Miller, Wick R., James L. Tanner, and Lawrence P. Foley. “A Lexicostatistic Study of Shoshoni Dialects.” Anthropological Linguistics 13, no. 4 (April 1, 1971): 142–64.
Glottochronology measures the differences between related languages over time. The idea is that if two groups of people speak the same language and are then separated, their individual languages will change over time. This principle was first developed by Jakob Grimm (of fairytale fame) when he postulated what is now called Grimm's Law. Here is a short and adequate explanation of Grimm's Law from the Wikipedia:
Grimm's Law (also known as the First Germanic Sound Shift or Rask's rule), named after Jakob Grimm, is a set of statements describing the inherited Proto-Indo-European (PIE) stop consonants as they developed in Proto-Germanic (the common ancestor of the Germanic branch of the Indo-European family) in the 1st millennium BC. It establishes a set of regular correspondences between early Germanic stops and fricatives and the stop consonants of certain other centum Indo-European languages (Grimm used mostly Latin and Greek for illustration).Essentially, all of the languages, known as Indo-European languages, are related and it is believed that they all began as one language, known as Proto-Indo-European (PIE), somewhere in India. See Wikipedia: Proto-Indo-European Language. The evidence for this linguistic change, as observed by the Grimm brothers, Jakob and Wilhelm, were the first to codify the observations of others into a general rule.
Why is this important to genealogists? Well, there are a few of us who trace our genealogy back to the time when our ancestors spoke a different language than the one we speak today. Perhaps, our ancestors spoke German, Danish, Norwegian or some other language. If we continue to investigate and research their origins, we will ultimately begin to see changes in the languages of the records as we go back in time. I am not talking here about the script that records the language, but the words themselves.
Written languages use a variety of methods to memorialize the spoken language. There is a complex relationship between what is written and what is spoken. Do we speak the way we do because of what we read or is what is written influenced by the way we speak? The answer to both questions is yes, there is a cross-developmental influence. Even if we disregard the effect of writing on spoken language, we will still find that the spoken language will change over time and is affected by geography.
At this point, you may be saying, if this is true, then show me how it works. Well, the most common evidence of the relationship of time to linguistic change is the existence of language cognates. Here is a list of cognates between several Western European languages from a website listing Indo-European features:
- English: Yes, mother, I have three.
- Icelandic: Ja, modir, eh hefi thrja.
- Swedish: Ja, moder, jag har tre.
- Danish: Ja, mor, jeg hav tre.
- Norwegian: Ja, mor, jeg har tre.
- German: Ja, mutter, ich habe drei.
- Dutch: Ja, moeder, ik heb drie.
- Flemish: Ja, moeder, ik heb drie.
- French: Oui, mere, j'en ai trois.
- Spanish: Si, madre, yo tengo tres.
- Portuguese: Sim, mae, tenho tres.
- Italian: Si, madre, ce h'ko tre.
- Romanian: Da, mama mea, eu am trei.
- Czeck: Ano, matko, mam tri.
- Polish: Tak, matko, mam trzy.
- Russian: Da, mat u men'a tri.
- Bulgarian: Da, maika, imom tri.
- Compare these to the non-IE Finnish: Kyllä, äiti, minulla on kolme.
The last example is from Finnish, a non-Indo-European language. A list like the one above can easily be constructed using Google Translate.
This is a good news/bad news situation for genealogists. The good news is that if your ancestors spoke an Indo-European language, learning to read that language is fairly easy. The bad news is that if they did not speak an Indo-European language, you have a stiff uphill learning curve. Remember, this issue is entirely separate from the issue of reading old scripts or alternative writing systems such as Cyrillic or Hebrew.
On a scale of one to ten, I would put learning a new writing script at about three. I would put learning a new Indo-European language at about six, but I would put learning a non-Indo-European language at about eight or nine. But remember, children learn their own language and writing system all over the world all the time.
From the standpoint of doing genealogical research in a "foreign" language (one you don't happen to speak) the task is a lot less demanding then moving to the country and trying to survive. Most of the documents you need to research use a very small set of the entire language. You may only have to learn a few dozen or a few hundred words to do very adequate research. As you go back in time, you will inevitably find that the language changes (and not just because of the use of Latin). This is why, when I see someone claiming a pedigree extending back before the 1500s, I automatically assume that they copied the information without doing any actual research. I have met very, very few people with the linguistic ability to do primary research is Old Church Slavonic, Old English or even Old High German.
So here is the question that needs to be asked. Do you have to speak a language to do valid genealogical research in that language? No, but it helps a lot. But you do have to learn a lot more about history and language than is normally assumed to do valid genealogical research even about a hundred years into the past. Let's get busy and start learning.