Are Aliens a Bunch of Smarty-Pants?
That depends on how long it takes to grow a brain
Spock: “To hunt a species to extinction is not logical.”
Gillian: “Whoever said the human race was logical?”
Star Trek, The Voyage Home
We expect aliens to be a whole lot smarter than us. Not only will
they possess the wisdom of the ages, but they will travel at warp
speed, have the ability to transform (or destroy) entire planets, and
their civilizations will span across galaxies. Until we find alien
life, however, we can only guess at how many intelligent
civilizations may be out there. Frank Drake made a stab at guessing
the number in 1961, when he formulated the “Drake Equation.”
According to this equation, there could be a million intelligent
civilizations in the Milky Way galaxy, and probably billions of such
civilizations throughout the universe.
The Drake Equation is based, in part, on an estimate of the number of
planets in the galaxy that might harbor life. Such planets would
have to exist in “habitable zones”–those regions around stars that
would best support life as we know it. These planets would be the
most likely places where life capable of achieving intelligence is
fostered and sustained.
To understand how intelligence develops, we have only one example to
study: the development of human intelligence on Earth. The first
life on our planet probably arose about 3.8 billion years ago, less
than a billion years after the Earth itself formed. But multi-
cellular life didn’t appear until nearly 3 billion years after that,
and the first animal life didn’t form until the Cambrian Explosion
600 million years ago. Intelligent life–which we broadly define as
human civilization–didn’t develop until a few tens of thousands of
years ago. Christopher McKay, a planetary scientist with the NASA
Ames Research Center, has defined intelligence as “the ability to
build a radio telescope.” If we go by McKay’s definition, then truly
intelligent life on Earth didn’t show up until the twentieth century.
Since intelligent life took a long time to develop on Earth, some
believe it will take just as long on other worlds. The
paleontologist Peter Ward and the astronomer Donald Brownlee
expressed this belief in their book, Rare Earth: Why Complex Life is
Uncommon in the Universe. Intelligent life on Earth, they say, is
due to a long chain of events that greatly relied on happenstance.
The odds of such a chain of events occurring on other worlds seem to
be impossible. Thus, as the title of their book indicates, they
believe that simple, microbial life may be common in the universe,
but complex life will be rare. They certainly don’t expect to find
very many advanced alien civilizations out there.
Other scientists disagree with this conclusion. They suggest that
animal life–or something resembling it–may have developed more
rapidly on other worlds. One proponent of this theory is McKay, who
wrote the essay, “Time for Intelligence on Other Planets,” in order
to determine the shortest possible time it would take for
intelligence to develop after the origin of life.
Crunching the numbers
Although the traditional view of evolution is as a constant push
toward greater complexity, the fossil record on Earth shows instead
that there were periods of rapid changes followed by long periods
where nothing much happened at all. McKay says such a drawn-out
style of evolution need not be universal. By removing what he calls
evolution’s “spurious” time periods, he says that intelligent life
could take as little as 100 million years to develop.
“Nothing in our understanding of evolution suggests that these
periods of stasis are required,” says McKay. “We believe they
represent mere historical happenstance.”
Another limiting factor for evolution on Earth was a lack of oxygen.
The early Earth had very little free oxygen until cyanobacteria and
other photosynthetic life forms began producing it about 2 billion
years ago. Oxygen may be the key to tissue multi-cellularity, and
thus the formation of large, multi-celled organisms capable of
developing a brain. The build-up of oxygen also led to the
development of an ozone layer, shielding life on Earth from the Sun’s
harmful UV rays.
But this need not be the case on other worlds. Perhaps some planets
begin with substantial amounts of atmospheric oxygen. Slower
tectonic activity would make more oxygen available, as would a less
iron-rich geography. A planet with early access to oxygen might see
life, and intelligence, evolve much faster than on Earth.
Other factors affecting Earth’s evolution were cataclysmic events
such as asteroid impacts. Such events would kill off complex life,
but these events could also clear the way for the development of more
advanced forms of intelligence. The creatures with superior brains
may have been better able to save themselves from the sudden changes
in their environment caused by these events.
Many of the factors that went into the development of life on Earth
remain a puzzle to us, so there may be many other characteristics of
a planet, or even a solar system, that affect the development of
intelligence. For instance, some scientists have noted that
intelligence did not arise on Earth until the Sun hit middle age.
Perhaps, they suggest, intelligence cannot evolve until the planet’s
star reaches a certain stage in its own evolution.
Chris McKay, however, says he has not heard a compelling argument as
to why human level intelligence needed the Sun to be middle aged.
“I would say that the build-up of oxygen is the only good
environmental requirement,” says McKay.
Why only one?
The Earth’s fossil record indicates that, despite periods of stasis
or of setbacks like asteroid impacts, most organisms evolve toward
greater complexity. Some of Earth’s life forms have gone extinct,
while others became cornered in evolutionary dead ends. But as a
whole, evolution has moved toward increasing the complexity of the
central nervous system, culminating in the development of the brain.
(The “brain” as an organ within the skull did not develop until the
emergence of the first vertebrate animal.)
Since evolution seems aimed towards the development of intelligence,
a planet should be able to evolve not just one, but many intelligent
species over time. Yet on Earth, humans were the only species who
developed “radio telescope-building” intelligence.
“It might be argued that among mammals, humans developed intelligence
first and are thereby effectively precluding the development of
intelligence in any other species,” says McKay. “It follows from
this argument that intelligence evolves once and only once on a
planet, because once evolved it changes the rules of the interaction
between species and effectively dominates the planet from then on.”
Human intelligence may never have developed if the dinosaurs had not
gone extinct. During the age of the dinosaurs, our ancestors were
small, rodent-like creatures scavenging for food in the low grass.
Perhaps we had to wait for the dinosaurs to disappear before we could
evolve beyond a certain point. However, says McKay, this theory
still does not explain why the dinosaurs didn’t become the Earth’s
first telescope-builders. They dominated the planet for over 150
million years, occupying all the niches mammals currently occupy.
“That is more than twice the time between the end of the Cretaceous
and the construction of the first radio telescope,” says McKay. “One
might speculate that perhaps Stenonychosaurus (also known as Troodon)
or her progeny did build radio telescopes but their civilization was
destroyed by some internal or external catastrophe. Perhaps the
lifetime of their civilization was so short, compared to the
resolution of the geologic record, that it is simply lost without
trace in the depths of time. It is difficult to say what evidence
would survive of human civilization–if it was terminated now–after
65 million years of tectonic activity, erosion, and sea level
change.”
Since it seems that intelligence only evolved once on Earth, despite
other opportunities to do so, perhaps not many forms of intelligence
could evolve on other planets. McKay says that, considering the
Earth’s evolutionary history, the odds for developing intelligence
elsewhere may be less than one in three (65/215). Still, given the
potential number of habitable planets in our Galaxy alone, that could
mean there are many millions of intelligent species out there.
“The odds I computed are just a rough upper limit based on the
history of Earth as we now know it,” says McKay. “For us to be the
only intelligent radio builders in the galaxy, the odds would have
much lower–about 1 in million.”
What’s next?
Despite all the rationale behind one viewpoint or another, the
question of how many intelligent civilizations are out there can only
be answered if we discover alien life. NASA is planning to launch
the Terrestrial Planet Finder in 2012. This satellite will operate
for 6 years, searching for Earth-sized planets around distant stars.
In the meantime, scientists with the Search for Extra Terrestrial
Intelligence (SETI) continue to explore the electromagnetic spectrum
for alien transmissions. The SETI Institute recently published “SETI
2020,” a book detailing the focus of SETI strategies between now and
the year 2020.
Source: Leslie Mullen, Astrobiology Magazine
