[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Progress in Evolution



Jay Reynolds wrote on 10/28/95
I have often heard "ancestral" used for "non-derived" in the sense
intended here.  The word is perhaps particularly useful in cladistic
applications, because of cladistics's emphasis on comparing characteristics
present or absent in various descendents of some common ancestor.

Reply

Ancestral characteristics are generally an average of a comparison between
two closely related operational taxonomic units, perhaps species, perhaps
not.  Thus, a common ancestor is a predecessor that may or may not be proven
to exist with available data and/or fossil evidence.  Remember, cladistics
is a science that uses parsimony and accepts only a monophyletic origin
hypothesis to produce the simplest and most parsimonious gene tree or
species tree.  Parsimony algorithms were originally developed for
morphological character analysis.  One underlying assumption is that
morphological change occurs along simpler lines than does genetic change,
since pattern genes are a small part of an organisms genome.  Another
assumption is that environmental factors such as natural selection, operate
faster on morphology than physiology.

-Chip Pretzman