Buzz
In 1859, Charles Darwin released his revolutionary work, 'On the Origin of Species', in which he put forward the theory of natural selection. Darwin argued that over time, the body and organs of living organisms gradually evolve to better serve their purpose, while features that lose their utility shrink and eventually vanish.
Like all other living beings, the human body is the product of millions of years of evolution through natural selection. Essential body parts have adapted to become highly specialized for their functions, while unnecessary ones have faded away. But what specific parts have we lost along the way? Let’s explore.
10. Brow Ridges
Various species of early humans, such as Homo erectus, Homo heidelbergensis, and Neanderthals, possessed prominent brow ridges. These ridges, located just above the eyes, sloped backward into the top of the skull, resembling the facial structure of chimpanzees and gorillas.
In modern humans, the brow ridges have disappeared, replaced by flat faces and high foreheads that rise straight up before merging with the top of the skull. But why did this happen?
While the exact reasons for the presence of brow ridges in ancient humans and their eventual disappearance remain unclear, researchers speculate that the change may have been driven by social factors. Anthropologist Grover Krantz conducted an experiment in which he wore a Homo erectus-inspired mask in public, only to notice that people avoided him and even crossed the street to avoid passing him.
This suggests that brow ridges were likely perceived as unfriendly, leading to their gradual disappearance as humans became more social and began forming larger communities. In exchange, our skulls shrank, and we developed more expressive and mobile eyebrows that help convey subtle messages and emotions.
9. Claws
According to logic, herbivores have hooves, carnivores have claws, and omnivores typically have either claws or fingernails. In fact, all omnivores would have had claws if not for primates—a diverse group of closely related species that includes humans, apes, lemurs, lorises, monkeys, and tarsiers.
The first primates had claws, which they used for digging and scratching, but they eventually lost them when they adapted to tree-dwelling. While claws are helpful for climbing, they became a hindrance when moving from one branch to another. This prompted early primates to develop hands and fingernails, which allowed them to both climb and grip branches effectively.
8. Prehensile Feet
We've all likely seen images of apes using their feet to grasp objects or swing from tree branches. These are prehensile feet, a distinctive trait of apes and primates. Imagine them as feet that can serve as an additional hand when needed.
Humans are the only primates without prehensile feet. While we once had them, we no longer do.
Early humans possessed prehensile feet until they transitioned to walking on the ground. Over time, their toes became straighter and less flexible, evolving to support walking and running. The first four toes lost flexibility, with the large toe being the last to evolve.
7. Canine Teeth
A man with gold front teeth, a close-up of his mouth
If you look closely at the teeth of chimpanzees, gorillas, orangutans, and other large apes, you'll immediately notice their long and sharp canine teeth. Humans also have canine teeth, but ours are more symbolic. They're neither long nor sharp, and are barely distinguishable from the rest of our teeth.
So, why don't we have the prominent, sharp canines of other apes?
We actually did, but we lost them as they became less useful. Like other apes, early humans developed large canines for fighting other males to establish dominance. The winner of these battles would gain exclusive mating rights to several, or even all, females in the group.
However, as early human infants became more vulnerable to predators, the importance of dominance battles faded. Human males began to focus more on protecting their young than fighting for mating rights. As a result, our canine teeth gradually became shorter and are now the smallest they've ever been.
6. Long Arms
The first humans, who appeared around six million years ago, had long arms and short legs, resembling modern-day apes. In contrast, we now have shorter arms and longer legs. What led to this shift?
The explanation lies in their diet and body structure. Early humans were shorter and primarily ate plants, requiring a larger digestive system to process their food. This caused their rib cages to expand to accommodate the bigger digestive organs.
However, around 1.9 million years ago, as humans moved to hotter regions and incorporated meat into their diets, their bodies became narrower. With meat requiring a shorter digestive tract, their digestive organs shrank as well.
At the same time, early humans developed longer legs, which allowed them to travel greater distances while hunting and chasing prey. Their legs continued to lengthen until Homo erectus emerged, the first of our ancestors to leave Africa. With exceptionally long legs, they were able to effectively dissipate body heat.
5. Big Stomachs
The human brain has grown larger ever since the appearance of Homo habilis two million years ago. The brain size of Homo habilis was about 600 cubic centimeters. However, 1.5 million years ago, Homo habilis became extinct, making way for Homo erectus, whose brain was around 900 cubic centimeters.
Researchers understand that our brains grew larger due to access to more food. Interestingly, our stomachs shrank at the same time. On the surface, this seems counterintuitive since larger brains need more energy, and therefore more food. Logically, our stomachs should have gotten bigger to accommodate the extra food.
The opposite occurred because early humans shifted from a diet of low-nutrient plants to a more nutrient-rich omnivorous diet, which included a significant amount of meat. As a result, their stomachs shrank since meat provides more nutrients and energy than plants.
4. Large Eyes
Some early human species had notably large eyes. This includes Neanderthals, our close relatives, who interbred with early Homo sapiens for about 5,000 years before they went extinct.
Researchers think Neanderthals developed large eyes after migrating out of Africa to the colder regions of Europe and Asia, where sunlight was scarce. Their eyes grew larger to capture more light. Homo sapiens, on the other hand, have smaller eyes because we remained in Africa, where sunlight was abundant.
Interestingly, some believe Neanderthals' large eyes may have been a disadvantage and could have played a role in their extinction. Researchers suggest that Neanderthals dedicated more of their brainpower to processing visual information, leaving less room for other essential functions, like developing the complex social skills that helped Homo sapiens thrive.
3. Whiskers
Most mammals have whiskers, but humans do not. In fact, we used to have whiskers but lost them about 800,000 years ago. To understand why we lost them, we need to explore the function of whiskers in other animals.
Animals use their whiskers as an extension of their vision. Every whiskered creature has two types of whiskers: long and short. The long whiskers help animals navigate in the dark and through narrow spaces, while the short whiskers are used to identify objects.
Humans, however, lost their whiskers as we adapted to assign the functions of both types of whiskers to other sensitive parts of our bodies—our fingertips, lips, and genitals. These areas take in sensory information from our environment, similar to whiskers, and send it to the brain.
2. Fur
Why do humans have hair, while apes have fur? To understand this, we need to trace our roots back to the Australopithecus afarensis, a hominin species thought to be the ancestor of the first humans.
The Australopithecus afarensis resembled apes more than humans. Imagine it as an ape with some human-like traits. It had ape-like arms, legs, and fur but also had a larger brain and could walk upright like humans.
Humans lost their fur when the Australopithecus afarensis moved from the dense forests to hunt in the open savannah, exposing them to more sunlight than they were accustomed to.
However, fur and sunlight are not a good mix. Fur blocks sweat and traps heat, which could have caused overheating in the bodies and brains of the Australopithecus afarensis. To prevent this, they began shedding their fur to allow sweat and heat to escape more easily.
1. Tails
Modern humans still grow tails in the embryo and retain small tailbones after birth. These tailbones are remnants of the longer tails we once had. However, we lost our tails twice—first we grew them, then lost them, only to grow them again and lose them a second time.
Humans first lost their tails when the Aetheretmon, an extinct fish believed to be the ancestor of all land-dwelling creatures, lost one of its two tails.
The Aetheretmon had two tails, one on top of the other. The first was a typical tail fin used for swimming, while the second was a fleshy tail that helped it swim faster. Over time, the fish lost most of the fleshy tail, retaining only the regular tail fin.
Millions of years later, the Aetheretmon completely lost its regular tail fin as it evolved from a sea creature to a semi-aquatic, and eventually, land-dwelling creature. Meanwhile, the fleshy tail that was once lost regrew into the tail we now see in most land animals.
As hominids evolved into apes and humans, they lost this fleshy tail when they began walking on two legs. Apparently, tails would have interfered with their upright posture. Today, humans, chimps, and gorillas are tail-less, while many monkeys retain long tails, though those that walk more upright tend to have shorter tails.
