When it comes to having sex, first-born girls are not as quick as their younger sisters, according to a new Australian research.
The study into the sexual appetites and behaviours of siblings, by researcher Fritha Milne, from the University of Western Australia, has shown that the order in which children are born into a family affects their reproductive behaviour later in life.
Previous studies have shown firstborns are more likely to be confident and family oriented while the middle-born children have the toughest time.
Now, it looks like there are differences when it comes to reproductive strategies, including the age at first sexual intercourse, first pregnancy and first birth.
Middle-born children stand out in the survey results, with females 2.6 times more likely to fall pregnant at any given age.
Middle-born males have sex for the first time at a younger age than their brothers.
However, middle-born children of both sexes tend to have fewer children of their own and last-born females are younger when they have sex for the first time.
Milne said that her work confirmed the first five years of a child's life are important.
"During this time the young must elicit support and resources from the parents," the Courier Mail quoted her, as saying in an Australasian Society for Human Biology conference.
"If there are any siblings, then the siblings have to compete for the limited resources of the parents.
"In order to maximise the resources that the children get they have to find themselves a different niche within the family to get those resources from the parents," she added.
Milne said that the firstborn tends to "align themselves to the parental status quo", which partly explains why she followed in her father's footsteps.