What Makes Us Human?

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Understanding the evolution of Homo sapiens, and how humans came to be human, has been a fascination for people since Darwin’s time, but it has also proved to be one of the most controversial of the sciences. Humans and Chimpanzees diverged about 7 million years ago and during this time a great deal of anatomical and behavioural changes occurred which now distinguish us from our closest relatives. Despite this, we still share over 99% of our genetic make-up with Chimpanzees; only 1% of our genes truly make us human. What is the manifestation of this 1%? Some of these differences are very clear visually; we are taller and less hairy, with larger brains and an upright, two-legged stance. Other differences are slightly more subtle; we have language, we use tools, we have culture and art enabled by abstract thought, we have a concept of self… but as that list continues, it becomes increasingly difficult to determine whether Chimpanzees, or indeed other animals, also share these qualities. If Chimpanzees can be taught language, then this indicates they have a brain capable of understanding and learning language, and thus, surely they can in some sense be said to have language themselves? Other characteristics are even more difficult to pin down; how do you measure self-awareness? Although there is a long list of traits that most people would consider to be exclusively human, the situation is in fact far less clear cut than that.

Success in the primate lineage began long before humans appeared on the scene, and new primate species began to emerge in large numbers during the Miocene (23 – 5  million years ago). Following an early expansion out of Africa, modern humans are believed to have evolved from the hominid species that remained there; Homo ergaster (Wilson et al, 1987). Homo ergaster was the first hominid species to resemble modern humans, at least from the neck down. He appeared around 2 million years ago and had a skeleton designed for long distance walking and running. He also used sophisticated tools and he is believed to have been socially more similar to modern humans, possibly even being the first hominid species to use fire. Meanwhile, in Europe Neanderthals were evolving, and Homo erectus in Asia. A second expansion out of Africa brought these three species into direct contact, leading to conflict as well as collaboration.

We have gained a great deal of understanding of the behaviour and intelligence of our early ancestors through the study of their fossils, as well as fossilised tools and artefacts. Not only can we deduce the physical attributes of our ancestors in this way, but also their behaviour, sociality and complexity of thought. DNA analyses are also providing vital insights into not only what early humans were like, but how they came to be that way.

Over the next four articles, I will review our current understanding of the evolution of our species, of our intelligence and our social traditions. I will also discuss the traits that are often said to be uniquely human, and discuss examples from the animal kingdom that call this into question. What does it truly mean to be human, and are we really a product of some special, unique, trait? Or are we simply a sum of our parts?

Articles in this Series:

  1. Part One: A Brief History
  2. Part Two: Intelligence and Language
  3. Part Three: Anatomical Adaptations
  4. Part Four: Culture and Faith

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