We have 3 billion base pairs in our genome. With so much raw material, we should have had some 3 million genes. Instead we have a paltry 30000 genes, which uses up just 10% of our genome. So what is the rest doing? It has been called “nonsense” DNA, and Francis Crick—no less—dismissed it as “little better than junk.” Strangely, it seems to abide by Sturgeon's Law, which says that “ninety percent of everything is crap.” Just think: Issac Newton, Mother Teresa, Sachin Tendulkar, and Adolf Hitler had only 10% of their genome driving them. Imagine what they might have achieved if the remaining 90%—the “crap”—had kicked in!
But surely frugal nature would not pointlessly load us with so much junk. There has to be a reason for its presence. I am fascinated by the explanation that this junk - these meaningless sequences in our DNA - are the “fossils” of genes past. As the evolutionary biologist Susumu Ohno put it, “The Earth is strewn with the fossil remains of extinct species; is it any wonder that our genome too is filled with the remains of extinct genes?” We have after all evolved from simple molecules that learned to make copies of themselves, through humble single-celled creatures, to our present complex form. Surely we did not start out with the three billion base pairs, or the 30000 genes, that we have now. Bits and pieces must have been added on (and shed) over the eons.
Imagine the early Earth: teeming with exuberant life forms, each desperately trying to establish a foothold on the evolutionary ladder. No price was too high to pay for survival. Our first unicellular ancestors must have had fierce drawn-out battles with innumerable bacteria and viruses. Countless numbers on both sides must have perished before some truces were arrived at. Free-living bacteria were permitted to live within our cells disguised as mitochondria if they would agree to generate energy for our daily use. Deadly retroviruses agreed to lay down arms if they could insinuate themselves into our genome and function as genes and thus be spared harassment by the cell’s deadly arsenal. Even as new genes were added, other functional genes—having served their purpose —must have mutated away into “junk.” In this junk, therefore, is the story of our evolutionary past. And what a story that must be! For in this corrupt code is the story of our survival; in it are the traces of our wings and scales, of our horns and tails.
But why is this junk DNA being preserved? Some 40 million base pairs are believed to have been discarded since our ancestors migrated out of Africa. But so much excess baggage is still being retained. There must be a purpose. Perhaps it is because in it lies not just our past, but also our future. As the genetic clock ticks on, random mutations will continue to take place in the nonsense sequences and, every now and then, a new meaningful sequence—a new gene—will appear in the meaningless jumble to take us a step further in our evolutionary journey. We have traveled only a small fraction of our journey. Most of the road lies ahead.
But the onion, I understand, has 12 times as much DNA as a human. The salamander has 40 times as much! Does that portend a greater destiny for these “lower” life forms? Why not? Who knows which species will inherit the Earth next? Some 65 million years ago the dinosaurs ruled the Earth, with no one to challenge their dominance. Our furry forebears probably spent most of their time scurrying about in the undergrowth trying to avoid being caught for snack by a foraging dinosaur. And then a bolt from the blue: a shooting star crashed into the world and turned it upside down! Today, we visit the KFC outlet and gnaw on pieces of the closest surviving relatives of the dinosaurs!
The dinosaurs were around for 200 million years, and where are they now? We have been around for just 5 million years, and already we strut about like we own the Earth. Tread softly Homo sapiens, you only have the Earth on lease. Tomorrow it may be the turn of the onion!
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