Evolution is not a theory of chance
Creationists often use the word "chance" or "random chance" as a synonym for "evolution" or "natural processes". This betrays a misunderstanding of how evolution works, since it is not simply a random process. Mutations in DNA occur apparently at random, but evolution is more than just mutations since it involves natural selection as well.
According to evolution deniers:
- "[Evolution] then proposes that another series of undirected accidents produced the astonishing diversity and complexity of all living things. [...] Many biologists and other scientists feel that DNA and its coded instructions came about through undirected chance events that took place over the course of millions of years."
This relies on the more plausible idea that randomness itself cannot produce life:
"If, nevertheless, any one should be found so senselessly arrogant, as to suppose man alone knowing and wise, but yet the product of mere ignorance and chance; and that all the rest of the universe acted only by that blind haphazard; I shall leave with him that very rational and emphatical rebuke of Tully, to be considered at his leisure: “What can be more sillily arrogant and misbecoming, than for a man to think he has a mind and understanding in him, but yet in all the universe beside there is no such thing: Or that those things, which with the utmost stretch of his reason he can scarce comprehend, should be moved and managed without any reason at all?”"
- — John Locke
- "How could something so complex [as a tree] arise from a random, undirected evolutionary process?"
Natural selection is not chance
While there exists a random component to evolution, in the form of mutations, the main driving force behind it is natural selection, which non-randomly eliminates deleterious traits over time and allows beneficial ones to survive. This is comparable to a sieve that creates order by non-randomly separating sand from gravel, even if they were thoroughly intermixed.
Mutations need not be random
The theory of evolution by natural selection does not rest on mutations being random. All that is necessary is that a population have heritable variation. If one location on a chromosome, say, were much more prone to mutation than others, or if a retrovirus always caused a specific type of mutation at a specific location, natural selection would still act upon the resulting variation.
In fact, it is well known that not all types of mutation are equally likely, and mutations are more likely in some areas of the genome than in others. In this sense, mutations are not entirely random. When biologists say that mutations are random, they mean that they are random with respect to fitness (survival and reproduction). That is, mutations occur without regard to whether they will be beneficial to the organism, deleterious, or neutral.
Related creationist tactics
Creationists, particularly intelligent design proponents, will sometimes create numbers that are almost entirely meaningless in respect to the 'possible arrangement of molecules for just one strand of DNA' or another biological molecule. Examples include the statement that "the probability that a protein containing just 100 amino acids would form spontaneously is less than 1 chance in 10 to the 65th power". Exemplary practitioners of this argument include William Dembski of the Discovery Institute and venomfangx of Youtube fame. This is sometimes known as "creationist math(s)". Firstly, you do not use probability on past events, as this doesn't work. Also, these bogus calculations miss the fact that the arrangement of atoms in a molecular structure is not governed by chance, but by chemistry, which is not random. (For example, there are elements in the periodic table that are more or less likely to form chemical bonds. Extreme examples of this include the highly reactive alkali metals (sodium, potassium, lithium, etc.), which are never found in elemental forms in nature, and the noble gases (xenon, radon, argon, etc.) which rarely form chemical compounds.) Creationists also claim that mutations cannot be beneficial. However, there are two examples of this, within humanity alone. There was a baby that had a gene not found elsewhere on the planet, that has fully formed muscle structure (the kid looks like he takes steroids every other day... after lifting weights for 6 hours) and there was a family that has almost unbreakable bones. These are both examples of beneficial mutations, that happened, within humanity.