The Parable of the Good Samaritan is pretty well-known. Even if you haven't had much exposure to the New Testament of The Bible, you probably know the gist of the story: Traveler gets the crap beat out of him by thieves, who then leave his half-dead body by the side of the road; a couple of ostensibly holy men walk by, but go out of their way to avoid even making eye-contact with the poor guy; finally, a Samaritan comes along and gets the traveler some much-needed medical attention.
The tale is meant to be ironic, as in, "Isn't it crazy that a Samaritan helped that dude when the holy men wouldn't?" Personally, though, I never really understood why the Samaritans had such a bad rap to begin with.
Turns out, the missing context of the Good Samaritan is rooted in a dispute that connects ancient ethnic animosity with 21st-century genetics.
The story starts around the 7th century BCE, when the Assyrian Empire conquered the Kingdom of Israel. Part of that process involved swapping a chunk of the Ancient Israeli population with Assyrian citizens–the deported Israelis were sent to live in Assyria, and vice versa. But that was only a small part of population. Many more were left behind.
Meanwhile, Israel wasn't the only Hebrew state. The Kingdom of Judah, just to the south, hung around, running more-or-less independently and worshiping the Deity Currently Known as God (among others) until the 5th century–when it got itself conquered by the Babylonians, who pulled a similar citizen swap.*
Fast forward some 70 years. The exiled Judaens return to their homeland. When they get there, they find a bunch of people who claim to be descendants of those left-behind Israeli citizens who weren't taken captive by Assyria. They call themselves the Children of Israel and practice a religion that's similar to, but not exactly like, the one practiced by the Judaens themselves. Naturally, conflict ensues. The Children of Israel insist that the Judaens are worshiping God all wrong. The Judaens insist that the Children of Israel are really just Assyrians in drag and are, natch, worshiping God all wrong. Over time, the Judaens come to be known as the Jewish people, while the Children of Israel are called Samaritans. By the time the Parable of the Good Samaritan was recorded, Jews generally thought of Samaritans as untrustworthy, blasphemous and potentially evil. Thus, the irony.
As the 21st century dawned, the few Samaritans left (712 in 2007, up from a low of 146 in 1917) still claimed to be descended from the ancient Hebrew tribes. Jewish religious authorities still disagreed. And strong evidence either way was still lacking. Until 2004.
See, that tiny population (which wasn't real big on converts) led to a decent amount of inbreeding. In fact, according to research done in the late 1990s, 84% of Samaritan marriages are between cousins–making them the most highly inbred population on the planet. Unfortunately, that title comes with a propensity for genetic abnormalities, concern about which eventually led several Samaritans to turn their DNA samples over to a team of genetics researchers.
The results turned up some surprising confirmation of the Samaritans' personal origin stories. The study compared Samaritan Y-chromosome DNA (genetic information passed mostly intact from father to son) and mtDNA (ditto, but from mother to daughter) with that of several different Jewish populations from across the Middle East and Africa, as well as with a couple of non-Jewish groups from the same areas. Not only do the Samaritan Y-chromosomes seem to be closely related to Jewish Y-chromosomes, but most of the Samaritans actually carry a distinctive set of Y-chromosome mutations known as the Cohen Modal Haplotype–which is connected with men descended from the ancient Jewish priestly class.
On the other hand, Samaritan mtDNA doesn't match up to its Jewish counterparts at all, said Marcus Feldman, Ph.D.,professor of biological sciences at Stanford University and part of the research team that studied the Samaritans in 2004.
To Feldman and his colleagues, the genetic evidence suggests that modern Samaritans are descended from Hebrew men, left behind after the Assyrians conquered ancient Israel, who went on to marry non-Hebrew women. It's probably not just coincidence that Samaritan ethnicity (at least, the official social recognition of that ethnicity) is traditionally passed to a child through its father–exactly opposite from the way Jewish ethnicity has been traditionally passed down.
In that way, the evidence suggests that both the Jews and the Samaritans are right, sort of. If you believe ethnicity is something passed down from the mother, then the Samaritans probably aren't Children of Israel. But if you think ethnicity comes from the father's side (or, you know, from both parents) then the Samaritans have a good case. It's all about how you use culture to interpret the science.
*The details of this history, by the way, aren't real clear, as much of what usually gets reported as "Israel and Judah Facts" comes directly from the Bible, sans independent corroboration. But the basics of two kingdoms, conquered and dispersed are generally backed up by extra-Biblical historical records.