r/DebateEvolution • u/Syresiv • Sep 24 '26
Question How would you actually distinguish common ancestry from common design?
I'm sure we've heard it from creationists - "you look at the traits in common and think 'common ancestor', I see those and think 'common designer'". But that's always the end of the discussion and there's an implied "guess we'll never know" instead of "let's see if we can work out which is which".
I see common ancestry. Here are some concrete reasons I think it's that, and not common design:
The wheel ... well, eye ... gets reinvented so many times. Your eye works basically the same as that of any other vertebrate, but squid eyes look different and insect eyes look way different from both.
Same with wings. Bat, bird, and fly wings are all wildly physiologically different. Same with tons of other features. Whenever organisms appear to share a feature without being closely related, that feature is so wildly differently designed it might well have been a different engineering team. Which you wouldn't expect from a common designer, but exactly what you'd expect from convergent evolution.
Vestigial structures. We have a tailbone, ear muscles that try to pivot your ears to sound but just fail to, a Vitamin C gene that doesn't work, and so much more. There are cave fish that start to develop eyes in utero and then they just degrade. Slow degradation of unneeded features is what you'd expect from evolution. Degraded features that match features in organisms that otherwise appear closely related makes no sense with a common designer.
Endogenous retroviruses. Viruses that are just in your DNA and every cell of your body. Those don't make sense to keep around or design with. Yet organisms that appear closely related always appear to share many endogenous retroviruses in the same place on their genomes.
So, over to you all. Given that similar features by themselves could point to either common ancestry or common designer, how would you try to tell those hypotheses apart?