Great article from Tom Chivers: – My son, Billy, was born three weeks and two days ago. People say he looks like me, but he very obviously looks like a baby, or at a pinch Sir Winston Churchill; he sleeps, and feeds, and poos, and when he wants us to help in the process of one of those things, he cries. He’s an ordinary baby – objectively and unarguably better than all other babies ever, of course, but not qualitatively different. Four limbs, 20 digits, blue eyes, good lungs, comical facial expressions.
But an “ordinary baby” is an extraordinary thing. He is the product of a direct unbroken chain of information transfer going back 1.5 billion years, and, in a complicated fashion, far, far more. His tiny, pot-bellied little body is made of some number of trillions of cells – liver cells, brain cells, smooth and striated muscle cells, red blood cells, macrophages. Each of them is a descendant of two fused cells, my sperm and his mother’s egg which combined their divided chromosomes to form an embryo. And those cells are themselves descendants – through cell division in my body, and his mum’s, and before that the odd unzipping dance of meiosis – of the eggs and sperm in his grandparents, and their parents, and so on. His grandfather, my dad, was born in 1952 – three generations of Chiverses born under Queen Elizabeth II, a fact I find both strange and comforting. But I want to look further back than that.
My wife and I both have entirely British ancestors for several generations; the likelihood is, then, that the backwards trace of our ancestries would bump into each other pretty rapidly, certainly within the last thousand years; the 30 or so generations in those last 1,000 years would mean that we’d each have over a billion ancestors, more than the world population at the time. We’re all cousins of varying degrees. What that means is that at some point, going backward, you reach the most recent common ancestor (MRCA) of all humans; estimates put that at somewhere between 2,000 and 3,500 years ago, depending on how much interbreeding there was between different populations, although I have seen other estimates of up to 10,000 years. At some point in that area, there lived a man or woman who was not only the N-greats grandparent of Billy, and the (N-1)-great grandparent of me, but of you, and Barack Obama, and of Miley Cyrus, and every other human being alive. All the way through those thousands of years, those cell divisions were carrying on; the vast majority of cells were an evolutionary dead end, because they made skin cells or liver cells and died with the body. But a tiny minority were sperm and egg cells that joined to form new humans; the information in the chromosomes is shuffled and passed on, shuffled and passed on. Read the rest of Tom’s great article here My newborn son Billy, four billion years old today