This is some very basic biology: when resources are unlimited and there are no pressures on a species, its population grows exponentially. There’s also no evolution other than random mutations; without selection pressures (regardless of whether it’s natural or artificial), the genetic information content of a species doesn’t change appreciably.
Biologists make use of this to perform tests on certain cells. If you simply put a population of cells in a petrie dish and left them there, they start out by doing this:
Well, humans haven’t evolved much at all over the past 10,000 years (at least). But we have reproduced with amazing efficiency. In fact, there are humans pretty much everywhere on Earth. How has the human population grown? Exponentially. Take a look:
And now we have reached the point where the human impact on Earth has become significant. And we will soon (within the next 5 generations at best) be competing with one another for the resources of the Earth for survival, not just for profit. The current population density is 13 people per square kilometer, but as the population grows, more land needs to be designated for feeding that population. Take a look at our current population density:
Most of the world looks like it’s doing okay for now. But right now there are 1.3 billion people in China and 1.1 billion in India. Now, let’s consider only what will happen if population continues to grow, just in India, at the same rate it has grown since 1951. No social issues, no political issues, no ecological issues. By 2180, there will be over 31 billion people just in India, with a population density of 55 Indians per square kilometer of land on Earth. And by 2400, there will be over one trillion Indians.
My point is that Earth can’t sustain one trillion humans. If we don’t stop reproducing at an exponential rate, we will place selection pressures on humanity, and humans will either evolve or die off. And soon. But if we can keep human population reasonable, and the human impact on the planet reasonable, then we’ll be able to remain humans, and rule the planet, for as long as we like. I like this idea — let’s use what we know about evolution for good, and ensure the long-term survival and dominance of our species. (Plus, it gives us a big number to put into the Drake Equation!)