Let there be humans...

I was talking to MV about evolution and he recommended a Nat-Geo documentary titled 'The human family tree' for me to watch. To anyone who is interested in knowing about the origins of us humans in a lucid and interesting way, I would also recommend this highly engrossing documentary.

I have an intense peeve against most of my teachers during my early formative years, a trait that they share with an overwhelming majority of all teachers - they were either too incompetent or too inconsiderate. The fact that they could make 'acquisition of knowledge' boring is almost too difficult for me to comprehend now. Biology, for instance, is a subject that I remember with a special hatred but I also realize that my boredom with it was more a result of how it was taught rather than what was taught. Despite all my formal education then, I have managed to save 'curiosity' from the deathly throes of uninspiring teachers. And I have lately become curious about the origins of humans and what legacy we share with other creatures on Earth. That science decodes the labyrinthine links and interlinks between all existing living organisms today with the help of genetic studies, fossil records, and radioactive dating is fascinating in itself, but I'm more thrilled by what they have found.

Mitochondrial DNA is one of only two parts (The other is Y-chromosome) of the genome which are not shuffled around by evolutionary processes. It gets passed down the generations unchanged. It is amazing that every single one of us 6.7 billions living humans has the same Mitochondrial DNA - one that they have inherited from a woman who lived in Africa about 160,000 years ago. She has been termed the 'Mitochondrial Eve' and is, in some sense, the scientific mother of all humans alive today. Her descendants, in what is termed as the Out of Africa theory, left Africa for the first time around 60,000 years ago and moved on to populate the rest of the world. Starting from Middle-East, South Asia was colonized 50,000 years ago, Australia and Europe by 40, and East Asia (Korea and Japan) by 30, and North America by 16,000 (although this last date is controversial). In their quest for territory, our direct ancestors met the already existing species from the Homo genus like the Homo Erectus and Neanderthals and did to them what we are naturally good at doing - annihilation. I find it amazing to think that most of our early literature which is religious and mythical in nature and derives inspiration from otherwise ordinary battles and natural phenomena concerns but a minuscule fraction of the total human experience. Imagine how much more rich our history and our culture would have been, if only it had the resources to tap into the thousands of stories of hardships and courage that must dot our existence during the last 200,000 years.

Then again, the last 200,000 years is nothing but a slight flutter in the larger story of evolution of life on Earth. It is often naively suggested that we have descended from monkeys. The truth is that all the living species, both animals and plants, are cousins and not one of them has descended from the other. And in this family tree, the closest cousins to us modern humans are Chimpanzees and Bonobos, and the common ancestor to all 3 of us lived about 5 million years ago in Africa. It was a bit like humans and a bit like Chimps but nowhere like monkeys (it had no tail). So our branch of the family tree joins Chimps and Bonobos at 5 million years from now. This combined branch joins Gorillas in Africa at a common ancestor who lived 7 million years ago. This branch of our common ancestor joins the common ancestors of Orangutans at about 14 million years ago in Asia! Gibbons join us about 18 million years, and it is only if we go back 25 million years ago that we find the common ancestor who gave birth to all apes including us and so called Old World monkeys like langoors and baboons.

Ancestors of other species join us as we keep going back (New World monkeys at 40 mya, Tarsiers at 58 mya, Lemurs etc. at 63 mya) and we finally reach the K-T boundary - 65 million years ago. There is a thin layer of Iridium present all across the world at a depth in the Earth's crust which corresponds to a time 65 million years in the past. While Iridium is rare in Earth, it is common in meteorites. The Chicxulub crater is a titanic impact crater - 100 miles wide and 30 miles deep - buried below the Yucatan peninsula in Mexico and it has been dated at 65 mya. And the last fossils of terrestrial dinosaurs date back to 65 mya. It was only after the K-T boundary that the age of mammals began when their dinosaurial predators went extinct. It is weird to think that had that meteorite not impacted the Earth and wiped off the dinosaurs, humanity might not have had the chance to begin. On that fateful day 65 mya, all of our ancestors all across the world most probably went deaf and blind from the catastrophic impact, and were hanging in there by the skin of their teeth - all they could perhaps manage was to live long enough to reproduce - but that was enough...

If you really think about it, even 65 million years is but a small drop in the ocean of galactic time. As someone very smart once said, 'humans are what happens when you give 14 billion years to the hydrogen atom.'