Creationists:

Evolution supposedly takes place over a period of millions of years. That's a long time, but not nearly long enough to accommodate the complexities of life. The human genome consists of some 30,000 genes, and it is utterly improbable it could ever have resulted from chance.

Darwinians:

(1) Chance plays a small role. Darwinism does not claim that life forms arise purely by chance. Chance is one element in evolution, but it is guided by the principle of natural selection. According to Darwin, in every generation the children deviate from the parents in some random ways (this is the chance part), but then the environment leads to some children procreating more than others (this is the natural selection part). There is thus a force acting (natural selection); it is not haphazard, though it is impersonal and without forethought.

[Anaology: suppose you find a beach where the seashells and the seaweed are all lined up in separate rows. Do you conclude that some intelligence designed it this way? Here's a simpler explanation: the detritus was  originally randomly scattered (the chance element), but then the tide (an active but impersonal, unintelligent force) systematically, on average, buffeted the various matter differently according to their size and weight, thus leaving them in an apparently engineered array.]

(2) Do not misunderstand chance. Consider this random number: 789,454,103,410. What are the odds I came up with this number? One in a trillion, i.e. one in a million million. The odds are vanishingly small, and yet it happened! Does this mean that it was a miracle? No, it means that the concept of chance needs to be used more carefully.

How soon would I arrive at the same number if I were to try again? If I tried to get to 789,454,103,410 in a single trial, the odds would be astronomically against me; and to repeat a single trial many times would hardly help. But imagine a different procedure: I randomly generate a twelve-digit number, and if any digit matches my target then I get to keep it. (For example, on my first trial I might get --9,---,---,4--.)  If I continue generating random numbers, building on what I already have, then I could very quickly get to any desired number. This is the way evolution works; it builds on past partial successes.