[Creative Cultivation Program] "From fish to humans" has more evidence, is the human middle ear transformed from fish gills?

Author: Liu Sen

Recently, there is a very interesting news. Chinese scientists revealed for the first time that the human middle ear was once the gills used by fish to breathe! This made some netizens very happy. Some netizens said, no wonder some people can never be woken up, it turns out that ears are used for breathing. Some people recalled their childhood, when their teachers often criticized them, "Didn't you hear what I said just now? Are your ears used for breathing?" Others marveled that our ears are fish gills, so doesn't that mean we humans evolved from fish? This statement is really not wrong.

Fossils of ancient fish | Tuchong Creative

As early as 1822, the famous French anatomist Saint-Cyran discovered that fish are structurally identical to amphibians, reptiles, and mammals. Therefore, quadrupedal vertebrates, including humans, actually have a common ancestor, which is fish. This hypothesis has also been proven correct by later fossil evidence. So, you who are watching the video now may be walking with a pair of pelvic fins, holding a mobile phone with a pectoral fin, and listening to my explanation with fish gills. It is not surprising that our middle ear evolved from fish gills.

But how did the gills of fish evolve into the middle ear structure? Paleontologists previously only found part of this process, that is, the middle ear structure originated from the blowhole of fish, and speculated that the blowhole may have evolved from the first pair of gills behind the eyes of fish. However, there has been no relevant fossil evidence for this speculation. Hearing this, fish gills, middle ears, and blowholes, I think everyone may be a little confused again, so if we want to understand this process, we must first understand what these body structures are.

Schematic diagram of human ear structure | Tuchong Creative

First, let's talk about the structure of human ears. Our ears are actually a very complex auditory system, which includes three parts: the outer ear, the middle ear, and the inner ear. There are the tympanic chamber, three ossicles, namely the stapes, the malleus, and the incus, as well as the Eustachian tube leading to the mouth. The middle ear composed of these parts is the secret of the sensitive hearing of mammals, including humans. But when you pinch your nose, close your mouth and blow hard, you will feel that the eardrum of your ear is very swollen. This shows that our ears are connected to the mouth. The Eustachian tube that connects them evolved from the blowhole structure of our fish ancestors, and the bones around the blowhole evolved into the three ossicles in our middle ear. These are all proven by fossil evidence and embryological development.

However, in order to find evidence that the blowhole evolved from fish gills, paleontologists have been searching for more than 100 years and have not found it. It was not until May of this year that a team led by Chinese paleo-ichthyologist Ge Zhikun published a research review, confirming that the human middle ear evolved from the gills used by fish for breathing. This process only requires two steps, but it took 20 years to find this process. First, they found 7 fossils of primitive true armored fish the size of a fingernail during a field excavation of the Silurian strata in Changxing, Zhejiang in 2002, and named them Dawn Fish. After that, the Dawn Fish fossils were subjected to high-precision 3D scanning and 3D reconstruction of the skull, and it was discovered that the structure that evolved into the blowhole was called the tongue-mandibular sac. However, in order to prove that it is a gill with respiratory function, the most important link in the entire chain of evidence is still missing, that is, to find fossil evidence of gill filaments preserved in the gill sac.

To this end, their team conducted several years of field excavation work in the Early Devonian strata in Qujing, Yunnan. In 2017, they finally found the first fossil of a broad turtle with gill filaments completely preserved in the gill pouch in the strata 400 million years ago near the Qujing Miandian Reservoir, further proving that the tongue-jaw pouch structure is a gill with normal respiratory function and can exchange oxygen, thus providing the most accurate anatomical and fossil evidence for the origin of the blowhole of vertebrates. At this point, the evolutionary chain of the human middle ear has basically been completed.

We can still find many amphibious fish coming ashore | Tuchong Creative

Let's restore the whole process of the fish gills becoming our middle ears. 400 million years ago, our ancestors were a group of cute-looking ancient fish. They had no chins yet, and there was a huge single nostril between their eyes, which served as a respiratory organ for inhaling water. After inhaling water, we exchange oxygen through the gill sacs behind the eyes. But when we grew a chin and evolved into jawed fish, and really had a mouth, the single nostril became the double nostrils we have today. But this pair of nostrils has no respiratory function. It is not connected to the mouth, and only has the function of smell, which is used to smell. However, our breathing needs have not decreased, so the first pair of gill sacs behind the eyes were transformed into water blowholes, which became respiratory organs for inhaling water as a new way of breathing. The water blowhole structure helped future fish to breathe in freshwater hypoxic environments, and also allowed our ancestors to go deep into the land through rivers, lakes and lakes. When our ancestors really began to land, the pair of nostrils used for smelling were finally connected to the mouth and became the main respiratory organ, while the drainage holes lost their respiratory function. Finally, in the process of conquering the land, our ancestors developed a stronger need for hearing, and the abandoned blowholes were reused and evolved into our middle ear cavity. The pile of bones around it gradually became smaller and entered our middle ear, transmitting the sound to our brain, giving us sensitive hearing.

So, the next time you listen to some beautiful music, celebrate the wonders of evolution and think of those ancient fish ancestors who gave us the privilege of enjoying our auditory pleasures.

This article is produced by the Science Popularization China-Creation Cultivation Program. Please indicate the source when reprinting