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.
Now, if you told someone that they look like they have a fish face, it would probably come off as an insult. However, everyone has a fish face to some degree. That's because a particular part of our faces is actually inherited directly from our fish ancestors. The "philtrum" is the groove located below your nose and above your top lip. This little patch of skin is largely ignored since it serves no purpose; however, it is a clue to where and how our faces formed.
Your face takes shape pretty early on in the womb, and it is the combination of three sections that come together in the fetus at the exact same time: your eyes have to come down and in, your jawbone and palate have to come up, and your nostrils and the middle part of your lip have to come down. The process is the same in fish fetuses, and the philtrum is the remaining leftover from all of this activity.
Many animals have the ability to make sound – using vocalizations to accomplish a wide variety of tasks, from finding a mate to warning trespassers to step off. Researchers have drawn parallels between human speech and certain mammalian ancestors, but far less research has been done to link human speech to underwater ancestors.
However, in 2008, Andrew Bass conducted a study that observed the neural circuitry responsible for vocalizations in toadfish. What Bass and his team found was that the neural pacemaker circuit responsible for making vocal sounds in these fish is very similar to the neural connections present in the vocal circuits of mammals. In other words, the studied toadfish had a collection of neurons at the base of their nascent brains that mirrored the collection of neurons that humans possess at the base of their brains. These neurons allow both of our species to make noises. Additionally, muscles, nerves, and bones that are vital to human speech are present in fish. Gill arches in fish have evolved over time into parts of the lower jaw and pharynx.
All animals have in common the fact that they start out as a single cell. From that single cell, a worm forms, a penguin forms, a fly forms, a human forms, all developing into embryos that resemble the finished creature. Notably, fish embryos look a lot like human embryos. That's because fish body structures are the basis of human body structures. Both fish and human embryos have a head, a body, and a tail – although, obviously the tail disappears in humans.
Additionally, both embryos have gill arches in the neck region. In fish, these become gills. However, in humans, they morph into parts of the jaw, middle ear, and voice box.
Although, for a long time, scientists assumed that ears came with the evolutionary transition to land mammals, there's evidence to suggest that this feature, like so many others, came courtesy of our fish ancestors. There are two bones in the middle ear of humans (and other mammals) that are the same as two bones present in fish. In physiological terms, the quadrate and articular bones seen in fish correspond to the incus and malleus in humans.
In laymen's terms, this basically means that gill openings are the precursors to human ears. A structure called the hyomandibula in fish, which protruded into the gills, created a chamber where sound would later be amplified in mammals.