William Turkel's Spark from the Deep is a fascinating book that explores a little-known aspect of how we came to understand and control electricity: the role played by electrogenic animals such as electric eels and rays. Such animals, he writes, "inspired [us] to colonize an electric world", and in doing so, they profoundly transformed both our world and ourselves.

The book explores diverse areas of science and history, going well beyond mere descriptions of what happened to provide explanations of how and why biological and cultural evolutionary processes brought us there. A good example concerns Turkel's discussion of vivisection, which makes useful reading for anyone with occasion to defend animal research today. To observers in the ancient and early modern world, strongly electric fish posed quite a mystery because of their ability to inflict pain at a distance. The mechanisms behind this ability could only be found by "opening the box", but the act of doing so was (and still is) morally contentious.

Turkel argues that vivisection played an important role in the development of science because "treating humans and other animals as subjects for experiment or disassembly lowered the conceptual barriers between ourselves and our animal kin". In addition, he writes, vivisection "lowered the barrier between animate and inanimate. If an electric fish could be used as an apparatus, it might also be possible to build an artificial device that could generate a shock like an electric fish". This is exactly what Alessandro Volta did when he presented his first battery to the Royal Society in 1800, calling it his "organe électrique artificiel". What better example of the value of pure versus applied research than the fact that our ubiquitous battery was invented to mimic a part of a fish?

Turkel also points out that many modern medical devices "would not exist if it had not been for the variety of grisly experiments" undertaken in the early days of electricity research. In 1774, for example, a child who arrived "dead" at a hospital was resuscitated by electric shock. But for Turkel, these episodes are more than just interesting anecdotes from the history of medicine and technology; they also contain information about what characterizes us as a species. "We humans," he writes, "are unique in our willingness to treat just about anything as apparatus, including ourselves, one another, human body parts, other animals, animal body parts, inanimate objects, and hybrids of some or all of the above."

The reductionist practices of disassembling animals into functional components naturally led to questions about how they had been initially assembled. For Charles Darwin, electric fish were a "special difficulty" that became chapter 6 of his book On the Origin of Species. In it, he wrote: "It is impossible to conceive by what steps these wondrous [electric] organs have been produced...I have to make, in my mind, the violent assumption that some ancient fish was slightly electrical."

Darwin's "violent assumption" was, in fact, a wonderful example of the dynamic evolution of scientific theories. Nearly 100 years later, scientists confirmed his prediction, eventually discovering hundreds of species of weakly electric fish and multiple indisputable evolutionary pathways by which such electricity developed. Darwin actually predicted this multiplicity in a general sense, writing that "I am inclined to believe that in nearly the same way as two men have sometimes independently hit on the very same invention, so natural selection...has sometimes modified in nearly the same manner two parts in two organic beings, which owe but little of their structure in common to inheritance from the same ancestor." What a shame that so many adults today are ignorant of these incredibly powerful (and aesthetically and intellectually beautiful) theories that our ancestors worked so hard to discover and articulate.

Another gem in Turkel's book is his explanation of Darwin's reluctance to publish his On the Origin of Species until 1859 – 15 years after a previous work, Vestiges of the Natural History of Creation, "brought evolutionary debate to the mainstream". In Vestiges, the anonymous author (later revealed to be Robert Chambers, a Scottish journalist and geologist) argued that everything in nature is governed by physical laws, and electricity played a key role in this grand unification scheme. The debate that followed its publication was acrimonious. Turkel argues that Vestiges can be interpreted as proposing "a vision of nature appropriate to the industrial age and the middle classes". Consider how dramatically machines and pollution were changing people's relationships with each other and the world. Were these changes an inexorable consequence of natural law? One might see parallels today regarding climate change.

While electromagnetic phenomena were radically transforming industrial society, physiologists began exploring how to measure feeble bioelectricity in more typical animals. In the 1820s, the most sensitive -current-measuring instrument available to scientists was a freshly pithed frog leg. Within a year of Alexander Graham Bell's 1876 invention of the telephone, Emil du Bois-Reymond and his students were listening to bioelectric signals from muscles and nerves. Their instruments opened up completely new kinds of perception – a prerequisite to manipulating and controlling those newly discovered domains. In more recent times, electric organs have been the source for purified ion-channel proteins and DNA, and weakly electric fish remain some of the best model systems for a more holistic "neuroethological" approach to understanding brain function. Unfortunately, funding for such "exotic" research has virtually dried up, in spite of its history of important discoveries.

Turkel demonstrates throughout his book how evolution is an incredibly powerful key, one that can unlock and explain disparate questions about how and why we came to be who and where we are in this world. His concluding chapter contains a concise summary of chemical evolution that was a prerequisite to biological evolution, and also the pre-prerequisite of cosmological evolution. Evolution does for history what calculus does for mathematics. Our pursuits of pure science starting with electric fish led us on an unpredictable path to the most important and transformative discoveries in human history. But although the path was unpredictable, the fact that humanity would embark on such a journey is deeply encoded in our genes.