This is the second part of my attempt at discussing why humans are the dominant species on earth. In the first part I discussed how our brain grew to be so big. That post can be found here. — @notacinephile/why-humans-are-the-dominant-species-on-earth

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A friend of mine recently wondered, if we, such a sophisticated complex species, are the result of natural selection, isn't it too linear?
Let’s talk about it.

In retrospect and with the aid of written history, we see a gradual rise of civilization, first a slower incline—faster and faster as millennia passed. We don’t see any other species that can rival our intellect within this window of time. It’s always us. Aren’t we just too conveniently prospered like everything meant to be?

The truth is—a few thousand years is nothing on an evolutionary scale. For the last 12 thousand years we’re in the Holocene age, the human era—none of the other human species lived during that time. They were all gone. Extinct to oblivion. But that doesn’t mean they weren’t here. Their existence and cultures are discovered through paleontology (the study of fossils) and archaeology. Their own evolution and relationship with us, homo sapiens, shows us that our path to ascension wasn’t linear at all.

Unlike Chimpanzees and Gorillas, other human species are from the same genus we belong to, homo. And apart from us, there were Homo erectus (who roamed east Asia), Homo neanderthalensis (who roamed Europe and western Asia), Homo soloensis (from the Java Islands), Homo floresiensis (pygmy humans from Flores Islands), several other species from Africa such as Homo rudolfensis, Homo ergaster. Another species from Siberia, Homo denisova.
It’s important to note that all of these species were “humans” and existed at the same time in different parts of the world. They are not a successor to one another, rather brothers of equal footing. We are likely to be able to mate with them and produce healthy offspring.

What happened to them then?

In 2010 and 2015 two new homo species were found. This indicates that not all human species are still known to us and we know very little about most of their cultures. We’ve found traces of DNA evidence in modern humans nonetheless, suggesting that at one point we’ve mated with multiple human species. Are you suffering from allergies? Depression? Your Neanderthal DNA might be the cause of that!

Most of them went extinct for a number of possible reasons. Natural selection is there of course and there were us, homo sapiens, who are likely to be one of the major causes of their demise.

Let’s talk about Homo Neanderthals to serve as an example who went extinct about 30,000 years ago. Among other human species, we know a lot about them from archaeological evidence.

They evolved separately in a different continent. They were bigger than us, had a more muscular build and hunted bigger animals (evident from their hunting tools). They were social, cared for their families and moved in bands.
When us sapiens arrived at their homeground, experts suggested two theories,

1. Competitive Replacement—humans had slightly better cognitive and social abilities than the Neanderthals and with our bigger numbers we drove them to extinction over a few thousand years. The small whatever number remained of them— joined us, hence our small portion of Neanderthal genes.
2. Violence and extermination—Our encounter with the Neanderthals weren’t peaceful at all, we fought over resources and wiped them out. Neanderthals were great fighters but no match for our large numbers and superior social skills.

The theory of violence is the most accepted one. Sounds unbelievable?

Look at our own history. Even disregarding all the destruction we’ve caused to the climate, disregarding other species like mammoths, elephant birds our ancestors hunted and made go extinct, disregarding the modern humans who destroyed entire habitats and ecosystems—We, for all our intelligence and social skills, killed our very own people by the score! Even the slightest skin color, beliefs can make us wipe people completely. Our history is full of brutal ethnic cleansings and genocides. We can’t even stand the difference in ideas and jump at slitting throats. Is it too hard imagining us wiping out a rival human species? I think not.

We are the last human species on earth and we are here now because of sheer chance, through natural selection. It wasn’t preordained or predetermined. If it wasn’t us, it would be another human species, that is to say, a species very similar to us in cognitive and social abilities.

So, no, it wasn’t a convenient linear rise. We tore through many other human species and if, by any chance, the whole thing could happen all over again, there’s no guarantee that Sapiens would be the victors.

No matter how hard we try to imagine ourselves apart from the animal kingdom, we are not. We stand here today, before our slain brothers, slayed by us.

Citations:
https://www.nature.com/articles/nature13727
https://science.sciencemag.org/content/328/5979/710/tab-pdf
https://www.pnas.org/content/108/37/15123
https://www.sciencemag.org/news/2016/02/our-hidden-neandertal-dna-may-increase-risk-allergies-depression