AAT is the theory that our ancestors (humans) lived in aquatic settings.
“The aquatic ape hypothesis (AAH), sometimes referred to as the aquatic ape theory (AAT), proposes that the ancestors of humans went through one or more periods of time living in more aquatic settings than modern non-human apes and that this history accounts for many of the characteristics of species in the Homo genus that are not seen in other primates, such as chimpanzees or gorillas. “
Not a new theory at all, been around for a very long time.
Interesting however. Read more here.