Helen Fisher's courageous investigations of romantic love -- its evolution, its biochemical foundations and its vital importance to human society -- are informing and transforming the way we understand ourselves.

Fisher describes love as a universal human drive (stronger than the sex drive; stronger than thirst or hunger; stronger perhaps than the will to live), and her many areas of inquiry shed light on timeless human mysteries, like why we choose one partner over another.

Brene Brown is a research professor at the University of Houston Graduate College of Social Work.

Brown studies human connection -- our ability to empathize, belong, love. She has spent the past ten years studying vulnerability, courage, authenticity, and shame.

She is also the author of The Gifts of Imperfection: Let Go of Who You Think You're Supposed to Be and Embrace Who You Are.

SheQuotes quotes women exclusively on Twitter and Facebook. This week's favourite quotes are listed below. If you use these quotes, please attribute them to the women who said them.

Get the best of SheQuotes 2011 <== Everyday Feminine Wisdom Vol 1. Submit your own feminine wisdom here.

"A woman on a mission needs no permission." ~ @TheSingleWoman