Scarlett Johansson believes monogamy is "unnatural".

Scarlett Johansson

Scarlett Johansson

The 'Captain America: Civil War' star thinks it is "a lot of work" to be in a relationship with just one person but understands the notion that marriage is "very romantic".

She said: "Well, with every gain there's a loss, right? So that's a loss. You have to choose a path. I think the idea of marriage is very romantic; it's a beautiful idea, and the practice of it can be a very beautiful thing. I don't think it's natural to be a monogamous person. I might be skewered for that, but I think it's work. It's a lot of work.

"And the fact that it is such work for so many people - for everyone - the fact of that proves that it is not a natural thing. It's something I have a lot of respect for and have participated in, but I think it definitely goes against some instinct to look beyond."

And the 32-year-old actress - who was married to Ryan Reynolds between 2008 and 2011 and is thought to have now separated from her second husband Romain Dauriac - feels marriage can "change" a relationship and sees getting hitched as a "responsibility".

She told the March/April issue of Playboy magazine: "I think marriage initially involves a lot of people who have nothing to do with your relationship, because it's a legally binding contract, and that has a weight to it.

"Being married is different than not being married, and anybody who tells you that it's the same is lying. It changes things. I have friends who were together for 10 years and then decided to get married, and I'll ask them on their wedding day or right after if it's different, and it always is. It is. It's a beautiful responsibility, but it's a responsibility."