For Leonardo da Vinci, painting did not mean merely copying the appearance of nature. Rather, it involved understanding nature's laws and using them to create a figurative world that enhances our awareness of reality. Leonardo's visual understanding meant that his scientific studies often took the form of beautiful drawings. His art and science sprang from the same source, providing a unified vision of the world and communicating a sense of wonder that is, according to Plato, the source of all philosophy and original investigation. Leonardo's will to 'know' was undoubtedly one of his strongest impulses, and his relentless questioning of how things work extended to all branches of the natural sciences of his day.

The Universal Leonardo project — an extraordinary collaboration of art and science historians, co-curated by Nature columnist Martin Kemp — does justice to Leonardo's broad interests in a series of events across Europe. The exhibition of drawings and manuscript pages at London's Victoria and Albert Museum describes how Leonardo 'thought on paper', for example, and the display at the Alte Pinakothek in Munich explores the scientific analyses of one of Leonardo's early paintings, the Madonna and Child.

Leonardo's Madonna and Child and his drawing of an ox heart (right) can be seen at the various Universal Leonardo events. Credit: ALTE PINAKOTHEK, MUNICH

Details of the exhibitions can be found in an extensive (and clever) website at www.universalleonardo.org, which also makes Leonardo's thought processes accessible to a wide audience. Its 'explore' page graphically highlights the links between Leonardo's art and science by identifying several themes running through the whole of his work.

The theme 'The Body of Earth', for instance, deals with the view — widespread in ancient and medieval times — that Earth is a macrocosm living according to the same laws as the human body. Blood circulation was seen to correspond to the movement of water in rivers (the veins of Earth) towards the sea (its heart). Leonardo accepted this model until late in life, when he saw inconsistencies that forced him to abandon it. He realized, for example, that the sea — unlike the heart — only received water; it did not pump it. He had tried to postulate the existence of subterranean rivers (arteries) bringing water to the top of mountains, but understandably failed, and the idea of the evaporation of water did not fit in with the macrocosm analogy.

One-quarter of the London exhibition is built around the macrocosm/microcosm theme, and illustrates it with drawings on hydrodynamics, cartography and anatomy, including some of the organs of animals. The drawing of the heart of an ox combines supreme beauty in the rendering of the plasticity of the form with penetrating and accurate observation of details, particularly of the coronary blood vessels.

Leonardo's work on palaeontology should also be understood in this context. At first sight, his astonishing studies of fossils give the impression that he was far ahead of his time. He refuted the contemporary idea that fossils formed following Noah's flood, and dismissed the neoplatonic theory that they grew inside rocks. He laid out in his unpublished notes a number of principles that were not clearly redefined by palaeontologists until the twentieth century, such as the idea that growth rings in a fossil could be used to age it. But his aim was to find evidence to support a pre-modern, macrocosmic model of Earth, in which the elements were in constant flux, and the levels of water and mountains were constantly changing. As Stephen Jay Gould has pointed out, if we hope to understand Leonardo's true greatness we should abandon the metaphor of a “spaceman from a more advanced universe” (often accompanied by a condescending vision of the past), and look at his achievements within the context of his own time.

The Universal Leonardo project also allows present-day science to investigate Leonardo's works. X-ray radiography and infrared photography, for instance, were used to probe below the surface of the Madonna and Child. The results confirm that Leonardo often changed his mind and modified his compositions at different stages of their execution. They also highlight the importance of geometry in his conception of form. In addition, the Munich exhibition displays 20 drawings of the Madonna and Child by a young Leonardo and his contemporaries.

One of the claims that Sigmund Freud made in his 1910 book Leonardo da Vinci and a Memory of his Childhood was that Leonardo had an unusually strong relationship with his mother. There is no documentary evidence for this, but the bond between mother and child in Leonardo's Madonna paintings and drawings appears deeper and stronger than in those by other artists. I like to think of his anatomical drawings of the fetus nestled in the protecting warmth of the womb (see Nature 396, 25; 1998) as the scientific counterpart of this theme.

The scope for seeing connections between art and science in Leonardo's work is nearly boundless. By pointing some of them out, the Universal Leonardo project invites the visitor to move back and forth between these two fields — something Leonardo himself seems to have done continually.