Since the turn of the century, the term "systems biology" has grown from one used by a few theoreticians of biology into one of the fastest-growing areas of biology. Centres and departments have opened up in universities around the world. To physiologists this is a strange development. The systems approach has been a main feature of physiology ever since Claude Bernard introduced the concept of control of the internal environment.¹ William Harvey can also be viewed as a systems biologist. ² What then is new and why is this field a frontier? What is new is that we have now reached the bottom of the reductionist agenda with the full sequencing of genomes. That is a landmark achievement but it has not answered the question 'what is life?'³ People have realised therefore that the time has come to study the ways in which the parts interact. The great majority of this work has originated in biochemistry and molecular biology. But I will argue that, without the insights of higher-level study of physiological function, systems biology will not succeed in its mission. The future of biology is physiology by another name, and with an important new twist, which is that it must become more mathematical and embrace important developments in theoretical biology. Physiology also needs to reconnect with evolutionary biology. ⁴

1. Noble, D. Claude Bernard, the first Systems Biologist, and the future of Physiology. Experimental Physiology93, 16–26 (2008).

2. Auffray, C. & Noble, D. Conceptual and experimental origins of integrative systems biology in William Harvey's masterpiece on the movement of the heart and the blood in animals. International Journal of Molecular Sciences10, 1658–1669 (2009).

3. Noble, D. The Music of Life. (OUP, 2006).

4. Noble, D. Neo-Darwinism, the Modern Synthesis, and Selfish Genes: are they of use in physiology? Journal of Physiology589, 1007–1015 (2011).