Human Evolution: How Did We Become The Earth’s Dominant Species?

Our species, Homo sapiens, is found all over the world. We have had such an outsized influence on our planet that our period of dominance has been given a name – the Anthropocene. But where did we come from, and what has given our species this much power over the planet’s future?

Several characteristics set us apart from the other great apes or hominids, a family of tailless primates including bonobos, chimpanzees, gorillas, and orangutans.

  • We are hairless, lacking our closest relatives’ furry coats.
  • As a species, we switch from quadrupedal to bipedal movement during our early lives.
  • We are also characterized by high intelligence and large brains, which have enabled us to create complex societies and forms of communication.

The story of how we came to be is also the history of life itself.

While trying to explain why species are remarkably well-adapted to their environments, Charles Darwin and Alfred Russel Wallace independently conceived of the process of evolution.

Charles Darwin and Alfred Russel Wallace independently developed theories on how species evolve and adapt to their environments
Charles Darwin and Alfred Russel Wallace independently developed theories on how species evolve and adapt to their environments. Credit: Wikimedia/Julius Jääskeläinen

Let us imagine that 100 individuals live in a desert, where water is scarce. Forty of these individuals do not require much water, and pass this characteristic or trait on to their children. The individuals with this trait will be far more comfortable in the desert than the ones who are thirsty all the time! Over time, it makes sense that most or all individuals will have that non-thirsty trait. This trait will make them different from individuals who do not live in the desert. In time, they might even form a separate species.

Thus, evolution is how organisms pass on heritable characteristics to their offspring, leading to speciation.

The theory of evolution, accepted by the scientific community and forms the bedrock of modern biology, comes with a truly mind-blowing implication – that all life on earth is related!

Evolutionary biologists estimate that the last universal common ancestor or LUCA lived between 3.5 and 3.8 billion years ago. LUCA gave rise to the dizzying diversity of life we see today, including bacteria, fungi, plants, and animals.

Simplified_tree_of_life_with_LUCA_and_LECA_multilanguage
All life on earth evolved from the Last Universal Common Ancestor or LUCA. Credit: Wikimedia

It follows that species with a more recent common ancestor will be more similar than species that diverged from each other a longer time ago. For example, we believe that humans diverged from chimpanzees between 7.5 and 6.5 million years ago. However, the common ancestor of humans and chimpanzees diverged from gorillas between 8 million and 19 million years ago!

Thus, we are more closely related to chimpanzees, with whom we share 98.8% of our DNA, than to gorillas, with whom we share 98.3% of our DNA. However, we are all anthropoids, a group that also includes monkeys.

Together with the prosimians, which includes the lemurs of Madagascar and the bush babies of Africa, we form a diverse group called primates. Fossils of the first primates have been found in Africa, Asia, Europe, and North America – they were prosimians, looked somewhat like lemurs, and lived during the Eocene epoch.

During the Oligocene epoch, the first anthropoid monkeys evolved from the prosimians. The New World monkeys, seen today in South America, have broad noses, while the Old World monkeys, found today in Africa and Asia, have narrow noses.

Some researchers think that the ancestors of New World monkeys floated from Africa to South America on log rafts! They remained separated for millions of years. New World monkeys are all arboreal or tree-dwelling, while Old World monkeys can also be terrestrial or ground-dwelling.

The next big evolutionary step took place during the Cenozoic era, about 25 million years ago. This was when apes diverged from the Old World monkeys, losing their tails, developing larger brains, and spending more time on the ground.

We share many similarities with our fellow great apes!
We share many similarities with our fellow great apes! Credit: flickr/Kali Yuga Photography

While chimpanzees and gorillas look very different from humans, there were once other species that were a lot more like us. Scientists refer to the species more closely related to humans than chimpanzees as hominins. Like us, other hominins walked on two feet and included Australopithecus, Homo erectus, and the Neanderthals.

Hominins originated in Africa. Australopithecus lived between 4 and 2 million years ago and gave rise to the genus Homo to which we belong. Homo habilis, which is the earliest known representative of our genus, lived about 2.8 million years ago and used stone tools. Over time, the brains of hominins got larger.

Homo erectus and Homo ergaster began to use fire and make more complex tools. Eating cooking food may have decreased the size of our teeth and jaws, which are smaller than our ape cousins. By 1.8 million years ago, our ancestors had left Africa and moved into Asia and Europe.

This would not be the last migration out of Africa – more modern Homo species such as H. heidelbergensis may have migrated out of Africa between 50,000 and 100,000 years ago. Over time, modern humans replaced other hominins such as the Neanderthals to become the only remaining extant species of this group.

Neanderthals lived in Europe and Asia for more than 350,000 years before suddenly disappearing about 40,000 years ago. While they looked quite similar to us, they had sloped foreheads, large pelvises, and wide noses. Since they disappeared around the same time that H. sapiens was migrating out of Africa, many scientists believe that we are at least partially responsible for their extinction.

In some places, humans may have overcome Neanderthals with their advanced technology; in others, our ancestors may have interbred with them, leading to up to 4% Neanderthal DNA seen in some European and Asian communities! In yet other regions, perhaps climatic changes wiped out the Neanderthals before our ancestors even met them.

Skulls of Homo sapiens (left) and Neanderthal (right) at the Cleveland Museum of Natural History
Skulls of Homo sapiens (left) and Neanderthal (right) at the Cleveland Museum of Natural History. Credit: Wikimedia/hairymuseummatt (original photo), DrMikeBaxter (derivative work)

All these twists and turns in our evolutionary history led us here, to a world where we are indisputably dominant. It might not have worked out this way – the chances that we would evolve all the traits that make us successful, such as bipedalism, opposable thumbs, our big brains, and our hyoid bones, are extremely low – maybe even one trillion to one.

If we consider the four and a half billion years that have passed since the earth was formed to be one year, then a human life lasts just one and a quarter seconds. If the solar system formed on New Year’s Day, then the dinosaurs went extinct on 26th December, and human beings arrived at 11:35 p.m. on New Year’s Eve! For a species that has occupied the planet for such a short amount of time, geologically speaking, we have made immense changes to the world, for good or for ill.

Some human populations have genes that are protective against malaria. Communities in high-altitude regions like Tibet are better adapted to living in regions inhospitable for most of us. These are clear signs that humans are still evolving, and nobody knows where we will be a few thousand years from now.

Flesch Kincaid Grade Level: 9.7 

Flesch Kincaid Reading Ease: 54.8

Glossary

Anthropocene: A proposed unit of geologic time describing the most recent period of Earth’s history during which human activity began to have a significant impact on planetary systems.

Anthropoid: Humans and the species that are most closely related to them, such as monkeys and apes. This group is also referred to as simians.

Arboreal: In this context, animals that live in trees, as opposed to ground-dwelling animals.

Bipedal: Using only two legs for walking, like humans, as opposed to using four legs, like cats.

Cenozoic: Meaning ‘recent life’, this era began 66 million years ago and continues to this day.

Eocene: This epoch was a part of the Cenozoic era between 56 and 33.9 million years ago.

Evolution: A process by which the genetic material of a population changes over time, as organisms adapt to their environments through favorable traits that give rise to new species.

Extant: Communities, species, or other groups that remain in existence, as opposed to those that have gone extinct.

Extinction: The dying out of species or other groups due to natural causes (as in dinosaurs) or human activity (such as the dodo).

Hominids: Extant species are bonobos, chimpanzees, gorillas, humans, and orangutans, as well as their extinct relatives, which comprise the great apes.

Hominins: Humans and their extinct relatives that are more closely related to them than to chimpanzees, including the Neanderthals, Homo erectus, and Australopithecus.

Hyoid bone: The u-shaped bone in our neck that supports our tongue and is thought to have contributed to our ability to produce complex sounds and given rise to the formation of language.

Oligocene: This epoch of the Cenozoic era lasted from 33.9 to 23 million years ago.

Primates: A diverse order of mammals including lemurs, lorises, tarsiers, monkeys, apes, and humans.

Prosimians: Primates that are not anthropoids (humans, apes, and monkeys). These include lemurs, lorises, and tarsiers.

Quadrupedal: Walking on four legs, and not two (bipedal).

Species: A group of organisms that are biologically similar and can breed with each other.

Terrestrial: In this context, animals that live on land (ground-dwelling) instead of in trees (arboreal).

Trait: A genetically determined characteristic that is inherited from a parent.

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