The Origin of Humans on Earth

The origin of humans is a subject that is no better or conclusive than the previous topics we’ve covered. In fact, it has generated even more alternative theories and controversies than the origin of the Universe. For a very long portion of our human history, people from different parts of the world have had different theories on this subject; the root of which however, is one common entity – God.

And this is not exactly surprising since ‘God’ has been the default go-to answer to anything that is puzzling and ambiguous, both in the past, and to an extent, in the present days as well. Hence most theories on the origin of humans have stemmed from the religious beliefs or scriptures of various parts of the world. Be it Adam and Eve in Genesis or the Purusha (considered the first human) in Hindu scripts, people had this common consensus that ‘God created us’.

So, when the idea that humans evolved from Apes made rounds initially, there was unsurprisingly a huge uproar and controversy and the theory was considered blasphemous, mainly for two reasons. One, it contradicted people’s notion on the subject and seemed to be in opposition to religion. And two, people could not chew the fact that they could actually be the descendants of apes. In fact, it was forbidden to teach students the ‘Origin of Species’ in some of the states of the United States of America (of all countries on earth) for most part of the 20th century, because it completely contravened the Christian religion of the time. Similar was the case in many countries. 

Thankfully, due to years of scientific advancement and supporting research and evidence, we seem to have reached a consensus now, and we accept the theory of Apes being our forefathers. Humans are descendants of Apes, a member of a big family known as the Great Apes, with Chimpanzees, Gorillas, and Orangutans as our nearest relatives. When trying to fathom how we humans actually came to be from the primate heritage, picture a female ape, about 6 million years back in time. This single female ape would have two daughters. One would go on to give rise to the Chimpanzees, and the other to Humans.

Interestingly, along with other descendents of Apes mentioned above, we also had other Human Species. But before diving into our family tree, let us get familiar with the concept of Family, Genus, and Species.

Species are the category of animals that are closely related to each other and are capable of exchanging genes or interbreeding (like all lions belong to the species Leo). Genus comes just above the species and below family in an organism’s taxonomic hierarchy whereas species is the lowest and final level of the classification. Genus includes a large number of closely related species that can mate (if induced to) but cannot reproduce fertile offspring (think of the fertile Horse and the fertile Donkey giving rise to the infertile Mule). And family are the group of animals that once descended from a common ancestor (like Tiger, Lion, and Cat all coming from a common ancestor and hence put together in the same family Felidae).

The scientific name for us present world humans is Homo Sapiens, where Homo stands for the human genus and Sapiens is one of the various species under the genus. Homo means Human in Latin, so all other animals having the genus Homo (whatever be their species) are considered to be humans, and hence are our siblings. And Sapiens mean wise in Latin – not very surprising considering that is exactly how we like to think of ourselves.

The first Human is considered to have originated about 2.5 million years ago in East Africa, from an earlier genus of apes known as Australopithecus. After the wave of migration of these early humans from East Africa to North Africa, Europe, and Asia, changes in their respective environments and different adaptations led to the rise of different human species. For example, the ones who migrated towards Central Asia and Europe evolved into the Homo Neanderthalensis and the ones who migrated towards Eastern Asia evolved into the Homo Erectus.

We have no concrete idea about the exact number of species of Humans to ever exist, and new information regarding this is still being discovered today (like the finding of a fossil finger in the Denisova cave in Siberia led to the discovery of Homo Denisova). Another important fact to keep in mind is that evolution didn’t follow a linear trajectory –  there is no straight line of descent, contrary to what most seem to believe. It is not like the H. Erectus evolved into the H. Neanderthalensis and the H. Neanderthalensis to other human species. There wasn’t just one particular human species inhabiting the earth at a particular time, earth was home to multiple human species at the same time.

Our species H. Sapiens is considered to have originated in Eastern Africa around 150,000 years ago. And around 70,000 years ago, they spread into the Arabia Peninsula and then quickly populated entire Europe and Asia.

So, what really happened to other species when H. Sapiens started to populate the better part of the world?

There are two popular theories regarding this:

  1. Interbreeding Theory
  2. Replacement Theory

According to the Interbreeding Theory all these early humans were able to mate and produce fertile offspring (despite belonging to the different species) and what we have today – present day humans – is the fusion of different human species.

Replacement Theory however, contradicts the Interbreeding Theory, and suggests that all other human species were replaced, or maybe even killed by our species, and what we have today is a pure Sapiens species human.

Although Replacement Theory is the one that is most widely accepted, two shocking insights came forward in 2010, that unhinged its foundation. Scientists managed to map the Homo Neanderthalensis genome, and compared it with the DNA of contemporary humans. The Neanderthal DNA was found to be present in the DNA of the modern human population of the Middle East and Europe. The DNA extracted from Homo Denisova (discovered the same year) was also found in the DNA of the modern Aboriginal Australians and the Melanesians. Although the number was not exactly huge (4 percent in the case of Homo Neanderthalensis and 6 percent in the case of Homo Denisova), it is still significant and provides a revealing insight into how different species could have mated to reproduce a fertile offspring. With possible further research, studies and discoveries, we might be in for even more groundbreaking insights.

If Replacement Theory is to be believed and all humans today are pure Sapiens, there should not be much genetic diversity between the people on earth. However, if there is some truth behind Interbreeding Theory, there could be significant genetic differences between the people (mostly Africa, Europe, and Asia where different waves of migration of different human species culminated in the past).

Debates have been going on regarding this subject – if the further pursuit in scientific research should be encouraged, or should the possible consequences be taken into account before venturing further into the matter. While I personally think science should always be objective and new ideas backed by legitimate findings should be explored, I can understand why this particular case could be a sensitive area, as a possible revelation in the future that different parts of humans have significant genetic differences could have devastating racial consequences.

Anyway, getting back to the story of human origin, let’s sum up all that we’ve learned till now with a quick wrap up.

So, to summarize in a sentence, early humans originated from the Apes in Eastern Africa, with different human species originating and migrating in different points of time, ultimately leading to the replacement (partial or complete) of all species by the Homo Sapiens.

But, before we come to an end, there are still two very important questions that need to be addressed.

First, how were the Homo Sapiens, otherwise a seemingly innocuous-looking animal with average size, able to leapfrog far more mammoth and ferrous animals in the hierarchy to take control of the world?

Second, what enabled these Sapiens to replace entirely (or almost entirely) their own siblings, that is the other human species?

To answer these questions, I will take the leaf out of the book Sapiens by Yuval Noah Harrari, which is sort of like a must-read book if you are interested to know about the overall history of humans.

We will address these two important questions we mentioned above in our ‘Long-Story-Short’ narration of human history in one article!

PS. Do read Sapiens! 

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