It is easy to tell that certain languages are related; by simply compare words that have the same or similar meaning. But knowing that two languages are traceable to a single parent language might not tell us very much.
For example, we know that western hemisphere was settles by people who migrated from Asia and crossed the land bridge over what is now Bering Strait.
We also know that this land bridge did not exist for very long and it was possible to cross only during the most recent ice age, when the sea level was low enough.
Therefore we probably assume that the people who made the crossing spoke the same language or at least very similar language. If we follow this logic to its conclusion, all Indian languages are related, since they all descended from a common ancestor language.
Anthropologists who have worked with Native American groups and are familiar with more than one language are much aware that some Indian languages are much more closely related than others.
Indian tribes did not simply settle in one place and stay there for thousands of years, instead, they migrated and intermingled, moving back and forth from one area to another, so that their languages grew more similar in some places and less so in others in a constantly changing patterns.
How certain languages are related?
