Matthew B. answered • 09/16/19
Bioinformatics and Human Biology Major, Stanford University - 2015
Chance events, like for example a mutation in a gene, will have a disproportionately large effect on small populations over large populations.
Say, for example, you have two islands, one with a population of five butterflies, and one with a population of 50. All the butterflies are blue. Say one butterfly on each island undergoes a mutation that makes it red. This doesn't directly impact it's ability to breed - it's just... red. Say the mutation has a 50% chance of being passed on to offspring, and that each butterfly pair produces two offspring (replacement reproduction rate).
The chance of the small population containing red butterflies after 100 generations is ~18.9%, while the odds of the large population containing any red butterflies is ~4.2%. This number drops further as your population grows (though simulating it - the method I used to get these numbers - becomes computationally intensive).
