It is an everyday observation that the offspring of elephants are elephants and the offspring of humans are humans. Our biology is, quite literally, written in our DNA, and the copying and transmission of this genetic information is the most extraordinary process on earth.The ideas of genetics are revolutionary, from Mendel’s perfect 19th century description of the mechanism of heredity, through the molecular revolutions of the 20th century to the present day. Today, new technologies are galvanising disruptive change, not only in our understanding of biology, but in our ability to intervene in the very nature of life itself. What can we change? How? Why? And indeed, should we meddle at all?“The bravest”, said Thucydides, “Are surely those who have the clearest vision of what is before them, glory and danger alike, and yet notwithstanding, go out to meet it”.