We have three choices:
1) There were more than 30 people on the Ark (and therefore the bible is fallible)
2) The flood didn't cover the entire world and at least 22 other humans survived (and therefore, again, the bible is fallible)
3) 43 different alleles evolved after the flood.
(very slightly paraphrased from http://holysmoke.org/cretins/ark.htm)