Every once in a while I wander back and browse a bit more through the results of several DNA tests I’ve taken, and end up wasting more time pondering the mysteries they reveal.

Here’s one of them.

I have a 2nd cousin–our grandmothers were sisters, and we have always known that we descend from common great-grandparents on our mother’s Hawaiian side of the family, Kina Kahooilimoku and Robert William Cathcart. In recent years, we’ve gotten to be good friends, and I’m closer to him than any other known cousins. Meda and I both met and spent a little time decades ago with his grandfather, and with his father, so we’re familiar with the family ties.

But the amount of DNA we share is significantly less than would be expected of a 2nd cousin, according to Ancestry.com. According to the company’s calculations, there is only a 3% chance that we are 2nd cousins, versus a 27% chance we are half-second cousins. The latter would mean that our grandmothers were not sisters, but half-sisters. And, since it’s hard to misidentify a child’s mother, it would likely mean that one of us traces back to a different great-grandfather.

This came to my attention when two women about my age, sisters, showed up on my list of matches with nearly as much DNA overlap as my known second cousin. And they have an associated family tree identifying their great grandfather as William Dennis Toomey.

Hmmm, a clue.

My great-grandmother, Kina, had children by three men during the mid-1880s. Two of those children by William Dennis Toomey, followed by three children attributed to Robert William Cathcart.

So I am trying to evaluate a working hypothesis to account for less shared DNA with a “known” 2nd cousin on my Cathcart side than expected, and a DNA match with sisters descended from Toomey.

Could my grandmother have actually been a daughter of Toomey?

There’s some family lore in favor of this hypothesis. My grandmother, Heleualani, apparently bore a striking resemblance to her half-sister, Florence (Flora) Toomey. My mother recalled them having the same stocky body type, similar hair and facial shape. And in some photos of events in which they were both present, my mother wasn’t able to easily tell them apart.

That was the possibility that came to mind first when I saw Toomey on the family tree of those two sisters on my DNA match list.

But there’s a key against this. If they are descended from Kina and Cathcart, we would be 2nd cousins, and the amount of DNA we share should be greater than the cousin I now suspect might be a half-2nd cousin. And that’s not the case. But DNA is not inherited in a rigid pattern, so all these probabilities are just that, probabilities.

And there are many other possibilities, of course.

It’s complicated. I’ve done DNA tests with different companies, and uploaded my DNA results to a couple of others to see matches in their data bases. Now, using these different testing systems, I’m trying to test different hypotheses. If my great-grandfather was Toomey rather than Cathcart, what differences would I expect to see in my list of DNA matches? Are there other people on my list of DNA matches with Cathcart or Toomey in their family trees? Any additional clues there? It will help if I can eliminate one or more of the most plausible explanations.

And then there’s another background issue. My great-grandmother was from Hana, and a number of generations lived in that area between Keanae and Kaupo. The population was relatively small, intermarriage was common, creating problems discerning direct genealogical connections from the background of shared DNA.

Ancestry.com has an algorithm that attempts to correct for this by screening out the DNA “noise.” How well this works is, well, another unknown.

While trying to think through all this, I stop. Does it really matter? If this branch of my family tree turns out to have taken an unexpected turn, so what? Am I a different person that I previously thought? Is my connection to my cousin different? No, I don’t think so. But then why worry about it? I’m not sure.

It’s more that this expected DNA finding creates questions in my mind that I would naturally would like to answer. So it takes its place alongside other questions posed by my DNA results. Why do my Lind family DNA matches suddenlly disappear four or five generations back? What or who is the family link to the large number Australian and New Zealand “cousins,” including lots of Maori?

It’s at this point that I usually put the whole matter aside again and turn my attention to more immediately productive things.

But the nagging questions continue somewhere in the back of my mind.