Pondering Next Rung on the Evolutionary Ladder
11/30/99
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Title: Pondering Next Rung on the Evolutionary Ladder
Source: The New York Times
Status: Copyright 1999, contact source for permission to reprint
Date: November 30, 1999
Byline: Malcolm W. Browne
If evolution is still unfolding, and most scientists believe it is,
just how complex an organism could the evolutionary process create,
before hitting some fundamental limit?
People leading independent lives, as we do today, might not be the
end of the human evolutionary line. Is it possible that one day we
might subordinate impulses toward individual behavior and merge into
an organic community, a kind of human superbeing with its own sense
of self?
No one can predict what might happen in the next million years or
so, but it's fun to speculate.
One thing is certain: an important rung in the evolutionary ladder
was the transition from single-celled to multicellular existence. And
that rung may have been the first of many along an endless road to
complexity.
How to account for that first step, which our remote ancestors took
eons ago, still poses many puzzles.
But however the progression from individual independence to
collective life may have unfolded, it seemed to have required some
kind of chemical internet, by which independent cells communicated
with one another and learned to enhance their collective well-being
by acting in concert.
Surely, the human race has already hit upon something like that.
A fundamental step in the process entails inducing many independent
individuals to join together and march in lockstep. Scientists in
Denmark recently discovered an intriguing new manifestation of this
behavior in cells of baker's yeast -- the kind that makes bread dough
rise.
Yeast cells ordinarily lead lives independent of one another as they
leaven bread dough, ferment grape juice or cause yeast infections.
But a team led by Dr. Sune Dano of the University of Copenhagen
reported in a recent issue of Nature that they had engineered a yeast
community in which all the cells produced synchronous pulses of a
chemical called NADH, one of the substances created when an organism
breaks down sugar to generate energy.
This chemical oscillation of yeast, in which concentrations of NADH
rhythmically rise and fall, has been observed before. But the trick
in this case was finding a way to keep the oscillations going
indefinitely. To do this, Dr. Dano said in an interview, the
scientists exploited a theory for which the Belgian chemist Ilya
Prigogine was awarded the 1977 Nobel Prize in Chemistry. In simple
terms, Dr. Prigogine showed that despite the laws of thermodynamics
that make most physical processes run downhill, an upward march
toward increasing complexity can be achieved in "open" systems.
Open systems, which Dr. Prigogine dubbed "dissipative structures,"
are those to which energy is constantly added and waste (in the form
of entropy, a measure of a system's disorder) is removed. Trees and
people are examples of dissipative structures.
In Dr. Dano's application of this idea, a glass tube containing yeast
cells was constantly replenished with fresh cells, along with glucose
and cyanide, while waste matter and excess liquid were constantly
removed and discarded. When conditions were adjusted precisely,
clock-like chemical oscillations were induced in the yeast culture,
and they continued indefinitely, as long as fresh yeast cells,
glucose and cyanide were continuously added in the right amounts and
excess fluid was removed.
Collective chemical oscillations in yeast colonies, the scientists
concluded, "suggest an evolutionary path from unicellular to
multicellular behavior."
Yeast cells are not the only creatures that routinely cross the
boundary between one-celled and multicellular existence.
Single-celled bacteria can form huge mat-like colonies that live
almost like multicellular creatures, and evidence that such mats
existed even during the earth's early years has been found in ancient
rock.
Soil amoebas -- highly complex single-celled organisms -- live
independently from one another when there is plenty to eat. But in
impoverished environments they join together to produce spores, and
in their collective state they can move relatively fast, sensing
light and warmth as guides to food supplies.
The creation of collective beings from single-celled organisms has
been going on a long time.
Millions of years ago, shells of single-celled animals (called
nummulites) were deposited in huge layers in the limestone later used
by ancient Egyptians in building the Sphinx.
Among the oldest multicellular animals with an apparent sense of self
are the sponges, which can exist either as independent, freely moving
cells or as huge assemblages of cells held together by skeletons made
of protein and minerals, and containing complex food-filtering
plumbing. Once thought to have no power of locomotion, sponges have
been shown to be capable of creeping over a surface at a speed of a
few millimeters a day to seek out food.
At higher levels of organization, many individual insects (ants and
bees for example) are essentially mere components of the superbeing
represented by the colony or hive.
Communication provides the coherence allowing such superbeings to
function; the complicated dance steps used by bees to inform their
hive-mates of the directions and distances to food sources serve as
their colonies' internet.
Higher still on the complexity ladder are birds that flock and fish
that swim in perfectly choreographed collective patterns.
One of the strangest creatures is the naked mole rat, a nearly blind
little animal living in East African deserts that spends its life
underground within a "eusocial" organization, as biologists call it,
more like that of insects than of other mammals. Each individual in a
mole rat colony serves as a cog in a big wheel; only one female in a
colony produces young, and the other animals have the specialized
jobs of searching for food, caring for the young, guarding against
predators and house-cleaning.
For a naked mole rat, the sole focus of existence is the colony;
individual life outside the colony is meaningless.
Aldous Huxley's 1932 novel, "Brave New World," envisions a human
society in which individuals are programmed before birth as "Alpha-
plus intellectuals," "Epsilon-minus morons" or any of the
intermediate levels, predestining everyone to specific occupations
in a rigidly structured society, not unlike that of mole rats.
Today, the world has sufficient "carrying capacity" to sustain its
human population in the guise of individuals capable of independent
action. But might a day come when we run out of necessities and are
forced to evolve toward a eusocial superbeing?