When people think about evolution, they often conjure up a mental picture that has humans branching off on the descendants-of-apes limb of the big animal-kingdom family tree. However, if you look further back in evolutionary history, you will see evidence that humans are also related to fish. That's right – fish! The evolution from fish to human was obviously a long, drawn-out process; however, the traits that humans inherited from fish show an uncanny resemblance in many instances.
If you're still wrapping your mind around the whole theory of evolution or are getting hung up on our simian brethren, prepare to have your mind blown by our aquatic ones.
You Can Thank Your Fish Ancestors For Those Pesky Hiccups
The process of breathing in humans is controlled mainly by the brain stem. The brain stem sends signals to the primary breathing muscles in the human body, which cause them to contract. The brain stem is also responsible for the breathing processes of our underwater ancestors. In bony fish as well as sharks, the brain stem sends signals to the muscles surrounding the gills. Since the signals have to travel further in humans, they sometimes meet interference and ultimately cause a spasm.
The spasm will cue a quick inhale followed by swift closure of the epiglottis. This spasm is also what we experience as hiccups.
Fish Are To Blame For Hernias In Humans
Some fish – like sharks – have their reproductive organs in their thoracic cavity. In humans, these are also placed up near the liver during development, but they do not stay there. For females, these descend and become ovaries. In men, these descend further and become the testes. As the gonads travel all the way down to the scrotum in men, this weakens the abdominal wall and ultimately makes men more prone to hernias.
Inguinal hernias are when parts of the intestinal tissue get pushed through the abdominal wall. This is usually due to built up pressure from lifting things or straining. Fish, however, don't have this problem as their gonads stay up at their chests.
Fish Eyes Aren't Just Important For Hipster Photoshoots
Eyes are extremely convoluted structures, and their evolutionary path is so complex that it baffled even Darwin. However, many experts are now in agreement that the eye can be traced back to an ancestor that existed over 500 million years ago. New research from Australian National University has given experts some new insight, and it is believed that the origins of the modern human eye can be traced to 400-million-year-old Devonian fish.
These particular fish were covered in a bony armor that preserved the soft parts of the fish that usually wouldn't make it into the fossil record. These fish had eye sockets with insertions for muscles and canals for nerves that supported their complex eye. Fish also have rods, cones, and the three chemicals responsible for humans being able to view color in the seven-color spectrum.
Human Appendages And Fish Gills Develop In Similar Ways
Some fish, such as sharks, have structures that grow out of their gill arches and support their gills. These appendage supports are called "branchial rays." Researcher J. Andrew Gillis believes that gill arches in ancient fish could be the origin of limbs in humans. The genetics behind these gill arch structures and limbs are very similar. A gene (called the Sonic hedgehog gene) is integral in the growth of human limbs, and Gillis found that the same gene has a nearly identical function in the development of branchial rays.
The gene sets the groundwork for the limbs and the rays and then facilitates the growth of the skeleton. It is possible that there is not a direct evolutionary link between the two processes; however, Gillis is confident in the aforementioned argument.