lamoran@gpu.utcs.utoronto.ca (L.A. Moran) (06/04/91)
Darrin Sharp asks,
"I know that outwardly, the live specimens (of lungfish) very
closely resemble the 400 million year old fossils. But how can
this be? Is it common for organisms to not evolve for 400 million
years? How long has it been since sharks and alligators/turtles/
crocodiles evolved? Any other species that haven't changed in this
long?"
There are no known examples of species that have not evolved for any
substantial period of time and this includes coelacanths or lungfish. It is
true that the external morphology of these animals closely resembles that of
organisms that lived about 60 million years ago. However, at the molecular
level these lungfish have evolved as much as any other extant organism.
There is no such thing as a living fossil.
It is a common misconception among non-biologists that evolution is associated
with morphological change. Such a misconception is fostered by the fossil
evidence that emphasizes such change.
Incidently, I believe that the modern lungfish (Latimeria) has anatomical
features that are different from those of the extinct organisms. Thus it is
not even correct to claim that there has been no morphological change.
-Larry Moranlamoran@gpu.utcs.utoronto.ca (L.A. Moran) (06/07/91)
In response to a question about whether coelocanths have evolved Christopher
Green mentioned punctuated equilibrium.
Jorn Barger then said,
"I'm a bit disappointed that only one coelocanth-followup mentions
this obvious-but-still-apparently-under-disseminated viewpoint. This
is hot stuff indeed, and theoretically revolutionary. The argument is
that the classic pattern of evolution is not a smooth, gradual blurring
from one species to another, but an alternation of relative quiescence
and relatively rapid phenotypic transformation."
I think that Jorn misunderstood the previous posters (including myself) who
said that lack of phenotypic change does NOT mean that evolution has stopped.
This is the same objection that I have to Eldridge and Gould's theory. They
tend to focus on changes in morphology, as seen in the fossil record, and
equate these changes with evolution. (In fairness this is actually an error
made more often by their uninformed supporters.)
I see evolution as a continual, relatively smooth, change in the frequency of
genes in a population. Sometimes these genes affect morphology, in which case
evolution is documented in the fossil record, but most of the time other
aspects of the organism are affected.
Jorn Barger then proceeds to offer an explanation of punctuated equilibrium,
"I'll take this opportunity to present again my best guess as to the
mechanism at work here:
What has to be explained is why there may be adaptive mutations present
in a genepool, _that don't spread through the entire population_.
What is the conservative principle balancing natural selection?
I claim it is sexual selection. If an ideal sexual stereotype is set
up early on in the evolution of a new species, as it must be, then it
may serve to reduce the sexual attractiveness of new adaptations that
deviate from that stereotype. Perhaps a wide range of favorable
adaptations can build up at the fringes of the genepool, in marginal
niches where a slight adaptive superiority counts for more than
sex-appeal, but never spread through the rest of the population,
breaking through instead only when a change in the environment makes
the niche marginal for the entire population."
There are several better ways of explaining why a favorable allele may not
become fixed in a population. But the main argument against sexual selection
is much more obvious.
Jorn, are you aware of the fact that punctuated equilibrium was based on the
analysis of the evolution of molluscs? The other supporting evidence relies
heavily on the evolution of other marine invertebrates and plants. I don't
think that sex-appeal or sexual attractiveness is very important in oysters,
ferns, grasses, and barnacles.
-Larry Moranlamoran@gpu.utcs.utoronto.ca (L.A. Moran) (06/07/91)
The latest issue of Nature contains the following paper. Gorr, T., Kleinschmidt, T. and Fricke, H. (1991) Close tetrapod relationship of the coelacanth Latimeria indicated by haemoglobin sequences. Nature 351, 394-397. The paper looks at the evolution of globin genes in a number of organisms including coelacanth. It is evident that these genes have not stopped evolving in the line leading to the modern coelacanth. This is the sort of evidence that many of us have been referring to when we point out that lack of morphological change over a long period of time does not mean that evolution stops. -Larry Moran
lamoran@gpu.utcs.utoronto.ca (L.A. Moran) (06/08/91)
Several people, including me, pointed out that coelacanths are not "living
fossils" and that all organisms evolve even though there may be little
obvious change in external morphology.
Arlin Stoltzfus doesn't seem to like these ideas very much since he says,
"Previous respondents have made rigid statements, and I hope they
haven't discouraged you. As several people have pointed out, it is
a bit odd to speak of a "living fossil," and it is quite true that
all extant species are "modern" in the sense of living in the present
and being the product of the last 4.6 billion years of evolution.
However, the respondents misunderstand the word "primitive." Also,
to insist that there is no such thing as a living fossil and that all
organisms evolve at the molecular level is to miss the point, since
it does absolutely nothing to explain why the coelocanth (if that is
how one spells it-- I forget) and other primitive species have
undergone less apparent morphological change than one might expect."
I hope that I understand what Arlin is trying to say here. Apparently he
agrees that the term "living fossil" is incorrect and should not be used.
I assume that he agrees with the main point of this thread which was a
response to the question "Can organisms stop evolving for 400 million years?"
The answer is NO, do you agree Arlin?
Arlin is raising a second but related point, namely why do some organisms have
an exteranl morphology that is similar to that of extinct organisms.
In his opening paragraph Arlin uses the term "primitive species", but then he
goes on to say,
"Primitive" may be a value judgement sometimes-- when used in
reference to professional hockey, for example-- but in evolution
it can have a precise meaning, when used carefully. Any two species
will have had a common ancestor at some time in the past: the species
that is more similar to the ancestor is more primitive, in the exact
sense. Usually, it is misleading to talk about whole organisms-- much
better to speak of component properties. The ancestor of humans and
whales walked on land. The terrestrial habit of humans can thus be
considered primitive in comparison to the whale's marine habit. One
can think of E. coli (as opposed to H. sapiens) as primitive in that
it is unicellular, however, many features of this bacterium are
probably not primitive. Thus, it is easy to use the word "primitive"
in an exact and objective way, provided that one actually knows
something about the relevant ancestor (this is often difficult)."
Actually you demonstrate that it is NOT "easy" to use the word "primitive" in
an exact sense! If you are referring to characteristics then it is permissible
to point to a "primitive" characteristic as one which has been around for a
long time. For example, when comparing whales and humans it is OK to say that
functional limbs are "primitive" compared to the derived characteristic of
degenerate limbs. Where people usually err is in assuming that a single
characteristic defines an organism; as, for example, in stating that humans
are more primitive than whales. Arlin makes this very mistake when he says
that "the species that is more similar to the ancestor is more primitive".
(In fairness he then qualifies his statement - but he should never have said
it in the first place if he really understood the precise meaning of
"primitive".)
Arlin Stoltzfus then says,
"The coelocanth looks alot like some 400 MY-old fossils, and that
is why people can correctly call it primitive. To be precise, its
gross morphology is primitive:...."
Arlin, you are contradicting your own statements. It is NOT correct to call
a modern coelacanth a primitive organism. This is not a description of a
characteristic. Please BE precise.
Arlin Stoltzfus also says,
"The Port Jackson Shark is another morphologically primitive species:
it has a morphology similar to that of some sharks from the
Carboniferous period (ca. 300 MYA)...."
It would be more correct, scientifically, to say that the external morphology
of this shark is a primitive characteristic. This way you make it clear that
you are only comparing one characteristic.
Arlin concludes with,
"So . . . many respondents have corrected the way you stated your
question ("is it common for species to not evolve?") by pointing out,
as I have, that every organism is expected to evolve at the molecular
level, regardless of the rate of evolution at the morphological level.
But this doesn't answer the intent of your question, does it? Its
exciting to think of primitive organisms and to imagine that they are
a window to an otherwise murky past: you want to know why the coelocanth
appears to live the same way for 400 MY while other organisms diverge
from their ancestors and quickly acquire new properties!"
The first part of this paragraph is correct but the second part is confusing.
Arlin, it may be exciting to think of "primitive organisms" but by your own
definition and mine they do not exist. It IS appropriate to refer to some
primitive characteristics of organisms. When you refer to the "rigid"
statements that were made you were actually referring to rigorous statements.
There is a difference, especially in science.
-Larry Moranlamoran@gpu.utcs.utoronto.ca (L.A. Moran) (06/08/91)
I (Larry Moran) said,
"It is a common misconception among non-biologists that evolution is
associated with morphological change. Such a misconception is fostered
by the fossil evidence that emphasizes such change."
Boris Borcic commented,
"I am no biologist, but... isn't this a bit too dogmatic ? It is
certainly true that non-biologists show a bias towards a morphological-
change view of evolution, but calling this bias a _misconception_ is
(I feel) an unwarranted institutionalization of the bias towards the
molecular view of all things biological of _present-day_ biologists
(as a population)."
I hope that I'm not being dogmatic in the sense that I am advocating a belief
that is not founded on firm logical ground. In the case of evolution I am
referring to the standard textbook definition which is "a change in the
frequency of genes in a population". Thus I claim that it is a misconception
to assume that morphological change is the only kind of evolution. If Boris
or anyone else has a problem with this then I suggest that they come up with
a better definition of evolution or at least inform the rest of us that they
do not accept the scientific definition.
Note that the definition of evolution IS molecular and that it is agreed to
by biologists who presumably should know what they are talking about. Boris,
you admit that you are no biologist and yet you claim that biologists are
"biased" toward a molecular view. It sounds like you are saying that you know
more about biology than the biologists (otherwise you couldn't recognize the
"bias"). How do you justify such a statement?
Boris Borcic continues,
"Molecular variation per se doesn't strike me as the only and
undisputable foundation for measuring an amount of evolution. Evolution
is an ecological process as well as a molecular one, and it is not
obvious (to me, at least) that a measure of the evolution of a
particular organism/species by what is significant at the molecular
level should be automatically congruent to a measure of the same by what
is significant at the ecological level."
I don't understand what you mean by "ecological process". But, as I stated
above, you are free to create your own definition of evolution as long as
you tell us about it. We, on the other hand, don't have to agree with you!
Please tell us more about the Boris Borcic non-biologist definition of
evolution.
Boris closes with,
"Anyway, and whatever, you can't deny that orphan species such as
Coelocanth or Sphaenodon are a remarkable evolutionary phenomenon."
Oh yes I can! There are lots of examples, such as bacteria and single-celled
eukaryotes, that have an external morphology that has changed little in
several billion years. Look in a biology book under "stromatolites". The
only reason why Coelacanths have attracted attention is because we humans
have a bias towards those animals that are most closely related to ourselves.
Or towards animals that are bigger than a breadbox.
My own personal favorite among organisms that exhibit some "primitive"
characteristics is Pelomyxa palustris, a single-celled eukaryote that shares
some of the characteristics of the first eukaryotes. These characteristics
are over one billion years old. Sorta puts coelacanths to shame doesn't it!
-Larry Moran
PS Don't worry about your English - it's excellent. Most of us can't write
any better even though we learned English as a first language. Even after
four years of living in Geneva I still couldn't communicate effectively in
French, you should be proud.lamoran@gpu.utcs.utoronto.ca (L.A. Moran) (06/14/91)
I (Larry Moran) said,
"There are several better ways of explaining why a favorable allele
may not become fixed in a population."
and Jorn Barger replied,
"Fer instance? I'm perplexed at what appears to me a monolithic front
claiming in effect "there is no mystery to be explained here". Darwin
expected a gradual blending of morphologies. Of course there will
always be amino acid substitutions, but why in some species is the
morphology so static?"
Favorable alleles can be lost by chance in a population before they become
fixed. This chance occurence is part of one of the main mechanisms of
evolution; random genetic drift. Examples could be the accidental destruction
of the group of organisms that contain the favorable allele or loss due
to the fact that chromosomes are segregated during meiosis and not all
combinations are passed on to the next generation.
A favorable allele may also be linked to one which is selected against in
a given population. The net effect might be to eliminate both alleles.
Jorn, I think that you have read enough in these newsgroups to realize that
Darwin's ideas are not particularly relevant to modern thought on evolution.
It is not useful to quote Darwin, especially when you are attacking his
position. Most of us agree with you that Darwin's position on a lot of things
was wrong or incomplete.
The reason why morphology may not change drastically over a long period of
time should be fairly obvious. Several others have mentioned it here. If
an organism is well adapted, morphologically, to a particular environment
then most mutations in "morphology" genes will have negative fitness. They
will not become fixed in the population and the morphology will not change.
In some cases new structures might arise in part of the population and this
group could evolve in a different direction (with substantial change in
morphology).
There is no mystery to be explained here.
Jorn Barger also says,
"I'm not especially in the thick of biology these days. Philosophically,
though, I think it's always important in the sciences to spend a good
amount of thought on the farthest-out hypotheses imaginable, just so
as not to fall into the narrow traps of scientific pride."
I agree with you. The problem is that amateurs resent it when experts shoot
down their far-out hypotheses on scientific grounds. These amateurs then
start complaining about the science mafia and how bigoted we all are. What
amazes me is the hubris of some of those amateurs who post to talk.origins
and sci.bio. They seem to assume that they have some insight into evolution
that has never occurred to "narrow-minded" biologists even though these same
biologists have been studying evolution full time for 200 years. Give us a
little credit, eh!
-Laurence A. Moranbarger@aristotle.ils.nwu.edu (Jorn Barger) (06/14/91)
lamoran@gpu.utcs.utoronto.ca (L.A. Moran) writes: > The reason why morphology may not change drastically over a long period of > time should be fairly obvious. Several others have mentioned it here. If > an organism is well adapted, morphologically, to a particular environment > then most mutations in "morphology" genes will have negative fitness. They > will not become fixed in the population and the morphology will not change. > In some cases new structures might arise in part of the population and this > group could evolve in a different direction (with substantial change in > morphology). > > There is no mystery to be explained here. > > Jorn Barger also says, > > "I'm not especially in the thick of biology these days. Philosophically, > though, I think it's always important in the sciences to spend a good > amount of thought on the farthest-out hypotheses imaginable, just so > as not to fall into the narrow traps of scientific pride." > > I agree with you. The problem is that amateurs resent it when experts shoot > down their far-out hypotheses on scientific grounds. These amateurs then > start complaining about the science mafia and how bigoted we all are. What > amazes me is the hubris of some of those amateurs who post to talk.origins > and sci.bio. They seem to assume that they have some insight into evolution > that has never occurred to "narrow-minded" biologists even though these same > biologists have been studying evolution full time for 200 years. Give us a > little credit, eh! (Gee. Third time through the flame/ kill-region cycle, and I'm still smokin'...) I had no idea you were so old! You must have seen an lot of experts shot down in your time, by a lot of amateurs, I bet! I'm a little surprised that you haven't gained the wisdom of age... a bit cantankerous and crotchety, I guess? Well, sorry, old man, but _ageing_ has a purpose, so maybe it's time you kicked off, eh what? :^) :^) :^) :^) :^) Shall I make it four cycles? Naaaaah... The problem, I would say, comes when "experts" begin to believe that "amateurs" can't possibly have _any_ new insights, and ask them to slink away at the magic words "Give us some credit". But to return to evolution: If, over millions of years, the typical pattern is for those few favorable morphological mutations _not_ to spread through the entire population, then genetic drift and unlucky allele-linkages are not sufficient explanations. If they are not sufficient explanations, then others must be proposed. My scientific strategy, amateur that I am (thank God), is to look for the deep metaphors, and treasure the most imaginative ones. Evolutionary theory may be inching out of the pit of the Darwinian metaphor, but I don't see many strong contenders being advanced. The metaphor of a contest between the sexually stereotypical and the unstereotypical-but-better- adapted has the terrific virtue of challenging the way we think about the universe, the biosphere, and our place here. I say it deserves more thought than "Plants and clams don't have much choice."
mtp@allwet.zso.dec.com (Michael T. Peterson) (06/15/91)
barger@aristotle.ils.nwu.edu (Jorn Barger) writes: >The problem, I would say, comes when "experts" begin to believe that "amateurs" >can't possibly have _any_ new insights, and ask them to slink away at the >magic words "Give us some credit". I think you're paranoid. I've never run across any "experts" who have maintained, even in jest, that "amateurs" have no insights. By the way, I consider myself an "expert amateur" in that I have a PhD in Molecular Biology, but have not been paid for my expertise in over 12 years. Where does that leave me. On this same point, consider: Amateur is to Professional as Novice is to Expert. You need to get your terms clear. Whether or not you get paid for your knowledge of biology is NOT a criterion for expertise. I know quite a few "professionals" who get paid for what they do who are about as biologically sharp as a marble -- Rifkin, for example. So, what do you claim to be, an amateur or a novice! >But to return to evolution: If, over millions of years, the typical pattern >is for those few favorable morphological mutations _not_ to spread through the >entire population, then genetic drift and unlucky allele-linkages are not >sufficient explanations. Are you confusing the terms "species" with "population". If you really did mean to use the term "population" in its biological sense then you may not fully understand genetic drift. Genetic drift occurs among [isolated] populations within a species. By definition, a favorable mutation in such a population will not spread to the rest of the species. Therefore, the explanation is sufficient. So, suppose you mean "species", instead of population: Still, this makes no sense. To be precise, there are no "morphological mutations". There are only genetic mutations that express themselve morphologically (among other modes of expression). A mutation is "favorable" precisely because it is propagated down through the generations. Said another way, if a mutation is favorable and the individual within the species is not part of an isolated population it will be propogated down through the generations. >If they are not sufficient explanations, then others must be proposed. True, but in this case the explanation(s) are quite sufficient. >My scientific strategy, amateur that I am (thank God), If you interpret the tone of my response as antagonistic it is precisely because of the attitude(s) this seems to express. I suspect your resentment of "expertise" springs from your own feelings of inadequacy. >is to look for the deep metaphors, and treasure the most imaginative ones. As opposed to what, the correct ones? >Evolutionary theory may be inching out of the pit of the Darwinian metaphor, >but I don't see many strong contenders being advanced. How about punctuated equilibrium explained as a population-biology modeled by chaotic theory and non-linear dynamics. By the way, this theory does not substantially damage the fundamental tenants of Natural Selection, it only provides an explanation of how Natural Selection exerts its pressure in non-gradual ways. >The metaphor of a contest between the sexually stereotypical and the >unstereotypical-but-better- adapted has the terrific virtue of challenging the >way we think about the universe, the biosphere, and our place here. I say it >deserves more thought than "Plants and clams don't have much choice." Gizbah?
lamoran@gpu.utcs.utoronto.ca (L.A. Moran) (06/15/91)
Jorn Barger says,
"I'm not especially in the thick of biology these days. Philosophically,
though, I think it's always important in the sciences to spend a good
amount of thought on the farthest-out hypotheses imaginable, just so
as not to fall into the narrow traps of scientific pride."
Jorn's far out hypothesis was that a lot of evolution could be explained by
sexual selection. He was especially taken with the idea that morphological
change might be inhibited because of sexual preferences. When I pointed out
that sexual preferences among molluscs and plants didn't seem like a viable
mechanism he responded with a theory about the shape of pollen grains having
an influence on rate of evolution.
With respect to the idea that we should consider far-out hypotheses, I said,
"I agree with you. The problem is that amateurs resent it when
experts shoot down their far-out hypotheses on scientific grounds.
These amateurs then start complaining about the science mafia and
how bigoted we all are. What amazes me is the hubris of some of those
amateurs who post to talk.origins and sci.bio. They seem to assume
that they have some insight into evolution that has never occurred
to "narrow-minded" biologists even though these same biologists have
been studying evolution full time for 200 years. Give us a little
credit, eh!"
Jorn Barger replies,
"(Gee. Third time through the flame/ kill-region cycle, and I'm
still smokin'...) I had no idea you were so old! You must have seen
an lot of experts shot down in your time, by a lot of amateurs, I bet!
I'm a little surprised that you haven't gained the wisdom of age...
a bit cantankerous and crotchety, I guess? Well, sorry, old man, but
_ageing_ has a purpose, so maybe it's time you kicked off, eh what?
The problem, I would say, comes when "experts" begin to believe that
"amateurs" can't possibly have _any_ new insights, and ask them to
slink away at the magic words "Give us some credit".
Jorn, I NEVER said that amateurs can't possibly have any new insights. On the
other hand, your statements seem to imply that experts can't possibly have any
expertise! Do you really believe that you have nothing to learn from these
experts. Do you really believe that we should adopt your idea simply BECAUSE
it is a far out hypothesis by an amateur? Are we not allowed to criticise it
on the basis of what is already known? Do you really want me to shut up so
that you won't be exposed to any knowledge? Have you ever considered the
possibility that your far-out hypothesis could be WRONG?
Jorn Barger continues,
"But to return to evolution: If, over millions of years, the typical
pattern is for those few favorable morphological mutations _not_ to
spread through the entire population, then genetic drift and unlucky
allele-linkages are not sufficient explanations.
If they are not sufficient explanations, then others must be proposed."
Of course! How could I have been so stupid! Jorn Barger says that genetic
drift and other explanations are not sufficient explanations for loss of
a favorable allele. Now I see the light! Please come and give a seminar here
so that my colleagues can also be exposed to your remarkable amateur insight.
Jorn Barger again,
"My scientific strategy, amateur that I am (thank God), is to look
for the deep metaphors, and treasure the most imaginative ones.
Evolutionary theory may be inching out of the pit of the Darwinian
metaphor, but I don't see many strong contenders being advanced. The
metaphor of a contest between the sexually stereotypical and the
unstereotypical-but-better-adapted has the terrific virtue of
challenging the way we think about the universe, the biosphere, and
our place here. I say it deserves more thought than "Plants and
clams don't have much choice."
You are perfectly entitled to "look for the deep metaphors, and treasure the
most imaginative ones". You are not entitled to call this science.
Professional scientist that I am (thank god) my scientific strategy is to
find the most satisfactory explanation that is consistant with the facts.
The reason that you don't "see" any strong contenders to replace Darwinism
or neo-Darwinism is NOT that they don't exist! It's because YOU don't see
them. If you want to learn about modern theories of the mechanism of evolution
then read a book. Or, you could ask someone to explain it to you.
Sexual selection is well known - it is discussed in most evolutionary biology
textbooks. There is no evidence that sexual selection influences evolution
in clams or plants, nor is there any obvious way for this to occur. I say
that your ideas deserve more thought.
Why does sexual selection challenge the way we think about the universe? You
must have a very strange way of thinking about the Universe! (-: Are you
aware of the fact that Darwin himself discussed sexual selection?
You may have the last word on this topic, I don't see much point in
continuing.
-Larry (old crotchety) Moran