The Diversity of Human Species

Humans have not always been the only species of our kind on Earth, nor have we been the longest-lasting. Homo sapiens have existed for roughly 300,000 years, whereas Homo erectus thrived for about 1.5 million years—an impressive duration by comparison.

For a time, it was believed that we briefly coexisted with Homo erectus in Indonesia until approximately 35,000 to 50,000 years ago. However, findings from the Solo River Terrace Project in 2011 indicate that Homo erectus had disappeared at least 143,000 years prior to our arrival.

The Smithsonian Institution highlights that we are one of many human species, with various relatives tracing back to our primate ancestry. Although not all human species inhabited the Earth simultaneously, we did share the planet with several hominins.

Homo floresiensis — The 'Hobbits'

The only known remains of Homo floresiensis were discovered on Flores Island in Indonesia. Dubbed "Hobbits" after J.R.R. Tolkien's characters, these individuals averaged just 3 feet 6 inches in height and had notably large feet.

Homo floresiensis lived between 100,000 and 17,000 years ago. Their relatively recent existence continues to puzzle scientists, who expected them to exhibit more advanced traits in line with other contemporary species. Their skeletal remains bear similarities to those of human ancestors over a million years old.

Isolated on an island with scarce resources, these "Hobbits" were not only diminutive in stature but also had brains only one-third the size of modern humans, resembling those of chimpanzees.

While it appears that Homo floresiensis coexisted with our ancestors, there is currently no evidence to suggest any interaction occurred, likely due to their isolation.

Homo neanderthalensis — The 'Neanderthals'

According to the Natural History Museum, we possess more knowledge about Neanderthals than any other extinct human species. This is largely because they, like us, practiced burial rituals that helped preserve their remains. Neanderthals lived approximately 400,000 to 40,000 years ago.

Initially, Neanderthal populations were located throughout Europe and Asia, while modern humans were evolving in Africa. Eventually, as modern humans migrated from Africa, they encountered Neanderthals in northern regions.

Visually, Neanderthals were quite similar to us, albeit stockier, with prominent brow ridges and larger brains. Their physical attributes suited them well for colder climates, and they were adept hunters of large Ice Age fauna. Evidence suggests that they created sophisticated tools and engaged in close-range hunting, as indicated by injuries on remains akin to those sustained by modern-day bullfighters.

Research also indicates that Neanderthals had social structures and demonstrated compassion. Effective communication was essential for their hunting strategies, and they seemingly cared for injured members of their community, as evidenced by their burial practices.

Denisovans

Our understanding of Denisovans emerged in 2008 when Russian paleoanthropologists uncovered a fragment of a pinky bone in Denisova Cave in the Altai Mountains. This bone belonged to a young girl who lived around 40,000 years ago. By 2010, researchers classified her as a member of a new species called Denisovans, named after the cave itself.

Denisovans are believed to have lived from approximately 500,000 to 30,000 years ago, with evidence of their presence found across regions including Serbia, Russia, Southeast Asia, and China. Unfortunately, due to the scarcity of discovered remains, little is known about their physical appearance, though they may have resembled modern humans of Asian descent.

After departing Africa, our ancestors encountered Denisovans. Evidence from Denisova Cave indicates that modern humans, Neanderthals, and Denisovans coexisted for at least 100,000 years. Additionally, interbreeding occurred in New Guinea until at least 40,000 years ago.

Interbreeding Among Human Species

All three human species—Homo sapiens, Neanderthals, and Denisovans—interbred at least once. Notably, the remains of a woman who lived 90,000 years ago revealed a genetic composition that was a 50/50 mix of Neanderthal and Denisovan ancestry. Furthermore, scientists have identified traces of both Neanderthal and Denisovan DNA in modern humans today.

Research by National Geographic highlights that non-African populations may carry up to 2% or more Neanderthal DNA, with an estimated 70% of Europeans possessing such genetic material. This interbreeding likely contributed to the development of genes responsible for keratin production, enhancing our skin, hair, and nails. Additionally, these genes may have bolstered our immune systems.

Non-African populations are not the only ones with traces of interbreeding; the Australian Museum states that living Europeans and Asians have inherited about 1–4% of their DNA from Neanderthals, while certain groups, such as Tibetans and Australian Aboriginals, carry 3–5% Denisovan DNA. Interestingly, research published in Cell suggests that there were three distinct types of Denisovans, as traces of all three have been found in the DNA of a large sample from Southeast Asians.

The interbreeding with Neanderthals and Denisovans is believed to have enhanced our immune responses and contributed to lighter skin tones, colored hair, and varied eye colors—traits that became advantageous in colder climates after our migration from Africa.

While the exact circumstances that led to interbreeding remain unclear, it raises questions about whether such unions were born from affection or dominance, or perhaps a combination of both. What is evident is that this intermingling has left a lasting genetic legacy.

The Fate of Our Human Relatives

Aside from the possibility of the 'Hobbit' humans' extinction due to isolation and resource scarcity, the reasons for the decline of Neanderthals and Denisovans remain unclear. The prevailing theory suggests that Homo sapiens likely played a role in their extinction.

Unlike earlier human species, there were no significant natural disasters or other apparent causes for Neanderthals and Denisovans to disappear, especially after they had thrived for thousands of years without significant issues. Their decline seems to correlate with the migration of modern humans from Africa, as both species vanished roughly 5,000 years following our departure.

Briana Pobiner, a paleoanthropologist at the Smithsonian, posits that modern humans created competition for resources and territory upon migrating north. Despite Neanderthals’ proficiency in hunting Ice Age animals and their adaptations to cold environments, modern humans possessed advanced weaponry and long-distance trade networks, as well as the knowledge to create clothing for climate protection.

Reflecting on Human Evolution

Examining our history reveals a pattern of violence. Homo sapiens have dominated the world, often through force. We have harnessed and killed animals for our benefit and exploited our environment similarly.

When we contemplate the numerous instances of dehumanization, violence, enslavement, and imprisonment within our species over the past few hundred years—especially in the last 50—it becomes plausible to consider that we might act similarly towards those who differ from us.

While we yearn for connection, we were once not alone in our world. Other beings, similar yet distinct from ourselves, existed, but perhaps our inherent nature led us to act otherwise.

Concluding Thoughts

It appears that our drive for dominance and destruction is a fundamental aspect of our nature. While this may not be the most admirable trait of humanity, it has certainly allowed us to establish our place in the world. Yet, our conquests have not ceased.

Even after overcoming all conceivable challenges, we continue to turn against one another, seeking division based on race, religion, sexuality, socioeconomic status, gender, or political beliefs.

This leads to the question: Are we destined for extinction by our own actions, similar to how we potentially eradicated other human species? Or do we have the ability to alter this trajectory? Perhaps we can choose to embrace our differences rather than view them as threats.

How many times must we recognize that diversity strengthens us? The Neanderthal and Denisovan DNA within us offers a testament to this truth. Learning from one another not only enriches our knowledge but also nurtures our compassion. How can we aspire to engage with other intelligent beings when we struggle to coexist with each other?

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