They need it, therefore if it randomly happens, they will keep the outcome.
Imagine a game where you are given random cards, and you choose which of them to keep and which of them to discard. If you need e.g. cards with high numbers, you can “develop” a high-numbered hand by keeping cards with high numbers and discarding cards with low numbers. Yet you have no control over which cards you receive. For example, if you have bad luck and always get only low numbers, you cannot “develop” a high-numbered hand. But only a few high numbers are enough to complete your goal.
Analogically, species receive random mutations. If the mutation makes the survival and reproduction of the animal more likely, the species will keep this gene. If the mutation makes the survival and reproduction of the animal less likely, the species will discard this gene. -- This is a huge simplification, of course. Also the whole process is probabilistic; you may receive a very lucky mutation and yet die for some completely unrelated reason, which means your species cannot keep that gene. Also, which genes provide advantage, that depends on the environment, and the environment is changing. Etc.
But the idea at the core is that evolution = random mutation + natural selection. Random mutation gives you new cards; natural selection decides which cards to keep and which ones to discard.
Without mutations, there would be no new cards in the game; each species would evolve to some final form and remain such forever. Without natural selection, all changes would be random, and since most mutations are harmful, the species would go extinct (although this is a contradiction in terms, because if you can die as a result of your genes, then you already have some form of natural selection: selecting for survival of those who do not have the lethal genes).
Sometimes there are many possible solution for one problem. For example, if you need to pick fruit that is very high on the trees (or more precisely speaking: if there is a fruit very high on the trees that no one is picking yet, so anyone who could do so, would get a big advantage), here are things that could help: a longer neck, longer legs, ability to jump, ability to climb trees, ability to fly, maybe even ability to tumble the trees. When you randomly get any card in this set (and it doesn’t come with big disadvantages which would make it a net loss), you keep it. Some species went one way, other species went other way. -- A huge simplification again, since you cannot get an ability to fly in one step. You probably only get an ability to climb a little bit, or to jump a little bit. And in the next step, you can get ability to climb a little bit more, or to jump a little bit more, or to somehow stay in the air a little bit longer after you have jumped. Every single step must provide an additional advantage.
They need it, therefore if it randomly happens, they will keep the outcome.
Imagine a game where you are given random cards, and you choose which of them to keep and which of them to discard. If you need e.g. cards with high numbers, you can “develop” a high-numbered hand by keeping cards with high numbers and discarding cards with low numbers. Yet you have no control over which cards you receive. For example, if you have bad luck and always get only low numbers, you cannot “develop” a high-numbered hand. But only a few high numbers are enough to complete your goal.
Analogically, species receive random mutations. If the mutation makes the survival and reproduction of the animal more likely, the species will keep this gene. If the mutation makes the survival and reproduction of the animal less likely, the species will discard this gene. -- This is a huge simplification, of course. Also the whole process is probabilistic; you may receive a very lucky mutation and yet die for some completely unrelated reason, which means your species cannot keep that gene. Also, which genes provide advantage, that depends on the environment, and the environment is changing. Etc.
But the idea at the core is that evolution = random mutation + natural selection. Random mutation gives you new cards; natural selection decides which cards to keep and which ones to discard.
Without mutations, there would be no new cards in the game; each species would evolve to some final form and remain such forever. Without natural selection, all changes would be random, and since most mutations are harmful, the species would go extinct (although this is a contradiction in terms, because if you can die as a result of your genes, then you already have some form of natural selection: selecting for survival of those who do not have the lethal genes).
Sometimes there are many possible solution for one problem. For example, if you need to pick fruit that is very high on the trees (or more precisely speaking: if there is a fruit very high on the trees that no one is picking yet, so anyone who could do so, would get a big advantage), here are things that could help: a longer neck, longer legs, ability to jump, ability to climb trees, ability to fly, maybe even ability to tumble the trees. When you randomly get any card in this set (and it doesn’t come with big disadvantages which would make it a net loss), you keep it. Some species went one way, other species went other way. -- A huge simplification again, since you cannot get an ability to fly in one step. You probably only get an ability to climb a little bit, or to jump a little bit. And in the next step, you can get ability to climb a little bit more, or to jump a little bit more, or to somehow stay in the air a little bit longer after you have jumped. Every single step must provide an additional advantage.
Yes this. Of course it is not a given that something that would be a useful adaptation will develop randomly.
Great analogies with the hand of cards.
Ditto to Ander’s comment—very nice summary and analogy, many thanks :)