We may speak of ‘language evolution’ ignoring the origins question. Note that while language (uncountable), meaning a type od communication system (and the human ability to use it), is part of our biological endowment and works in a similar way in all human groups, there are thousands of very different individual languages (countable), most of them subdivided into regional or social dialects. What is the source of this variety? Has it always been there, or was there a time when all humans spoke one language?
Languages are transmitted from generation to generation of users. The transmission is cultural, not biological. Infants acquire or pick up their first language from their social environment (starting with their close family and caretakers, then drawing upon other sources of linguistic input). As opposed to formal learning, acquisition happens naturally and involves no explicit teaching. Children learn the vocabulary of their native tongue, work out its grammatical rules and master all the subtle ‘language-games’ connected with the social uses and functions of language.
Every language has its population of users – a historically continuous ‘speech community’ which maintains its code of communication through generations. We know that languages change in the process. The change is slow but inevitable. If a speech community splits in two or more parts, e.g. as a result of migration, different changes accumulate in the resulting groups of speakers, making communication between them increasingly difficult. Thus an originally common language produces different ‘daughters’, separated by communicative barriers.
As we examine the living or historically attested languages, we discover that many of them can be grouped into families – sets displaying structural correspondences that point to shared descent (a common ancestor in the past). For example, French, Spanish, Italian, Romanian and other Romance languages derive historically from the colloquial varieties of Latin once spoken across the Roman Empire. As the Empire collapsed and broke down into smaller and relatively isolated political units, spoken Latin was geographically fragmented, giving rise to numerous local languages.
|The offspring of Latin (somewhat idealised and simplified)|
While new languages emerge in this way, other, less lucky ones (and even whole families) die out – sometimes because a speech community is wiped out by a natural disaster or by inter-ethnic violence; more usually, because their original speakers have abandoned their old code, adopting instead one imposed by some other group. It is easy to see that the rise and fall of languages depends crucially on external (non-linguistic) factors: the history of human migrations, conquests, accidents of political and cultural history, vagaries of social prestige, etc. Let’s call those long-term and large-scale processes linguistic macroevolution. It is the story of language differentiation and extinction, the origin of linguistic families, results of contact between different speech communities, etc.