The E. coli long-term evolution experiment [0] has observed 65000 generations in 28 years. That's the length of about 0.88-1.27 human generations. But humans

The E. coli long-term evolution experiment [0] has observed 65000 generations in 28 years. That's the length of about 0.88-1.27 human generations. But humans no longer rely on only sexual reproduction, mutation, and horizontal gene transfer to evolve. We have this CRISPR/Cas9 mechanism now, which is putting us closer to doing something like flipping a known SNP--perhaps changing rs6152(G) to rs6152(A), to prevent baldness. Or we can splice the Bt gene into ourselves, so we won't ever be eaten by corn borer larvae. In five human generations (110-160 years), humans will probably be able to replace/augment their mitochondria with captive subcellular oompa loompa biomachines. But even in 5000 human generations, we would not replace aerobic O2 metabolism with anaerobic N2 metabolism, simply because N2 is not as reactive as O2, thus is not as useful biologically in any environment where oxygen is available. It's more likely that we would add a supplementary anaerobic metabolism such that nitrogen asphyxiation results in a hibernation or torpor state, rather than death. Complexity pays off sometimes. [0] https://en.wikipedia.org/wiki/E._coli_long-term_evolution_experiment https://en.wikipedia.org/wiki/E._coli_long-term_evolution_ex...