"The second law of thermodynamics states that closed systems always go from order to disorder. Therefore, it is impossible for simpler life forms to evolve into more complex ones."

This is one of the oldest, and most popular creationist pseudoscience arguments. It's been kicking around for more than a century, thanks to general public ignorance of thermodynamics. In fact, it's wrong on so many levels that it's hard to know where to start! There are several possible answers:

ANSWER #1

This argument assumes that complexity is synonymous with ordered energy, ie- that complexity is the opposite of entropy. In reality, the opposite is true: more complex systems are actually more disordered, and are likely to contain more entropy: look up "chaos theory" if you want more information.

ANSWER #2

Living organisms are not closed systems. It is possible for the entropy in a living organism to decrease over time (in fact, this generally happens when you die). Moreover, evolution does not take place within a single living organism anyway; it is a broad process that takes place in animal populations as certain varieties reproduce successfully while others do not.

ANSWER #3

You start life as a single-celled organism (the fertilized egg), and gradually develop into a human being. Your own existence disproves the notion that a natural increase in complexity is physically impossible.

ANSWER #4

The fact that we can construct skyscrapers and automobiles obviously proves that the laws of physics do not prohibit the creation of complexity.

"But that's deliberate human intervention!" a creationist might object. Well, that's where we discover a strange assumption on their part: you see, they seem to believe that physical laws can be overridden through human intervention. However, while it would certainly be very convenient if we were able to override the laws of physics at will, it just doesn't work that way. If something is truly a law of physics, then it cannot be overcome regardless of human intervention. So the fact that humans intervene in the construction of an automobile does not disprove the fact that it clearly demonstrates the fallacy of their misinterpretation of the 2nd law of thermodynamics.

Fallacy watch:

• Straw-man fallacy (it is something of an understatement to say that this argument contains grotesque misrepresentations of thermodynamics).