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About 375 million years ago, a strange-looking fish was named. Tiktaalik landed Utilizes new adaptations. These include leaf-like fins to provide propulsion for “walking” on land, and air sacs in the throat to breathe oxygen from the air. TiktaalikIt has gills and is the oldest known common ancestor of tetrapods, or animals with four legs.
Quadrupeds have evolved into countless species over hundreds of millions of years. homo sapiens. So if humans evolved from fish, why don’t they have gills?
Part of the answer is practical. The gills must remain wet in order to work, which is not ideal for animals that do not live in water.The surface area of the gills is large, with thousands of small blood vessels, allowing oxygen to easily access the bloodstream. When water rushes over the gills, oxygen diffuses inside and carbon dioxide diffuses out. chris organ, an evolutionary biologist at Montana State University. If land animals had gills, they would dry out quickly, making it an inefficient way to breathe. Human lungs, on the other hand, are excellent at drawing oxygen from the air into the bloodstream through gas exchange.
However, lungs existed long before the transition from sea to land. “The lungs are actually surprisingly primitive.” evolution,” Neil ShubinAn evolutionary biologist at the University of Chicago. Tiktaalik fossil in 2004he told Live Science. When our fishy ancestors still lived underwater, they already had lungs in addition to gills.
“Fishes don’t come onto land and say, ‘I need lungs, let’s evolve lungs,'” Organ told Live Science. Only fish with lungs were able to invade land and survive. If a fish without lungs tries to live on land, it will die. “The key is to have these traits that evolved for other reasons, thereby allowing this animal to take advantage of this new environment,” he added.
Related: Can fish and other marine animals drown?
Similarly, scientists believe that our fish ancestors evolved arms to move on the ocean floor, which later came in handy for finding food and moving on land, Organ said. says. This is where natural selection comes into play. These arm-like structures were useful on land, so animals evolved longer limbs and hands over the next several million years. The same thing may have happened in the lungs. Scientists don’t know exactly how human lungs evolved because soft tissues like lungs don’t easily fossilize, Organ said.but Existing evidence suggests Early lungs evolved first into the simple lungs of lizards and then into the segmented lungs characteristic of mammals. especially, Mammals evolved to have diaphragms The muscles that regulate our breathing date back perhaps 300 million years.
Conversely, structures that are no longer useful are often retired. Over time, Organ said, gills shrunk and became restricted to juveniles, eventually disappearing from land-based land animals altogether during the Carboniferous period, about 315 million years ago. It was around the time that the first reptiles and the first bird and mammal ancestors began to evolve.
It may seem strange that primitive fish had lungs. Although gills are good at extracting oxygen from water, they can’t always provide large amounts of oxygen, especially for larger animals that require more oxygen. Seasonal changes can also affect the amount of oxygen in the water, Shubin points out. For example, if there are a lot of dead leaves in the water, they absorb oxygen. Therefore, air sacs (primitive lungs) allowed fish to swallow air above the water surface to supplement their oxygen intake.modern lungfish over 400 million yearsalso had this same function, which helps explain why land travel was possible.
But we haven’t completely lost our early gills. Human fetuses have questionable physical characteristics. Small folds called pharyngeal arches resemble gills, but we don’t use them for breathing. And while they’re not exactly gills, Shubin said, they’re definitely remnants of early gills, like ancient recipes that now make things different than they did before. Throughout fetal development, these arches become part of the jaw, throat, and ears. “All creatures with heads go through the pharyngeal arch stage,” Shubin says. In other words, an animal’s head cannot form without the pharyngeal arches.
Aquatic gill-breathing species also have arches like this during embryonic development. The only difference is that the arches grow into real gills, and the bones, muscles, nerves and arteries around them develop, Shubin said.
It’s thanks to our inner fish that we can now use our lungs to breathe without those pesky gill slits getting in the way.
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