Who was the first person ?

Who was the first person ?

by : Aria Ratmandanu

" The question of who was the first person, and when they lived, doesn’t have a precise answer. It’s kind of fuzzy, like the answer to the question: When did you stop being a baby and become a toddler ? "

Who was the first person really ?

             This may surprise you, but there never was a first person – because every person had to have parents, and those parents had to be people too! Same with rabbits. There never was a first rabbit, never was a first crocodile, never a first dragonfly. Every creature ever born belonged to the same species as its parents (with perhaps a very small number of exceptions, which I shall ignore here). So that must mean that every creature ever born belonged to the same species as its grandparents. And its great-grandparents. And its great-great-grandparents. And so on forever.

           Forever ? Well, no, it’s not as simple as that. This is going to need a bit of explaining, and I’ll begin with a thought experiment. A thought experiment is an experiment in your imagination. What we are going to imagine is not literally possible because it takes us way, way back in time, long before we were born. But imagining it teaches us something important.

              So, here is our thought experiment. All you have to do is imagine yourself following these instructions. Find a picture of yourself. Now take a picture of your father and place it on top. Then find a picture of his father, your grandfather. Then place on top of that a picture of your grandfather’s father, your great-grandfather. You may not have ever met any of your great-grandfathers. never met any of mine, but I know that one was a country schoolmaster, one a country doctor. Still, even if you don’t know what your father’s father’s father looked like, you can imagine him as a sort of shadowy figure, perhaps a fading brown photograph in a leather frame. Now do the same thing with his father, your great-great-grandfather. And just carry on piling the pictures on top of each other, going back through more and more and more great-great-greats. You can go on doing this even before photography was invented: this is a thought experiment, after all.

           How many greats do we need for our thought experiment ? Oh, a mere 185 million or so will do nicely!”

Mere?

It isn’t easy to imagine a pile of 185 million pictures. How high would it be? Well, if each picture was printed as a normal picture postcard, 185 million pictures would form a tower about 220,000 feet high: that’s more than 180 skyscrapers standing on top of each other. Too tall to climb, even if it didn’t fall over (which it would). So let’s tip it safely on its side, and pack the pictures along the length of a single bookshelf.

How long is the bookshelf ?

About forty miles.

The near end of the bookshelf has the picture of you. The far end has a picture of your 185-million-greats-grandfather. What did he look like? An old man with wispy hair and white sidewhiskers? A caveman in a leopard skin? Forget any such thought. We don’t know exactly “what he looked like, but fossils give us a pretty good idea. Believe it or not, your 185-million-greats-grandfather was – a fish. So was your 185-million-greats-grandmother, which is just as well or they couldn’t have mated with each other and you wouldn’t be here.

             Let’s now walk along our forty-mile bookshelf, pulling pictures off it one by one to have a look at them. Every picture shows a creature belonging to the same species as the picture on either side of it. Every one looks just like its neighbours in the line – or at least as much alike as any man looks like his father and his son. Yet if you walk steadily from one end of the bookshelf to the other, you’ll see a human at one end and a fish at the other. And lots of other interesting great- … great-grandparents in between, which, as we shall soon see, include “some animals that look like apes, others that look like monkeys, others that look like shrews, and so on. Each one is like its neighbours in the line, yet if you pick any two pictures far apart in the line they are very different – and if you follow the line from humans back far enough you come to a fish. How can this be ?

               Actually, it isn’t all that difficult to understand. We are quite used to gradual changes that, step by tiny step, one after the other, make up a big change. You were once a baby. Now you are not. When you are a lot older you’ll look quite different again. Yet every day of your life, when you wake up, you are the same person as when you went to bed the previous night. A baby changes into a toddler, then into a child, then into an adolescent; then a young adult, then a middle-aged adult, then an old person. “And the change happens so gradually that there never is a day when you can say, ‘This person has suddenly stopped being a baby and become a toddler.’ And later on there never comes a day when you can say, ‘This person has stopped being a child and become an adolescent.’ There’s never a day when you can say, ‘Yesterday this man was middle-aged: today he is old.’

             That helps us to understand our thought experiment, which takes us back through 185 million generations of parents and grandparents and great-grandparents until we come face to face with a fish. And, turning round to go forwards in time, it’s what happened when your fish ancestor had a fishy child, who had a fishy child, who had a child … who, 185 million (gradually less fishy) generations later, turned out to be you.”

               So it was all very gradual – so gradual that you wouldn’t notice any change as you walked back a thousand years; or even ten thousand years, which would bring you to somewhere around your 400-greats-grandfather. Or rather, you would notice lots of little changes all the way along, because nobody looks exactly like their father. But you wouldn’t notice any general trend. Ten thousand years back from modern humans is not long enough to show a trend. The portrait of your ancestor of ten thousand years ago would be no different from modern people, if we set aside superficial differences in dress and hair and whisker style. He would be no more different from us than modern people are different from other modern people.

                How about a hundred thousand years, where we might find your 4,000 - “greats-grandfather? Well, now, maybe there would be a just noticeable change. Perhaps a slight thickening of the skull, especially under the eyebrows. But it would still only be slight. Now let’s push a bit further back in time. If you walked the first million years along the shelf, the picture of your 50,000-greats-grandfather would be different enough to count as a different species, the one we call Homo erectus. We today, as you know, are Homo sapiens. Homo erectus and Homo sapiens probably wouldn’t have wanted to mate with each other; or, even if they did, the baby would probably not have been able to have babies of its own – in the same way that a mule, which has a donkey father and a horse mother, is almost always unable to have offspring. 

            Once again, though, everything is  “gradual. You are Homo sapiens and your 50,000-greats-grandfather was Homo erectus. But there never was a Homo erectus who suddenly gave birth to a Homo sapiens baby.

             So, the question of who was the first person, and when they lived, doesn’t have a precise answer. It’s kind of fuzzy, like the answer to the question: When did you stop being a baby and become a toddler ? At some point, probably less than a million years ago but more than a hundred thousand years ago, our ancestors were sufficiently different from us that a modern person wouldn’t have been able to breed with them if they had met.

             Whether we should call Homo erectus a person, a human, is a different question. That’s a question about how you choose to use words – what’s called a “semantic question. Some people might want to call a zebra a stripy horse, but others might like to keep the word ‘horse’ for the species that we ride. That’s another semantic question. You might prefer to keep the words ‘person’, ‘man’ and ‘woman’ for Homo sapiens. That’s up to you. Nobody, however, would want to call your fishy 185-million-greats-grandfather a man. That would just be silly, even though there is a continuous chain linking him to you, every link in the chain being a member of exactly the same species as its neighbours in the chain.”

DNA tells us we are all cousins.

                 Although we may lack the fossils to tell us exactly what our very ancient ancestors looked like, we are in no doubt at all that all living creatures are our cousins, and cousins of each other. And we also know which modern animals are close cousins of each other (like humans and chimpanzees, or rats and mice), and which are distant cousins of each other (like humans and cuckoos, or mice and alligators). How do we know? By systematically comparing them. Nowadays, the most powerful evidence comes from comparing their DNA.

              DNA is the genetic information that all living creatures carry in each of their cells. The DNA is spelled out along massively coiled ‘tapes’ of data, called ‘chromosomes’. These chromosomes really are very like the kind of data tapes you’d feed into an old-fashioned computer, because the information they carry is digital and is strung along them in order. They consist of long strings of code ‘letters’, which you can read and count: each letter is either there or it isn’t – there are no half measures. That’s what makes it digital, and why we say DNA is ‘spelled out’.

             All genes, in every animal, plant and bacterium, “that has ever been looked at, are coded messages for how to build the creature, written in a standard alphabet. The alphabet has only four letters to choose from (as opposed to the 26 letters of the English alphabet). We write the DNA letters as A, T, C and G. The same genes occur in many different creatures, with a few revealing differences. For example, there’s a gene called FoxP2, which is shared by all mammals and lots more creatures besides. The gene is a string of more than 2,000 letters.

              You can tell that FoxP2 is the same gene in all mammals because the great majority of the code letters are the same. Not quite all the chimpanzee letters are the same as ours, and somewhat fewer of the mouse ones are. Of the total of 2,076 letters in FoxP2, the chimpanzee has nine letters different from ours, while the mouse has 139 letters different. And that pattern holds for other genes too. That explains why chimpanzees are very like us, while mice are less so.”

             Chimpanzees are our close cousins, mice are our more distant cousins. ‘Distant cousins’ means that the most recent ancestor we share with them lived a long time ago. Monkeys are closer to us than mice but further from us than chimpanzees. Baboons and rhesus macaques are both monkeys, close cousins of each other, and with almost identical FoxP2 genes. They are exactly as distant from chimps as they are from us; and the number of DNA letters in FoxP2 that separate baboons from chimps is almost exactly the same (24) as the number of letters that separate baboons from us. It all fits.

            And, just to finish off this little thought, frogs are much more distant cousins of all mammals. All mammals have approximately the same number of letter differences from a frog (about 140), for the simple reason that they are all exactly equally close cousins: all mammals share a more recent ancestor with each other (about 180 million years ago) than they do with the frog (about 340 million years ago.

              But of course not all humans are the same as all other humans, and not all baboons are the same as all other baboons and not all mice are the same as all other mice. We could compare your genes with mine, letter by letter. And the result? We’d turn out to have even more letters in common than either of us does with a chimpanzee. But we’d still find some letters that are different. Not many, and there’s no particular reason to single out the FoxP2 gene. But if you counted up the number of letters all humans share in all our genes, it would be more than any of us shares with a chimpanzee. And you share more letters with your cousin than you share with me. And you share even more letters with your mother and your father, and (if you have one) with your sister or brother. In fact, you can work out how closely related any two people are to each other by counting the number of DNA letters they share. It’s an interesting count to make, and it is something we are probably going to hear more about in the future. For example “For example, the police will be able to track somebody down if they have the DNA ‘fingerprint’ of his brother.

            Some genes are recognizably the same (with minor differences) in all mammals. Counting the number of letter differences in such genes is useful for working out how closely related different mammal species are. Other genes are useful for working out more distant relationships, for example between vertebrates and worms. Other genes again are useful for working out relationships within a species – say, for working out how closely related you are to me. In case you are interested, if you happen to come from England, our most recent shared ancestor probably lived only a few centuries back. If you happen to be a native Tasmanian or a native American we’d have to go back some tens of thousands of years to find a shared ancestor. If you happen to be a !Kung San of the Kalahari Desert, we might have to go back even further.

             What is a fact beyond all doubt is that we share an ancestor with every other species of animal and plant on the planet. We know this because some genes are recognizably the same genes in all living creatures, including animals, plants and bacteria. And, above all, the genetic code itself – the dictionary by which all genes are translated – is the same across all living creatures that have ever been looked at. We are all cousins. Your family tree includes not just obvious cousins like chimpanzees and monkeys but also mice, buffaloes, iguanas, wallabies, snails, dandelions, golden eagles, mushrooms, whales, wombats and bacteria. All are our cousins. Every last one of them. And the most wonderful thing of all is that we know for certain it is literally true.