What are some "evolutionary mishaps" in humans?

Question

I'm curious about things like the recurrent laryngeal nerve, which runs all the way down, under the aortic arch, then back up to the vocal cords. In early vertebrates, bodies were configured differently, and so the nerve took a direct route. Over millions of years as anatomy changed and necks elongated, the course of the nerve remained the same. Now it has a very inefficient course.

Are there other examples in humans like this? Anatomical curiosities that made sense at one point, but are now "outdated".

Answer 1

There is a huge number of what you are asking about, commonly referred as evolutionary baggage or evolutionary holdovers and come in a wide variety of severities.

1. You breath and eat using the same tube (esophagus), in fish temporarily blocking the esophagus has little impact since they can still breath, the esophagus is behind the gills.

2. You only get two sets of teeth, a weird feature unique to mammals believed to be connected to our ancestors being insectivores. Teeth in general evolved as temporary continuously replaced structures that mammals have press ganged into acting as permanent structures.

3. You are trying to support your body upright on your spine, this is like trying to build stilts out of rope. Spines evolved for support of a horizontally oriented body so are quite good at remaining flexible while supporting horizontal load. This is very detrimental in a upright stance and the reason humans have so many back problems.

4. Your retinas detach because our eyes are built out of folds. Vertebrate eyes form by layers of tissue folding back on itself creating a weak connection between the two layers, cephalopods start with a single layer which thickens and differentiates. This difference is irrelevant with the most primitive form of the eye but locks vertebrates into having a permanent weak point in the our complex eyes. Here is a great work up on it.

5. There is a slew of vestigial muscles in humans. the vary in functionality, from the remains of whisker muscles in the upper lip (vibrissal capsular) with zero function in humans but function to control whiskers in most mammals. The palmaris longus has so little function in humans it is missing in about a fifth of the population, but is vital in climbing primates.

6. The tailbone in humans is essentially functionless, at least in the sense there is no reason for it to be several separate pieces. Two important tendons attach to it, but there is no reason for it to be ~4 bones/ossification centers, this makes it fragile and easy to break, but since important tendons for supporting the anus attack to the end the number of bones can't be reduced.

7. Hernias happen because the testes exist the body cavity during development, this is unique to mammals, everything else keeps the testes on the inside. Mammals did it to keep the testes cool with the evolution of fur and endothermy because important proteins in the testes do not tolerate heat well, birds who had the same problem just evolved heat resistant testes proteins.