I'm having trouble believing this one, but then again, maybe it was a mistake for us apes to give up a useful mood indicator, and if so maybe a bioengineered solution is in order.

This reminds me that British author Marjorie Boulton once wrote a short poem in Esperanto called simply "Vosto" ("Tail"):

Sur la dekliva vojo evolua
hom' pagis altan koston:
jen, kiel ĉi katid' en ĉaso ĝua
priĝojas sian voston!

Roughly translated:

On the inclined road of evolution
Man paid a high price:
Behold how this kitten in joyful chase
Enjoys its tail!