We interact with other forms of live every day without thinking about it: patting the dog, carving a roast chicken, mowing the lawn. Even the petrol in your car came from dead prehistoric sea plants and animals. Following my DNA test, I considered human evolution back to the very origins of life itself. It’s 200,000 years since humans started looking like they do today, 2.5 million years since the appearance of the first humanoid species, 65 million years since the first primates, 200 million years since the first mammals, 600 million years since the first simple animals, 1 billion years since multicellular life, back to the first simple cells 3.8 billion years ago. DNA is the thread that links them all, as well as all the birds, fish, amphibians, reptiles, insects, bacteria, plants and seeds that have ever existed on Earth.
How it began remains the deepest question in history. If religion is your thing, it may be the work of a supernatural being. If you prefer science, it may be the natural forming of a simple molecule complex enough to make more of itself. The only truth is, nobody knows. The diversity of life on Earth was beautifully explained by Charles Darwin in 1859 in his theory of evolution by natural selection, which has became a major principle of biology today. Modern genetics has shown the clear relationship between all organisms on Earth. All animal and plant life share ancient DNA coding all the way back to when they diverged around 1.5 billion years ago. Despite obvious differences in shape, size and form, these common stretches of DNA all carry out the same job – telling the organism when and how to grow, reproduce and eventually die.
The percentages of DNA that we share with other species show just how closely related we are: 93% with Rhesus monkeys, 85% with mice, 75% with cats, 60% with Fruit Flies, 50% with bananas and 30% with yeast. It is the percentage differences that make us what we are. Between humans they are very subtle – differences in height, facial features, skin colour etc. Between species they are dramatic, as we see in the huge range of different organisms on Earth.
Famously, our closest living relative is the chimpanzee, which shares 98.4% of our genes. Our brain is twice as big as theirs and developed to the point where we can communicate through speech and writing, as well as create new ideas and complex technology. But like them we are highly social and live in groups. We both invest much in our offspring and teach them how to live and behave during their long growth to adulthood. We are both capable of problem solving and using sophisticated strategies requiring cooperation and influence. We are both status conscious, manipulative and capable of deception. Physically we have the same arrangement of internal organs and bones, share several important blood types and get many of the same diseases. We have the same arrangement, type and number of teeth with which we eat a wide range of foods including vegetables, fruit, nuts and meat. Our eyes face forward and we have binocular vision – we see in 3D and in colour. We have five fingers and toes on the end of each limb, with nails rather than claws. Our thumbs are opposable for precision grip. Our grip is strong; even as babies it can be strong enough to support our own body weight – handy for clinging to a mother’s fur in the event of a quick getaway. No doubt about it – humans are apes.
Closest relation – a chimp with alopecia shows just how close
But our bodies still retain remnants of a more ancient evolutionary past. The small fold of tissue on the inside corner of your eye is the remnant of a ‘third eyelid’ present in other animals such as birds, reptiles, and fish. Your ears contain unused muscles which once allowed them to ‘prick up’ to hear potential threats (some people can still wiggle their ears as a party trick). Wisdom teeth appear in adulthood as a relic from when had larger jaws with more teeth to grind down foliage. Tiny muscles on your upper lip and sinus area were once connected to sensory whiskers. The coccyx at the base of the spine is the remnant of a lost tail. You get goose bumps when you are scared to raise your long lost coat of fur to appear larger and scare off predators, or when you are cold to trap an extra layer of air and keep warm.
Although we are advanced enough to create vehicles to pilot ourselves away from the gravitational pull of the planet, as well as weapons powerful enough to render its surface largely uninhabitable, humans are a product of biology and so are a part of the natural world. We are animals. Think about it the next time you’re in the bath.
Further Reading:
5 ways a DNA Test can change your world view:
