On Thu, 16 Apr 2009, Chris Doss wrote:
> It's sort of hard to find a trait shared by all humans that leaves out
> all other animals.
IIUC, virtually no species is defined by a unique trait, evolution being what it is. Species are defined (literally, biologically defined) by clusters of traits. And on that methodology, homo sapiens sapiens is no harder to uniquely distinguish than a species of fox.
But if, for the fun of it, you want to try and find a single thing that humans have that no other animal has, I'm surprised nobody has yet volunteered the one that Doug suggested at the very beginning of this thread, namely language.
Despite some endearing tricks with apes and a parrot named Alex, it's pretty widely accepted by linguists that, while many animals communicate, and often in very complex ways, only humans have language in the full sense of the term. There are many features the distinguish language, but IIUC one simple test nobody else has been able to pass yet is the ability to discuss something located in the past or future, or simply elsewhere.
Michael