This - this - was my life's work. My past - humanity's future. Foundation. So beatiful. So alive. And nothing can...Dors! - Isaac Asimov

Humanity today forms a single species and can interbreed freely. Differences in color of hair, skin and eyes are largely due to differences in the quantity of a pigment called melanin, and this does not affect humanity's essentially unitary character. Nor do differences in the shape of the eye or nose, in the shape of the skull, or in height.

no matter how sure scientists think they are, nature has a way of surprising them.

There's something so damned undignified at going to destruction through sheer thickheaded stupidity. What's the use of being men if that's how you have to die." "Stupidity," muttered Bronowski.