Modern research supports the idea that the basic categories of plants and animals have changed little over vast periods of time.
Is that a direct quote?
That sentance alone torpedoes their belief in the flood story. To believe in a world wide flood 4000 years ago, one has to accept that animals, and humans as well, have changed drastically over 4000 years. Much more quickly than any modern research indicates it takes life to evolve, or as the WTS wants to put it, 'adapt'.
Remember, the WTS uses the word 'kind' when talking about how many animals were on the ark. There were two (or seven, depending on which verse you're reading) of every 'kind'... so they're were two canines, not two of every type of breed of dog. And from that 'kind', the canine, came all the types of wolves, coyotes, dogs, dingos, etc that populate the planet today. And this all happened in just 4000 years. Yet, above they accept that "the basic categories of animals have changed little over vast periods of time"