Meaning of the underlined sentences

Meaning of the underlined sentences

The passage below is from Jellyfish age backwards by Nicklas Brendborg.

Researchers are still doing twin studies, but they have also begun employing new study designs to untangle genes and environment. For instance, Google-owned Calico (California Life Company), has conducted a study in collaboration with Ancestry.com, which hosts more than 100 million family trees. These family trees include enormous amounts of data on the lifespans of different families, which can, of course, be analysed.

The result of the study confirmed the low heritability of longevity. That is, while your genes are highly influential on many traits, they don’t matter much to how long you live.

Actually, the Calico researchers discovered that genes might be even less important than suggested by twin studies. They found that married couples – who generally are not related – have more similar lifespans than opposite-sex siblings. And, overall, there is a correlation between the lifespans of a given family and those who marry into it. This might be of some comfort if your mother-in-law has moved in and refuses to give up the ghost.

I have a question on the underlined sentence.

Is this sentence mean that genes’ effect between simple siblings is much less important than that of twins.

(Am I right?)

Thanks in advance.