There was a time when the population of humans was zero. There were creatures that were very similar in many ways, but were not human. For there ever to be one human, a non-human is required to birth a human. There were once zero humans, so to get to a billion humans, we can't jump from zero humans to 1,000 humans without first having 100 humans. Likewise, we can't jump from zero humans to 100 humans without first having 10 humans. It follows, there had to be a first human. That first human is required to have been birthed by a non-human. Now that one human exists, there cannot be a second human unless that first human can birth a human offspring when fertilized by a non-human.
No. There was a population of non-humans. Over a long time, many generations, the population changed, and each new generation in the population became more and more human like until the entire population was human.
KTS says that if CDH can mate with the first human and the first human can mate with the last non-human, then all three are human. It seems you started with 3 humans instead of 1.
Not quite. What I am saying is the difference between parent and offspring is so small that you'd always consider them a separate species. Remember my coloured square analogy? If you take any two squares next to each other, you'd consider them to be the same colour because the difference between them is so small you can't notice it. But over time, the colour does change from blue to red.
Sectio says that there was a group of non-humans. That group separated from each other and after a long time one group could not mate with the other group. It seems you started with non-humans and ended with two groups of non-humans that couldn't breed (divergent evolution).
This is the same thing, basically. I'll stick with a variation of my coloured squares.
Imagine you have a group of squares that are all coloured blue. They live in the forest. One day, the river nearby changes course (maybe due to a flood, erosion, earthquake or some other reason), and now the river goes straight the the middle of the forest of the blue squares. Some blue squares are on one side, the other blue squares are on the other. Now, blue squares eat a few things. They can eat worms, and they can also eat fruit that is pollinated by mice.
But because the river goes through the forest, there's a problem. The mice that pollinate the fruit are all stuck on the north side of the river. The north side will get plenty of fruit, but on the south side, the fruit will die out because there are no mice to pollinate it. And all the worms are on the south side, and they can't get to the north side because they can't cross the river.
So, there are blue squares on the north side and on the south side. But they have different problems. The blue squares on the north side will adapt to be better able to survive on the fruit, because it grows where they are and it is now the only food available to them. As they become gradually better adapted to fruit eating (remember, before they had to be good at both kinds of food, but now they can specialize in fruit), they slowly become green squares over many generations.
But the blue squares on the south side won't become well adapted for fruit eating. Why would they? It doesn't give them any benefit, because they can't get any fruit. But they will become better adapted for worm eating, and they slowly become yellow squares as a result.
So, we started off with a single population of blue squares which were divided into two groups. Each group faced different pressures and adapted in different ways. It's the same story as my original blue to red squares, except this time we split the blue square group into two groups that have different challenges to face. The different challenges drive the evolution of each group in different directions.
Incidently, this is why sharks and dolphins look so similar. They are both facing the same challenges. Both have to hunt in water. But they still bear signs of where they really came from.
mzunga says assume human baby is Creature A and when that baby is old we call it Creature Z. For every microsecond that elapses, that human is slightly different so we could call it Creature A1, A2, A3. You could further timeslice to approach infinity and label each of those as a different creature. It seems you illustrated generic evolution using the imagery of a baby growing old.
Yeah, he's saying the same thing as my original coloured squares thing, except he's using the idea of different ages instead of different colours.
If there were once zero humans and now humans are abundant, there had to be a first. It's not clear to me why that statement is false. Thank you for any additional details you can provide so I can understand why there was never a first human.
Go back to my analogy with the coloured squares. The squares start off blue and gradually change to red. There's never going to be a point where the squares stop being blue and instantly start being red. If you take any square that you consider to be blue, then the square just before it is also going to be what you would call blue. It has the tiniest bit of red mixed in with it, but despite that, you'd still call it blue. So blue squares never come from red squares, they always come from blue squares. Just blue squares that aren't quite as blue.
