Encyclopedia of Evolution.pdf - Online Reading Center

language, evolution of
is not considered language, since it involves no conscious
thought.
• In some cases, animal communications involve conscious
concepts that may correspond to what we would call
words. Vervet monkeys, for example, have different kinds
of calls for aerial predators (such as raptors) and terrestrial
predators (such as snakes), which evoke different kinds of
responses (hiding down in the vegetation from the former,
running away from the latter) in the hearers.
Human language represents an unprecedented level of
complexity. Apes can make between 300 and 400 signs, at
maximum, while a human child (when his or her brain is about
the same size of those of nonhuman apes) knows at least 6,000
words. Human language always involves not just concrete concepts
about immediate objects and events but abstract concepts
as well (for example, the past or the future). True language
also has a framework of grammar, which puts the concepts in
relation to one another and into motion. All human languages,
and no other forms of animal communication, have abstract
words and grammar. The production of language apparently
requires a large brain, particularly a large prefrontal cortex,
which is unique to the genus Homo. An absolutely large brain,
not just a relatively large one, is necessary for intelligence and
language (see allometry). The large brains of cetaceans allow
complex communication. The expanded portions of the cetacean
brain are different from those that have expanded during
human evolution (see convergence), and it is unclear whether
their communication, however complex, contains the abstract
elements of true language.
Language requires not only a large prefrontal cortex, to
keep track of and relate all the complex concepts, but also
specific brain structures:
• The Wernicke’s area is essential for the understanding of
language; damage to this area makes a person unable to
understand language but does not inhibit the ability of the
person to speak words. The victim may speak long strings
of words that make no sense together. The part of the monkey
brain that is homologous to the human Wernicke’s area
allows monkeys to recognize the calls of other monkeys.
• The Broca’s area is essential for the production of language;
damage to this area makes a person unable to speak, even
though the victim may understand language perfectly. The
part of the monkey brain that is homologous to the Broca’s
area allows monkeys to control facial muscles.
Although many fossilized crania of hominins have been
found, and cranial capacity (brain volume) can be estimated
for many, few of them have the detailed preservation necessary
for the detection of Wernicke’s or Broca’s areas. Therefore
anthropologists cannot know whether the earliest species
such as Homo Habilis and H. rudolfensis, or intermediate
species such as Homo ergaster, Homo erectus, or Homo
HeiDelbergensis, had language. There is even some doubt
as to whether Neandertals, despite the fact that their brains
were as large as those of modern humans, had true language.
Earlier hominin species had the ability to produce some
of the sounds involved in language. They apparently did not
have the full range of language capacity that Homo sapiens
possesses:
• The production of a range of vowel sounds requires a long
larynx, or throat. australopithecines did not have a long
larynx. Even Neandertals had an upper larynx, as preserved
in some skulls, more closely resembling that of the earlier
hominin species than that of modern humans. Therefore
Neandertals, despite their strength, may have had squeaky
voices with a very limited range of vowel sounds. However,
more than just a long larynx is necessary for the production
of a range of vowel sounds. The hyoid bone (the only
bone in the human body that is not connected to another)
is the site of attachment of several larynx muscles. Neandertals
had hyoid bones indistinguishable from those of
modern humans.
• The production of a range of consonants is the product of
tongue and lips, not the larynx. Some scientists have pointed
out that it is the consonants, rather than the vowels,
that define language. Written Hebrew, for example, included
only the consonants, until small marks were added
later beneath the consonants to denote vowel sounds. In
response to the claim that the inability to form the full
range of vowels would have made Neandertal speech inadequate,
a famous letter in a scientific journal said, “Et
seems emprebeble thet ther speech wes enedeqwete bekes ef
the lek ef … vewels …” thus indicating that consonants are
essential, vowels merely helpful, in language. Anthropologists
know very little about the complexity of consonant
sounds that earlier hominin species may have produced.
Chimpanzees appear unable to produce the same range of
consonant-type sounds that humans can. Although scientists
know nothing about the tongue and lips of H. ergaster
or even of Neandertals, they do know something about
the nerves that controlled their movements, because nerves
pass through canals in the bones. H. ergaster apparently
had fewer nerves controlling the muscles of the face and
throat than do modern humans, but Neandertals had large
openings for nerves that controlled the movement of the
tongue.
The long larynx in adult humans is what allows adult
humans to choke. When a person swallows, the epiglottis
closes off the trachea; and food can slip into the trachea,
blocking it. Other vertebrates, and human babies, with short
tracheas, do not have this problem. Babies can swallow and
breathe at the same time. It has been suggested that language
ability was the principal factor in the evolution of the long
trachea. If so, the evolution of language ability came at great
cost: the risk of choking on food.
Language ability appears to be associated with specific
genes:
• Williams syndrome, in which people have impaired mental
ability but produce a constant stream of vivid words with
rich vocabulary, is associated with a single mutation.
• SLI (Specific Language Impairment), in which the people
have no instinct for grammar, is also associated with a specific
mutation.