The next two sections of chapter four both deal with different versions of the anthropic principle. Simply put, the anthropic principle states that any universe (or world) in which intelligent life exists must have the right conditions to allow intelligent life to exist. Therefore the fact that our world and our universe have the right conditions for intelligent life is unremarkable.
On the one hand, it is hard to argue against the anthropic principle, because it is self evidently true (ie it is a tautology). Obviously if the conditions on the earth or in the universe were different, such that intelligent life could not exist, then there wouldn't be any scientists to study it. From this, we can safely conclude that no scientists will ever be able to demonstrate that it is impossible for intelligent life to exist in our universe.
So, in a sense, it is completely unremarkable that our planet and our universe are "just right" for us. Indeed, they could not possibly be anything else. Of course, it is only unremarkable that our universe allows intelligent life to form if intelligent life itself is unremarkable. I do not believe that to be true. Instead I think our existence is very remarkable.
Now, the funny thing about the anthropic principle is that there are a couple of different versions of it. Different people use this principle to make different conclusions. Some people use it to argue for the existence of God, while others use it to argue for the existence of multiple universes.
Dawkins uses the anthropic principle to support the idea that there must be a complete scientific explanation for the emergence of intelligent life. He interprets the anthropic principle as, "Intelligent life exists, therefore there must be a scientific explanation for how intelligent life came to exist." This is only true if we assume that the origin of intelligent life has a scientific explanation.
Dawkins holds the assumption, along with many scientists, that anything that exists (or has existed) has a scientific explanation for its existence. This belief is not based on evidence, or at least not direct evidence. It is a kind of faith, although it is rarely acknowledged as such.
All too often this faith gets a free pass. People who believe in God, or in the resurrection of Jesus, are often ridiculed for believing in something that can't be proven. On the other hand, people who believe that everything that exists has a scientific explanation rarely face ridicule, even though their own beliefs are just as unprovable.
Many scientists, including Dawkins, operate under the assumption that there is ultimately a scientific explanation for everything. The problem (at least in Dawkins' case) is that they seem to think that their own beliefs are indisputably true. That simply isn't the case. There is no guarantee that every problem that scientists attempt to solve has a scientific solution. The scientists believe that a solution exists but until they find it, they can't be sure.
Before I finish this post I want to make something clear. I don't have a problem with scientists who believe that what they're studying has a scientific explanation. In fact, I think it's a good thing. Science wouldn't advance if scientists didn't believe in what they were doing. I just want to point out that the scientist's belief is an act of faith, in much the same way that a religious person's belief in God is an act of faith.
Next week I'll take a closer look at these final sections of chapter four. I'll talk more about how well the anthropic principle works on the planetary and universal scale.