Anytime a JW says that evolution is wrong, I respond, "Well obviously it's not totally wrong because if you don't believe in evolution you don't believe in the Bible."
That at first glance sounds like some kind of apostate statement, but I'm taking the stance of defending the Bible so they don't really get too much of an "apostate" vibe. It does, however, confuse them, because they have no idea what I'm talking about and all they know is that NOTHING in the Bible supports evolution. So they let me explain. And that explanation goes something like this:
"How many different species of animals are on the earth today? Millions, right? Do you really think that Noah took every species of animal onto the ark?"
Here they will either say "no" if they accept that some evolution had to take place between then and now, or "yes" if they are a real hard-core fundie. If "yes"...
"The word used in Genesis for the 'kinds' of animals taken into the ark is not the same thing as our modern 'species.' As the Insight Book Vol. 1 states on page 327:
'It is true that encyclopedias refer to over a million species of animals. But Noah was instructed to preserve only representatives of every 'kind' of land animal and flying creature. Some investigators have said that just 43 'kinds' of mammals, 74 'kinds' of birds, and 10 'kinds' of reptiles could have produced the great variety of species of these creatures that are known today.'"
"So in just 4,000 years, can you imagine how much evolution had to take place for those few animals to give us the variety of life we see today? If anything, evolution works even faster and is more powerful than scientists generally give it credit for. We really have to give God credit for these marvelous capabilities he put into living things, don't we?"
There is not much they can do at this point other than accept that the Bible demands a powerful evolutionary process. If you're lucky, you'll get out of this conversation with them saying, "Hmm, I never thought about that before." If you're not, they'll say, "Where did you get that? The internet?"