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A developmental biologist ponders life on Earth and beyond

Life Through Time and Space

Wallace Arthur
Harvard University Press
289 pp.
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On 21 August, North America will experience its first total solar eclipse in decades. Precise maps and times for the event are readily available, detailed down to the second and meter. The nationwide anticipation of this phenomenon is testament to our precise understanding of the necessary celestial mechanics to so perfectly predict this event.

More complex aspects of astronomy and biology, however, have not yet succumbed to human understanding. In his ambitious book Life Through Time and Space, Wallace Arthur tackles an extraordinarily difficult set of topics. What is the origin and fate of the universe? How did life, and eventually intelligent life, come into existence on Earth? How does a fertilized human egg transform into a complex person with only DNA to guide development?
The book is organized in “triplets,” as Arthur calls them in the preface: The first is on astronomy or astrobiology, the next on evolution, and the final one focuses on embryology. Should a reader find any particular chapter less than interesting, it is a short wait before the topic shifts.

Arthur does an excellent job in the astronomy-focused chapters. There is a concise and effective explanation of our modern understanding of the origin of the universe—a play-by-play of fractions of a second. Although it is sometimes glossed over in accounts of the Big Bang, Arthur rightly notes that the early universe contained both matter and antimatter and that these two forms of matter annihilated each other into photons when they were brought together. Arthur also points out the fortuitous fact that there was slightly more matter than antimatter in the early universe; without this asymmetry, the universe would be pure energy—no stars, no planets, and certainly no life. His breadth of coverage extends to exoplanets discovered by the Kepler space telescope and the likelihood of alien intelligent life.


Insights derived from early embryonic development may shed light on the origins of extraterrestrial life, argues Arthur.

In the section on biology and evolution, I particularly enjoyed Arthur’s treatment of the evolution and origin of animal life. Here, he uses a metaphor of trees rising from the sea to describe the different branches of evolution that led to the many forms of life on Earth today. One such tree produced animal life, another plant life, and still others led to funguses and brown seaweeds.

The same chapter discusses the mystery of the “Cambrian explosion,” which I had before believed to be a burst of evolution and new species. Arthur reveals, however, that it also may have been just an epoch of intense fossilization.

Arthur’s field of study is embryology (in particular, evolutionary developmental biology), but I found these sections the hardest to follow or appreciate. The idea that a single fertilized egg can develop first into a fetus, then into an infant, and eventually into a fully grown adult human capable of thinking and understanding the world is truly a marvel. However, I am not sure I understand the mechanisms that drive and make possible human development any more than I did when I started the book, even if I know much more about what happens and in what order.

Cosmologists often wrestle with understanding the early universe because the most we can observe are photons from billions of years ago. But, as Arthur reveals, despite having direct access to their subjects, biologists often struggle to make sense of their chosen topics, too. Both of these complex sciences represent huge challenges. Arthur writes, “Maybe a close cousin of the chimpanzee … shouldn’t expect to be able to understand the origins of everything. … [B]ut that won’t stop us from trying.”

In the book’s closing chapters, Arthur pivots to broad concerns about humanity’s ultimate undoing, be it at our own hands or from an external cause. No species has ever survived anything close to 4 billion years on Earth—the expected remaining lifetime of our Sun—and extinction, he notes, has been the most common fate. Here, he writes passionately and strongly against religious fundamentalism, both past and present, that suppresses truth-based inquiry.

Although promising a lack of jargon up front, Arthur allows plenty to seep in. One cannot discuss the intricacies of the brain, for example without using the word “axon,” but phrases such as “temporal topography of development” could surely have been written more simply.

By the end, readers will have learned a great deal about three very complex and important subjects. However, those without a biology background may find themselves struggling through certain chapters at times. Still, overall, Arthur writes clearly about many complex and varied subjects, and his enthusiasm for the material shows.

About the author

The reviewer is an astrophysicist and freelance writer based in Washington, DC, USA.

  • Torbjörn Larsson

    The astrobiology part sounds interesting. But the article description of evolution of complex multicellular life is confusing to me. One – admittedly among several – current description of the phylogeny is a “fungimal” (Opisthokonts) clade. a SARP clade that among other lineages contains separate plant clades, and a likely polyphyletic Excavata clade.