Who says that an alien with technological intelligence
has to be just like us? The Divergent Evolution
One of the main lines of thought in contemporary astrobiology is that extraterrestrial intelligent
life will be very similar to us in many ways, especially when higher levels of organization
are considered. This is because the processes that give rise to life are assumed to operate
independently of the environment, and also because physics severely limits the variety
of feasible options. Therefore, the probability that intelligent life is evolving elsewhere in the
cosmos may be very high, although the probability that it is humanoid in type may be very low.
The truth is that we know very little. For example, we do not know if Earth was the lucky
winner of a cosmic lottery or if life has appeared elsewhere in the universe. We do not even know
if a hypothetical ET would follow the same laws that we know on the only planet that definitely
supports life. There is little doubt that physical and chemical laws apply throughout the universe,
but there is not the same certainty about biological laws. Frankly, if we were to encounter
life on another planet, we might not even be able to recognize it. In short, our first contact with
advanced aliens might be a blow to our self-esteem as we face, who knows, a more intelligent species
than our own. But if that first contact ever happens, we should be prepared for another twist:
the aliens may be so different from us that they won't even realize that we are sentient.
At first, glance, trying to imagine the physical appearance of a technologically
advanced extraterrestrial seems like an absurdly impossible task. For one thing, we don't even
know if intelligent beings of extraterrestrial origin exist, let alone what their home planet
might be or what their morphology might be. Our challenge is therefore limited to using
what we know about the evolution of intelligent life on Earth, considering
possible extraterrestrial planetary environments, and making a series of reasonable assumptions.
THE TWO VIEWS The disagreement about the likely appearance
of intelligent extraterrestrials is divided into two opposing positions. On the one hand, some take
a more anthropomorphic view of ET and believe that it would be essentially humanoid, with two arms,
two legs, a head on top of the body, and the major sensory organs located on the head. On
the other hand, some exobiologists believe that intelligent ET could appear in a completely exotic
form because the creature would inevitably have followed an evolutionary path completely different
from that of humans and would have arisen in a planetary environment very different from Earth.
THE ANTHROPOMORPHIC VIEW Many scientists believe that aliens
may not be so different from us, and to support this hypothesis they usually cite a well-known
phenomenon called convergent evolution. Essentially, species exposed to the same
environmental pressures tend to develop similar anatomical features through natural selection.
This is why a mammal like a dolphin looks similar to a cartilaginous fish like a shark.
Even a creature that evolved and lived in the liquid ocean of a distant exoplanet
would probably evolve a fish-like form to move quickly. After all,
the laws of physics are the same here as they are on the other side of the galaxy.
According to proponents of the humanoid form, speculation about
ET morphology must take into account what happened here on Earth, where it was in
an aquatic environment that organic matter based on carbon compounds began to develop. And it was
the first marine creatures that developed the characteristic that would determine
the future form of Earth's inhabitants - that of bilateral symmetry in body shape.
This form, in addition to being the most "economical" in terms of genetic programming,
minimized resistance and turbulence in the water and became the characteristic
of all marine creatures, then transferred to terrestrial animals.
---- Proponents of the humanoid form also argue that
intelligence - as it is tied to the use of tools - can only arise as an evolutionary adaptation
among terrestrial species. The use of tools by marine creatures would be extremely difficult
due to the density and viscosity of water. Moreover, it seems likely that intelligence
can only arise in predators. What about birds? Well, there are some really intelligent ones,
like the crow, for example... But for an alien in the form of a bird to build tools and develop
a technological type of intelligence, it would need appendages similar to ours... arms, hands,
and fingers. Which is obviously incompatible with an animal that uses its upper limbs to fly.
Yes, because the development of legs, arms, and grasping
appendages is a delicate evolutionary step on the ET's path to intelligence.
Primitive technology requires the ability to hold and manipulate basic tools and weapons
with a certain degree of sensitivity, such as clubs, spears, knives, and tendons for bows.
And the ability to combine all of this with movement speed, otherwise our
E.T. runs the risk of remaining forever confined to their comfort zone and never being able to
travel around the galaxy aboard a spacecraft. The issue of the number of limbs is one of the
most controversial when discussing the morphology of intelligent ET. The four limbs we have are the
product of genetic inheritance from our earliest mammalian ancestors, which was in turn inherited
from fish with four fins that ventured onto land. But is there an optimal number of limbs?
Well… a single limb would obviously be completely useless… For strictly mechanical reasons,
three points are geometrically required to define a surface plane: two points form only a line.
ETs trying to stand on only one or two levers will promptly fall face down. We humans can
remain upright only because our large feet provide additional points of contact with the ground,
but without fingers or toes, at least three legs are necessary.
Are tripod aliens possible? Traditional biologists say no. A three-legged creature
must lift at least one limb off the ground, at which point it loses its planar support base,
a statically unstable and dynamically precarious situation. Four-legged creatures seem better from
an engineering standpoint since the creature can remain balanced when one leg is in motion.
Ancestral fish only had fins in pairs, so should all limbs evolve in pairs as well?
Xenobiologists are not convinced. Most running bipeds and quadrupeds keep two or fewer limbs
on the ground during locomotion, so dynamic three-point stability is probably unnecessary.
Terrestrial life need not always evolve from fish with even fins: the descendants of a starfish,
for example, might have an odd number of legs. More than four legs are also plausible for
massive, intelligent animals. Odd appendages are often used for highly specialized purposes, such
as the prehensile tail of monkeys and the flexible trunk of elephants. The key to superior multipedia
is neural control. The neural circuitry for an extra limb is far less than that needed to add,
say, another eye. Muscles require thousands of new neurons, but eyeballs require millions. About
one-third of the mammalian brain is devoted to sensory functions, while only a small fraction
is devoted to motor control; aliens are much more likely to have extra arms than extra eyes or ears.
As we mentioned earlier, vertebrates on Earth have four limbs only because they share a
common ancestry with four-finned fish. Had we instead evolved from Euthacanthus, a Devonian
fish with no less than seven pairs of fins, we might be hexapods or even heptapods today!
After all, there are many advantages to living on six legs. On high-gravity worlds,
hexapods are a good way to distribute mechanical stress and reduce the risk
of bone fractures. Injury or loss of a limb is more catastrophic for
four-legged humans than for six-legged humans (who have "spare" limbs).
Hexapods also have better balance because, unlike quadrupeds, they can maintain a stable supporting
tripod on the ground even at high speeds. And it should not be too difficult
to coordinate all those legs... In short, according to mainstream biologists,
there seems to be no escape from the dictatorship of the principle of evolutionary convergence...
The exotic forms invoked by some astrobiologists may exist, yes, and maybe the most common,
but the point is that they are not evolutionarily plausible, nor can they explain how they could
have achieved technological intelligence in the absence of the most basic manipulative skills.
EXOTIC BIOLOGY However, many scientists argue that there
is very little chance that an alien life form could remotely resemble us, given all the possible
variables that could make a difference...such as environmental ones, referring to the particular
geological, atmospheric, and meteorological conformation of the planet; physical ones
(first and foremost, the force of gravity, which is different from Earth's);
planetary ones (e.g., a habitable planet could have a more complex orbit and spatial geography
than Earth's); and biological ones, related to the evolutionary process and natural selection.
One possibility often suggested by more radical exobiologists is that extraterrestrial life may
depend on the chemistry that does not require the carbon atom. Although carbon chemistry is
undeniably the optimal chemistry on planet Earth, one can hypothesize that biological life is built
around silicon, which is very common in the sand and used specifically to make electronic circuits.
This could affect the body structure of extraterrestrials, as they may
require different types of proteins, enzymes, nucleic acids, and other cellular components.
For example, an alien might have very thick, tough skin to protect itself from radiation,
or a completely different vascular system to transport
nutrients and oxygen throughout the body. In the 1960s and 1970s, the famous astronomer Carl
Sagan was convinced that technologically advanced species could evolve indifferently on land, sea,
or air, with unimaginable chemistry, shapes, sizes, colors, appendages, and opinions.
This, in turn, influenced the science fiction of those years,
which began to imagine non-humanoid or even decidedly exotic life forms, such as sentient
clouds of interstellar gas thousands of kilometers in diameter, or bizarre "balloon"-shaped creatures
floating in Jupiter's gas belts, using a hydrogen-based metabolism instead of oxygen.
Some suggest that extraterrestrial intelligent beings might resemble insects, birds, fish,
or even plants. They could have a spherical shape, be sticky jellyfish-like creatures (like the
heptapod beings proposed in the movie Arrivals), or even exist as a planet-sized ocean intelligence
like the one in Stanislaw Lem's novel Solaris. But old-school biologists shake their heads and
ask, "How could these creatures have become intelligent? They seem to us to be only
fanciful hypotheses, without the slightest relation to physical and biological laws!
And to this, the exobiologists reply that if the goal is to scientifically hypothesize intelligent
alien life forms, then it is necessary to abandon all anthropocentric preconceptions and accept
creatures that differ from us in every parameter. The principle of convergence is a popular one in
the field of evolution, it is true, but it would hardly be able to reproduce all the physical
characteristics familiar to us in creatures scattered over billions of other distant worlds...
True, we won't have an answer for many years, decades, or even centuries,
but it's still nice to talk about it and to anticipate issues that
will affect our great-grandchildren very closely in the near future...
P.S. And you, what do you think? Are you on the
side of the old biologists or on the side of the exobiologists?