This is a really interesting mystery. There may
be more than one answer. For example, picking
up on our moods might be due to animals paying a
lot of attention to our facial expressions,
body movements, and voices. Social animals like
dogs, horses, and dolphins depend on understanding
each other without language. So they may have
evolved some pretty sophisticated brain circuits
to detect and interpret what other individuals are
about to do. Humans may depend too much on what
people say and not even notice the tiny,
involuntary cues we give about our mood.
There was a famous example of this over 100 years
ago. A man taught his horse (Clever Hans) to do
many things. He seemed to be counting and doing
math, including square roots. He used his hoof to
tap answers. A team of experts observed the horse
and man working together and could find no tricks.
The horse’s owner was not a fraud. Then another
investigator started looking at the man much more
carefully. He noticed small, involuntary movements
that he made, such as leaning a tiny bit forward
(which signaled Hans to start tapping), and
slightly relaxing when Hans had made the right
number of taps (which signaled Hans to stop). Then
the investigator found that if Hans couldn’t see
the person who knew the answer, he’d just tap
randomly. Hans was clever at reading people, but
not at square roots (as far as we know).
Now experiments are designed to avoid the
“Clever Hans Effect.” For example, if dolphin
trainers are testing whether dolphins can learn
the meaning of whistle commands, the trainer might
be blindfolded so that she or he was not
unconsciously looking at the hoop the dolphin was
supposed to grab.
There may also be a chemical difference that
animals like dogs can smell. Dogs have much
better noses than humans. They also use a lot more
of their brain to process smells. So if a
person who is about to have a seizure has a
slightly different scent, the dog may notice.
Do you think that humans consciously or
unconsciously selected for the ability to “read”
humans when they started breeding dogs or horses?
Would wolves or wild horses be equally good at
figuring out human moods?
Thanks for asking