From Newsgroup: talk.origins

https://www.science.org/content/article/major-highway-human-nervous-system-gets-complete-road-map

The vagus nerve has been a standard example of design by biological
evolution. It is a crazy design for animals like giraffes because it
ends up regulating the jaw and face of the animal, but doesn't grow
directly from the brain to the jaw and instead grows from the brain down around the heart and back up the neck to the jaw.

Some researchers have mapped out this path through the various
anatomical structures. How this relates to TO is that the vertebrate
jaw is derived from a part of the embryo called the branchial arches
often called gill slits because they initially developed into the part
of the circulatory system that became fish gills. Initially the vagus
nerve system was involved with the gills and heart, so the nerves grew
from the brain to this region of the embryo. As vertebrates evolved
some of the gills evolved into the jaw structure (jawed fish, our fishy ancestor). The vagus nerve remained associated with the new jaw
structure. Terrestrial vertebrates kept the jaw, but lost the gills and evolved a head and neck. The vagus nerve still had to grow down to the
heart, but now had to grow back up to the head. This quirk of evolution
makes the design of the giraffe look like pretty poor planning. The
vagus nerve has to grow over 3 meters in length when it's target is just
a few centimeters from the brain. The map that these researchers have developed reflect the evolution of the system in the early vertebrates.

Ron Okimoto

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