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07/04/2002
Punctuation and Apple Brown Betty
When I was at Bell Labs, many outside scientists favored us with
lectures. Stephen Jay Gould was one of them. To be perfectly
honest, I don''t recall anything specific that he said but I do
remember enjoying his talk immensely, thanks in large measure
to his great sense of humor. Gould helped to shake up the world
of paleontology and to give new life to the fossil record. He was
a highly visible and involved scientist, who wrote and spoke
extensively, helping to bring the lay public into contact with the
scientific issues of the day. According to an "appreciation" by
Jerry Adler in the June 3 Newsweek, Gould published a 1433-
page work, "The Structure of Evolutionary Theory", only two
months before his death. Gould died of cancer at the age of 60 a
few weeks ago.
Gould''s death comes 30 years after the 1972 paper by Niles
Eldredge and Gould titled "Punctuated equilibria: an alternative
to phyletic gradualism". This doesn''t sound like a paper that
would shake up paleontology and would be seized upon by some
creationists to cast doubt upon Darwin''s theory of evolution. All
this in spite of the fact that Eldredge and Gould were certainly
not questioning the existence of evolution, but merely pointing
out an alternate route for evolution to occur. The general
understanding of Darwinian evolution had been that evolution
proceeds gradually, with different species forming slowly over
periods of many thousands or millions of years. As a result, the
fossil record should show fossils changing gradually from one
form to another as the layers of earth piled up.
But there was a problem - the so-called "missing links". Instead
of finding this continuous record of change, there were gaps. A
new species would appear in one layer without any obvious
transitional species in an earlier layer. These gaps were usually
explained by assuming that geological forces were such that the
missing intervening fossils just weren''t preserved due to any
number of factors such as changing rates of sedimentation,
volcanic activity, earthquakes, flooding, erosion, disintegration
of the fossils - you name it. All of these reasons sound sensible.
After all, it''s remarkable that circumstances allowed the wealth
of fossils that are preserved in strata that can be dated over
billions of years.
But what about the "gradualism" in the title of that 1972 paper?
What Eldredge and Gould did was to seize upon the gaps, those
missing links. They proposed that the apparent sudden changes
in species were just that -"sudden" changes. Their view was that
species stayed pretty much the same, even for tens of millions of
years. There might be changes in the forms of a species but
these changes still preserved the essential nature of the species.
For example, suppose the climate was warm and wet and there
were very large turtles enjoying these conditions. Now suppose
that the climate changed to one that was very dry and that this
dry climate persisted. The turtles might gradually evolve to
become much smaller to conserve the amounts of water and food
required to survive in the dry environment. However, they
would still be turtles. Another possibility would be that the
turtles would simply die out and become extinct, unable to cope
with the new environment.
Now let''s take another example (I''m making this up). Suppose
we have a continent, half of which is a lush jungle environment.
Suppose also that this lushness borders an equally large expanse
of open grassland. This grassland won''t be very attractive to a
species of animal, let''s call it a "fruiteater", that thrives on the
fruits found in the jungle. Now suppose that one of our
fruiteaters is born with a genetic "defect" that affects its sense of
taste and it happens to nibble on some grass at the border. To its
surprise, with his defective palate, it finds the grass more tasty
than the fruit. Let''s assume this fellow mates and passes this
taste for grass to its offspring. Well, there''s the rest of the
continent with all that grass ripe for the taking! These offspring
decide to leave their fellow fruiteaters and exploit all that grass.
They have a problem however. Their legs and hands were made
to swing in trees and their stomachs are not really all that attuned
to digesting grass. But, again by chance, another "defective"
gene shows up that allows a helpful bacteria species to colonize a
fruiteater''s gut and assist the fruiteater to digest the grass.
Now things happen "suddenly". (Remember, "suddenly" can be
tens of thousands of years in geologic terms.) With all that grass
out there, the fruiteater, now a "grasseater", multiplies rapidly.
After a while, it loses its tail, no longer needed to hang from a
tree. With lots of kinfolk in the grassland, other mutations are
passed along that make the grasseater more suitable for its new
surroundings. Finally, one of the male grasseaters wanders off
looking for a mate and by chance ends up in the jungle. This guy
doesn''t recognize those strange looking fruiteaters and they don''t
recognize him. For sure, neither has any desire to mate with the
other. We now have evolved a brand new species and, thanks to
the golden opportunity provided by all that open grassland, it
happened in a flash, geologically speaking.
A few hundred million years later, when paleontologists look at
the fossil record, what do they see? A thick layer in which
fruiteaters have been around for millions of years, while on top
of that is a layer in which this grasseater suddenly appears. In
other words, we have a long period of equilibrium "punctuated"
by the appearance of a new species. The transition to the new
species gets lost in the miniscule layer corresponding to those
measly tens of thousands of years. Hence, "punctuated
equilibrium".
The concept of punctuated equilibrium has deeper philosophical
consequences. Most of Darwin''s followers espoused what
biologists now call the "microevolution" view. In this view,
most evolutionary changes occurred within given species via
natural selection. Natural selection was thought by many to be
particularly applicable to man and the apes. The idea was that
superior (e.g., smarter) apes survived and passed their genes
down to their offspring. As a result, apes would become
progressively smarter and man was the ultimate outcome.
Undoubtedly, this sort of thing has happened many times during
the course of life on earth. If one carries this argument to its
logical conclusion, there is an unstoppable evolution of life
towards more and more "superior" species as the millennia roll
by.
In the punctuated equilibrium or "macroevolution" scenario,
we''ve seen that a chance occurrence or mutation resulted in the
adaptation of our fruiteater to having a taste for grass. Is the
grasseater superior to the fruiteater? Obviously, it depends on
the environment. Suppose that jungle dries up and converts to
grassland? Chances are good that the fruiteaters would go
extinct, losing out to the established grasseaters. In other words,
on this "macro" scale, the whole species is in competition for
survival, not just the individuals within a species. As the
Newsweek article puts it, if Gould is right, we individual
members of Homo sapiens are all in it together and that''s the
revolutionary doctrine that Gould left us.
Gould wasn''t just a highbrow Harvard professor. He shared a
childhood passion with Rudy Giuliani - a love of the New York
Yankees. Both maintained their interest in sports and Gould
even wrote an article trying to explain the decline in the number
of .400 hitters in baseball since Ted Williams. Incidentally, the
July Reader''s Digest featured an interview with Rudy Giuliani,
whose actions on September 11 certainly "punctuated" our view
of that tragedy. After visiting Ground Zero recently, I was taken
by a section of vignettes titled "Our America" in the same issue.
The articles were by authors such as Peggy Noonan, Senator
Arlen Specter, Sandra Day O''Connor, Tom Brokaw and others.
Apropos of my Ground Zero visit, I found one story especially
touching. The story''s author stated that, after September 11, his
wife and stepdaughter formed a group that collected and
delivered needed items to the rescue workers at Ground Zero.
Among the items were such things as hard hats, respirators,
batteries, etc. One evening, as they left a restaurant to make a
delivery, the cook asked that they take with them a bag which
contained 12 freshly baked apple brown bettys, the restaurant''s
"best dessert".
The author recalled thinking at the time that this was a lovely
gesture, but meaningless in the overall context of the situation -
12 brown bettys for thousands of workers. But, after distributing
the items to the workers, the last piece of brown betty went to an
older fireman, sitting alone and totally exhausted. Eating the
brown betty brought a smile to his face and he said "Thank you.
This is the most lovely thing I''ve seen in four days - and it''s still
warm!" The author said that those 12 "trivial" brown bettys had
"turned into little drops of gold " Could this have been a case
of punctuated equilibrium? The author of the article was
Stephen Jay Gould. May he rest in peace.
Allen F. Bortrum
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