• Project STEMinist

Evolution Between Humans and Our Ancient Ancestors

Over the course of time, the human species has evolved from fish, reptiles, and eventually, early primates. Some of the adaptations that have occurred allow us to live on land and function the way we do today. To understand some key differences that have changed between us and our ancient animal ancestors, I have explained some adaptations that have occurred. One adaptation between our fish ancestors and humans that has formed is the location of the testicles. In both fish and humans, the structure has ​two oval-shaped organs in the male reproductive system.​ The fish are cold-blooded in the water, and the testicles require that cool temperature to produce sperm; they are located near the fish’s heart. Humans and mammals on land are warm-blooded, which means they ​maintain a nearly constant body temperature irrespective of the temperature of the environment. Sperm cannot survive at body temperature on land because it must be at a cooler temperature. Over the years of evolution, male humans now have their testicles descend into a sac of skin called the scrotum. This new location away from the heart is useful because it not only allows creatures to be warm-blooded and reproduce on land, but it also helps the testicles to remain at the optimum temperature for sperm production, and therefore, species reproduction. The formation of body hair is an adaptation between our reptile ancestors and humans. Originally, most animals on land did not have body hair. After a mass extinction, several species began burrowing underground and only came out at night for food to avoid being hunted. Long whiskers evolved around the animal's nose and mouth, and this adaptation was advantageous because it helped animals with sensory. In the dark, they could sense their surroundings and the dimensions of a burrow using their face whiskers. Over time, more and more hair developed. Animals out at night and in harsh climates needed this insulation to survive cold temperatures. Body hair began to develop as a way to control temperature. The more body hair, the more insulated the animal is. An adaptation between our early mammal ancestors and humans that formed was color vision. Early primates could only see primary colors and had limited wavelengths that their DNA encoded to read. Eyes rely on opsin in the retina to tune in to certain wavelengths of light. Signals are then interpreted by the brain to see a variety of colors. Early primates with limited color vision had two active opsin genes. Each opsin gene is encoded in the DNA, and they are located near each other. One of the two opsin genes was duplicated, and an opsin gene copy had a mutation that allowed it to detect new wavelengths of light. When this third opsin gene mutation was added and turned on, the brain was ready to show more vivid colors. Enhanced color vision is super advantageous because it allows animals and humans to spot predators, determine the ripeness of fruits, spot the most nutritious foods to survive, and see the world much clearer.

As a result of evolution over time, humans have several vestigial structures that prove how we evolved. V​estigial structures are attributes of humans that are retained during the process of evolution that have lost some or all of their ancestral function in a given species. ​One vestigial structure present from our earliest fish ancestors in embryos is gill arches. Almost all humans only have the structure as an embryo, and they morph into part of the jaw structure. However, some may still be born with a gill near their ear and have it through adulthood. This structure is used by fish to​ exchange gases by taking in oxygen and releasing carbon dioxide out of the fish. Gills in fish have a bed of very small blood vessels with thin walls that the gases can diffuse across that allow a fish to survive. ​The yolk sac present in human embryos is another vestigial structure from reptile ancestors. ​This is still encoded in the human genome, but not useful in modern humans. In ancient mammals, the primary purpose of the yolk sac was to provide nourishment for the embryo during the stages of development. The yolk sac evolved when reptiles began laying eggs on land and needed their eggs to be properly protected and nourished without being in water. The yolk sac provides hydration and nutrients outside of the water. Another vestigial structure present in adults is the coccyx structure. The coccyx structure, known as the tailbone, ​is a triangular arrangement of bone that makes up the very bottom portion of the spine below the sacrum. In early primates, ​the structure was to connect an external tail to the spine. A tail helped our ancestors to live in trees and maintain stability and balance on the branches. Even though it does not have a use in humans, humans still have a coccyx in their skeletons. In fetuses, any tail is absorbed during development. All in all, learning about evolution aids modern humans in understanding why we live the way we do today. All modern species originated from an ancient animal or species and evolved. If we can understand the steps of evolution over time, modern humans could possibly predict what future generations will look like and how we can help our ecosystem survive. Evolution unlocks unlimited possibilities!

BY: Kenedy Quandt

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