Gary Rosenberg wrote:

<His more general request for one phylum giving rise to
another is also problematic. If I found evidence that one phylum gave rise
to another, I would consider the phyla to be synonyms, so the example would
evaporate.>

** If one phylum can't give rise to another, wouldn't all extant phyla have
to be present in the fossil record all the way back to the Pre-Cambrian?
There weren't any Chordates in the Cambrian.  Where did they subsequently
come from, if not from pre-existing phyla?  Are chordates therefore
synonymous with whatever preceded them?  If new classes can't arise from
pre-existing ones, why were there no mammals in the Paleozoic - and where
did they subsequently come from, if not from pre-existing classes
(presumably reptiles)?

<If one thinks that a combination of
microevolution and macroevolution occur, there is no reason to expect that
the point at which the mollusk line and crustacean line diverged was
macroevolutionary. Maybe it was a microevolutionary divergence, and then
macroevolutionary changes happened somewhere along the branches>

** Since virtually all spontaneous mutations of any major proportions are
lethal, and virtually all survivable (without medical intervention)
mutations are minor in their effect, it is reasonable to say that every
divergence is "microevolutionary".  If mollusks and crustaceans did in fact
diverge from some common ancestral form, it didn't happen by half of a
litter growing legs while their siblings grew a foot and a shell.
Evolutionary changes are small.  Seconds are small.  But string together 3
billion or so of them and you get a century.  Evolution is typically
sloooooow.  But even at the rate of one survivable mutation per thousand
years, a million changes will occur in a billion years.  Can a species
change in a million ways and still be assignable to the same family?  order?
class?  phylum?

<What if something evolved entirely by macroevolution? Blammo, in one giant
mutation, something vastly different appeared>.

** Actually this happens all the time.  We call such changes "birth
defects".  In nature, they die, so the changes do not become incorporated
into the species.
In our own species we are happily able to save some individuals so
afflicted, by bringing our relatively superior intelligence into play, but
only when the effects of such genetic change are relatively minor.

<For the purposes of debate on Conch-L, can we define microevolution as
"gradual genetic change within a species" and macroevolution as "genetic
changes that lead to large scale differences above the species level"?>

** Yes, we can do that - provided we can also define "microtime" as the
amount of time required to bring about genetic changes within a species, and
"macrotime" as the amount of time required to produce large scale
differences above the species level.  If we can divide ongoing evolutionary
change into "types" based on amount of time, I don't see why we can't divide
time into "types" based on amount of evolutionary change??  How about
"microrust" for the process that causes slight changes in a piece of iron
exposed to the elements, and macrorust . . . oh dear, I am getting either
silly or sarcastic, neither of which I like to be, so I'll stop.


Paul M.