Can a DNA match of 1967cM across 72 segments be a first cousin?

Question

My husband had DNA testing through Ancestry. A woman of about the same age shares 973 cM across 45 segments. We determined that she was probably a first cousin; a child of my husband’s paternal uncle.

We had a cousin, one of this uncle’s sons, also take the Ancestry DNA test. He shares 1953 cM across 57 segments with this woman, so I think that it’s pretty clear that they are half siblings. The timing and circumstances fit well.

The really strange question that popped up though was that my husband and his male cousin shared 1967 cM across 72 segments. Their fathers were brothers, so even if my husband’s uncle was by some chance his father, it would not make sense. This new found female cousin is showing up as a cousin and nowhere near a half sibling. Could Ancestry’s DNA testing be that far off or could a first cousin have that much DNA in common?

Answer 1

The Shared cM Project 3.0 tool v4 suggests these relationship probabilities for 1,967 cM (based on stats from The DNA Geek):

• 100.00% Grandparent Aunt / Uncle Half Sibling Niece / Nephew Grandchild
• ~ 0% ** Great-Aunt / Uncle Great-Niece / Nephew

** this set of relationships is just within the threshold for 1967cM, but has a zero probability in thednageek's table of probabilities

A relationship of first cousin is not amongst them. The expected range for first cousins is 553–1225 cM with a mean of 874 cM.

Something that may or may not be worth considering is whether a relationship of double first cousins may be what you are looking at. The Shared cM for that would be similar to that of half siblings.

Answer 2

1967 cM is a half-sibling, aunt or uncle, niece or nephew, grandparent or double first cousin.

They have a expected match of 1750 cM with a range from 1317-2312.

It's more likely that your husband and his male cousin are double first cousins. That means his uncle had a child with his mother's sister. This also explains why his cousins are half-siblings and not full siblings.