""Humans are descended from monkeys" / "The Earth goes round the Sun" / … is a pretty extraordinary claim, and extraordinary claims require extraordinary evidence."

Dismissing as "extraordinary" any claim to which you are politically opposed is not good science. (Frankly, the Sagan quote is in itself not good science until you can get everyone to agree on what is "extraordinary".)

Meanwhile, an entirely appropriate riposte to GP would have been: ""Genetics is the most important ingredient here." is a claim, and claims require evidence."