So, another study has come out showing that people, especially young people, with sisters have an easier time in life, emotionally speaking. Deborah Tannen's unsurprising take on this is that it's all about emotions and the interchange of them , because sisters may be out there doing more communicating with their family. Certainly, this is backed up by the saying, "A son is your son until he takes a wife, but a daughter is your daughter all your life." Perhaps the same can be said about sisters?
As someone who grew up in a family so female-heavy it was nearly a matriarchy (both parents have three sisters, and only my mother has a brother; I grew up with a bio-sister and a stepsister, but no brothers), I think I can speak to this. It's not just about warmth and feeling loved, which I do think that male relatives provide in many cases, just as well as female relatives. But what having a lot of sisters (and aunts) can do for you is make your life a hell of a lot easier, especially if you're a woman. In our society, at least, women are often tasked with the work of keeping the social life of a family moving: planning events, cooking food, spreading news, sending cards, making phone calls, buying gifts, remembering birthdays, etc. The more women you have in your family, the more you can spread this work around. For instance, if I have some big news to tell the whole family, I simply have to give it to one female family member, secure in the knowledge that everyone will know before too long. It's great.
Of course, I'm an exploitative person who should always feel guilty, because I have a bad habit of letting this entire situation allow me to be dude-like in my relationship to my family. If I need to send a birthday present to someone, but because I'm bad at being female, I forgot to write down their address, I'll just call my sister. Forgot to ask for baby pictures of the newest relative so I could coo at her? My sister's on it, sending them along so that I can remember, now prompted, to coo. Have no idea what the etiquette for a dress/gift/dish to bring to an event is? I have a sea of female relatives to pester. They're awesome. They let me be the brother I never had. One theme I've often seen in happiness studies is that happiness tends to go up when your free time does. If you have sisters out there sharing the work of, say, putting together baby showers and passing around wedding photos on Facebook, that frees up more of your time to pour a glass of wine and watch reruns of Lost , a great contributor to human happiness.
Painting of "The Sisters" by Edmund Tarbell for Wikimedia Commons.