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Ancestors and descendants
Ken Kinman asked, a while ago, whether one were more closely related to one's
parents and siblings, or to one's descendants a thousand generations removed.
That is an interesting question, and I feel it is best resolved by turning it
around: are my descendants a thousand generations removed more closely
related to me, or to my parents and siblings? The answer, as I think is
fairly obvious, is that they are more closely related to me, and that at some
level, those descendants possess--or their ancestors possessed--certain
features that link them to me, to the exclusion of the rest of my family.
Thus, if I were creating a classification from my family tree, I would be
justified in erecting a group containing myself and all of my descendants, to
the exclusion of my parents and siblings.
Likewise, I might examine a collection of living and fossil organisms, decide
they forma a natural group, and call them "birds". I might then happen upon
some specimens of _Deinonychus_ and _Ceratosaurus_. I would fairly quickly
notice that _Deinonychus_ and "birds" share a number of features not present
in _Ceratosaurus_, and I would therefore erect a group that included
_Deinonychus_ and birds, but not _Ceratosaurus_. But _Ceratosaurus_ shares
many features with the first two taxa that are not found in _Plateosaurus_,
so I group the first three together to the exclusion of the fourth. And so
on, and so on, until (ideally) I have classified every individual organism
accessible to scientific study.
My question to you, Dr. Kinman, is this: what is it, in your eyes, that
would make this "bottom-up" classificatory system less useful than one which
groups _Deinonychus_, _Ceratosaurus_, and _Plateosaurus_ together to the
exclusion of the birds?