Re: Dawkins' video (was: a transitional turtle)

Glenn R. Morton (
Mon, 08 Jun 1998 19:51:12 -0500

At 01:34 PM 6/8/98 -0500, mullerd@chplink.CHP.EDU wrote:
> You stated: (regarding DNA information increasing)
> "A highly compressible sequence - 010101010101010101 has
> little informaiton and is highly compressible being
> represeneted by a shorter sequence of "8' 01"".
> I was going to cite examples of higher organisms and ask you
> if when they lose certain abilities and requirements for
> survival, (warmer fur, webbed feet, etc), can they get it
> back?

In some instances, it can happen, but it is rare. consider these examples:

"Reversals of long-lost structures do occur but evidently result from the
co-option of genes that continue to survive in other roles. Among living
cats, Lynx possesses primitive field features in its dentition. The
carnassial teeth of the lower jaw (M1) in Lynx exhibit a third cusp at the
hind edge of the tooth. Fossil evidence indicates that this structure was
lost and then regained in this lineage. Lynx also exhibits the
reappearance of the second molar, M2. This tooth has been absent in felids
since the Miocene, about 20 Myr. Kurten has suggested that the regain of a
cusp on the rear edge of the carnassial and the reappearance of M2 are
correlated and result from a 'reactivation of the molarization field,'
which brings M2 above the threshold of realization. Suppression of M2
probably did not involve the loss of any structural genes, since the same
genes are presumably required for the morphogenesis of all teeth. In this
case, regain of a lost structure after a long period of eclipse may not
represent activation of any silenced gene but stem from changes in the
level of gene activity controlling the size or strength of the molarization
"Other reversals have been noted in complex structures, including the
reappearance of 'lost' muscles in the limbs of some birds and limbs in
usually limbless tetrapods. It has also been possible to experimentally
reverse toe number in guinea pigs by selective breeding from three toes to
a more primitive four toes. This reversal appears to be the consequence of
the continued maintenance of an ancestral developmental pathway that can
produce more toes in guinea pigs and can be elicited in the appropriate
genetic background. As is the Lynx molar, toe number is a meristic trait:
once the anlage is provided, the 'toe program' is played out
automatically."~Charles R. Marshall, Elizabeth C. Raff and Rudolf A. Raff,
"Dollo's Law and the Death and Resurrection of Genes", Proc. Natl. Aca.
Sci. USA, 91, pp 12283-12287 esp. 12287

"Guinea pigs normally have four digits on the front feet (no thunb) and
three digits on the hind feet (digits I and V absent). This condition is
found in all wild species of the family Caviidae and in the closely allied
family Hydrochoeridae.
"A larger number of digits is found in general in the species of other
families of the hystricoid rodents. The reduction in the Caviidae and
Hydrochoeridae is thus in all probability a very ancient character.
"It is a frequently stated principle of paleontology (Dollo's law) that
lost parts never return. Nevertheless, it is well known that an extra
digit, resembling in every respect (when well-developed) a normal little
toe is not an especially uncommon occurrence in the guinea pig. Castle
(1906) found a guinea pig with one imperfectly developed little toe and was
able by selection and inbreeding to build up a race in which this digit was
invariably present and perfectly developed incluind bones, muscles and nail
and even a new plantar tubercle on the foot. I have found a similare
little toe in several independent stocks. It has also been described by
Stockard (1930) and by Pictet (1932). The appearance of the little toe in
two grades of development is shown in figure 1. Its position and structure
have been the same in all stocks in which it has been observed. THis type
of polydactyly must be sharply distinguished from the duplication of a
digit which has occurred associated with other abnormalities of the foot in
a few cases in stocks which have no special tendency toward the development
of the reversionary type."~Sewell Wright, "An Analysis of Variability in
Number of Digits in an Inbred strain of Guinea Pigs," Genetics, 19, 1934,
p. 506

"The breeding results could be accounted for neither on the basis of a
simple recessive, nor of a simple dominant. Castle concluded that the
extra toe was probably inherited in a manner intermediate between blending
and alternative inheritance and that there was some sort of latency in
normal guinea pigs. In a later publication (1911) he noted that 'an
alternative explanation is possible that the development of the fourth toe
depends upon the inheritance of several independent factors and that the
more of these are present the better will the structure be
developed."~Sewell Wright, "An Analysis of Variability in Number of Digits
in an Inbred strain of Guinea Pigs," Genetics, 19, 1934, p.508

"There is not much difference in the characteristics of 3-toed and 4-toed
individuals apart from digit number. The Beltsville data show a lower
percentage of 4-toed born dead than of 3-toed (15.8 percent vs. 22.9
percent). Not much confidence can be placed in this, however, since it is
possible that a rudimentary little toe was overlooked more frequently in
the young born dead than in those born alive in these records in which
digit numbers were recorded merely as a matter of routine in a large colony
of which family 35 constituted only a small portion. In the Chicago data
the feet were examined with the greatest care in all stillborn animals of
family 35 and no significant relation was found (30.3 percent born dead
among polydactyls and 33.0 percent among normals).~Sewell Wright, "An
Analysis of Variability in Number of Digits in an Inbred strain of Guinea
Pigs," Genetics, 19, 1934, p.533.

> However, to simplify my question, you're saying that the
> primordal soup cells contained the same DNA information or
> information that is compressed in a similar code as in ,
> oh...say the human brain cell today?
> Oh, hey,...that Truman Show post was truly intended as
> humor.
> Your brother in Christ,
> Dan Muller

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