In the study population genetics and prehistory, the question of how people with particular genes ended up one place from a distant destination frequently have answer that are only vague surmises because we have no historical accounts and limited archaeological data. Every once and a while some bit of data is so singular that we can do better. But, that is the exception and not the rule, and still leaves myriad details of the process fuzzy.
Once historical and business records are present, however, detailed accounts can be pieced together from business records, journals and news accounts, supplemented by the usual evidence from genetics and physical anthropology.
One of the things we know is that thousands of people from Madagascar were brought to the New World as slaves.
We know this with exquisite detail that recounts:
* the exact points of departure and points of arrival,
* the precise dates of departure and points of arrival (sometimes to the hour),
* the routes taken by the ships,
* the name of each of the ships and who owned and insured those ships,
* the names of the crew on those ships,
* the exact number of people and their gender and approximate age on each ship,
* how many people died en route on each individual voyage and the cause of each death,
* the purchase prices and sale prices for the slaves, and
* the manner in which the people sold came to become slaves.
Often it is even reasonably possible to determine where these people were taken as slaves after they arrived, and with DNA evidence, it is frequently possible to detect the signature of ancestry from Madagascar which is distinctive because it contains an Indonesian component.
It isn't easy reading, but a precise understanding of how historical events have actually played out is critical to developing a more accurate intuition about the narratives that underlie less well documented gene exchange events.
This component is present in a surprisingly large share of African-Americans whose New World roots are in places where people from Madagascar were delivered as slaves. This is because all contributions to a gene pool are soon found in most members of the total population after a few generations under conditions approximating panmixia which are close enough to reality in this context to be a good model of reality, even though the Madagascar component was not a huge share of the total population of slaves imported to the New World.