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.
Your Sense Of Balance Evolved From A Fish's Sense Of Direction
Our sense of balance (or lack thereof, depending on who you are) can be traced back to balance organs present in fish. The "lateral line" is a series of depressions with groups of hair cells beneath them. These function to detect differences in water pressure and allow fish to adjust their position relative to certain currents. Even the most ancient fish had sense organs.
Over time, the depressions evolved into the grooves of the inner ear. The nerve cells present in the inner ear are what have become of the hair cells in those primitive fish. The membrane of the oval window also started as a structure in fish. This membrane transmits changes in air pressure to the fluid of the inner ear.
Fish Have Similar Mechanisms Of Sensory Perception To Humans
Zebrafish are used in many studies because they are transparent, and researchers can use visual markers to track certain biological functions in the fish. The University of Queensland conducted a study that gave scientists further insight into how humans developed the ability to use certain senses in accordance with accompanying movements. Zebrafish have a midbrain structure that is called an "optic tectum."
The tectum in zebrafish functions like the superior colliculus in humans. The main stimuli detected by the tectum and superior colliculus are visual stimuli collected by the retina. The tectum is also associated with eye movement and corresponding head movements.