This may be true, but I don't think anyone knows for sure, and it seems likely to me that the brain has the property of sensitivity to initial conditions, meaning that it's likely to do different stuff in different Everett branches.
Yvain recently asked about this on his blog -- he tends to agree with you:
So this suggests that [....] over timescales like that of human history we will see an overwhelmingly large number of universes that are completely identical on the human level - ones where electrons ended up in slightly different positions but no harm done [...]
More on-topic for the grandparent: Greg Egan's novella Oracle talks about the ethical issue of bad stuff happening in other Everett branches.
There must be chaotic amplification of quantum events going on. Any macroscopic system at finite temperature will be full of quantum events, like a molecule in an excited state returning to its ground state. The quantum randomness is a constant source of "noise" which normally averages out, but sometimes there will be fluctuations away from a mean, and sometimes they will be amplified into mesoscopic and macroscopic difference. This must be true, but it would be best to have a mathematical demonstration, e.g. that the impact of quantum fluctuations on the transfer of heat through an atmosphere will amplify into macroscopically different weather patterns on a certain timescale.
From the last thread:
Meta: