Evolutionary Spandrels

From: Judy Chatwin (JAC295@psy.soton.ac.uk)
Date: Fri Apr 19 1996 - 11:17:37 BST

What is an evolutionary "spandrel"?

This essay will look at what is understood by an evolutionary
"spandrel". It will highlight some of the theories of evolution and
then look at language in more detail. The conflicting ideas which will
be discussed concern the idea that language has evolved through natural
selection or as a spandrel. Most ideas seem to have a counter-argument
and this have been mentioned. Conclusions may be drawn from the
evidence presented.

The concept of an evolutionary "spandrel" has come about from an
architectural term relating to a necessary by-product of creating
something else. The exact analogy quoted by Pinker and Bloom (1990)
relates to Gould and Lewontin"s (1979) reference to the arches and
spandrels in the dome of the San Marco basilica in Venice; "Spandrels -
the tapering triangular spaces formed by the intersection of two rounded
arches at right angles ... are necessary architectural by-products of
mounting a dome on rounded arches." This feature has been elaborately
decorated with mosaics. An easy mistake would be to assume that the
triangular spaces had been put there intentionally as part of the
detailed decoration. In fact, they were there because of something
else. This argument is used by Gould and Lewontin to explain some
aspects of evolution which they do not feel can be accounted for by
natural selection. Epiphenomenal spandrels are seen as those which exist
but are of no real interest, such as the redness of blood, the V-shaped
space between a pair of fingers or the fact that there are a
prime-number of digits on each limb. Such spandrels have no direct
relevance to any behaviour or function and give no clues as to whether
the structures that they are associated with were shaped through natural

The next rung up the ladder is to look at those spandrels which have
been modified and put to better use. This cannot be done alone and
requires the intervention of natural selection. It may be seen as the
process responsible for the modified design of an already existing part
in order to put it to more effective use.. This is where nature makes
the best possible use of what already exists to suit its own needs and
purposes; remembering that it does not have an empty page on which to
begin its creativity.. These are usually a single, unique part or
repeated shapes or processes involving simple physical or geometric
laws, such as hexagonal honeycombs and spiral markings. These are
modified and arranged alongside other more complex processes in order to
perform a function. Ultimately, they can only be explained by natural

The nonselectionist aspect of evolution concerns unmodified spandrels.
This is used to describe a structure that already has a useful purpose
but that original function is usurped by another. Gould (1987a) (as
cited by Pinker & Bloom (1990)) talks about a wading bird that uses its
wings primarily as a sun visor when looking for fish in the water. It
is difficult to argue successfully that something with such a complex
engineering design as the wing would have evolved through natural
selection for the primary purpose of blocking out the sun. A simpler
structure would have done the job just as well.

This explanation of spandrels attempts to clarify what is being
discussed in terms of nonselectionism. It is also important when
looking at evolution to be aware of two other possibilities which exist
outside of selectionism.

Firstly, Gould proposed the theory of "punctuated equilibrium". He
disagreed with Darwinian naturalism and proposed that evolution occurred
in bursts. These were followed by longer periods where no change
occurred. Pinker & Bloom (1990) disagree with this and firmly believe
that evolution is gradual from generation to generation. They see
"adaptive complexity" as the main explanation for this theory.

Secondly, "exaptation" Gould & Vrba, (1982), (as cited by Pinker &
Bloom, 1990) refers to situations where new uses are found for parts
which were originally adapted to a different function. It also refers
to spandrels that had no function at all but existed because of
architecture, history or development. This may be illustrated by
looking back to the common origins of parts of bat wings, seal flippers,
horse forelimbs and human arms. This theory of "exaptation" may be seen
as a parallel to Darwin"s term "preadaptation". This is the time when
the "part" in question is fulfilling the two functions - the old and the
new. Gould has been seen as presenting a revolutionary theory of
evolution, undermining much of Darwin"s original theories. This
parallel illustrates that it is not so radical but more of a change in

Acknowledgement is made regarding the importance of natural selection
and Gould and Lewontin are in agreement that certain structures, such as
the vertebrate eye, must have come about through this physical process.
There is no other possible explanation. The Darwinian view that
selectionism is "the most important of evolutionary mechanisms" (Gould
and Lewontin (1979); as cited by Pinker & Bloom (1990)) is accepted but
they believe that there are nonselectionist explanations for some
biological traits.

Pinker & Bloom acknowledge that natural selection is not perfect and
that some traits evolve at the cost of others, these are referred to as
"inherent trade-offs". For example, an animal may possess an elaborate
appearance to make it attractive to the opposite sex but not to such an
extent as to prevent it fleeing from predators. Some compromise has to

Having looked at some evolutionary theories, this essay will now
concentrate on a particular area for discussion - language. This is not
referring to external languages such as French, English or Japanese.
These are only symbols used to transmit feelings and emotions. The area
in question is that relating to the universals that form the basis for
the theories of universal grammar. Debates may occur as to whether
language exists because of our physiology or our culture. However, for
the purposes of this essay it may be assumed that the evidence supports
the physiological view. The issue of concern is whether the ability for
language has evolved through natural selection or by nonselectionist
means. This does not mean to discount any environmental involvement but
to clarify the issue being discussed. Is language an evolutionary

Chomsky turned around long-standing beliefs on language acquisition in
his review of Skinner"s Verbal Behaviour. In it he argued that language
was not learned but dependent on "an innate, species-specific module
that is distinct from general intelligence" (Pinker (date?)). He drew
these conclusions from his observation that children had the ability to
learn languages that contain very subtle and abstract principles. They
are able to do this without teaching or imitation.

If it is to be believed that language came about through natural
selection then it would be reasonable to suggest some precursor should
exist in our closest relatives, the chimpanzees. Although they can be
taught certain hand signals and even sounds there is no evidence that
they have the ability for language as such. Consequently any link
between gesture and language in chimpanzees has been rejected as having
no connection with the universals being discussed. Pinker does not see
this as a stumbling block in his argument for natural selection.
Instead he points out the time factors involved. Chimpanzees and
humans shared common ancestors around 6-7 million years ago. This means
that there are about 300,000 generations in which language could have
evolved. This may be compared with the mathematical scenario whereby a
mouse like animal is subject to selection pressure for increased size.
This pressure is so small that it cannot be observed or measured for
individual variation; it would take 12,000 generations for it to evolve
to the size of an elephant. Such a time span is seen as geologically
"instantaneous", making 300,000 generations sound more than sufficient
for language to evolve. Presumably a complex cognitive function such as
this would involve far more individual variations than simply size.

Gould puts forward the argument for the nonselectionist view of language
as a spandrel. This view is supported by Chomsky and
Piattelli-Palmarini. He does not doubt that the evolution of the
enlargement of the brain had an adaptive basis. He does, however,
question the purpose of that increase in size. He suggests that
language may be a by-product of such rather than the reason for it. He
sees the mind as a single general- purpose computer, believing that any
sophisticated machine will perform tasks that it was not programmed to
do by virtue of its complexity.

Pinker & Bloom suggest that the increased size of the brain may affect
its quality but do not see it as a sufficient condition for language.
Simply increasing the number of neurones in a circuit or putting more
circuits into the brain does not ensure that more refined abilities will
occur. Such an increase would require detailed design, which could only
come about through natural selection. Pinker & Bloom feel that this is
not explained in Chomsky"s nonselectionist theory. They say that "the
most likely explanation for the complex structure of the language
faculty is that it is a design imposed on neural circuitry as a response
to evolutionary pressures."

Piattelli-Palmarini (1989) (as cited by Pinker & Bloom (1990)) suggests
that "Grammar is not completely predictable as an adaptation to
communication, therefore it lacks design and did not evolve by
selection." He makes the point that these specific linguistic phenomena
are not actually essential for human survival or reproduction,
therefore, it seriously calls into question its evolution through
natural selection. He believes that if language had been an adaptation
then it would have been both different and better. However, he does not
offer an alternative explanation for the existence of language only a
criticism for the lack of adaptive support.

Pinker & Bloom suggest that just because an explanation cannot be found
for one specific aspect of language, it does not necessarily mean that
the entire module is a spandrel. Some human organs may contain many
spandrels (such as the redness of blood), does this mean that the organ
is a spandrel?

The alternative view relating to this is that language evolved through
natural selection. It is seen as a gradualistic, Darwinian approach
which came about as a series of steps. In order for this theory to hold
firm, individuals must have possessed some genetic variation in their
grammatical ability which created tiny mutations each beneficial to its
owner. These individual characteristics must have had some reproductive
advantage for them to have been maintained by the species during
evolution. Also there has to be enough time and space separating our
species from our non-linguistic primate ancestors for this to have
occurred. Pinker & Bloom admit that there is no conclusive data to
support these issues but still believe that there is no other plausible
explanation. Chomsky fails to explain the inevitable genetic variations
that occur when putting forward his theory for language as a spandrel.

Although communication is possible at a primitive level, it has been
suggested that there are reproductive advantages for having better
grammar. Those who have the ability to gain the attention of the
listener and have strong powers of persuasion surely must be at an
advantage over the less articulate. Good linguistic skills could make a
Darwinian difference.

Pinker and Bloom firmly believe that language fulfils the requirements
for adaptation. Their argument suggests that it is a complex design
which provides a reproductive or survival function. This is supported
by their belief that it provides the ability necessary to communicate.
This theory denies any possibility that language may be a spandrel of
any general cognitive learning ability because of its dissociability.
Disease and damage have shown that it functions independently of, for
example, normal intelligence.

The above has shown that there are two possible schools of thought
regarding the human, innate ability for universal grammar. Pinker &
Bloom have attempted to argue in favour of it as a result of natural
selection, whereas Gould and Chomsky see it as an evolutionary spandrel.
 The arguments in favour of natural selection seem greater than the
opposing theories. Language is a complex process requiring many
different abilities, it is hard to accept that anything so fundamental
and intricate is nothing more than a by-product of another part.


Pinker (date?), "Language Acquisition", Chapter to appear in L R
        Gleitman, M Liberman, and D N Osherson (Eds), An Invitation to
Cognitive Science, 2nd Ed. Volume 1: Language. Cambridge, MA: MIT

Pinker, Steven & Bloom, Paul (1990), "Natural language and natural
selection", Behavioral and Brain Sciences (1990) Vol 13, pp 707-784

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