Everything You Need to Know AboutHuman Evolution

Our evolutionary history tells us who we were and why we are the way we are.

1Skin color is simply an evolutionary type of sunscreen.

Origin of skin color

Climate has a big role in evolutionary changes, if you are shorter and stockier you retain more heat, ideal for colder environments. There is a lot of diversity among humans, most noticeable is distinctions in skin color. This color is determined by the amount and type of pigment melanin in one’s skin. People with ancestors from sunny regions have darker skin than those who were born in regions with less sunlight.

Ultraviolet Light (UV) is needed to produce vitamin D, but too much UV can be harmful. Man originated in the sun dominated land of Africa, our skin was dark because our bodies produced large amounts of melanin to filter the harsh UV. As some of our ancestors traveled to less sunny regions further from the equator, the UV was weaker. To still allow enough UV in for the production of vitamin D, their bodies lowered their defenses by lowering the amount of melanin inside their skin. This resulted in a lighter pigmentation of their skin.

2The human eye evolved in gradual stages. Each stage functional, each found in nature today.

Evolution of the eye

The human eye gradually improved over 364,000 years, starting as just a light-sensitive cell. Euglenids, a microorganism, use this today to swim towards a light source for photosynthesis. The flat piece of light-sensitive cells eventually formed a cup shape, which gives flatworms the ability to detect objects and the angle light is coming from. In abalone shellfish that cup shape became more pronounced, allowing it to more precisely detect the angle of light. Edges shade the light so the angle can be based on what cells are shaded and what cells detect the light.

The opening became smaller, like the eye of the chambered nautilus. A smaller pinhole opening produces a sharper image and greatly increases the ability to detect the angle of a light source. As transparent liquid fills the eye a primitive lens forms, which provides marine snails and the octopus with an even sharper image. As the slight and gradual changes continue the dense liquid forming the lens also forms the iris, leading to an eye similar to that of land mammals.

3The various stages of the human brain's evolution can also be seen in nature today.

Earthworm brain evolution

In hydra, a tiny aquatic invertebrate, consists a collection of connected neurons called a “nerve net.” These neurons communicate with each other and react to outside stimuli such as vibrations. In earthworm a similar collection of nervous tissues that run the length of its body, extend into each segment, causes muscle contraction to produce movement. These nerves, however, are controlled by a rudimentary brain, instead of outside stimuli. If the brain of an earthworm is removed, the earthworm will move continuously. These are the forerunners of the structures that, in some species, have become the central nervous system of the brain. They allow organisms to react to their environment.


evolution of the brain

With a central nervous system in place, the various sections of the brain evolved with various vertebrate. These sections have a layered architecture, with newer parts built on top of the earlier parts. The first and most ancient, the R-complex (the R refers to reptiles), developed as an extension of the upper brain stem. This area influences our territoriality, mating, and aggression – our basic “survival brain.” Above the R-complex lies the limbic system that first appears in the earliest mammals, and produces our emotional states. Our cerebral cortex is the thick outer layer of our brain, our “thinking cap.” With this new brain mass, we developed the traits that make us uniquely human.

Over time the size and density of the cerebral cortex grew, allowing for complex thought, conscious judgment, and self-reflection. But no matter how complex the brain gets, it still functions in quite a simple manner. In computers, all of the images, videos, and programming derives from nothing more than a pattern of two digits. The brain operates in the same way, but instead of 1s and 0s, it is based on the “spike” or “no spike” of neurons firing. For a detailed look at how the brain operates, watch the video to the right.

4Transitioning to walking upright had its advantages and set backs.

walking upright

The change from knuckle-walking, as chimps do, to bipedal walking started while our ancestors lived mostly in trees. This then improved during increased time on the ground, as environmental changes caused trees to become scarce.

Transitioning to walking on two legs had many evolutionary advantages. It allowed us to see further, freed our hands, and even conserved energy. Metabolic and biomechanical comparisons indicate that humans walking on two legs consume only a quarter of the energy that chimpanzees use while knuckle-walking on all fours. This transition, however, did come at a cost.

5Humans suffer many spinal related issues, because spins were not meant to be upright.

evolution of the spine

Our spines are a heritage from distant ancestors who carried themselves horizontally, in water and later on land. In quadrupeds the spine functioned more like a flexible suspension bridge, supporting the body’s organs. The human spine has been transformed into a weight bearing column and formed an s-shape to move the balance point over our feet. This puts it under unprecedented stresses, causing the spinal discs to dislodge and pinch nerves resulting in pain and fractures.

6The human birth canal is perhaps the greatest downside of walking upright.

evolution of birth

The young of other primates move around independently soon after they are born, humans though give birth to very helpless young. Human babies develop slower in the womb and are born prematurely, still underdeveloped compared to other primates. The brain of human newborns is only a quarter of its full size, whereas chimpanzee infants are half grown at birth.

The reason is, our pelvis adapted to provide stable support for the upper body which has given rise to a bowl-shaped pelvis that is very effective for walking upright but causes restraints in the birth canal. This restricts the size of the birth canal and even causes it to be twisted. Its inlet is widest from side to side but its outlet is widest from top to bottom so that, halfway through birth, the baby has to rotate from facing sideways to facing downwards. Additionally, the outlet is too small for a developed baby to fit through. Because of this, humans must be born before they finish development, and in some cases, their cranial bones are even squeezed together and overlap to fit through. Human birth is so complicated that before the era of modern medicine 1 out of every 5 births resulted in the death of the mother.

7Homo sapiens are a very young species, we came into existence very recent in Earth's history.

evolution calendar of life

If the entire history of the earth was laid out on a 12 month calendar, with the formation of Earth starting on January 1st and now being December 31st, then humans would have first appeared about 15 minutes before midnight on new year’s eve. All of recorded history would only stretch back to the last 16 seconds.

In just 7,000 years humans first left Africa and spread across the globe. This journey is traced by artifacts, fossils, and an unbroken genetic line. In tracing that line we use markers within DNA that doesn’t get mixed and shuffled at each generation, Mitochondrial DNA (passed on by only females) & the Y chromosome (passed on by only males). Below is a map that shows the migration of early Homo sapiens.

8Our hominid family tree.

To the left is a phylogenetic tree of our hominid family legacy. With so many various species of hominids discovered, and many more left to be discovered, it is difficult to know for sure which species descended from which branch of the hominid family tree. Thanks to known time periods of when each specimen lived, structural similarities, discovery locations, and genetics we can piece together a pretty accurate phylogenetic tree of our ancestors.


Humans were not made from dirt because a deity wanted someone to worship him. Instead, our history is far richer than that. We were shaped by nature, beat the odds of survival, and are comprised of ancestral gifts given to us by various specious from our evolutionary past.