Joined: Oct. 2007
|Quote (Evolution-FTW @ Jan. 24 2010,12:29)|
|In Scotland, Evolution isn't even taught.|
It saddens me, because now I have to start teaching it to myself.
There's one thing I'm wondering though, what is the evidence for the common ancestor? We don't have a fossil of it, so how do we know it existed?
When something can't be seen in and of itself, you have to look for less-direct evidence.
As an example, take black holes. By definition, you can't see a black hole, because the damn thing's gravity is so strong that not even light can escape its ferocious pull. So how can you tell whether or not black holes exist? By looking for indications of their gravity. One possibility: If you happen to see a bunch of stuff moving around as if all that stuff were orbiting a single massive body, but you can't see anything at all where that massive body ought to be, you might just be 'looking' at a black hole.
Another possibility: Say you can measure how fast an object is moving in its orbit, and you keep on measuring until you've got at least one complete orbit's worth of data. You can use that data to figure out (a) the radius of the object's orbit, and (b) the strength of the gravity field the object is orbiting within. Depending on how strong the gravity field is, compared to the radius of the object's orbit, you might be 'seeing' a black hole there, too.
Does that help you understand how you can learn about something by indirect means?
Now, what sort of indirect means could you use to learn something about a common ancestor you don't have access to? Well, by definition, a common ancestor has descendants, right? And descendants tend to inherit things from their ancestors. As well, descendants tend not to inherit stuff from living things that were not their ancestors. This means that a bunch of critters that are all descended from a common ancestor, should be more similar to each other than are a bunch of critters which aren't all descended from a common ancestor. So if you see a bunch of different species which are a lot more similar to each other than they really have any right to be, those species might all be descended from a common ancestor; if they are, it's a good bet that the traits which are most common to all of these species, are traits which they all inherited from their common ancestor.
Obviously, I haven't even pretended to get into the nitty-gritty details of How It's Actually Done In Practice. But does the above text at least give you a sense of how a person who was interested could learn about a common ancestor they don't have access to?