I may add one thing to that last post. Another option is that instead of continuing to grow in numbers the human species shrinks. Then we may become more homogeneous. In fact that's probably what happened at least one time to our ancestors way back, and that may explain why we are one of the least genetically diverse species on earth, despite obvious regional physical differences.
So as a species we are faced with two main options (status quo is not an option): either we continue expanding, eventually overflowing out of this planet and ineluctably diverging genetically, OR shrinking in numbers, possibly becoming an endangered species, either by some large scale catastrophe, or very slowly, without even noticing it. Both preserving the earth, our nest, and swarming towards the stars are necessary elements of our survival as a species--and parent of species to be.

what is this?

I am a Homo sapiens, one of a growing mass of ~6 billion, a heterogeneous bunch, a big not-so-melted pot of spiced diversity.

This rich human genetic cuisine is displayed through people's physical appearance, which our tribal minds sorts out as kinds. Let's celebrate, rather than deny, this diversity resulting from the immemorial ebb and flow of human migrations. The complex interplay of population isolation and mixture went back and forth uninterrupted since our ancestors emerged from archaic forms of human over a hundred thousand years ago. Living in small tribes or bands until the intensification of horticulture into full scale agriculture and farming after the end of the last glacial age, there we are; a few of us still rooted in the ancestral lifestyle of hunting and gathering, and most of us post-industrial humans of planetary awareness.

The human species today shines as a fuzzy kaleidoskopic landscape of admixed populations and genetic isolates. Unlike a regular kaleidoscope, the borders are rarely sharp. Geographic and cultural patterns are discernible but the complexity is mind boggling. How melted is the genetic pot? Look at a metropolis like New York City or Sao Paulo; not so melted, he.. Will it ever be? Should it be? As much as some individuals tend to mix, most still stick to people who look alike. I have sometimes heard a question going like this; are we to become, in hundreds of years, a single homogeneous mass of people? Will everybody eventually merge to the same skin color and facial features? No way. Even with an increased number of admixed individuals, there will always be a gradation of admixture levels, whether subtle or sharp. There will always be geographic and cultural distances working as isolating mechanisms. And if after all these centuries we do finally migrate outside of our planet, then these isolating mechanisms will become even stronger. And natural selection pressures in different planets or orbital stations may even add some spice and modify our species to physical types never seen before, or new human species yet to evolve.