What were the evolutionary changes that gave humans our unique characteristics? Are humans still evolving, and if so what are the driving forces? Geneticists and evolutionary biologists are now getting the tools to address these fascinating questions, but crucial challenges lie ahead.

Comparative genomics now allows us to pinpoint sequences that have evolved specifically in the human lineage. But how did these sequences contribute to changes that differentiate humans from other primates? An enlightening approach would be to express these sequences in transgenic non-human primates and look at the phenotypic outcome. But such a strategy would be fraught with ethical difficulties — the topic of a Science and Society article on p658. Because of great apes' evolutionary closeness to humans, studies in these animals are the most likely to give informative results in this scenario. But, the authors argue, the very features that would make transgenic apes so useful in this context would also expose them to unacceptable harm.

The study of ongoing human selection also has its controversies; perhaps the most fundamental one being whether modern humans are evolving at all. However, thanks to long-term studies of multiple generations, we now have good evidence that humans continue to evolve, as discussed in the Review on p611. But the study of selection in contemporary humans is a young field with a number of important issues to address. For example, how do we take account of the complex effects that changing environments and strong cultural influences have on selection? And how do we disentangle complex interactions between correlated traits that could all have effects on lifespan or reproductive success? The attention that is being paid to these issues promises exciting advances over the next few years.