Download Language, Nature and Nurture – Can genes settle the debate?

Language, Nature and Nurture –
Can genes settle the debate?
By Richard Kunert, Suzanne Jongman and Tineke Prins
Is language innate or learned? Is it nature or nurture? The greatest minds have tried to find
answers to this question. For decades the debate has raged between the most prominent
scientists from Noam Chomsky and Steven Pinker to B.F. Skinner. Much has changed
between the start of the debate and today. We now know much more about the human
genome and its role in everyday activities than even ten years ago. This has transformed the
nature-nurture question into something different altogether. Let’s lead you on a travel back
to our distant past, a journey on an imagined island where German children transform Thai
and a visit to the household of a family crippled by language problems. Through all of
these visits a picture emerges proving neither the nature nor the nurture camp right.
Perhaps, we asked the wrong question: genes don’t settle the debate. Instead, they
transform it into a ‘nature and nurture’ discussion.
But wait, how could genes change the debate? Haven’t we already heard all the arguments?
Not nearly. The human species shares a surprising amount of genes with our closest
evolutionary cousins but they don’t talk while we do. How did that happen? Was nature or
nurture responsible, or did they even act together? One can ask the same questions about
different peoples rather than different species: why are there so many different languages in
the world? Did they just occur by random chance through different cultures or are there
deeper genetic differences between peoples responsible – nurture or also nature? Finally,
we all know people better at languages and some who are surprisingly poor at it. A look at
one family reveals some surprising patterns: it’s not just in the upbringing. Across these
three levels – species, population, individual – one encounters a new set of questions which
go beyond the old trenches of the nature-nurture debate. But let’s first go on a journey into
our evolutionary past. Sure nature is responsible for evolution. Or is it?
The making of a language species – humans
Consider our closest evolutionary cousins, the
creating humanity
great apes. Why do we have language and they do
not? Some genetic difference must underlie this
Did we, the human species, start the evolution of
language?
Standard
Darwinian
evolutionary
theory, as we learned in our biology classes in
high school, would answer this question with a
decisive no. Darwin introduced the concept of
natural selection as the key mechanisms for
evolution. Organisms are in competition for
survival and reproduction and only those that are
best adapted to the environment will endure, also
known as survival of the fittest. Through this
difference, sometime after the human and
chimpanzee lineage diverged a change must have
occurred that proved to be the basis for the
development of speech and language. This line of
thought was sparked by the discovery of the gene
FOXP2 that was shown to play a role in
successful language use and was soon referred to
as the language gene in popular media. FOXP2 is
also present in chimpanzees but with two changes
in the DNA sequence.
process, genes that code for advantageous traits
will be passed on to the next generation whereas
It has been suggested that the causal chain of
less beneficial traits will disappear. One way for
evolution of language started with this mutated
variation between organisms to occur is through
DNA sequence leading to the emergence of some
the process of mutation. Mutations are changes in
type of language which in turn proved to be
the DNA sequence that can either have no effect
beneficial for humans in adapting to the
or prove to be beneficial or detrimental for
environment as it allowed for the development of
adaptation to the environment.
culture.
FOXP2: ‘The language gene’
FOXP2 (or forkhead box protein P2) is responsible for regulating many genes involved in the development of the
brain and lungs. Individuals that have a mutation of the FOXP2 gene suffer from speech and language disorders,
and have difficulties expressing and articulating language.
FOXP2 was discovered by Anthony Monaco and Simon Fisher. When investigating the ‘KE family’, in which half
of the members (spread over three generations) suffered from severe language problems, they found that the
problems of the affected family members were due to a defect on chromosome 7. The finding was confirmed by
another case outside the KE family: patient CS showed similar language problems as the KE family. These
problems were caused by the same defect on chromosome 7, exactly where the researchers suspected FOXP2
to be.
FOXP2 is also present in animals, but with changes in its DNA sequence compared to that of the human gene.
Researchers have looked at the role of FOXP2 in, for example, songbirds and mice, and the results of their
research suggest that FOXP2 supports the brain’s ability to learn sequences of movements. In humans, it
influences the development of the nervous system, and parts of the brain involved in motor skills. This fits with
the idea that the human version of FOXP2 has played a vital role in evolving the complex muscle articulation
needed for language.
One way language could have led to human
passed on. However, the construction of dams by
culture as we know it today is suggested by
beavers alters the environment considerably; one
Dunbar. He argues that language was a necessary
instance is the altered river flow resulting in
trait to allow humans to live in large social groups
changed nutrient availability. By building a dam,
which left them better adapted to environmental
beavers have created a new niche with different
pressures. One way bigger groups are better
selection pressures compared to the previous
adapted is for instance that individuals are better
environment. Not only genes adaptive for dam
protected against predators. To be able to maintain
living in a group there has to be some form of
Cultural niche construction
social bonding, grooming is used to this extent by
There are several examples of human niche
other primates. However, grooming is time
construction where cultural practices have led to
consuming and puts a limit on the size of the
altered selection pressures. Yam cultivating
group. Language could have started as a form of
cultures in West Africa are such an example. To
gossip for social bonding, vocal grooming instead
of
manual
grooming,
allowing
for
larger
communities to live together.
grow yam, forests needed to
be cleared
increasing the amount of standing water, which
in turn caused a rise in the number of
mosquitoes carrying malaria. This increased the
So the proposed chain of evolution is: first genes,
then language and finally culture. Could it have
been the other way around? Odling-Smee and
frequency of the sickle-cell S gene variant in the
yam
cultivating
population;
normally
an
unfavorable variant as it causes the disease
sickle-cell anemia but it also offers protection
Laland take such a radically different approach to
against malaria disease. No such increase was
the evolution of language. They argue that
found in neighboring populations that do not
adaptations are not just called for by problems
grow crops. Thus, the agriculturalists themselves
posed
created a natural selection pressure leading to
by
environmental
change,
but
that
organisms themselves change the environment
that then needs to be adapted to. In other words,
organisms partly create their own environment
genetic changes.
Another instance of cultural niche construction is
dairy farming and lactose tolerance. Most
humans become intolerant to lactose after
and their own natural selection pressures. This is
childhood, but there are adults that carry a
called niche construction and implies that not only
variant of the lactase LCT gene and remain
genes are passed on from generation to generation
tolerant. There is a high correlation between the
but also the environment that is in part created by
frequency of this gene variant and cultures that
past generations.
have a history of dairy farming and milk drinking.
One example to show the difference between
available dairy products had an advantage over
standard
niche
those individuals that could not, causing the
construction is dam building by beavers. Darwin
gene variant for lactose tolerance to be passed
evolutionary
Individuals that
theory
and
would argue that dam building was adaptive and
genes that favored this behavior were selected and
could
consume
the
newly
on to new generations and increasing its
frequency.
building will be passed on, but also genes adaptive
Still, there is a growing opinion that genes do
for the newly created environment. Thus, beavers
nonetheless play a role.
are actively involved in altering their own
adaptation requirements.
Before looking at this opinion, it is worth asking
why genes shouldn’t play a role in language. A
There is increasing evidence that humans also
computational model by Andrea Baronchelli of
create their own niche, through the development
Northeastern University presents a good case. It
of culture. Odling-Smee and Laland argue that a
suggests that the great diversity of languages is
similar process was at the basis of the emergence
due to fast language change – even within my own
of language: humans created a niche that
lifetime new words like ‘googling’ or ‘chillaxing’
demanded the use of language. They hypothesize
have emerged without anyone raising an eyebrow.
that the fast growing advances in technology and
This in turn favours generalist language learners
cultural complexity led to the necessity for better
who are able to learn any language equally well.
and faster ways to communicate to transfer
Why? Well, genes are slow to change. Language
knowledge. Humans therefore might have created
presents
their own selective environment where language
mechanisms. Instead of adapting to one language
became an adaptive trait through cultural niche
in particular, people who can learn any language
construction: having language allowed for faster
are at an advantage.
learning, transmission, and innovation. Thus,
those individuals with language were better
adapted to the demands of the self-created
environment and their genes were passed on to the
next generations. Perhaps we need to rethink the
causal chain of evolution of language, we
ourselves may have been the start.
Why my mother tongue is what it is – the tone in
genes
a
moving
target
for
evolutionary
It is thus crucial to look at the rate of language
change: is it slow enough for genes to change in
response to it? An examination of the connections
between modern languages of the same family
gives some clues as to the real rate of language
change. These languages emerged out of a
common origin and separated millennia ago. Any
commonalities are likely remnants of their
common origin language which is long dead. For
example, the first European visitors to India
The evolution of language has led to a great
noticed curious commonalities between Indian
linguistic diversity with languages passed on from
languages such as Sanskrit (3 = ‘tráyas’) and
parents to children. Did genes shape these
European ones such as ancient Greek (‘treĩs’) and
languages? Did they determine my own mother
Latin (‘trēs’). Since the time of the split between
tongue? Intuitively, one is inclined to answer with
European and Indian languages these words do
a resounding ‘no’. Of course not, if you had been
not appear to have changed much.
adopted by Thai parents, you would speak Thai.
But given that this was (presumably) not the case,
your mother tongue is just your parental language.
Nowadays, this can be extended beyond mere
anecdotes. In a 2007 article in Nature, Mark Pagel
and colleagues showed that the more often a word
is used today the more likely it is to be similar
at least those language features which have been
across languages with a common origin, even if
found to be consistent for thousands of years.
this connection lies 7,500 years in the past. Using
structural features, such as grammar systems and
the inventory of language sounds, one can look
even up to 12,000 years into the past. These
numbers correspond to up to a quarter of the time
the
world’s
languages
had
in
order
to
differentiate! So, yes, language vocabulary and
structural features do indeed change quickly, but
still, there are exceptions, for example among the
very common words. This opens up the possibility
that genes – which are quite stable – do influence
What is missing so far is an actual example of
such a gene-language link. It was found by Dan
Dediu and Robert Ladd who looked at tone, a
feature which is a relatively stable language
characteristic. Tone refers to the use of pitch
differences to differentiate words. Take this Thai
tongue twister, for example: /mǎi mài mâi mái/.
The same consonants and vowels get repeated
with different pitches – notice the diacritics above
the a – resulting in the sentence ‘Does new silk
burn?’
Figure 1: Geographic distribution of one version of A) ASPM, B) Microcephalin, and C) tone language.
Dediu and Ladd noticed a surprising parallel
the gene-tone relationship is unusually strong; for
between the location of tone languages and the
hardly any other genes or linguistic phenomenon
location of different versions of two genes in the
it is that strong. Therefore, it seems to reflect
world, the so called ASPM and Microcephalin
some fundamental relationship between ASPM,
genes, as can be seen in Figure 1. It turns out that
Microcephalin and tone. The most straightforward
explanation would be that we are looking at tone
formal teaching or instruction. If learning to speak
genes – if you have them in one version you can
and understand a mother tongue comes natural to
learn tone, otherwise not. Dediu and Ladd reject
us, how is it that people differ in their language
such a direct account – my own ASPM and
proficiency? Why are there people that don’t have
Microcephalin versions do not determine whether
any trouble speaking a language, whilst others
I will ever be able to learn Thai. Instead, genes
struggle to find the right words? Is this in our
could exert a subtle effect, nudging successive
environment and upbringing, or might it be in our
generations of language learners in a certain
nature, our genes?
direction. Imagine a bunch of German babies were
dropped on a lonely island and they learnt Thai
from Thai native teachers. They would probably
manage very well and their teachers would be
very proud. Without their teachers noticing it,
however, the German children struggled a bit with
the Thai tone system. Over generations, this
struggle would reduce tonality bit by bit. Were
Thai teachers to discover this island again a few
hundred years later, they would be astonished
what an odd version of Thai people spoke on the
island. A Thai without tone.
It is clear that our environment affects the process
of learning a language. A very socially competent
and highly educated parent will address her child
in a different way than a less socially competent
and poorly educated parent. In other words, the
socioeconomic status of the parents will determine
the input a child receives, and the context within
which
words
are
acquired.
Psycholinguists
Naigles and Hoff-Ginsberg have shown that for
children who acquire new verbs, it is the
frequency with which each verb occurs in the
parental input that has the greatest effect on
So, because language is a not a homogenous ever-
acquisition speed. Moreover, the way the words
changing system, but instead a mix of stable and
are distributed as well as the content of the adult
less stable features, the former could potentially
speech play an important role. So the verb go that
be influenced by genes which are known to be
occurs often in the speech of the parents, and in
stable as well. So, did genes shape my mother
many different linguistic structures such as
tongue? In a sense yes, the combined genetic
questions, commands, and statements, will be
background of generations of German speakers
learned earlier than the verb run which occurs less
shaped German. In another sense no, my genes
often and in less diverse syntactic frames. did not determine that German would end up
being my mother tongue. Both answers are true.
Why some talk and some say nothing
Does this mean that members from the same
family, growing up in the same environment,
receiving the same parental input and who live in
the same society will show the same pattern in
It is clear that peoples differ in their genetic and
language learning? No it doesn't, because some
their language backgrounds. But so do different
differences might not occur through nurture, but
individuals within each language group. We all
instead through nature.
learn to speak our native language without any
Genetic
variations
can
individual
Language is an impressive feature of the human
differences, as in the case of the KE family. This
species, which we tend to forget as it seems that
family was treated for their severe speech and
every child learns language with relative ease. It
language disorder at the Institute of Child Health
takes much more effort to learn mathematics than
in London. Investigating the language abilities of
it does to learn words. Yet there are differences
the KE family members with speech and language
between people. These can be subtle differences,
problems,
team
for instance which specific words we use to tell
discovered that the affected members of the
the same story. These individual differences arise
family had the following characteristics in
because of environmental diversity. But even
common: problems in processing words according
when the environment is identical, changes in
to
language performance are found: genetic variation
Vargha-Khadem
grammatical
rules,
cause
and
her
difficulties
with
understanding complex sentences, problems with
reading and writing words and troubles moving
their mouths. For example, affected members of
can cause differences too.
Why we need both nature and nurture
the KE family have problems with the production
So, nature or nurture? Going from 4 million years
of morphological markers. Such members would
ago to the present day, to a hypothetical future, it
not know how to fill in the blank in the following
seems that this is the wrong question to ask.
sentence: “This creature is smaller than this one,
Instead, the question should have been in which
but this creature must be the ….”, while an
ways and to what extent the two interact.
unaffected member would have no trouble giving
Language might well have evolved because
the answer ‘smallest”.
humans created their own cultural niche, which
How can we explain this difference given the very
similar environment of the family members?
Simon Fisher and colleagues searched for the
damaged gene in the KE family, performing a
genome-wide scan of DNA samples taken from
the family members. They noticed that the KE
family’s disorder was inherited in a simple
fashion: as the result of a defect in a single gene,
the FOXP2 gene. In the KE family, half of the
members (spread over three generations) were
affected by a mutation of the FOXP2 gene, while
the other half was unaffected. In this case, the
genes explained the differences in language ability
between
the
environment.
family
members,
not
the
resulted in genes necessary for language, which in
turn happened to be beneficial. More than just
whether language evolved but also which
language evolved appears to be linked to genes –
as in the case of tone languages – and upbringing.
Finally, how well it is used appears to be an
interaction of how you grow up as well as what
genes you have inherited. On all three levels
nature and nurture are not adversaries claiming to
be right while proving the other one wrong.
Instead, they complement each other. Each one
provides a piece of a bigger picture which neither
would be able to provide by itself. The natureversus-nurture debate? More like the nature-andnurture puzzle.
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