Natural selection on

peppered moths vary in darkness. some have a lighter coloration and some have a darker coloration. before the industrial revolution only 2% of the moth population was darker coloration. after the industrial revolution, 95% of the population showed this darker coloration. birds eat the moths they can see on the trees.

In the 1950s, christian anfinsen demonstrated the renaturation of the protein ribonuclease (rnase) in vitro. after reduction (to reduce the disulfide links) and the addition of urea (to denature the protein), the protein was in an unfolded state. after removing the urea and the reducing agent, the protein refolded, with greater than 90% activity. if the urea were removed after oxidation occurred, the protein had less than 5% activity. why would the protein not refold correctly if the urea were removed after the reducing agent was removed? (in other words, what would happen if the urea were removed after oxidation? )