The role of expert testimony in court has been widely discussed in the UK in recent years, fuelled by the highly emotive subject of “cot death”. However, the debate is not a new one. After all, the legal process has, for many centuries, turned to scientists for guidance in court. The problem is that scientists – especially in a new field – can strongly disagree about the underlying science and its interpretation. There can be a mismatch: the law requires certainty, while science looks for an absolute truth.

In Laws of Men and Laws of Nature, Tal Golan explores this mismatch – and much more – in a thorough and entertaining review of the history of the partisan expert witness in England and the US. The legal instinct, he says, is suspicious of extrapolating from artificially created facts to the original events of the case under consideration. This has been the short-coming of many pre-eminent scientists who have acted as expert witnesses. Indeed, it is as true today as it is was when, for example, Michael Faraday’s testimony was mocked in court during a dispute between a sugar manufacturer and its fire insurers in the early 19th century.

The case was brought by Severn King & Co, which had used a new process for refining its sugar that led to a spectacular fire in 1819 that devastated its factory. As cynics may have guessed, the company’s insurers refused to honour the policy because they had not been notified about the use of the new process. The case turned on whether the new process was safer than the old process, which led the insurers to engage Faraday as their lead expert witness.

Although Faraday carried out experiments relating to the cause of the fire, he ignored those factors that he considered to be scientifically irrelevant. This gave the sugar manufacturer’s lawyers plenty of scope to deconstruct his evidence on the basis that these factors were relevant. Several other scientists gave evidence for the manufacturer, which won its claim. The judge, however, expressed his exasperation regarding the vast body of contradictory evidence that the scientists had amassed.

Today, scientific expert witnesses are used throughout legal practice in, for example, patent disputes and in criminal cases. However, it was not always so. Although the law had, since the Middle Ages, acknowledged the importance of the assistance of science, there was – bizarrely – nothing to distinguish an expert witness from a witness of fact. A scientist had no legal basis for expressing their opinion, where, of course, their expertise lies.

This changed following a dispute that took place in the 1780s concerning the silting-up of Wells harbour in Norfolk. Golan provides a brilliant and detailed account of the litigation, in which the claimants argued that the silting-up was a consequence of land reclamation near the harbour. The court accepted evidence from a civil engineer named John Smeaton, who acted on behalf of the landowners that this was not the case. Although the jury was ultimately not swayed by Smeaton’s argument, the decision by the court to accept his evidence is widely cited as the root of modern rules on expert evidence. Golan’s analysis of the relevance of this case is one of the book’s outstanding contributions.

Having established the birth of expert testimony, Golan then examines the use of expert witnesses and the problem of contradicting experts. Legal theory accepted that – in the words of Lord Gilbert’s seminal text Laws of Evidence – the “best evidence that the nature of the thing is capable of could be produced by science and science alone”. Of course, experts can openly express different opinions and the usefulness of scientific experts in court was doubted: how is someone who is not a scientist – such as a judge or jury – to know which of two contradicting opinions is correct? The court is looking for certainty and yet the expert scientists dispute the scientific truth.

During the 19th century, scientists discussed how to maintain the public’s perception of their integrity, impartiality and objectivity. A common view of scientists was given in the 1860s by the chemist Robert Smith, who said that “the [scientist in a courtroom] simply becomes a barrister who knows science. But this is far removed from the idea of a man of science. He ought to be a student of the exact sciences who loves whatever nature says in a most disinterested manner”. This altruistic view was widely held. For example, in November 1885 the editor of Nature launched a scathing attack on “professional scientists”, especially those appearing as witnesses in court.

A minority of scientists, however, thought differently. Some, such as the experienced expert witness William Odling, argued that the truth “could only be arrived at by the conflict of testimony”. Golan’s work demonstrates that today’s debate about whether party-appointed experts are better than court-appointed experts was just as alive – possibly even more so – in the 19th century.

This sabre-rattling continued for sometime, but was essentially sidelined in England by legal reforms to court procedure that, for example, reduced the use of juries. In the US, however, these reforms were not introduced, and Golan describes how evidence from scientific expert witnesses evolved there. He does this by examining how scientific evidence – in the form of blood micrographs, X-ray images and experimental psychology such as lie-detector tests – were used in court. In doing so, he demonstrates how the law accepts new science as evidence and the development of tests for assessing expert evidence.

Golan manages to deal with what can be dry subjects – law and science – in a readable format. At times he deviates into the full background history of an aspect, which may well serve his primary purpose as a historian. Tensions between scientific practice and the legal process are identified, and he recognizes how science and technology have been used successfully and unsuccessfully in court. Although he describes the present position in the US, he does not appear to deal with the current issues in England.

This is a valuable, well researched and entertaining account of the history of scientific expert evidence. Both lawyers and scientists should find it illuminating, but scientists who are thinking of acting as an expert in legal proceedings should look elsewhere for guidance. As the English rules of court procedure put it, the overriding duty of an expert is to help the court on matters within his or her expertise. An honest expert who remembers this should steer clear of trouble.