Exoanatomy - Jothi's World
Transcript Exoanatomy - Jothi's World
Could ET really have ridden
An intro to exoanatomy.
© ss jothiratnam
The speculative “study” of the
biology and anatomy – of
(intelligent) extraterrestrial life
Is this science fiction?
Surprisingly enough, not really. Even
though SETI has not as of yet managed
to bring Alien musical-hits to the Top of
the pops, we can still speculate
meaningfully about alien physiology.
How sure are we that aliens
Two approaches to answering this question:
Drake equation (Frank Drake)
When radio astronomy was in its infancy, Drake
realised that we could receive radio signals
from alien civilisations. His eqn. was created to
decide how best to go about searching for these
signals, by providing an estimate of the likely
relative abundance of radio emissions fm.
N = R* . fp . ne . fl . fi . fc . L
N = R* . fp . ne . fl . fi . fc . L
N = no. of planets in our Gxy. w. intell. life on them
R*= rate of formation of relatively sun-like stars
fp= fractn. of stars w. planets
ne= av. no. of planets around such a star
fl= fractn. of above planets w. life
fi= fractn. of above planets w. intelligence
fc= fractn. of above planets w. civilisation
L= life-span of a technological civilisation
R* = 1 - 10 (empirical)
fp = .2 - .5 (empirically-based estimate)
ne = 1 - 5 (empirically-based estimate)
fl = 1 (evol’n. of life a trivial & inevitable conseq. of the operation of laws of chem. & phys.)
fi = 1 (emergence. of intell. a trivial & inevitable conseq. of the operation of laws of evol’n.)
fc = .1 (dev. of civil. a strong conseq. of the operation of laws of social evol’n)
L = 103 - 105 (based on ours, likely to be wiped out w/i 1000 to 100,000 yrs)
thus N = 20 - 2.5x106
Notice that this eqn. goes fm Qs of
astronomy/astrophysics to Qs of
biology, to Qs of sociology.
Ca. 1010~1011 stars per galaxy
Somewhere in excess of 1010 galaxies in the known univ. (based on
I.e. estimated 1020~1021 stars in the known universe
Guess at how common planetary systems are. Being very conservative,
guess 10- 6 (in actuality, the frequency looks to be at least one in 103, if not
better based on recent discoveries of extra-solar planets)
Of these planets, how many have the capability of supporting life? Here,
we’re on even thinner ice. For the previous estimate, we could reasonably
determine that 10- 6 was a conservative estimate; but for the present case,
we have absolutely no idea what a reasonable guess might be, all we can
hope for are contingent estimates. Sticking with the 10- 6 figure again for
example gives 108~109 planets with life on them This works out to an
average of less than one life-bearing planet per ten galaxies in the known
Stat. analysis contd.
Given the prevalence of complex hydrocarbons, and especially
amino acids in space - on other planets in our solar system and on
some of their satellites (for example on Titan, one of the moons of
Saturn), and on some meteors and comets - however, this estimate
seems overly conservative. Thus, the probabilities seem to be very
strongly in favour of there being life elsewhere in the universe, and
very probably at a large number of sites in any given galaxy.
(N.B. Incidentally, this set of calculations does not provide any
support for visits by UFOs to cornfields in Kansas. I mean if you
were an alien, would you really travel a gazillion light-years to visit
So chances are that life, even
intelligent life exists out there.
The question is what might it look
We now know enough about
biology and several related fields
(biochemistry, biophysics, etc.) to
speculate meaningfully about
what aliens might look like, and
what they almost certainly – within
the bounds of present knowledge
at least – could not look like.
The ground rules I
Basic laws of chemistry and physics are valid
throughout the universe
Basic Darwinian scheme is valid throughout the
Life is a behavioural phenomenon which is
dependent on the interaction of systems of longchain molecules, that is to say, life is chemicallybased
These molecules are composed of the same
elements which have been identified in the
periodic table of chemical elements
The ground rules II
The periodic table is an exhaustive catalogue of
all possible combinations of protons, neutrons,
Thus a given complex molecule will have the
same dimensions throughout the universe
In order to create complex neural circuitry, a
certain number of long-chain molecules will
always be required. In other words, the size of
the chemical elements (the atoms) imposes
definite limits on the size and functioning of
complex systems of long-chain molecules – that
is to say, on life-forms
Ground rules III
Finally, there is the question of water.Would
these aliens necessarily be water dependent?
The big advantage of water is that it is a very
good solvent, since it is a polar molecule. For
living things, liquids are likely to be very
important, because fluids are a good way to
transport food, and remove wastes. Whether this
liquid would necessarily be water, it is hard to
say, but there is certainly a strong case to be
made in its favour.
Basic Darwinian scheme
Variability: Each individual living thing is not an exact copy of its predecessors. Every
individual is different, and because of these differences, has slight advantages over
other members of its species in some ways, and is disadvantaged in other ways.
Variability leads to mutations which are variably adapted to their environment.
This variability is caused by random variations in the building plans of the organism
(the genes). The genetic codes’ structure is meta-stable in a particular way – it
preserves its overall structure: dogs don’t give birth to cows, but varies slightly: brown
dogs can give birth to white puppies.
All organisms in any eco-system are in competition with other organisms for selected,
limited resources. There are only so many things to eat, so many caves to inhabit, so
many females to fecundate, etc, and so the best adapted tend to get the most, and
the best of whatever they need. Life is based upon each individual’s or group’s
aggressive, selfish, struggle for survival against other living things. This observation is
not invalidated the fact that in certain species, ants for example, the individual
organism is secondary to the group. What is key here is that the genetic information
survives: Usually, this is ensured by individual selfishness, but may in certain cases
pass by the means of group selfishness. To sum it up, life is tough, and only the
toughest (best adapted) get to survive and reproduce.
The environment is not static, but changes over time, leading both to the extinction of
existing species, and to the evolution of new ones all the time.
The extinction or survival of an organism is always based on its adaptability to its
So, given these ground rules,
what are intelligent alien lifeforms likely to be like?
There are two facets to this question: One is
how they might look, and the other is how
they might behave. I shall look only at the
former facet in this session.
Let’s start at the top. Would they
necessarily have heads?
Assuming that they would need to think, and that in order to think they
would need thinking machinery – i.e. a nervous system of some sort – it is
likely that the thinking would tend to be centralised simply because if the
thinking part of the nervous system were to be diffuse, information
processing would take much longer, and thought would not be as rapid as it
could be. Thus, yes, I think it likely that they would have “heads” i.e. a
location for the brain. Is it likely that their “heads” would be attached to one
end of their “bodies” however I am unable to say.
On earth, it is true that most life-forms equipped with a central nervous
system have it at one end of their bodies, This particular body-architecture
evolved about 550 million years ago because it placed the informationprocessing circuitry close to the sensory organs, but whether this is a
necessary condition of intelligent life or not, I cannot say. For radially
symmetrical body-forms like octopuses a central location certainly makes
more sense, but in the case of other body-forms I just don’t know.
Similarly, it is hard to say if they would
absolutely have to have skeletons or not.
Skeletons are an effective way of dealing with
the effects of gravity that all macroscopic entities
experience, as well as providing good leverage
points for muscle-attachment, but parts of many
living organisms, ranging from squids’ tentacles
to elephants’ trunks, seem to function perfectly
well without any skeletons at all.
Sensory organs I
Moving on to sensory organs, without doubt, they would
need these. The question is what sorts of organs would
they have? There are all sorts of signals that arrive from
the environment: Electromagnetic, electric, magnetic,
vibrational, chemical, pressure, thermal etc. Any of these
could serve to stimulate sensory organs, and it’s
impossible to say which of these intelligent aliens are
likely to make use of. All we can conclude is that they
are likely to have a few different types of sensory organs,
just like us: Some which are relatively directional (like
our eyes); Others which are relatively omni-directional
(like our ears); And yet others which function at the
chemical level like our sense of smell/taste.
Sensory organs II
They are also likely to have some sort of sense
of touch, since this is important in maintaining
the distinction between self and the rest of the
world, as well as in fending off attacks from the
environment (out there). If they had some sort of
electromagnet-wave detectors (“eyes”), chances
are that these would not function in the X-ray or
far ultra-violet range, since radiations at these
wavelengths damage complex molecules.
Sensory organs III
Would they have their detectors in pairs or not? Here, I
think that the answer is fairly straightforward. Those
senses which serve to locate objects in space need
some sort of three-dimensional imaging ability. In order
to do this, the organism needs a minimum of two
detectors of the same type: We have two eyes, and two
ears, the left one physically separated from the right one
for this very reason. Senses which do not serve to
localise stimuli however need not have detectors which
come in pairs. This is why we only have one tongue, and
why our nostrils are close together.
Sensory organs IV
Would they have more than two “eyes” or
“ears”? This I think is unlikely since each
extra organ needs a fair amount of
information-processing circuitry, and
redundancy is resource-consuming. There
is an important evolutionary principle at
work here: resource efficiency. Evolution is
an energy- and resource-efficient process.
Sensory organs V
Would they have some of their sensory organs
located as high up as possible (like us), or not? I
think that this would depend on what type of sensory
organs we were talking about. Sound and light
detectors are normally most effective when they are
placed high up, but other detectors might work
better if they could moved either up to the top or
close to the ground at will.
An important caveat here is that distance from the
CNS implies slower reaction times. This is why
terrestrial animals have reflex loops. Thus, there is
an argument to be made that aliens’ “heads” are
likely to have certain sensory organs on them.
Land, air or sea?
Would they be terrestrial? Again, whilst there is
no definite answer possible, I think it likely, In
order to be advanced, they would have needed
to develop tool-making technology, and toolmaking is likely to have remained rudimentary
without the aid of fire, or some other heat-source
of reasonable power, one hot enough to melt
metals. This is more likely to have happened on
land, than in a liquid (s.h.c. of liquids is high for
example, and their abilities to disperse heat is
generally higher than that of gasses), thus I think
it likely that they would be land-dwelling.
Air, sea or land?
You might be asking yourself, could they be avian? If they
were, I think it less probable that they would have developed
a high intelligence simply because flight imposes very strict
energetic and weight requirements: All flying organisms large
enough to have even moderately-sized brains have to adopt
serious weight-reducing architecture. This implies that a
massive central nervous system is unlikely to have evolved in
flying organisms, simply because of its weight. In addition,
flying requires such enormous amounts of energy that there is
not likely to be much left over to power a large brain. This
having been said however, on earth, there certainly are some
birds, particularly the nestor kea of New Zealand that seem to
exhibit high intelligence, so my foregoing conclusion is
necessarily a weak one.
Sea, land or air?
This is not to say that they might not have their roots in
non-terrestrial forms. They could easily have evolved from
“fish”-like ancestors (as we did), or “bird”-like ancestors, but
are likely to be land-dwelling.
Furthermore, they are likely to be surface dwelling,rather
than subterranean, and living on a planet (like us), rather
than on a meteor, or a star. This is because the chemistry
of life requires energy, and this energy is typically provided
by a star (like our sun), around which life-bearing planets
Their home planet is likely to have an atmosphere because
atmospheres shield the surface of their home planets from
cosmic and other “hard” radiation.
Their home-base is unlikely to be a star because stars are
too hot for complex chemical structures to form.
Could they shake hands? Could
they do the twist?
So, if they are most likely terrestrial, how many “arms” and “legs”
are they likely to have? I put it to you that an intelligent,
advanced life-form must have “hands” of some sort, instruments
with which to manipulate the world. In order to direct these
“hands”, a certain amount of “brain-power” is required, a certain
number of neural circuits. Furthermore, the more complex the
manipulative possibilities of these “hands”, the more neuronal
processing capacity they will require (cf. the anatomy of the brain
along the rift). Thus, a four-armed alien would need a
significantly larger brain than a two-armed one, and I have some
doubts about how much more efficient four arms would be over
two. Consequently, I think it more probable that they would be
two-armed. About their locomotive organs however, I can say
nothing. All sorts of possibilities are envisageable. A two-armed
serpentine form, for example, has no innate disadvantages, as
far as I can see, over any other form.
Could they sit on your couch?
How big (or small) would they be? Again, we need to return to
the premise that a certain minimum number of molecules,
composed of the elements of the periodic table, are required
in order to construct the machinery of a living organism, and
of its brain. As far as we know, only carbon and silicon are
capable of forming long-chain molecules of the type that I
think are necessary for life. Hence, an intelligent alien is
unlikely to be smaller than say a medium-sized dog. Could it
be much larger than us however, I am unable to say for
certain, although I am inclined to say no because very large
life-forms do not need to defend themselves as much as
smaller ones, and thus there is less selective pressure to
develop v. high intelligence. This is a weak conclusion
however. If, for example, their planet had a much lower
gravity, I suppose that one might expect very large aliens.
Although there would likely be other problems - see below.
Would they break your couch if
they were to sit on it?
There are problems with the idea of a very-low
gravity planet producing (presumably) v. large
intelligent life-forms. A low gravity means a thin
atmosphere (since it is the gravitational-field of a
planet which holds the atmosphere in place), and a
thin atmosphere does not shield the surface of the
planet from cosmic radiation, which is extremely
harmful to most complex molecules (cf. above). This
means that life, if it is present on such a planet, is
more likely to have evolved under some liquid on the
surface, or underground. This type of life for the
reasons explored above is not likely to be highly
A question of energy?
Occasionally, exobiologists have proposed that life might
evolve on cold, low-gravity planets situated far from their
parent star. I think that this is entirely possible, but I
doubt that these life-forms would be highly developed,
because far from the parent star, there is less energy
available for the chemistry of life, and thus the metabolic
rates of these “tele-stellar” aliens is likely to be very, very
low. For similar reasons, I think that our potential alien
are likely to have high metabolic rates (like mammals
and birds), rather than low ones, (like reptiles and
amphibians): They would most likely be the equivalent of
“warm-blooded”, if you like.
No Hare Krishnas out there
Similarly, because of energetic
requirements, intelligent aliens are more
likely to eat other organisms (to be
carnivores, or omnivores), rather than to
synthesize their own food. It’s simply
faster and more energy efficient to do so,
and furthermore there is more selective
pressure to develop intelligence amongst
hunting animals than amongst other forms.
Finally, are they likely to have developed sexual
reproduction? Alien abduction scenarios
notwithstanding, the answer is a weak yes.
Sexual reproduction introduces more variability
into the gene pool than does asexual
reproduction, and is, I think, in certain way
favoured by the forces of evolution, at least in so
far as complex intelligent organisms are
concerned. Whether there would be two, three,
or more partners involved however, I cannot say,
and shall leave the answer to this question up to
your fervid imagination.
ET phone home?
So, could ET really have ridden a bicycle?
I don’t know about pedalling it, but I think
“he” almost surely could have held on to
Would “he” have suffered from homesickness? Find out next time.