1. Instead, Hersh and her
colleagues suggest that tail
wagging made people happy.
2. Humans tended to select that
tail-wagging trait when
breeding dogs.
3. Scientists have found that
dozens of dogs' traits and
behaviors changed during
domestication.
4. She says this will help her
understand what dogs think and
feel while wagging their tails.
Which two sentences are main ideas of the
article?