Link to Pharyngula
from Pharyngula
People keep asking me this question after the creationist event here in town — Mortenson spoke about how creationism is so much more egalitarian than evolution, and how the Bible talks about these wonderful things people did in the book of Genesis, like Cain going out and founding a whole city, by himself! At a time when the world population was 4, however, that doesn’t seem like a great accomplishment. Anyway, some people thought that far, realized that in the creationist conception of an entire world population arising from two people only, there was an obvious problem in the second generation.
Have no fear, the creationists already have an answer, as I explained before. Cain had sex with his sisters. The creationists are even proud of this
explanation, and you can buy it on a postcard in their cheesy gift shop, which does make one wonder about their clientele a little bit.
The exhibit goes on to explain how this was OK, because Adam and Eve were perfect and carried no deleterious alleles that might have caused trouble when homozygous. They also chew us nonbelievers out for finding their stories a bit objectionable.
Since God is the One who defined marriage in the first place, God’s Word is the only standard for defining proper marriage. People who do not accept the Bible as their absolute authority have no basis for condemning someone like Cain marrying his sister.
And people who do not understand population genetics have no basis for arguing that a species can survive a population bottleneck of two.
Of course the creationists will not explain exactly why there was a need for an agriculturist with only four people in the world, and a agriculturist with a name that means smith. Modern day hunter gatherers in Brazil do not have smiths unless they are in contact with the outside world. Oh those Babylonian stories adopted by the followers of Yahweh. see: https://ericwedwards.wordpress.com/2013/07/29/the-myth-of-cain-and-abel/
The creationists could skip to the third or fourth creation myth in the bible starting at chapter 5, or really just go with everyone being destroyed by the flood and every person string their heritage back to Noah who happens to be the husband to the woman we can all actually trace our heritage too when homo sapiens nearly went extinct during the ice age about 50,000 years ago.
The truth is Cain’s wife was a mail order bride from a nearby village. There was also a musical with singing and lutes about being a poor man, but it was all on lutes only the stuff over human sacrifice to fertilize the fields was not as popular as the real thing.