Apparently the Watchtower writers do not study the history of the earth. There have been many mass extiction events in the past 500 million years. Over 95% of the species that ever existed are now extinct. One could argue that G-d does some regular pruning on this planet. Perhaps those T-rex guys got a little too cocky- 'poof'- lets start over again. Those Neanderthals just didn't worship Him enough, either-hmm-Maybe the Earth is just like a big lump of Play Dough to G-d.
Moshe