There are a lot of contingent claims in the study, done by Ancestry.com genealogist Joseph Shumway. The first is that an African man named John Punch became the first slave in 1640 -- more on that in a moment.
Obama's mother Stanley Ann Dunham was descended from slave-owning Virginians and Shumway's argument is that Punch had children with a white woman who inherited her free status and eventually 'passed' into the white population. He is thus the ancestor of the Dunhams. That's certainly not inherently implausible. There's a lot of African blood among Southern whites. Much more common was white men and black women, though in these very early decades race hierarchies weren't quite so nailed down.
Very few historians believe that the first 'slave' in what would become the United States became a slave in 1640. But Shumway's argument is at least plausible. Here's why.
In the first few decades of settlement in North America there was little of the fixed distinction between indentured servant and 'slave' -- at least 'slave' in the sense that later American history would understand it, which is permanent, heritable and tied to race. So the distinction was a bit more fluid in these early decades. But more importantly, the records we have seldom do us the favor of explicitly making the distinction.
Shumway notes that Punch was an "indentured servant in Colonial Virginia, [who] was punished for trying to escape his servitude in 1640 by being enslaved for life. This marked the first actual documented case of slavery for life in the colonies, occurring decades before initial slavery laws were enacted in Virginia."
This is a strained argument -- it's more about documentation than reality. But it may be true that this is the first explicit reference to lifetime slavery. There were relatively few Africans or slaves in Virginia before the 1660s and slavery only really began to take root in a big way late in the 17th century.
I'm inherently skeptical of any genealogical study put together by a company that is in the business of getting you to buy their genealogy hunting services. Ancestry.com has posted the details of its research here. I'm going to dig into them today. Take a look. Very curious to hear what you think.