From the development of the eye to the beauty of a waterfall to the exact value of the gravitational constant, theists may claim that anything natural with any quality to it whatsoever must have been deliberately crafted with humanity in mind. This is the Argument from Design.
Even if it were correct, it's a terribly egotistical way of looking at the world. And even if it were proven to be correct, no religion would have any basis upon which to claim that the designer or creator was its particular god or gods.
The basic answer to the argument from design is that there is no substantive evidence for it and therefore 1. to assume design in the presence of alternative theories supported by substantive evidence is putting one's head in the sand and 2. to assume design even in the complete absence of alternative theories is an argument from ignorance.
Beginning with evolution and the development of intelligent humans, there is a huge amount of geological, genetic and observed evidence to support the currently held view of the "tree of life". Evolution of subspecies is observed all the time, and contrary to a common objection whole new species have been seen to emerge, and recently. (This article on speciation has some examples.)
Contrary to another creationist talking point, there are tons of known transitional fossils. Contrary to Kirk Cameron, these don't look like half of one animal joined to half of another (like his famous Croco-duck). They're more like what you get if you morph a whole picture of one into a picture of the other, but stop halfway.
To dismiss evolution as a useless series of random changes is an argument from personal incredulity, which is a type of argument from ignorance. It's also wrong. The mutations are random, but only the beneficial mutations tend to be passed on by sheer survival and procreation skills. Evolution doesn't just try random things and get it right every time, it tries everything and goes with what works. It's like trying to hit a dartboard by spraying the whole wall with a machine gun. You'll miss a lot, but you'll hit it too.
Intelligence came about because at every stage in the development of primates, the ones who are just that little bit smarter than everyone else will always have the advantage. Over millions of years, it all adds up. Along with this comes morality (since good deeds are often rewarded), an appreciation of beauty (since it helps if what's pleasing to the eye is usually not diseased, poisonous or dirty) and emotions (to motivate us to do what's helpful to us and others).
Going back to the origin of life, abiogenesis as it was called could have occurred by a number of different chemical processes. So far scientists have used electricity (lightning) and a replica of the ancient atmosphere to create amino acids, which are pretty close. With a whole world full of chemicals being blown and washed into each other and billions of years to work, there was ample time and material for the components of the first replicating organism to slowly accumulate. The huge odds against this often given by folks like Hoyle generally assume that they all had to come together at once, which they didn't. Once one little bit of DNA was off and running, evolution and exponential growth took over.
Before we tackle the whole universe at once, let's consider Earth. Someone might claim that God put Earth exactly where it needed to be relative to the Sun so that liquid water and therefore life could form. We now know, however, that there are a lot more planets out there, and probably huge numbers of undiscovered ones. It's not that Earth was placed where liquid water could form. Rather, liquid water only forms on planets of the right temperature and Earth happened to fit the bill. Lots more planets might. This is called the anthropic principle: places aren't made for humans, humans just have a chance of turning up in hospitable places. Even on Earth there are many places we can't survive, like inside volcanoes and kilometres under the sea. So, we didn't emerge from there. Big surprise.
The largest design claim has to do with the fundamental constants of the universe. Six major ones are usually mentioned: those pertaining to gravity, electromagnetism, spatial dimensions and other less famous concepts. As is repeated endlessly, the slightest difference in any of them might result in matter being unable to form or stay together. This is the "fine-tuned universe" argument.
The problem is that even if this is true, there could still be other values of the constants which support matter. Perhaps instead of changing one or two slightly, you need to shift four of them by a huge amount. Considering that some of the constants could even be negative, you've got an infinite six-dimensional sample space in which to test hypothetical universes. We may never know whether our values are the only valid ones. Or, we may stumble upon another valid combination and that'll be the end of this argument.
Besides, the anthropic principle applies again if you consider the theory of a multiverse. If there are multiple (perhaps infinite) universes each with its own set of constants, of course we're going to turn up in the universe with a friendly combination. Other life forms may be thriving in universes where we wouldn't last for a second, and understanding how would require us to re-learn physics from scratch.
Contesting the argument from design is hard work, because to be most effective you need to know the going theories for whatever phenomenon is in question. I've tackled the most common ones, but be prepared for just about anything useful or pretty to be presented as direct evidence for gods. Then you need only find out where it really came from.
- SmartLX