Cliff Lundberg writes
in message <4.1.20000519143551.009c94e0@pop.sfo.com>:
> Bertvan@aol.com wrote:
>
> >I am an ardent admirer of Margulis. She once said "Darwinism
> >will one day be regarded as a quaint 20th century superstition."
> >or something like that. Has she written something lately?
> >Do you know a good book or internet material on this "not-so-new
> >theory of cellular evolution"?
Here's another quote from Margulis:
"Biologists have no doubt that evolution occurred. They even know
what drives it: the growth of any population of organisms beyond
the ability of the environment to support them, the appearance of
organisms that have novel genetic traits, and the greater growth
of some of those variant organisms leading to changed populations
over time - the process known as natural selection. But biologists
are still debating the details of how it occurs. The theory of
evolution, like any other scientific theory, is being continually
revised and refined.
... Scientific meetings on these subjects often generate great
disagreements. These disagreements have been misrepresented to the
public by creationists as evidence that the theory of evolution is
in doubt. On the contrary, they are evidence that what is going on
is the pursuit of science and not the shoring up of dogma."
Farewell To Newton, Einstein, Darwin..., Allen Hammond and Lynn
Margulis, Science 81, Dec 1981, pp.55-57. Quoted from page 56.
> No, but I hope someone else here does.
I found the following link which appears to present
a good background of the theory in layman's terms.
http://falcon.cc.ukans.edu/~jjmohn/endosymbiosis.htm:
The gap between eukaryotes, cells with nuclei, and prokaryotes,
cells which lack nuclei, is considered by many biologists to be
the most profound missing link in evolutionary history. In an
attempt to describe the way in which this gap was bridged, scientists
have proposed the serial endosymbiosis theory (SET). The term
"endosymbiosis" specifies the relationship between organisms which
live one within another (symbiont within host) in a mutually
beneficial relationship. The SET states that the evolution of
eukaryotes from prokaryotes involved the symbiotic union of several
previously independent ancestors. According to the theory, these
ancestors included a host cell, an ancestor of mitochondria, an
ancestor of chloroplasts, and, more controversially, a prokaryote
that brought with it the structures that today provide cellular
motion.
The idea that the eukaryotic cell is actually a colony of microbes
was first suggested in the 1920s by American biologist Ivan Wallin
(Fausto-Sterling 1993). The originator of the modern version of
the SET is biologist Lynn Margulis. In 1981, Margulis published
the first edition of her book entitled Symbiosis in Cell Evolution
in which she proposed that eukaryotic cells originated as communities
of interacting entities that joined together in a specific order.
With time, the members of this union became the organelles of a
single host (Margulis 1993). The organelle progenitors could have
gained entry into a host cell as undigested prey or as an internal
parasite after which the combination became mutually beneficial to
both organisms. As the organisms became more interdependent, an
obligatory symbiosis evolved.
...
One early and important discovery in support of the SET occurred
in the laboratory of Kwang W. Jeon, a biologist at the University
of Tennessee. Jeon witnessed the establishment of an amoeba-bacteria
symbiosis in which new bacterial symbionts became integrated in
the host amoeba (Jeon 1991). In 1966, when the bacteria first
infected the amoebas, they were lethal to their hosts. However, as
time progressed, some of the infected amoebas survived and became
dependent on their newly acquired endosymbionts within a few years.
Jeon was able to prove this dependency by performing nuclei
transplants between infected amoebas and amoebas lacking the
bacteria. If left alone, the hybrid amoebas died in a matter of
days. Yet if he reinfected these hybrids with the once-lethal
bacteria, the amoebas recovered and once again began to grow
(Margulis and Sagan 1987). This discovery served to demonstrate
that endosymbiosis could provide a major mechanism for cellular
evolution and explain the introduction of new species (Jeon 1991).
Although some of Margulis' ideas remain controversial, there is
mounting evidence in support of the SET (Fausto-Sterling 1993).
The bulk of this evidence serves to defend the notion of an
endosymbiotic origin of mitochondria and chloroplasts.
....
It has been nearly thirty years since Lynn Margulis first published
a book on the origin of eukaryotic cells. Since that time, biology
has undergone extraordinary changes. The most noticeable change is
the extensive accumulation of sequence data for both nucleic acids
and proteins. The collection of new data will undoubtedly lead to
continuous revision of the serial endosymbiosis theory of the origin
of the eukaryotic cell. Despite the uncertain future, the crucial
foundation has been laid. Symbiosis is now accepted by the scientific
community as an important factor in generating evolutionary change.
The next steps include the development of more elaborate methods
to interpret genetic and molecular sequence data and the undertaking
of a fresh look at the fossil record. These tactics might reveal
significant information concerning one of the most challenging and
fascinating problems in evolutionary biology, the origin of the
eukaryotes.
This archive was generated by hypermail 2b29 : Fri May 19 2000 - 19:14:58 EDT