estimates for various metabolic enzymes and DNA sequence variation. Isozymes are
variant forms of enzymes which mediate specific metabolic reactions. They are
identified by their distinct migration rates under electrophoresis, with development of
the paper electrophoretograms using the metabolic reactions. The results are mixed.
Limpets of the genus Lepetodrilus were shown by an isozyme analysis to have no
greater variation at great distances along the East Pacific Rise and Galapagos Rift
than at short distances. Even though features of their larval shells suggest they do not
feed much while planktonic, and thus have only short dispersal as larvae, their gene
flow is apparently high (Craddock et al. 1997). A similar result obtains for
Bathymodiolus thermophilus over 2370 km along the Galapagos Rift. Its larval shells
do suggest (by comparison to better-known shallow clams) a capability for feeding
and thus for long-distance dispersal (Craddock et al. 1995). According to Vrijenhoek
(1997), there are cases of vent animals with planktonic larvae that do show some
genetic gradients with distance, suggesting a stepping-stone model of dispersal. On
the other hand, vent animals that brood their young, like the amphipod Ventiella
sulfuris, show strong genetic differentiation between sites, and genetic distinction
increases with separation distance (France et al. 1992). Gene flow, and by implication
migration, between sites is very low in these forms. This species has only been found
at vent sites. How they and other brooders reach new sites is an open question.
Recently, Audzijonyte and Vrijenhoek (2010) have questioned the statistical adequacy
of sampling along ridges to determine genetic homogeneity versus divergence. There
is always more to be done.
Site for the Origin of Life?
(^) Since the mid-19th century, when Darwin established, by thorough review of
paleontological results, that life on Earth has gone through a progression of
evolutionary phases, the question of how life originally got started has waited for a
full and satisfying answer. Some continental thinkers had outlined this problem much
earlier (see Wächterhäuser 1997). Thinking about the problem has been active since
the 1920s (Oparin 1924, 1938), when sufficient knowledge of biochemical processes
was available to support speculation. Biomolecular knowledge has burgeoned since,
so these speculations have started to take on a semblance of actual possibility.
(^) Very shortly after the discovery of deep-sea hydrothermal vents, Sarah Hoffman, a
graduate student working at the time with J.B. Corliss (Corliss et al. 1981), noticed
the similarity between vent systems and an experimental approach to “synthesizing”
simple living forms attempted earlier by Sidney Fox (citing Fox 1971; see also Fox &
Dose 1972), who was in part inspired by geysers. The actual relation to Fox’s
experiments was not exact, only intriguing. His experiments had three levels:
production of amino acids, formation of protein-like structures (“proteinoids”) and