Martin Rees is a cosmologist and space scientist. He is currently on the Board of the Princeton Institute for Advanced Study and has served on many bodies connected with education, space research, arms control and international collaboration in science. He lectures, writes and broadcasts widely for general audiences. Ever since his book ‘Our Final Century?’ was published , he has been concerned with the threats stemming from humanity’s ever-heavier ‘footprint’ on the global environment, and with the runaway consequences of ever more powerful technologies. These concerns led him to join with colleagues in setting up a Centre for the Study of Existential Risks (CSER) based in Cambridge. Posthuman evolution, here on Earth and far beyond, will be the outcome of technological changes (genetics, cyborg and AI) rather than Darwinian selection.