Post by Andrewsarchus on Mar 20, 2017 8:40:36 GMT
There never was the first rabbit, never was there a first crocodile or a first dragonfly.
A very basic introduction.
A basic tree of life explorer
A more advanced tree of life explorer
An extract from Richard Dawkin's 'the greatest show on earth':
"Take a rabbit, any female rabbit. Place her mother next to her. Now place the grandmother next to the mother and so on back in time, back through the many years, a seemingly endless line of female rabbits, each rabbit sandwiched between her daughter and her mother. We walk along the line of rabbits, backwards in time, examining them carefully like an inspecting general.
As we pace the line, we'll eventually notice that the ancient rabbits we are passing are just a little bit different from the modern rabbits we are used to. But the rate of change will be so slow that we shan't notice the trend from generation to generation, just as we can't see the motion of the hour hand on our watches and just as we can't see a child growing, we can only see later that she has become a teenager, and later still an adult. An additional reason why we don't notice the change in rabbits from one generation to another is that, in any one century, the variation within the current population will normally be greater than the variation between mothers and daughters.
So if we try to discern the movement of the 'hour hand' by comparing mothers with daughters, or indeed grandmothers with granddaughters, such slight differences as we may see will be swamped by the differences among the rabbits' friends and relations gambolling in the meadows round about.
Nevertheless, steadily and imperceptibly, as we retreat through time, we shall reach ancestors that look less and less like a rabbit and more and more like a shrew.
One of these creatures I'll call the hairpin bend, for reasons that will become apparent. This animal is the most recent common ancestor that rabbits share with leopards. We don't know exactly what it looked like, but it follows from the evolutionary view that it definitely had to exist.
Like all animals, it was a member of the same species as its daughters and its mother.
We now continue our walk, except that we have turned the bend in the hairpin and are walking forwards in time, aiming towards the leopards.
Each shrew-like animal along our forward walk is now followed by her daughter. Slowly, by imperceptible degrees, the shrew-like animals will change, through intermediates that might not resemble any modern animal much but strongly resemble each other, perhaps passing through vaguely stoat-like intermediates, until eventually, without ever noticing an abrupt change of any kind, we arrive at a leopard.
Various things must be said about this thought experiment. First, we happen to have chosen to walk from rabbit to leopard, but I repeat that we could have chosen porcupine to dolphin, wallaby to giraffe or human to haddock.
The point is that for any two animals there has to be a hairpin path linking them, for the simple reason that every species shares an ancestor with every other species: all we have to do is walk backwards from one species to the shared ancestor, then turn through a hairpin bend and walk forwards to the other species. Second, notice that we are talking only about locating a chain of animals that links a modern animal to another modern animal.
We are most emphatically not evolving a rabbit into a leopard. I suppose you could say we are de- evolving back to the hairpin, then evolving forwards to the leopard from there it is, unfortunately, necessary to explain, again and again, that modern species don't evolve into other modern species, they just share ancestors: they are cousins. Third, on our forward march from the hairpin animal, we arbitrarily choose the path leading to the leopard. This is a real path of evolutionary history, but, to repeat this important point, we choose to ignore numerous branch points where we could have followed evolution to countless other end points for the hairpin animal is the grand ancestor not only of rabbits and leopards but of a large fraction of modern mammals.
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 it’s great-grandparents. And it’s great-great-grandparents. And so on forever.
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."
Was there a first human?
But how do we define the first Human? Should we define it as the moment we developed a human consciousness?
What do you make of the Adam and Eve story? Were all the ancestors before the "first human" irrelevant? Even though negating even one of them would lead to the nonexistence of several thousands of their descendants?
A very basic introduction.
A basic tree of life explorer
A more advanced tree of life explorer
An extract from Richard Dawkin's 'the greatest show on earth':
"Take a rabbit, any female rabbit. Place her mother next to her. Now place the grandmother next to the mother and so on back in time, back through the many years, a seemingly endless line of female rabbits, each rabbit sandwiched between her daughter and her mother. We walk along the line of rabbits, backwards in time, examining them carefully like an inspecting general.
As we pace the line, we'll eventually notice that the ancient rabbits we are passing are just a little bit different from the modern rabbits we are used to. But the rate of change will be so slow that we shan't notice the trend from generation to generation, just as we can't see the motion of the hour hand on our watches and just as we can't see a child growing, we can only see later that she has become a teenager, and later still an adult. An additional reason why we don't notice the change in rabbits from one generation to another is that, in any one century, the variation within the current population will normally be greater than the variation between mothers and daughters.
So if we try to discern the movement of the 'hour hand' by comparing mothers with daughters, or indeed grandmothers with granddaughters, such slight differences as we may see will be swamped by the differences among the rabbits' friends and relations gambolling in the meadows round about.
Nevertheless, steadily and imperceptibly, as we retreat through time, we shall reach ancestors that look less and less like a rabbit and more and more like a shrew.
One of these creatures I'll call the hairpin bend, for reasons that will become apparent. This animal is the most recent common ancestor that rabbits share with leopards. We don't know exactly what it looked like, but it follows from the evolutionary view that it definitely had to exist.
Like all animals, it was a member of the same species as its daughters and its mother.
We now continue our walk, except that we have turned the bend in the hairpin and are walking forwards in time, aiming towards the leopards.
Each shrew-like animal along our forward walk is now followed by her daughter. Slowly, by imperceptible degrees, the shrew-like animals will change, through intermediates that might not resemble any modern animal much but strongly resemble each other, perhaps passing through vaguely stoat-like intermediates, until eventually, without ever noticing an abrupt change of any kind, we arrive at a leopard.
Various things must be said about this thought experiment. First, we happen to have chosen to walk from rabbit to leopard, but I repeat that we could have chosen porcupine to dolphin, wallaby to giraffe or human to haddock.
The point is that for any two animals there has to be a hairpin path linking them, for the simple reason that every species shares an ancestor with every other species: all we have to do is walk backwards from one species to the shared ancestor, then turn through a hairpin bend and walk forwards to the other species. Second, notice that we are talking only about locating a chain of animals that links a modern animal to another modern animal.
We are most emphatically not evolving a rabbit into a leopard. I suppose you could say we are de- evolving back to the hairpin, then evolving forwards to the leopard from there it is, unfortunately, necessary to explain, again and again, that modern species don't evolve into other modern species, they just share ancestors: they are cousins. Third, on our forward march from the hairpin animal, we arbitrarily choose the path leading to the leopard. This is a real path of evolutionary history, but, to repeat this important point, we choose to ignore numerous branch points where we could have followed evolution to countless other end points for the hairpin animal is the grand ancestor not only of rabbits and leopards but of a large fraction of modern mammals.
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 it’s great-grandparents. And it’s great-great-grandparents. And so on forever.
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."
Was there a first human?
But how do we define the first Human? Should we define it as the moment we developed a human consciousness?
What do you make of the Adam and Eve story? Were all the ancestors before the "first human" irrelevant? Even though negating even one of them would lead to the nonexistence of several thousands of their descendants?