archeologist will find a person with scoliosis and think its a significant branch in evolution when it’s the same species/whatever with a birth defect that offers no advantage or disadvantage to reproduction
While this is not impossible, the argument usually goes that there are so few specimens that get fossilized that it's extremely unlikely for a particularly unique specimen to have been the one getting fossilized. Basically fossilization is "pick a random individual", and the odds of picking an individual with a rare condition are going to be very small.