Do You Believe Is True Even Though You Cannot Prove It?"
Stanford University, Author, A Primate's Memoir
of course, it is tempting to go for something like,
"That the wheel, agriculture, and the Macarena
were all actually invented by yetis." Or to do
the sophomoric pseudo-ironic logic twist of, "That
every truth can eventually be proven." Or to get
up my hackles, draw up to my full height and intone,
"Sir, we scientists believe in nothing that cannot
be proven by the whetstone of science, verily our faith
is our lack of faith," and then go off in a lab
coat and a huff.
first two aren't worth the words, and the third just
isn't so. No matter how many times we read Arrowsmith,
scientists are subjective humans operating in an ostensibly
objective business, so there 's probably lots of things
we take on faith.
mine would be a fairly simple, straightforward case
of an unjustifiable belief, namely that there is no
god(s) or such a thing as a soul (whatever the religiously
inclined of the right persuasion mean by that word).
I'm very impressed, moved, by one approach of people
on the other side of the fence. These are the believers
who argue that it would be a disaster, would be the
very work of Beelzebub, for it to be proven that god
exists. What good would religiosity be if it came with
a transparently clear contract, instead of requiring
the leap of faith into an unknowable void?
I'm taken with religious folks who argue that you not
only can, but should believe without requiring proof.
Mine is to not believe without requiring proof. Mind
you, it would be perfectly fine with me if there were
a proof that there is no god. Some might view this as
a potential public health problem, given the number
of people who would then run damagingly amok. But it's
obvious that there's no shortage of folks running amok
thanks to their belief. So that wouldn 't be a problem
and, all things considered, such a proof would be a
relief—many physicists, especially astrophysicists,
seem weirdly willing to go on about their communing
with god about the Big Bang, but in my world of biologists,
the god concept gets mighty infuriating when you spend
your time thinking about, say, untreatably aggressive
just to undo any semblance of logic here, I might even
continue to believe there is no god, even if it was
proven that there is one. A religious friend
of mine once said to me that the concept of god is very
useful, so that you can berate god during the bad times.
But it is clear to me that I don't need to believe that
there is a god in order to berate him.
Institute of Advanced Study, Author, Disturbing
I am a mathematician, I give a precise answer to this
question. Thanks to Kurt Gödel, we know that there
are true mathematical statements that cannot be proved.
But I want a little more than this. I want a statement
that is true, unprovable, and simple enough to be understood
by people who are not mathematicians. Here it is.
Numbers that are exact powers of two are 2, 4, 8, 16,
32, 64, 128 and so on. Numbers that are exact powers
of five are 5, 25, 125, 625 and so on. Given any number
such as 131072 (which happens to be a power of two),
the reverse of it is 270131, with the same digits taken
in the opposite order. Now my statement is: it never
happens that the reverse of a power of two is a power
The digits in a big power of two seem to occur in a
random way without any regular pattern. If it ever happened
that the reverse of a power of two was a power of five,
this would be an unlikely accident, and the chance of
it happening grows rapidly smaller as the numbers grow
bigger. If we assume that the digits occur at random,
then the chance of the accident happening for any power
of two greater than a billion is less than one in a
billion. It is easy to check that it does not happen
for powers of two smaller than a billion. So the chance
that it ever happens at all is less than one in a billion.
That is why I believe the statement is true.
But the assumption that digits in a big power of two
occur at random also implies that the statement is unprovable.
Any proof of the statement would have to be based on
some non-random property of the digits. The assumption
of randomness means that the statement is true just
because the odds are in its favor. It cannot be proved
because there is no deep mathematical reason why it
has to be true. (Note for experts: this argument does
not work if we use powers of three instead of powers
of five. In that case the statement is easy to prove
because the reverse of a number divisible by three is
also divisible by three. Divisibility by three happens
to be a non-random property of the digits).
It is easy to find other examples of statements that
are likely to be true but unprovable. The essential
trick is to find an infinite sequence of events, each
of which might happen by accident, but with a small
total probability for even one of them happening. Then
the statement that none of the events ever happens is
probably true but cannot be proved.
Senior Fellow, Manhattan Institute; Author, Doing
Our Own Thing
year, researching the languages of Indonesia for an
upcoming book, I happened to find out about a few very
obscure languages spoken on one island that are much
simpler than one would expect.
Most languages are much, much more complicated than
they need to be. They take on needless baggage over
the millennia simply because they can. So, for instance,
most languages of Indonesia have a good number of prefixes
and/or suffixes. Their grammars often force the speaker
to attend to nuances of difference between active and
passive much more than a European languages does, etc.
But here were a few languages that had no prefixes or
suffixes at all. Nor do they have any tones, like many
languages in the world. For one thing, languages that
have been around forever that have no prefixes, suffixes,
or tones are very rare worldwide. But then, where we
do find them, they are whole little subfamilies, related
variations on one another. Here, though, is a handful
of small languages that contrast bizarrely with hundreds
of surrounding relatives.
One school of thought in how language changes says that
this kind of thing just happens by chance. But my work
has been showing me that contrasts like this are due
to sociohistory. Saying that naked languages like this
are spoken alongside ones as bedecked as Italian is
rather like saying that kiwis are flightless just "because,"
rather than because their environment divested them
of the need to fly.
But for months I scratched my head over these languages.
Why just them? Why there?
So isn't it interesting that the island these languages
is spoken on is none other than Flores, which has had
its fifteen minutes of fame this year as the site where
skeletons of the "little people" were found. Anthropologists
have hypothesized that this was a different species
of Homo. While the skeletons date back 13,000
years ago or more, local legend recalls "little people"
living alongside modern humans, ones who had some kind
of language of their own and could "repeat back" in
modern humans' language.
The legends suggest that the little people only had
primitive language abilities, but we can't be sure here:
to the untutored layman who hasn't taken any twentieth-century
anthropology or linguistics classes, it is easy to suppose
that an incomprehensible language is merely babbling.
Now, I can only venture this highly tentatively now.
But what I "know" but cannot prove this year is: the
reason languages like Keo and Ngada are so strangely
streamlined on Flores is that an earlier ancestor of
these languages, just as complex as its family members
tend to be, was used as second language by these other
people and simplified. Just as our classroom French
and Spanish avoids or streamlines a lot of the "hard
stuff," people who learn a language as adults usually
do not master it entirely.
Specifically, I would hypothesize that the little people
were gradually incorporated into modern human society
over time—perhaps subordinated in some way—such
that modern human children were hearing the little people's
rendition of the language as much as a native one.
This kind of process is why, for example, Afrikaans
is a slightly simplified version of Dutch. Dutch colonists
took on Bushmen as herders and nurses, and their children
often heard second-language Dutch as much as their parents.
Pretty soon, this new kind of Dutch was everyone's everyday
language, and Afrikaans was born.
Much has been made over the parallels between the evolution
of languages and the evolution of animals and plants.
However, I believe that one important difference is
that while animals and plants can evolve towards simplicity
as well as complexity depending on conditions, languages
do not evolve towards simplicity in any significant,
overall sense—unless there is some sociohistorical
factor that puts a spoke in the wheel.
So normally, languages are always drifting into being
like Russian or Chinese or Navajo. They only become
like Keo and Ngada—or Afrikaans, or creole languages
like Papiamentu and Haitian, or even, I believe, English—because
of the intervention of factors like forced labor and
population relocation. Just maybe, we can now add interspecies
contact to the list!
University of Pennsylvania, Author, Authentic Happiness
"rotten-to-the-core" assumption about human nature espoused
so widely in the social sciences and the humanities
is wrong. This premise has its origins in the religious
dogma of original sin and was dragged into the secular
twentieth century by Freud, reinforced by two world
wars, the Great Depression, the cold war, and genocides
too numerous to list. The premise holds that virtue,
nobility, meaning, and positive human motivation generally
are reducible to, parasitic upon, and compensations
for what is really authentic about human nature: selfishness,
greed, indifference, corruption and savagery. The only
reason that I am sitting in front of this computer typing
away rather than running out to rape and kill is that
I am "compensated," zipped up, and successfully defending
myself against these fundamental underlying impulses.
spite of its widespread acceptance in the religious
and academic world, there is not a shred of evidence,
not an iota of data, which compels us to believe that
nobility and virtue are somehow derived from negative
motivation. On the contrary, I believe that evolution
has favored both positive and negative traits, and many
niches have selected for morality, co-operation, altruism,
and goodness, just as many have also selected for murder,
theft, self-seeking, and terrorism.
plausible than the rotten-to-the-core theory of human
nature is the dual aspect theory that the strengths
and the virtues are just as basic to human nature as
the negative traits: that negative motivation and emotion
have been selected for by zero-sum-game survival struggles,
while virtue and positive emotion have been selected
for by positive sum game sexual selection. These two
overarching systems sit side by side in our central
nervous system ready to be activated by privation and
thwarting, on the one hand, or by abundance and the
prospect of success, on the other.
UC-Berkeley; Coauthor, The Scientist In the Crib
believe, but cannot prove, that babies and young children
are actually more conscious, more vividly aware
of their external world and internal life, than adults
are. I believe this because there is strong evidence
for a functional trade-off with development. Young children
are much better than adults at learning new things and
flexibly changing what they think about the world. On
the other hand, they are much worse at using their knowledge
to act in a swift, efficient and automatic way. They
can learn three languages at once but they can't tie
This trade-off makes sense from an evolutionary perspective.
Our species relies more on learning than any other,
and has a longer childhood than any other. Human childhood
is a protected period in which we are free to learn
without being forced to act. There is even some neurological
evidence for this. Young children actually have substantially
more neural connections than adults—more potential
to put different kinds of information together. With
experience, some connections are strengthened and many
others disappear entirely. As the neuroscientists say,
we gain conductive efficiency but lose plasticity.
What does this have to do with consciousness? Consider
the experiences we adults associate with these two kinds
of functions. When we know how to do something really
well and efficiently, we typically lose, or at least,
reduce, our conscious awareness of that action. We literally
don't see the familiar houses and streets on the well-worn
route home, although, of course, in some functional
sense we must be visually taking them in. In contrast,
as adults when we are faced with the unfamiliar, when
we fall in love with someone new, or when we travel
to a new place, our consciousness of what is around
us and inside us suddenly becomes far more vivid and
intense. In fact, we are willing to expend lots of money,
and lots of emotional energy, for those few intensely
alive days in Paris or Beijing that we will remember
long after months of everyday life have vanished.
Similarly, as adults when we need to learn something
new, say when we learn to skydive, or work out a new
scientific idea, or even deal with a new computer, we
become vividly, even painfully, conscious of what we
are doing—we need, as we say, to pay attention.
As we become expert we need less and less attention,
and we experience the actual movements and thoughts
and keystrokes less and less. We sometimes say that
adults are better at paying attention than children,
but really we mean just the opposite. Adults are better
at not paying attention. They're better at
screening out everything else and restricting their
consciousness to a single focus. Again there is a certain
amount of brain evidence for this. Some brain areas,
like the dorsolateral prefrontal cortex, consistently
light up for adults when they are deeply engaged in
learning something new. But for more everyday tasks,
these areas light up much less. For children, though
the pattern is different—these areas light up
even for mundane tasks.
I think that, for babies, every day is first love in
Paris. Every wobbly step is skydiving, every game of
hide and seek is Einstein in 1905.
The astute reader will note that this is just the opposite
of what Dan Dennett believes but cannot prove. And this
brings me to a second thing I believe but cannot prove.
I believe that the problem of capital-C Consciousness
will disappear in psychology just as the problem of
Life disappeared in biology. Instead we'll develop much
more complex, fine-grained and theoretically driven
accounts of the connections between particular types
of phenomenological experience and particular functional
and neurological phenomena. The vividness and intensity
of our attentive awareness, for example, may be completely
divorced from our experience of a constant first-person
I. Babies may be more conscious in one way and less
in the other. The consciousness of pain may be entirely
different from the consciousness of red which may be
entirely different from the babbling stream of Joyce
Harvard University; Author, The Blank Slate
1974, Marvin Minsky wrote that "there is room in
the anatomy and genetics of the brain for much more
mechanism than anyone today is prepared to propose."
Today, many advocates of evolutionary and domain-specific
psychology are in fact willing to propose the richness
of mechanism that Minsky called for thirty years ago.
For example, I believe that the mind is organized into
cognitive systems specialized for reasoning about object,
space, numbers, living things, and other minds; that
we are equipped with emotions triggered by other people
(sympathy, guilt, anger, gratitude) and by the physical
world (fear, disgust, awe); that we have different ways
for thinking and feeling about people in different kinds
of relationships to us (parents, siblings, other kin,
friends, spouses, lovers, allies, rivals, enemies);
and several peripheral drivers for communicating with
others (language, gesture, facial expression).
I say I believe this but cannot prove it, I don't mean
that it's a matter of raw faith or even an idiosyncratic
hunch. In each case I can provide reasons for my belief,
both empirical and theoretical. But I certainly can't
prove it, or even demonstrate it in the way that molecular
biologists demonstrate their claims, namely in a form
so persuasive that skeptics can't reasonably attack
it, and a consensus is rapidly achieved. The idea of
a richly endowed human nature is still unpersuasive
to many reasonable people, who often point to certain
aspects of neuroanatomy, genetics, and evolution that
appear to speak against it. I believe, but cannot prove,
that these objections will be met as the sciences progress.
the level of neuroanatomy and neurophysiology, critics
have pointed to the apparent homogeneity of the cerebral
cortex and of the seeming interchangeability of cortical
tissue in experiments in which patches of cortex are
rewired or transplanted in animals. I believe that the
homogeneity is an illusion, owing to the fact that the
brain is a system for information processing. Just as
all books look the same to someone who does not understand
the language in which they are written (since they are
all composed of different arrangements of the same alphanumeric
characters), and the DVD's of all movies look the same
under a microscope, the cortex may look homogeneous
to the eye but nonetheless contain different patterns
of connectivity and synaptic biases that allow it to
compute very different functions. I believe this these
differences will be revealed in different patterns of
gene expression in the developing cortex. I also believe
that the apparent interchangeability of cortex occurs
only in early stages of sensory systems that happen
to have similar computational demands, such as isolating
sharp signal transitions in time and space.
the level of genetics, critics have pointed to the small
number of genes in the human genome (now thought to
be less than 25,000) and to their similarity to those
of other animals. I believe that geneticists will find
that there is a large store of information in the noncoding
regions of the genome (the so-called junk DNA), whose
size, spacing, and composition could have large effects
on how genes are expressed. That is, the genes themselves
may code largely for the meat and juices of the organism,
which are pretty much the same across species, whereas
how they are sculpted into brain circuits may depend
on a much larger body of genetic information. I also
believe that many examples of what we call "the
same genes" in different species may differ in
tiny ways at the sequence level that have large consequences
for how the organism is put together.
at the level of evolution, critics have pointed to how
difficult it is to establish the adaptive function of
a psychological trait. I believe this will change as
we come to understand the genetic basis of psychological
traits in more detail. New techniques in genomic analysis,
which look for statistical fingerprints of selection
in the genome, will show that many genes involved in
cognition and emotion were specifically selected for
in the primate, and in many cases the human, lineage.
Columbia University; Author, How The Universe Got
believe there is an external reality and you are not
all figments of my imagination. My friend asks me through
the steam he blows off the surface of his coffee, how
I can trust the laws of physics back to the origins
of the universe. I ask him how he can trust the laws
of physics down to his cup of coffee. He shows every
confidence that the scalding liquid will not spontaneously
defy gravity and fly up in his eyes. He lives with this
confidence born of his empirical experience of the world.
His experiments with gravity, heat, and light began
in childhood when he palpated the world to test its
materials. Now he has a refined and well-developed theory
of physics, whether expressed in equations or not.
simultaneously believe more and less than he does. It
is rational to believe what all of my empirical and
logical tests of the world confirm—that there
is a reality that exists independent of me. That the
coffee will not fly upwards. But it is a belief nonetheless.
Once I've gone that far, why stop at the perimeter of
mundane experience? Just as we can test the temperature
of a hot beverage with a tongue, or a thermometer, we
can test the temperature of the primordial light left
over from the big bang. One is no less real than the
other simply because it is remarkable.
how do I really know? If I measure the temperature of
boiling water, all I really know is that mercury climbs
a glass tube. Not even that, all I really know is that
I see mercury climb a glass tube. But maybe the image
in my mind's eye isn't real. Maybe nothing is real,
not the mercury, not the glass, not the coffee, not
my friend. They are all products of a florid imagination.
There is no external reality, just me. Einstein? My
creation. Picasso? My mind's forgery. But this solopsism
is ugly and arrogant. How can I know that mathematics
and the laws of physics can be reasoned down to the
moment of creation of time, space, the entire universe?
In the very same way that my friend believes in the
reality of the second double cappuccino he orders. In
formulating our beliefs, we are honest and critical
and able to admit when we are wrong—and these
are the cornerstones of truth.
I leave the café, I believe the room of couches
and tables is still on the block at 122nd Street, that
it is still full of people, and that they haven't evaporated
when my attention drifts away. But if I am wrong and
there is no external reality, then not only is this
essay my invention, but so is the web, edge.org,
all of its participants and their ingenious ideas. And
if you are reading this, I have created you too. But
if I am wrong and there is no external reality, then
maybe it is me who is a figment of your imagination
and the cosmos outside your door is your magnificent
former President, Weizmann Institute of Science
electron has been with us for over a century, laying
the foundations to the electronic revolution and
all of information technology. It is believed to
be a point-like, elementary and indivisible particle.
neutrino, more than a million times lighter than
the electron, was predicted in the 1920's and discovered
in the 1950's. It plays a crucial role in the creation
of the stars, the sun and the heavy elements. It
is elusive, invisible and weakly interacting. It
is also considered fundamental and indivisible. Is
do not exist as free objects, except at extremely
tiny distances, deep within the confines of the particles
which are constructed from them. Since the 1960's
we believe that they are the most fundamental indivisible
building blocks of protons, neutrons and nuclei.
has created two additional, totally unexplained,
replicas of the electron, the neutrino and the most
abundant quarks, u and d, forming three "generations" of
fundamental particles. Each "generation" of
particles is identical to the other two in all properties,
except that the particle masses are radically different.
Since each "generation" includes four fundamental
particles, we end up with 12 different particles,
which are allegedly indivisible, point-like and elementary.
Atom, the nucleus and the proton, each in its own
time, were considered elementary and indivisible,
only to be replaced later by smaller objects as the
fundamental building blocks. How can we be so arrogant
as to exclude the possibility that this will happen
again? Why would nature arbitrarily produce 12 different
objects, with a very orderly pattern of electric
charges and "color forces", with simple
charge ratios between seemingly unrelated particles
(such as the electron and the quark) and with a pattern
of masses, which appears to be taken from the results
of a lottery? Doesn't this "smell" again
of further sub-particle structure?
is absolutely no experimental evidence for a further
substructure within all of these particles. There
is no completely satisfactory theory which might
explain how such light and tiny particles can contain
objects moving with enormous energies, a requirement
of quantum mechanics. This is, presumably, why the
accepted "party line" of particle physicists
is to assume that we already have reached the most
fundamental level of the structure of matter.
over twenty years, the hope has been that the rich
spectrum of so-called fundamental particles will
be explained as various modes of string vibrations
and excitations. The astonishingly tiny string or
membrane, rather than the point-like object, is allegedly
at the bottom of the ladder describing the structure
of matter. However, in spite of absolutely brilliant
and ingenious mathematical work, not one experimental
number has been explained in more than twenty years,
on the basis of the string hypothesis.
on common sense and on an observation of the pattern
of the known particles, without any experimental
evidence and without any comprehensive theory, I
have believed for many years, and I continue to believe,
that the electron, the neutrino and the quarks are
divisible. They are presumably made of different
combinations of the same small number (two?) of more
fundamental sub-particles. The latter may or may
not have the string structure, and may or may not
be themselves composites.
we live to see the components of the electron?
Macquarie University, Sydney; Author, How to Build a Time
of the biggest of the Big Questions of existence
is, Are we alone in the universe? Science has provided
no convincing evidence one way or the other. It is
certainly possible that life began with a bizarre
quirk of chemistry, an accident so improbable that
it happened only once in the entire observable universe—and
we are it. On the other hand, maybe life gets going
wherever there are earthlike planets. We just don't
know, because we have a sample of only one. However,
no known scientific principle suggests an inbuilt
drive from matter to life. No known law of physics
or chemistry favors the emergence of the living state
over other states. Physics and chemistry are, as
far as we can tell, "life blind."
I don't believe that life is a freak event. I think
the universe is teeming with it. I can't prove it;
indeed, it could be that mankind will never know
the answer for sure. If we find life in our solar
system, it most likely got there from Earth (or vice
versa) in rocks kicked off planets by comet impacts.
And to go beyond the solar system is the stuff of
dreams. The best hope is that we develop instruments
sensitive enough to detect life on extra-solar planets
from Earth orbit. But, whilst not impossible, this
is a formidable technical challenge.
why do I think we are not alone, when we have no
evidence for life beyond Earth? Not for the fallacious
popular reason: "the universe is so big there
must be life out there somewhere." Simple statistics
shows this argument to be bogus. If life is in fact
a freak chemical event, it would be so unlikely to
occur that it wouldn't happen twice among a trillion
trillion trillion planets. Rather, I believe we are
not alone because life seems to be a fundamental,
and not merely an incidental, property of nature.
It is built into the great cosmic scheme at the deepest
level, and therefore likely to be pervasive. I make
this sweeping claim because life has produced mind,
and through mind, beings who do not merely observe
the universe, but have come to understand it through
science, mathematics and reasoning. This is hardly
an insignificant embellishment on the cosmic drama,
but a stunning and unexpected bonus. Somehow life
is able to link up with the basic workings of the
cosmos, resonating with the hidden mathematical order
that makes it tick. And that's a quirk too far for
Wired; Author, New Rules for the New Economy
orthodoxy in biology states that every cell in your
body shares exactly the same DNA. It's your identity,
your indelible fingerprint, and since all the cells
in your body have been duplicated from your initial
unique stem cell these zillion of offspring cells
all maintain your singular DNA sequence. It follows
then that when you submit a tissue sample for genetic
analysis it doesn't matter where it comes from. Normally
technicians grab some from the easily accessible
pars of your mouth, but they could just as well take
some from your big toe, or your liver, or eyelash
and get the same results.
I believe, but cannot prove, that the DNA in your body (and all bodies)
varies from part to part. I make this prediction based on what we know
about biology, which is that natures abhors uniformity. No where else
in nature do we see identity maintained to such exactness. No where else
is there such fixity.
I do not expect intra-soma variation to diverge very much. Indeed the
genetic variation among individual humans is already relatively mild,
among the least of all animals, so the diversity within a human body
is unlikely to be greater than among human bodies—although that
may be possible. More likely, intra-soma variation will be less than
racial diversity but greater than zero.
Biologists already know (even if the public doesn't) that the full sequence
of DNA in your cells changes over time as your chromosomes are shorten
each time they divide in growth. Because of a bug in the system, DNA
is unable to duplicate itself when it gets to the very very tip of its
chain, so at each division it winds up a few hundred bases short. This
slight reduction after each of the cell's scores of divisions is currently
seen as the chief culprit in cell death and thus your own death. But
the variation I believe is happening is more fundamental. My guess is
that DNA mutates in a population of the cells in your body much as it
does in a population of bodies.
The consequences are more than just curious. At the trivial end, if my
belief were true, it would matter where you selected to sample your DNA
from. And it might also affect when you get it, as this variation
could change over time. If true, this variation might have some effect
on locating the correct seminal cells for growing replacement organs
While I have no evidence for my belief right now, it is a provable
assertion. It will be shown to be true or false as
soon as we have ubiquitous cheap full-genome sequences
at discount mall prices. That is, pretty soon. I
believe that once we have a constant reading of our
individual full DNA (many times over our lives) we
will have no end of surprises. I would not be surprised
to discover that pet owners accumulate some tiny
fragments of their pet's DNA,which has somehow been
laterally transferred via viruses to their own cellular
DNA. Or that diary farmers amass noticeable fragments
of bovine DNA. Or that the DNA in our limbs somehow
drift genetically in a "limby" way, distinct
from the variation in the cells in our nervous systems.
But I consider all this minor compared to a possible major breakthrough
in understanding. We have a pretty good idea of how the "selection" in
natural selection works: less fit organisms die. But when it comes to
understanding how variation arises in Darwinian evolution all we can
say is "random mutation" which is another way of saying "we
don't know exactly." If there were intra-somatic variation and if
we could easily observe it via massive constant full-genome sequencing
then we might be able to figure out exactly how a mutation occurs, and
whether there are patterns to those mutations, and to what extant such
variation is induced or influenced by the body or the environment—all
ideas which currently challenge the Darwinian wisdom that the body does
not directly influence the genetic makeup of a cell. Monitoring genetic
drift within a body may be a window into the origins of mutation itself.
Even if these larger ideas don't pan out, the simple fact that DNA in
each cell of your body is not 100% identical would be worth investigating.
Such a fact would be a surprise, except to me.