Let's hear it for the bugs - not your creepy-crawlies, but
bacteria, the be-all (and possible end-all) of life on Earth,
according to Margulis. Here she describes the once radical theory
that cells have incorporated bacteria to mutual advantage and uses
that as a springboard to summarize a still more radical theory of
how species evolve. She calls it serial endosymbiosis theory (SET).
It is now conventional wisdom that the energy-producing
mitochondria in animal cells were once free-living bacteria.
Indeed, they have their own genes - different from nuclear DNA.
Margulis provides many examples of fruitful symbioses, including
sexual union itself as the merger of sperm and egg cells. According
to SET, there are successive steps or mergers that led to
multicellular life forms: In steps one and two the oldest bacterial
forms - the non-oxygen breathing "archaebacteria" found in deep
ocean vents - merged with swimming bacteria two billion years ago
to form the nuclear heart of animal, plant, and fungal cells and
provide the cilia for swimming. Later steps introduced a third
partner able to breathe oxygen and added the ability to engulf and
digest food (phagocytosis). The last step involved engulfing yet
another bacterium - but one these various new forms of life could
not digest: bright green photosynthetic bacteria. The bone of
contention here is the origin of ciliated cells - critical to
evolution for their vital role as sperm tails, among other things.
Margulis has a theory about their origin, but as they say, more
research is needed. Margulis's theory also dictates a change in
taxonomy to five kingdoms: bacteria at the base, then "protoctists"
(algae, slime molds, ciliates) next, and then animals, plants, and
fungi. Finally, she defends Lovelock's Gala theory, which she
interprets to mean that enormous interacting ecosystems on Earth
achieve homeostasis rather than that the planet is in the hands of
some benign Mother Earth. This is vintage Margulis - personal,
autobiographical, passionate, argumentative, at times over the top,
but full of ideas - at least some of which, in the past, have
proved to be right. (Kirkus Reviews)
Although Charles Darwin's theory of evolution laid the foundations
of modern biology, it did not tell the whole story. Most
remarkably, "The Origin of Species" said very little about, of all
things, the origins of species. Darwin and his modern successors
have shown very convincingly how inherited variations are naturally
selected, but they leave unanswered how variant organisms come to
be in the first place.In "Symbiotic Planet," renowned scientist
Lynn Margulis shows that symbiosis, which simply means members of
different species living in physical contact with each other, is
crucial to the origins of evolutionary novelty. Ranging from
bacteria, the smallest kinds of life, to the largest--the living
Earth itself--Margulis explains the symbiotic origins of many of
evolution's most important innovations. The very cells we're made
of started as symbiotic unions of different kinds of bacteria.
Sex--and its inevitable corollary, death--arose when failed
attempts at cannibalism resulted in seasonally repeated mergers of
some of our tiniest ancestors. Dry land became forested only after
symbioses of algae and fungi evolved into plants. Since all living
things are bathed by the same waters and atmosphere, all the
inhabitants of Earth belong to a symbiotic union. Gaia, the finely
tuned largest ecosystem of the Earth's surface, is just symbiosis
as seen from space. Along the way, Margulis describes her
initiation into the world of science and the early steps in the
present revolution in evolutionary biology; the importance of
species classification for how we think about the living world; and
the way "academic apartheid" can block scientific advancement.
Written with enthusiasm and authority, this is a book that could
change the way you view our living Earth.
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