Gary's summary of varied definitions of micro- and macroevolution points to
an important problem: be sure to define your terms.

As to the evolution of new species, the problems we have in figuring out
the limits of species illustrates the ongoing process of speciation.  A
classic molluscan example comes from land snails (genus Partula) on Moorea,
in a paper I had last week but cannot find right now.  Depending on what
level of difference  you consider sufficient, there are currently 4 to 10
species, showing varying degrees of differentiation.

New species can also arise much more quickly by hybridization.  A hybrid
may have the wrong number of chromosomes to reproduce with either parent
species.  As a result, it is reproductively isolated, which is one
definition of a species.  However, if it is able to reproduce asexually (or
if hybridization is frequent enough to produce hybrids that can reproduce
with each other), a new population can arise that is a new species.  This
is generally easy in plants, for which asexual reproduction (and, in many
cases, self-fertilization) is usually easy.  Wheat and corn are two of the
most familiar species that arose in this manner, and several examples have
been observed to form, either under artificial or natural settings.  There
is even one example at the genus level, where raddish and cabbage were
artificially hybridized.  This was agriculturally useless but it did
produce something that could not properly be assigned to either the raddish
or the cabbage genus.  Some mollusks are able to do this sort of
speciation, with either parthenogenesis (females producing young without
fertilization) or more complicated systems (Corbicula).  Almost all species
of Lasaea, for example, are parthenogenetic clones arising from past
hybridization events.

As to transitions at higher levels, this would depend on the definitions of
higher taxa.  Fossil transitions between classes, orders, families, and
genera can be found.  Depending on how tightly or broadly you define phyla,
some Cambrian fossils
could be considered transitional between phyla (e.g., if Onycophora [velvet
worms] are considered a separate phylum from arthropods, then the armored
lobopods, anomalocariids, and the like represent intermediate forms between
the phyla).  We cannot tell whether any of the speciation events observed
today are at the origin of new families or higher taxonomic units, because
that can only be determined in hindsight.  Maybe one of the land snails
from Moorea will invade a new habitat in which there is extensive
opportunity for new species.  After a few million years or so, there might
be enough diversity for a taxonomist to recognize a family and multiple
genera, but there is no way for us to forsee that today.

David Campbell

"Old Seashells"

Department of Geological Sciences
CB 3315 Mitchell Hall
University of North Carolina at Chapel Hill
Chapel Hill NC 27599-3315
USA

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"He had discovered an unknown bivalve, forming a new genus"-E. A. Poe, The
Gold Bug