The color of your eyes and your hair. Whether you can curl your tongue. The chance that you'll end up with diabetes or high cholesterol. Those are all things that come wrapped in your DNA, courtesy of your parents, grandparents and everyone who came before them. Genetics are pretty powerful and often predetermine who and what you'll be.

It makes sense to think that longevity is also tied up with your genes. But not so, suggests a new study on life span involving more than 400 million people.

How long we live is primarily determined by lifestyle, with less than 10 percent decided by DNA, according to the study published in the journal Genetics.

Researchers from the online family history site Ancestry.com teamed up with scientists from Calico Life Sciences, a company focused on the biology of aging, to study the link between genes and longevity.

They analyzed data from family trees — called pedigrees — that included year of birth, year of death, place of birth and family connections of an impressive 439,323,145 people.

Using mathematical and statistical calculations, researchers focused on relatives who were born across the 19th and early 20th centuries. They found that heritability estimates — or how much of longevity can be related to genetics — to be about the same as earlier studies found. That is, that genes determined about 20 to 30 percent of life space, with that dropping to about 15 percent for relatives of the opposite sex.

Spouses and in-laws

large extended family You don't have to be related to people to share similar life spans. (Photo: Gladskikh Tatiana/Shutterstock)

Interestingly, researchers found that the life span of spouses tended to be similar to one another. In fact, they were more alike than brothers and sisters.

A possible explanation could be that not only do spouses share the same environment, but they also share the same lifestyle and diet.

Possibly even more fascinating, researchers found that siblings-in-law and first-cousins-in-law had similar life spans, despite the fact that they aren't related and they don't typically share the same home. The researchers said we may be able to chalk this up to something they call "assortative mating."

"What assortative mating means here is that the factors that are important for life span tend to be very similar between mates," said lead author Graham Ruby of Calico Life Sciences, in a statement. That means that people tend to choose partners with traits similar to their own — in this case, how long they live.

Obviously, you can't tell someone's life span when you meet them. So assortative mating must be based on other qualities.

The researchers use the example of income, which is known to influence life span. Wealthy people tend to marry other wealthy people, so their life spans tend to be related.

Adding mating choice into their calculations, the researchers determined that heredity likely only determines about 7 percent of longevity, possibly even less.

Cathy Ball, co-author of the study and chief scientific officer at Ancestry told CNN, "although there is a genetic component, this study shows that there is a major impact from many other forces in your life."

Mary Jo DiLonardo writes about everything from health to parenting — and anything that helps explain why her dog does what he does.

How long you live doesn't have much to do with your genes
Don't look to your parents and grandparents when determining your longevity.