On Fri, 16 Jan 1998 14:24:57 -0600, Kevin Koenig wrote:
KK>An article from Popular Science Sept 1997 issue came to my
>attention-
>
>Biologist Jonathan Losos of Washington University, Saint Louis
>MO., studied Anolis sagrei lizards in the Bahamas. Anoles that
>lived on islands with taller vegetation and broad perches had
>longer legs. (Compared to . . . the article didn't say.)
>
>In 1977 & 81 groups of anoles were moved to islands that had no
>lizards. In 1991 Losos returned to the island and measured the
>adult lizards. On islands that had shorter vegetation the lizards had
>shorter limbs.
Because of the shorter vegetation, they probably measured them
with shorter sticks! [joke] ;-)
I haven't yet read the original article in NATURE (Losos, J. B., K .I.
Warheit and T. W. Schoener. 1997. Adaptive differentiation
following experimental island colonization in Anolis lizards.
Nature 387:70-73), but I have come across a mention of it in
a recent American Scientist. There noted evolutionist Keith
Stewart Thompson, while expressing his sympathy with the study,
questions whether it is true evolution:
"All of this makes one sympathetic with Nicholas Wade of The New
York Times, who recently wrote an article entitled "Leapin'
Evolution Is Found in Lizards." This was a report on an experiment
in which lizards of the species Anolis sagrei from an island in the
Bahamas were released onto an island lacking lizards and with a
different vegetation pattern (Losos, Warheit and Schoener 1997).
After 10 years, the limb proportions of the experimental population
had shifted significantly in the direction predicted on the basis of
the new host ecology. Whether the results document a case of
evolution depends, of course, on definitions. Certainly it is a
form of change over time, and such demonstrations are a necessary
requirement for documenting a case of Darwinian evolution caught in
flagrante delicto. But it is not sufficient to the case. All
evolution is change, but not all change is evolution. Rates of
change can be measured, as they were in this experiment; to call
them "rates of evolution" as do Losos, Warheit and Schoener begs the
most interesting question...it is quite clear that Darwin (and
indeed all his contemporaries including anti-evolutionists like
Lyell) saw no problem with local variation and the concept of
varieties within species. The question was not whether change on
that scale took place-obviously it did, and no one thought it was a
form of special creation-but rather whether that sort of change,
summed over time, could produce species. In the 1830s the consensus
view was that it did not: For each species there were natural
limits to the range of variability. Furthermore, extensive
artificial selection of animals and plants under domestication
(Darwin's model for natural selection) had apparently demonstrated
these limits experimentally. Darwin had to show that the limits
could be broken. So do we." (Thomson K.S., "Natural Selection and
Evolution's Smoking Gun", American Scientist, Vol. 85, No. 6,
November-December 1997, p518)
KK>Also, as stated in the article, they don't know yet if the changes
>that occurred are genetic in origin.
According to Thomson, the authors claim it is "nongenetic":
"Whether or not they provide the long-sought smoking gun of
Evolution, the experiments of Losos, Warheit and Schoener have the
potential to explore the mechanism(s) underlying the processes of
adaptation. The authors of the paper do not use the term ["natural
selection"]. Nor do they consider the short-term directional change
observed in these lizards to be evidence for founder effect or
genetic drift. Instead, the authors of this exciting Anolis study
present it as a possible demonstration of the potential
"macroevolutionary significance" of "phenotypic plasticity." They
argue for the "adaptive importance of nongenetic environmental
effects on morphological size and shape of animals." " (Thomson
K.S., American Scientist, November-December 1997, p518).
This is an interesting point. Lamarck's theory of the inheritance
of acquired characters has been rejected because (with a few debatable
exceptions) there seems no way for genetic information on physical
characteristics acquired in an organism's lifetime to be transmitted
dircetly to its sex cells. But I wonder how many of these studies
of so=called "evolution in action" (e.g. Peppered Moth, finch-beak
variations on the Galapagos, etc), are actually the Lamarckian responses
of organisms to their environment *in their lifetime*.
In other words, while the blacksmith cannot pass his bulging biceps
on to his sons, he (and his sons) can develop those muscles in his
own lifetime by a response to his environment (hard work in a
blacksmith shop). I see no reason why a finch in the harsh environment
of the Galapagos, couldn't grow a long or short beak depending on
the demands of the environment. This long or short beak itself could
not itself be passed on to its descendants, but the general ability to
grow long or short beaks could be.
I wonder if biologists who see their role in life confirming
Darwin's theory, ever check to see if it is confirming Lamarck, not
Darwin? One way to do it would be to measure the beaks of finches
as day-old chicks, rather than as adults.
KK>What I assume is news worthy is that the lizards underwent such a
>change so quickly. Indeed the article mentions this. If this is in fact
>evolution in action, to anyone's knowledge, would this be the first
>event of its kind that has been observed? I would think not.
>Perhaps someone has read about this in a science journal...
If lizards' legs changed significantly in length in the 14 years
between 1977 and 1991, I would think that would be unlikely to
be Darwinian evolution. Darwinian evolution is supposed to be
slow becuase it relies on the substitution of favourable genes
for unfavourable genes in a population. This means that those
individuals in the population who have the unfavorable genes
must die off without heirs. This is known as Haldane's Dilemma
and it implies that it takes about 30 times the population number
in generations for a Darwinian genetic change to become fixed in
a population:
"How well do the observed rates of evolution fit in with predictions
based on genetic arguments? The simplest genetic change which can
occur in a population is the replacement of one allele at a locus by
another, owing to natural selection in favour of the new allele. Now
selection implies the early death, or infertility, of individuals carrying
the less favourable allele. Haldane has calculated the number of such
deaths, spread over many generations, necessary before one allele has
replaced another. He finds that, unless selection is very intense, the
process usually involves a number of deaths equal to about ten or
twenty times the number of individuals in the population at any one
time, and occasionally to a hundred times this number he suggests
that the mean value is about 30 times the population number. Now
there is a limit to the number of selective deaths which can occur in a
single generation, which will in part depend on the maximum number
of offspring which a pair can produce. But even if a single female can
lay millions of eggs, as can for example a cod or herring, the vast
majority of deaths will be fortuitous, not selective; the few who
survive will usually do so because they have been lucky, not because
they have favourable genotypes. Even with intense selection, it seems
unlikely that more than half the deaths will be selective, and Haldane
suggests that an intensity of selection...of 0.1 is a more probable
figure. If so, it would take 30/0:1= 30C generations of selection
to replace one allele by another.
If changes are taking place at a number of loci at the same time, it is
reasonable to assume the same total intensity of selection. That is to
say, if a number of alleles a, b, c...are being gradually replaced by A,
B, C..., then a total intensity of selection of 0.1 means that in each
generation one individual in ten fails to survive because it carries one
or more of the alleles a b, c... whereas it would have survived had it
not carried those alleles. In this case, there will be an average of one
gene substitution per 300 generations. Species probably differ by
alleles at about 1,000 loci (that is, the number is probably greater than
100 and less than 10,000). If so, the evolution of a new species would
take about 300,000 generations. These calculations are only
approximate...But this estimate provides only an upper limit to the
rate of evolution, which may often be much slower than this, as it
has probably been for most bivalves during the last 300 million
years. It may occasionally be more rapid, if the intensity of
selection is greater than 0.1."
(Smith J.M., "The Theory of Evolution", Cambridge University Press:
Cambridge UK, Canto Edition, 1993, pp284-285)
Thus for a change in lizards in one or two generations, either the
population would have to be very small, or the selection would have to
be very intense, for the change in leg length to become fixed in the
population. On the face of it, it seems unlikely. We are expected
to believe that all (or at least most) of the Anoles lizards on this
island with long legs died out (why?) without leaving any descendants,
and only those lizards with short legs survived (why?) to leave
descendants, in only 14 years. I would be more inclined to believe
that the lizards with longer legs could run faster to get away from the
measurers!
Alternatively, the Anoles is a member of a family of chameleons, which
have the remarkable ability to change colour, depending on their
environment:
"ANOLE, American lizard-like reptiles of the family Iguanidae. There
are 165 species, of which the best known is the Green anole Anolis
carolinensis. Anoles, which are also known as American chamaeleons
from their ability to change colour rapidly, range from 5-19 in (12.5-
47.5 cm) in length. The toes of anodes are armed with small sharp
claws and have adhesive pads of minute transverse ridges which
enable them to cling to rough and smooth surfaces alike. The Green
anole is active in daylight and moves continuously and rapidly
searching for insects in bushes and trees. Male anoles have a reddish
throat sac which is extended to deter rival males from encroaching on
another's territory. FAMILY: Iguanidae, ORDER: Squamata
CLASS: Reptilia." ("Anole", "Encyclopedia of the Animal World",
Vol. 1, 1982 reprint, pp76-77)
Maybe these remarkable color-changing lizards can also change their
leg length, depending on their environment, within their own
lifetime? Maybe some finches can do it too? I would not be
surprised if no one has even thought of testing it, so entrenched
are Darwinian ways of thinking in biology. It may be that this
study is an exception, because Thomson admits that it is not a
traditional Neo-Darwinian interpretation:
"This less-than-traditional interpretation owes more to the ideas of
Waddington (for example, genetic assimilation) or Schmalhausen than
to the classical population genetics of Dobzhansky." (Thomson K.S.,
American Scientist, November-December 1997, p518).
Finally, there is always the possibility that the longer-legged
lizards managed to escape from the island. Carr mentions that
Anolis lizards may even travel on wind and water currents to
colonise islands:
"Although there can be little that many of the lizards that are
widespread members of island faunae got there across water barriers,
the exact method of their transportation is not known. The
zoogeographer P. J Darlington believes that winds have been of
little importance in distributing island reptiles Although this is
probably quite true, it seems to me that the anole lizards, which
are slim, light, arboreal and characteristic of island fauna, might
be an exception. But for most island reptiles, raft transportation
is surely a more important factor. It is a shame that the
distribution of animals by natural rafts has been so little studied.
There are various places in the world where much could be learned by
direct observation. The south shore of Trinidad, where flood water
from the Orinoco brings in all kinds of raft-borne waifs, would be a
good place to undertake such a project. In the Pictorial Museum of
Animated Nature, a 19th Century journal in which many wonders are
displayed, I recently came across an old record of reptile-rafting
to St. Vincent-an island some 150 miles north of Trinidad and
downstream from it in the Equatorial Current." (Carr A., "The
Reptiles", Time/Life Books: Netherlands, 1964, p82).
God bless,
Steve
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Stephen E (Steve) Jones ,--_|\ sejones@ibm.net
3 Hawker Avenue / Oz \ Steve.Jones@health.wa.gov.au
Warwick 6024 ->*_,--\_/ Phone +61 8 9448 7439
Perth, West Australia v "Test everything." (1Thess 5:21)
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