Throughout your academic careers, can you think of a single debate that is totally ridiculous, yet continually reoccurs, regardless of subject? If your answer is "Should we get a keg or individual beers?", then you've spent too much time away from class. No, I'm referring to the classic debate of "Nature verses Nurture". You get it in Biology, where evolution is explained by Darwin (genetics predetermine the fitness of an organism) or Lamarck (the environment dictates the final form of the organism). You get it in Psychology, where deviant behavior is explained away by looking at the lineage of the subject ("Hmmm... The previous twelve generations of his family have been raving lunatics") or the childhood experiences of the subject ("Well, he was slathered with honey, then hung in a dark closet to drip dry in an ant infested area on a weekly basis"). You get it in Anthropology, Sociology, Animal Science, Crop Science, Ethnic Studies, and even a bit in Music. You don't get it in math, though. Instead, in math you get the equally ridiculous debate of Leibniz verses Newton. These things happen... For this particular talk, we're not interested in either Leibniz or Newton. No, we are going to continue to beat the now pulverized equine corpse of "Nature verses Nurture", but this time we're going to look at it from the Linguistic point of view. ("There's nothing wrong with beating a dead horse; you can't really make things any worse, and it's good practice for when you find a live one.") So the debate unfolds in what should now be familiar terms. "Is the variability in communication behavior due to environmental factors (nurture) or genetic factors (nature)?".
Let's start out with environmental concerns. It's pretty obvious that people speak different languages. Well... Maybe not so obvious if you grew up in the United States, the land linguistic mediocrity. But trust me, there are indeed different languages. Those courses that you took in High School weren't just big jokes. People really speak those languages in other parts of the world. Unless you learned Esperanto. No one actually speaks Esperanto, and you were the subject of ridicule. For everyone else, however, you learned an honest to goodness natural language. Someone, at some time actually spoke the language you learned. "Why? Wouldn't it be easier for everyone to speak a common language? Like English?" Ahh, spoken like a true American.
The crux of the issue is one of communication. Languages change over time. Some words come into existence and others fall out of use. Some forms of sentence construction become more used, and others less used. Some other words are injected into the vocabulary by occupying forces. Pretty soon, languages (even those sharing common roots) diverge. Even if you look at only one language over time you see a sort of linguistic drift. Don't think so? Take a look at this excerpt from an Old English transcript: "Heald du nu, hruse, nu haeled ne mostan, / eorla aehte! Heaet, hyt aer on de / gode begeaton." Follow that? I didn't either. Twelve hundred years (and one Norman invasion) later, we find a significantly changed language. So, what caused the change? Did the people speaking the language evolve into some sort of more 'advanced' animal, capable of fewer 'ae' characters? Or did the language itself change without much underlying genetic change?
Perhaps more light can be cast onto this debate by looking into a few more examples. First the twin paradox. No, not the relativistic twin paradox, and this doesn't involve Schrodinger's cat either, so pipe down! First assume that the variability in human communication is either purely genetic or purely environmental. Now what would happen if you took a pair of identical twins from the US, both of whose parents were English speaking, and separated them at birth: One is going to be raised in Los Angles, and the other is going to be raised in China. If language was completely determined by genetics, then both children would speak English, despite the fact that only one of them was being brought up in an English speaking environment. If language was completely determined by environment, then the twin raised in LA is going to speak English (or some approximation thereof), and the twin raised in China is going to speak Chinese. The actual result of this experiment is classified, but I am allowed to tell you that it yielded the latter result. Really. You can trust me.
Let's also look within cultures, though. First let's look at one of my favorite subcultures: Computer Geeks. At work a few months ago, I had occasion to write the following phrase: "Error occurs if DMA CBC TDES KAT fails." Does this make any sense to any of you? It does to me. To expand, "Error occurs if Direct Memory Access Cypher Block Chaining Triple Data Encryption Standard Known Answer Test fails." Ok. Everyone probably understands the individual words, but relatively few people understand the actual meaning of the sentence as a whole. It's like that with any specialized field. The participants of the field have a vocabulary all their own. The syntax stays the same, but the vocabulary changes. When you describe something constantly, it becomes common for specialized terms to work their way into the conversation. The participants in these fields don't change geneticly; only their environment changes.
If that isn't enough for you, let's look at situations where children are separated from their parents while still acquiring language, and then found later in life. Fictional examples abound, of course. Everything from 'Mowgli' in The Jungle Book to 'Romulus' and 'Remus' in the story of the founding of Rome. These people never have any problem picking up language (in fact, one of them goes on to be King...) but in real life things tend to work out a bit differently. In situations like this the child does not speak in any normal human language. They can grunt, but they haven't picked up a normal vocabulary or syntax. This seems to defiantly indicate some sort of environmental factors.
If it were only a matter of that, this speech would be over. Tragicly, it is not. There is some equally compelling evidence that mode of communication is to some degree geneticly determined. Let's look at the family dog. This dog is raised in the company of humans all its life. People talk and interact with the dog constantly. It grows and matures, and yet it does not gain the ability to discuss philosophy, sports, or even the weather. What goes wrong? The dog's environment isn't markedly different from the toddler's, yet the toddler goes on to talk and the dog does not. The dog lacks the basic faculties for human speech. No matter what environment the dog is brought up in, it won't learn speech. Which is good, as that means you won't ever have to see a Chihuahua say 'Yo Quierro Taco Bell' in real life.
Examining human infants, you see further evidence that speech is to some degree geneticly influenced. In human languages, we group together sets of discrete sounds to make up words. These sounds are called 'phonemes'. The great majority of all human languages are made up using the very same phonemes. That is not to say that all languages include all phonemes; they don't. For example, native Japanese speakers have difficulty pronouncing the hard 'r' and 'th' sounds because they don't have these phonemes in their language. Young infants randomly string together many phonemes, even those not in use by the language of their environment. As the infant is exposed to a particular language, it reduces the phoneme set that it uses until it only uses the phonemes that occur in that language.
So, it appears that the answer isn't "Nature" or "Nurture". It's both. Well, it's safe to say that I didn't see that one coming. To address only one of the theories leaves out a great deal of the 'big picture'. If you claim that variation in communication is due to environment alone, then you must restrict yourself to normal humans only. Any sort of variation from normal humans leads to odd inconsistencies. The purely genetic argument starts to look ridiculous the moment you start looking at variations in speech between cultures, or even in the same culture over time. They work better together, and the moment everyone realizes that will be a grand day, indeed.