Aliens

I've done the math. In human form we're stuck here on Earth. If we ever do colonize the universe we will have to look different, apply our knowledge of genetics, and build a new species, piece by piece, bit by bit. Of course space colonization isn't necessary for our survival, so will probably be an accidental benefit of changes brought on by calamities here on Earth's surface. For example, resource wars, economic competition, cosmetic competition a la "extreme makeover", or just the desire for a better life for our children, could cause certain "enhancements" to become socially acceptible.

After all, why would we create a huge database for the human genome if this weren't the unconscious goal - to control our form. Consider the following facts:

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The human genome contains 3164.7 million chemical nucleotide bases (A, C, T, and G).

The order of almost all (99.9%) nucleotide bases is exactly the same in all people.

The average gene consists of 3000 bases, but sizes vary greatly, with the largest known human gene being dystrophin at 2.4 million bases.

The total number of genes is estimated at 30,000, much lower than previous estimates of 80,000 to 140,000 that had been based on extrapolations from gene-rich areas as opposed to a composite of gene-rich and gene-poor areas.

The functions are unknown for over 50% of discovered genes.

source - Human Genome Project
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For space colonization, invertibrate forms might be more advantageous to avoid bone wasting. Exoskeletal forms might be able to face hard vacuum without space suits, or even complicated life support systems. As thinking, feeling beings, there is no reason why they can't still be considered persons, with inalienable rights. Technically speaking, there is no such thing as "species" anyway, the natural variation between individual people is the same thing. Future humans might be like the Xindi races from Star Trek Enterprise television series. Different niches will be occupied, perhaps exclusively, by engineered descendents. And with control over the genome, such differences could perhaps be reversed within a single generation.

I don't know if differences could be reversed in the same fully grown individual. Even if a brain transplant were possible, growing a body could still take decades. And the moral and ethical issues surrounding this technology are an almost insurmountable barrier to progress. Considering the xenophobia in the world, that might be both a good and bad thing.