Though it is often--and justifiably--maligned, it is ignorance--and recognizing where it exists--that drives scientists to do groundbreaking science. For early career scientists, ignorance--and knowing what areas we are ignorant of--also provides compelling professional opportunities.

That is why we have chosen to supplement Science magazine's 125th Anniversary Issue: 125 Questions: What We Don't Know , which examines the gaps in scientific knowledge with profiles of a few of the young researchers who are trying to fill those gaps.

Philip Goulder , a researcher at Oxford University, studies the influence of an individual's genetics on HIV infection. His work could help explain why some individuals with a specific tissue type (HLA) can mount an effective immune control of HIV. If successful, Goulder's work may lead to the production of an HIV vaccine, which would deliver the same protection.

Licia Verde , a cosmologist at the University of Pennsylvania, examines the varied composition of the universe, including dark energy and dark matter, as well as how the universe formed and how it continues to evolve.

Eva Barroso , a genetics researcher at the Spanish National Center for Cancer Research (CNIO), attempts to determine whether disease susceptibility and treatment outcome are written in our DNA by producing an effective analysis of gene susceptibility for specific diseases.

Harmit Singh Malik , a researcher at the Fred Hutchinson Cancer Research Center, is finding rapidly evolving genes in a place known for its evolutionarily stability--centromeres--with possible implications for how, where, and when genes are expressed.

Clinton Parks is a writer for MiSciNet and may be reached at cparks@aaas.org.