Humans can be funny. Given two situations of comparable complexity, they have no difficulty in accepting one as having arisen spontaneously (with no designer or controller or creator involved), but they often insist on invoking a designer or creator ('God') for explaining the other. Consider the world economy. We all agree that it is extremely complex, and also that there is no central authority which designed what we see today. It has just evolved in complexity over time, and is self-regulating.
There are sovereign nations, each with an economy of its own. There is trade among the nations, and within every nation. There are independent stock markets, various currencies, and exchange rates which vary on a daily basis, with no central authority controlling the rates at will. Things look so well regulated that Adam Smith made his famous (but figurative) statement about there being an 'invisible hand' behind all the order and complexity of modern economy.
But come to the spontaneous evolution of biological complexity, and suddenly many people stop being rational, and postulate a God who must have created the complex life forms. This teleological argument was advanced, among others, by the British theologian William Paley. Suppose you are on a beach or an uncultivated field, and you come across a piece of rock. You find nothing striking about that (i.e., do not think of a creator of the rock), and move on. Next you see a watch. You are quite clear in your head that the watch must have been made by a watchmaker: Since there is a watch there must be a watchmaker, because there is evidence of design in the watch. Paley argued that, similarly, all the biological complexity we see around us points to the existence of a creator and designer, namely God.
People who subscribe to this line of reasoning have hijacked the phrase 'irreducible complexity' (IC) for making the point that, for example, a DNA molecule has complexity which cannot be explained or reduced to evolutionary causes involving evolution from simpler molecules. DNA controls the synthesis of proteins and yet, proteins must have pre-existed for the creation of DNA. Therefore, so the argument goes, God must be invoked for explaining such IC.
[I say 'hijacked' because the scientific meaning of IC actually pertains to logical randomness (cf. Part 67): An irreducibly complex system is one for which no compression of information is possible, meaning that its apparent information content is not substantially more than that of the algorithm or theory or mathematical formula needed for expressing or explaining it; the apparent complexity cannot be reduced by discovering a rule or law that generated it, because none exists.]
Richard Dawkins demolished the if-there-is-a-watch-there-must-be-a-watchmaker argument at length in his 1986 book The Blind Watchmaker: Why the Evidence of Evolution Reveals a Universe without Design. If God created the irreducibly complex life forms, he must have been endowed with a still greater amount of complexity, information, and intelligence. Who created that? How can you explain an observed complexity by invoking an even greater first-cause complexity? It makes far better sense to assert (and prove) that the degree of complexity rises incrementally, starting from less complex entities, aided by Darwinian natural selection and the availability of low-entropy or 'high-quality' energy from the Sun, all along remembering that we are dealing with thermodynamically open systems here (cf. Part 6).
Darwinian natural selection is not a totally random process. It acts on the genetic variation produced by random mutations and genetic drift, and helps the emergence of those individuals who have more of the adaptive traits useful for survival and reproduction.
The probability for the spontaneous evolution of the existing life forms is indeed very low. BUT A HUGE HUGE NUMBER OF ALTERNATIVE LIFE FORMS COULD HAVE ALSO EVOLVED. There are an enormous number of evolutionary pathways that could have been taken by organisms, and any of them could have been taken. This huge number should be multiplied with the very low probability of evolution of the existing life forms; then you get a much higher overall probability.
To understand this better, consider an analogy. You go out to the market place and see many people. Let us focus on one of them. Nothing miraculous that you saw that person. Now wind back in time a little bit, so that you are back home and, before going out, calculate the probability of meeting that particular person. Very low probability indeed. And yet you saw that person. It looks 'miraculous' only if you calculate the probability after the event, i.e. after singling out a particular person! It is downright silly to think that cosmic forces conspired and somebody pre-ordained that you would see that particular stranger today.
Feynman used to make fun of such tendencies. Here is what Bill Bryson (2003) wrote about him:
The physicist Richard Feynman used to make a joke about a posteriori conclusions - reasoning from known facts back to possible causes. ‘You know, the most amazing thing happened to me tonight,’ he would say. ‘I saw a car with the license plate ARW 357. Can you imagine? Of all the millions of license plates in the state, what was the chance that I would see that particular one tonight? Amazing!’ His point, of course, is that it is easy to make any banal situation seem extraordinary if you treat it as fateful.
Another analogy will be helpful. Consider a deck of 52 playing cards. Any of the cards can be at the bottom. For each such possibility, there are 51 ways of choosing the second card for placing on top of the first. There are 50 possibilities for what the third card can be, and so on. The total number of possibilities is 52 x 51 x 50 x . . .3 x 2 x 1. This works out to ~1068 ways in which the cards can be stacked one above the other, an enormous number indeed. There is only a 1 in 1068 chance that any particular stacking sequence will occur. And yet it would be stupid to think that a miracle has occurred because we have observed a particular configuration and not another.
I recommend the book Irreligion: A Mathematician Explains Why the Arguments for God Just Don't Add Up by John Paulos (2008) for becoming alert about the logical fallacies of the probabilistic kind that people tend to commit often.
A flower is a work of art, but there is no artist involved. The flower evolved from lesser things, which in turn evolved from still lesser things, and so on.
For more on debunking the IC argument, please click HERE.
The following video ('Dawkins makes an eye') will also be helpful in convincing you about the main theme of this post. The existence of the human eye had been used by the Creationists as strong proof in favour of the irreducible-complexity argument: The eye has to be there as a whole for being of benefit to the creature (so the Creator must have created it in one go); you cannot have half an eye for the faculty of vision, so went the argument. Dawkins demolishes the argument very patiently in this video.