Human Evolution Facts

We stood up and walked on two legs. We started eating meat instead of coarse plants.

We moved into hygienic homes. Every time humans have taken a step forward, we’ve put evolution to the test.

But our bodies haven’t been able to keep up with our ever-changing lifestyle, and their design is now out of step with the way we live.

Modern diet deceives the brain

As recently as a few hundred years ago, sugar was a rare delicacy; today, it’s everywhere. But sugar deceives the brain centers that regulate hunger, resulting in a host of lifestyle-related diseases.

The human diet has changed markedly in the most recent chapter of our history, and our metabolism has been slow to adapt. Until a few thousand years ago, humans consumed sugar only when eating fruit or honey, which in many places were available just a few months of the year. Sweets made up a tiny part of our diet then; now, the sugar in soft drinks, candy and processed foods comprises 17 percent of the daily calorie intake in the Western world.

Unfortunately, the sweet taste triggers the urge to have more, and since sugar can deceive the brain centers that regulate our feeling of being satisfied, we tend to consume too many calories. Eating large amounts of sugar also impairs the metabolism’s ability to regulate blood-sugar levels, which can play a role in the development of lifestyle-related diseases, including cardiovascular illnesses, diabetes and obesity.

HARMFUL: The metabolism’s inability to adapt to our new dietary habits — or vice versa — constitutes a growing threat to public health.

Teeth meant for grinding plants were designed for a bigger jaw

The big teeth at the back of the mouth were designed to grind the coarse plants that made up our ancestors’ diet. When our ancestors began to incorporate meat and cook their food, their jaws shrank, but the large molars, known as wisdom teeth, stuck around. However, some people are born without them, due to a special gene variant that determines whether or not a person will grow them.

HARMFUL: Wisdom teeth can crowd the other molars and cause infection, so they are often removed.

The third eyelid has no purpose

In the corner of the eye, near the nose, there is a small pinkish membrane, the remnant of something that once covered the eyeball like a curtain. This third eyelid, called the nictitating membrane, has now shrunk to negligible size in humans, although it still works in fish, reptiles, amphibians, birds and even some mammals. The often-transparent membrane is used to protect the eyes. For example, beavers dive with it drawn, and woodpeckers engage it to protect their eyes from flying wood chips when they are pecking at trees.

Scientists have found that the third eyelid grows rapidly in humans during early embryonic development, but stops while the eyeball continues to grow, leaving the membrane unable to cover it.

HARMLESS: Modern humans eyelids are sufficient to protect our eyes, but we still retain the vestiges of the third eyelid, which is useless, but also harmless.

Nasal organ no longer controls our sex drive

Early humans had relatively small brains, and thus much of their behavior was driven by instinct. As is still the case among most animals, instincts such as sexual urges were triggered by phero-mones, chemicals that are detected by a special organ in the nose. When humans became more intelligent and were able to control their behavior through deliberate choice, this vomeronasal organ (VNO) became superfluous. However, researchers estimate that 50 to 90 percent of people still have vestiges of it. The evidence is inconclusive, however, because the VNO can be present upon one inspection but undetectable upon another.

HARMLESS: The vomeronasal organ, which detects pheromones, has no known function in modern humans and is harmless.

New diet generated “blind gut”

The appendix was designed to break down tough plant matter, aided by large amounts of bacteria. But when early humans replaced plants with meat, it became unnecessary. Now it’s just a tube near the junction between the small and large intestines that is often

removed because it gets infected. Some scientists think that the appendix may have a new function, however: When intestinal flora are destroyed by food poisoning or antibiotics, some of the good bacteria can survive in the appendix and recolonize the intestines.

HARMFUL/USEFUL: The human appendix can be prone to inflammation, but it may also store helpful intestinal bacteria.

We were adapted to live in dirt

The body is built to defend itself against microorganisms, but in our clean modern homes, the immune system has too little to do, leading to allergies and autoimmune diseases.

In the past 100 years, people in the Western world have moved from primitive houses with poor sanitation to almost clinically clean homes. This improved hygiene, along with access to pure water, has had an invaluable effect on public health, because it makes the immune system’s fight against disease-causing microorganisms much easier. But when our surroundings become too clean, our defense mechanism may have too little to do. Viruses, bacteria and parasites found in dirt stimulate the immune system, giving it useful tools to fight infection and disease later. In an environment where there isn’t much for it to do, there is a risk that the immune system will be unable to ward off illness or that it will overreact to otherwise harmless substances, resulting in allergies.

This imbalance also can have much more severe consequences, sometimes leading the immune system to attack the body. An attack on the pancreas results in Type 1 diabetes; if it strikes nerves in the brain and spinal cord, it causes multiple sclerosis. Autoimmune diseases affect up to 8 percent of Americans and are becoming more common.

HARMFUL/USEFUL: Our efficient immune system protects the body against invading enemies, but also may react inappropriately when the environment is too clean.

The birth canal has become too narrow

When our early ancestors stood up and walked on two legs, it was a major step forward for mankind, but a step backward for women giving birth. As our ancestors began to solve problems and interact more socially, the brain developed and grew considerably over the millions of years that followed. Our heads grew too, to hold our bigger brains, making the passage through the birth canal a tighter fit.

Walking upright also altered our bodies weight distribution; in order to restore the balance, the pelvis became tilted toward the front of the body. This configuration also supports the internal organs and prevents them from falling out – a role that is played by the ribs in four-legged animals.

Now our pelvises are perfect for walking on two legs, but the birth canal is narrow and has several slightly different degrees of tilt, making it more difficult for women to give birth.

USEFUL: Thanks to modern medicine, maternity clinics and hospitals, we have managed to minimize most of the problems caused by the narrow birth canal, so now we enjoy all of the benefits of our reconfigured pelvis.

The embryo still has a tail

While other animals use their tails for many different purposes, humans no longer need them, so our tails have largely disappeared. However, we have retained the supporting structure in our lowest three to five vertebrae, which are partially conjoined and form the tailbone. The human embryo has a pronounced tail 31 to 35 days into its development, but it disappears as the rest of the body grows.

USEFUL: The tailbone is an integral part of the body, serving as the anchor for several muscles and keeping the rectum in place.

Raised quills protect against the cold

Goose bumps are an ancient reflex in which an animal’s hairs rise in order to provide better insulation against the cold; however, humans have lost most of their body hair, so this reflex no longer serves any purpose. But human hair follicles have retained the tiny muscles that raise the hair; when these muscles are tightened, small bumps appear. This is the same mechanism used when a dog raises the hair on its back.

HARMLESS: Since humans are no longer covered in hair, goose bumps have no purpose, but the phenomenon is harmless.