Alf P. Steinbach
There is obviously some disagreement over the precise definition of a
"species" so how about this: let's say a competent anthropologist from
2013 were able to travel back in time to the period during which humans
were evolving and could stay there for 50,000 years if necessary (please
don't pick me up on the logistics of this). Let's say they are also
able to examine *every* embryo that is produced by the pre-humans or
"near" humans of the time. Would you agree that at some point they are
going to be able to perform a thorough examination of a particular
embryo and make the determination that they classifiable as "Homo
sapiens"? OK, well all I am saying is that the first time this is
possible is when we have identified the "first human".
A more practical version of this experiment can be done with baking of
gingerbread persons like <url:
http://en.wikipedia.org/wiki/File:Gingerbread_men.jpg> and <url:
Presumably you and I can agree on a reasonable definition of "finished
gingerbread person", based on properties such as color, firmness,
temperature, blah blah.
I think we can even agree that in any particular performance of the
experiment -- nom nom, fresh gingerbread person! -- each of us can
pinpoint a particular gingerbread person as the first to be finished.
Except that we won't necessarily pick the same one.
So, each performance, we can fight over whose measurements and judgment,
not to mention /definition/, is most correct.
Cheers & hth.,
- Alf (seriously off-topic mode)