What are some of the recurring criticisms of darwin's theory of natural selection and how are they refuted?

One of the major criticisms of evolution has been centered
on the incredible complexity of living things. Creationists argue that it is
mathematically impossible for rare, chance events to have given us all the life forms we
see on the planet. Evolution, relying on small random changes, requires vast amounts of
time to work; however, five billion years, the estimated age of the Earth,
is a vast amount of time. Scientist have created mathematical
models that show that mutations occur at rates that make evolution
possible.

Creationists have, however, attacked the
scientific calculations of the Earth's age, saying it is much younger than scientists
contend. A variety of radioisotope measures such as Carbon-14 dating confirm the
scientific estimates, but creationists say that, since these methods depend on nuclear
decay, they are only valid if the amount of cosmic radiation has not changed much over
the millennia. Astronomers have studied other stars similar to our sun, and concluded
that it is quite likely that cosmic radiation has not changed sufficiently to affect
these dating methods.

Another common creationist criticism
is the lack of intermediate forms in the fossil record. Such intermediates would show
the gradual changes accumulated over generations, and would support the theory of
evolution. The fact is that for some species, such as horses, we do have a good record
of intermediate forms. For others, the lack of intermediates may be explained by the
theory of punctuated equilibrium, which states that long periods of environmental and
species stability may have been punctuated by episodes of instability, during which
evolution occurred much more rapidly as challenging environmental conditions favored
novel mutations rather than the status quo.