as a small bag of rocks for all the good it will do. OK so now you feel offended and you're still not convinced that you aren't supposed to meddle with eugenics. Fine! Here's the long answer.
Look, no one is saying you can't do it, I'm saying you shouldn't. We clearly can do it and we've been doing it for thousands of years. I have living proof that we can get some pretty interesting results via eugenics sleeping right next to me as I type this actually.
My sweet Suicide Dachshund here is the very embodiment of why we as human beings suck at eugenics. First of all, we don't know when to quit. Look, I will grant you that eugenics gave us all our domesticated farm animals, crops and pets. If we just turned a wolf into a dog and then stopped everything would be fine. But we didn't. We couldn't. It's just not in our nature! That's why we now have the Chihuahua and the Sphinx cat. It probably won't end there either, eventually someone will breed something that is even more of an abomination.
But beauty is in the eye of the beholder right? What I see as an unholy abomination others may see as a thing of beauty. That's true. Which brings me to my second reason: we value all the wrong things. Evolution can be a messy process but it works like a charm. It may be a blind watchmaker but it builds watches that work dammit! Human beings on the other hand are less pragmatic than nature. When we practice eugenics we focus on eye colour, hair, ears perking just so and tails curling in a very certain way (dogs, I'm focusing on dogs for now). That's how we end up with animals that have trouble breathing because we just had to have pets with flat faces. Our pets suffer from hip dysplasia and intervertebral disc disease because we would rather have them look a certain way than for them to have healthy and long lives. Great Danes have the shortest lifespan of any breed (according to Animal Planet's Dog Breed A-Z) and suffer from a horrible condition called "bloat" or "gastric torsion". See, their stomachs aren't attached to their ribcages so if they run around with a full stomach, their stomach can flip over and basically knot their intestines causing a very painful death for the animal. Natural selection would never tolerate such a condition. Artificial selection (aka eugenics) on the other hand totally would because we would rather have a certain shape of head and a certain length of leg than an animal that won't live a short, pain filled life. This is really bad when we do it to our pets. It becomes infinitely worse when we try do do it to ourselves.
See the third way in which we lack the intelligence for successful eugenics is the tiny issue that we do not know the future. Combined with our tendencies to value the wrong attributes, this spells certain doom. Let's run a little thought experiment for an example here. Imagine for a moment that the Nazis won World War 2 and that they then instituted and completed their eugenics program. Everyone on earth is now a 7 foot tall, blonde Adonis with a body like Mr Universe. We all have blue eyes, white skin and we can run faster, jump higher and bench press more weight than any humans ever. How useless would that all be? We don't push plowshares through the earth anymore, we don't stride across battlefields waving giant swords and axes at each other anymore! Unless everyone on earth is going to be an underwear model, having big muscles and wavy blonde hair is pointless. None of that is useful in the information age. How does being tall and handsome help you when you're stuck behind a computer all day? How does being strong and fast help you work in a cubicle? None of that would help you get into space either come to think of it. In fact I'm pretty sure there is a reason astronauts aren't built like Eastern European bouncers - in a space shuttle, space is at a premium! So if Hitler had his dreams come true, we may have very well bred ourselves right out of the space- and information ages entirely.
So there you have it. No matter how smart you are, you are too stupid to be good at eugenics. There is just no way you can understand enough or see far enough ahead to not screw it up for everyone involved. Evolution may not be perfect but it still does a better job of adapting species to their environment than we have ever managed. Actually someone said all this much better than I could way back when Eugenics was still the great white hope:
"The history of the race shows endless examples of the pain and suffering that men have inflicted upon each other by their cocksureness and their meddling.
We know something about biology. We know a little about eugenics. We have no knowledge of what kind of man would be better than the one that Nature is evolving to fit the environment which he cannot escape. We have neither facts nor theories to give us any evidence based on biology or any other branch of science as to how we could breed intelligence, happiness or anything else that would improve the race. We have no idea of the meaning of the world “improvement.” We can imagine no human organization that we could trust with the job, even if eugenicists knew what should be done, and the proper way to do it. Yet in the face of all this we have already started on the course, and the uplifters are urging us to go ahead, with no conception of where we are going, or what route we shall take!
In an age of meddling, presumption, and gross denial of all the individual feelings and emotions, the world is urged, not only to forcibly control all conduct, but to remake man himself! Amongst the schemes for remolding society this is the most senseless and impudent that has ever been put forward by irresponsible fanatics to plague a long-suffering race."
Extract from "The Eugenics Cult", an essay by Clarence Darrow that appeared in The American Mercury, Volume VIII, Number 30, June 1926 (available in full online here)