"Apparent" and "noticeable" are terms that point to characteristics that we, as humans, are able to notice. A 1% more chance of survival is hardly noticeable by

"Apparent" and "noticeable" are terms that point to characteristics that we, as humans, are able to notice. A 1% more chance of survival is hardly noticeable by a human being without the tools of controlled observation and statistics, however the mutation that allows it can spread very quickly through a population in a few generations. Optimization is a matter of fine tuning, so the effect of mutations has to be small enough to allow it. Sometimes a slightly larger mutation can create such an advantage that a cascade a smaller mutations ensues to fully exploit its potential. However I'd say it's more he exception than the norm.