You aren’t who you think you are,” Flannery O’Connor’s unlovely character Julian tells his mother after a tense bus ride in the short story, “Everything that Rises Must Converge.” Who we think we are matters by itself and also shapes the way we treat other creatures. Humans tend to think of themselves more highly than they ought, argues Alice Roberts, Professor of Public Engagement in Science at the University of Birming­ham in England. As a species, we have a history of thinking we are pretty special, the measure of all things, the pinnacle of creation. We arrive at this opinion in part from awareness of the amazing bodies we have. Roberts argues that instead, by understanding how we are related to other creatures, we should learn to delight in the body, even as we recognize we are not master of other animals. Roberts sketches out a tree of life that is not shaped like a pointy Christmas pine with Man at the top, but a luxuriously branching shrub, humans related to lancelets, agnathans, fish, frogs, mice, birds, and lizards on a twig of descent, the cousin rather than the superior of other animals.

Roberts, a winsome, television-savvy clinical anatomist, aims in this book as in her television programming to promote popular understanding of science, to make evolution relevant to ordinary readers. While the book has a lot to teach, it is not particularly dedicated to tracing the line of evolution from the fish to us. It skips around by body parts, sometimes dwelling in anecdote, comparison, or evolutionary theory, sometimes truncating interesting material too early, attentive mostly to the resonances between a particular human structure and its evolutionary origins. The book’s array of curiosities is designed to inspire the reader’s gladness about his new discovered relation to the sea squirt. This role, as bearer of good cheer, is very important to Roberts. Her task in the book is not merely to give us facts about embryology and evolution, but to disabuse and then to encourage.

It is significant to Roberts that she wrote this book after the birth of her daughter, because ­childbearing made her sensitive to the miracle of how a new human body comes to be: “Having my own children reawakened that sense of wonder in me: how astounding to have played host to that extraordinary act of creation.” She is on target in this recognition that the way humans “play host” to offspring is among the most thrilling features of our embodied lives, and should be of universal interest, not just to pregnant women. Insofar as everyone is of woman born, everyone ought to share this fascination. A mother’s collaboration in an embryo’s growth strikes me as just about the greatest story ever told, excepting the story of salvation. Regrettably, though, Roberts leaves this story too quickly, revisiting the embryo’s shaping but leaving off the account of the mother’s hospitality until nearly the end in a section on humans’ perplexing physiology of birth.

She uses our origins from an embryo to make a double argument. The amazement we properly feel imagining the growth of ourselves from single cells to complex adults can, by analogy, help us understand evolution. The journey from one cell to an adult man or woman may seem unbelievable but necessary to believe, in approximately the same way as the journey our species made from invertebrate water animal to human being. Roberts contends that explanations arising from a blend of anatomy, evolution, and embryology (shorthanded Evo-Devo) do best to explain who we are, telling where we came from, how we grow, and how we are shaped by environment. Roberts flirts with ­nineteenth-century German biologist Ersnt Haeckel’s discredited theory that ontogeny replicates phylogeny, that the embryo passes through the evolutionary stages of the species as it becomes recognizably human. She admits Haeckel’s errors but upholds his insight. If we look at the adult forms of humans, dogs, or fish, we see vast differences among the species, but looking at embryos instead shows our resemblance to putatively “lower” animals and illustrates the resourcefulness of the evolutionary process.

Given the time and place we inhabit, arguments about the status of the embryo nearly inevitably have implications for abortion. Roberts here stays away from the topic. But her book echoes content common in guides for pregnant women, considering that tiny embryo, first a single cell, then multi-celled blackberry, then a layered disk, then a rolling frisky creature, as not only a person but a particular person: you. Lyrically, Roberts narrates the moments when “[y]our heart started to develop incredibly early in embryonic development…. when you were still a flat jam sandwich,” and when “as a minute embryonic germ disk just a few millimetres in length, you rolled up to become a stack of nested cylinders, you were also making the beginnings of your guts.” Observing that by the fifth week “all sorts of other interesting things are starting to happen to this tiny embryonic you,” Roberts makes a point important to anti-abortion arguments. Though the embryonic “you” at that point does not look much like a human, this is a period of more dramatic development than in the later months, when the baby-looking baby is just putting on weight.

Her chapters follow a pattern. In describing the evolved us from head to toe, Roberts identifies a feature of the human body, looks at its embryonic development, then introduces another animal who seems remote from us. That gives her cause to describe how an attribute of our embryo resembles the other animal and reveals a relationship, usually a common ancestor. We are not only the relatives of apes but must admit fellowship with unglamorous ancestors, sea worms and snakes. For instance, because in embryo we have a notochord, which develops into spinal column and brain, we can see kinship with the fishlike lancelet. The lancelet may figure as Roberts’s favorite distant relative, given the frequency of her reference to it to illustrate evolutionary links. Further, considering the human heart, Roberts notes that while the “heart and the aortic arches of a five-week-old human embryo look uncannily like those of an adult fish,” our blood is not oxygenated in gills but in lungs. Interestingly, the “swim bladders,” or air bags attached to the gut in carp, trout, herring, and eels, may function nearly like lungs and consequently illustrate the link between fish and us, as an essential tool “for air-breathing when our tetrapod forebears hauled themselves out onto land.” Other body parts—skulls, ribcages, limbs, hands, and feet—also show marked resemblance to equivalent parts of other animals, especially when comparisons are made at embryo stage.

It is, as Nick Saban would say, all about the process. In animals, nothing is really “designed.” The process, not an in-the-beginning plan or a ruling telos, is what makes us and everything else. Roberts stresses that nothing is made ex nihilo, that body structures are not devised for their function. Evolution works with what is made available, shifting joints around or nudging a part to fit more than one purpose or putting a leftover bit of tissue to some other use. If you want a human voice, you start with a gill slit. The tissues that make our larynx and ear, for example, grow from the branchial bars in embryos, what in fish embryos would make gills. “Bits of anatomy don’t generally appear out of nowhere, there has to be a precursor, something that can be modified, duplicated, or have a little extra added to it.” Roberts observes, “Evolution is very good at re-purposing or recycling structures.” Because reptiles did not need gills, they developed different kinds of jaws. And then unlike reptiles, who have only one tiny bone, or ossicle, connecting eardrum to cochlea to allow hearing, we have two additional ossicles. Evolution found fresh use for a bit of the leftover jaw joint because we have a new jaw, and hearing was improved given this “trick of stealing bits of jaw for bits of ear.” Evolution is virtually personified in Roberts’s pages, a resourceful, clever spirit, a discernable way of acting in history.

“What is the chief end of man?” asks the first question of the Westminster shorter catechism, to which an unnamed schoolboy famously gave the erroneous answer: “his head.” Confronting that important piece of our anatomy, Roberts makes clear how little she will indulge notions of human uniqueness, asking first why creatures have heads at all. For a lay reader who never considered headlessness, the very question prepares us to be impressed with the answer. The answer is intentionally unimpressive. She points us to the acorn worm, a distant relative that “learned to swim,” to answer the question. Heads allow speed and sense, since “the faster you move, the more head-like your front is likely to become. For a free-swimming animal, it helps to have your senses stacked up-front, in a head where you first encounter novelty in your environment. Of course, it also helps if you have a brain, to process all that information coming in from your head-mounted sense organs.” There must be more to say—even in speculation, which is the status of many other evolutionary observations—about why we have heads than that they make useful boxes for holding tools of self-defense and nourishment. Roberts seems insufficiently impressed at the singularity of the big-brained ape publishing books about the origin of species and reminding her fellows not to be overproud.

The body is trying to tell us something, Roberts maintains. This is a worthy topic to pursue, because the body is not self-interpreting. Some ancients thought the liver was the seat of the soul, and we still treat the heart as the source of affection. It would be wonderful to have a reflective, humane guide to the meaning of all our parts; for many of us, medicine provides the default interpretation of the body, but it falls short in telling meaning. Some writers have offered interpretation of parts of the body, often with an emphasis on its purpose. Leon Kass, in writings like Toward a More Natural Science (1985) and The Hungry Soul (1994) reads in the structure of the human body the conditions for our reason and sociability. In his “theology of the body,” Pope John Paul II discerns in the body a sign calling us to God, the body itself expressing a “pre-given language.” Observing the complexity and beauty of the body even can draw one to recognize the existence of God. In Witness (1952), former communist Whittaker Chambers traced the start of his conversion to a moment when, watching his young daughter in her high chair, he looked hard at her ear: “My eye came to rest on the delicate convolutions of her ear—those intricate, perfect ears. The thought passed through my mind; ‘No, those ears were not created by any chance coming together of atoms in nature. They could have been created only by immense design.’”

Roberts wants every bit as much ardent attention given to the ear, but for an entirely other end. She wants her readers to gaze at a child’s gorgeous eyes or their own sturdy feet and not to mistake these for loving creation. No, Roberts wants readers to see their makeshift, haphazard, good-enough physical form as evidence of the process of natural selection. Your conclusion should be hers: “At the end of this anatomical journey you can look at your hand and see not only something which developed out of a minute limb bud in your own developing embryo, but something which evolved from a fish’s fin, over millions and millions of generations.” You are not special. What makes human beings distinct boils down to habitual bipedalism and big brains, and even those, Roberts notes, distinguish us only by degrees. Nor were those attributes bestowed upon us as a package deal at some turning point in history, transforming us away from the other apes. She compares the uniqueness of our big brain to the tail of a peacock, a curious pleasant adaptation, but no dividing line from the beasts. Given Roberts’s public opposition to creation science in Britain’s Christian schools, it is reasonable to guess that she expects that evolutionary gaze to nudge you to the next logical leap. Your own body can serve for you as a kind of a proof of the non-existence of God.

This book aims not only to inform readers about evolution but also to generate a particular attitude. We might wonder why she thinks ordinary people would take in three hundred-some pages of fairly rigorous science, and what she wants us to get in the process. Her expectation of readers is linked with her argument: if we properly understand who we are and where we come from, we will recognize evolution at work and learn to delight in both our relationship to other species and in the ­jerry-rigged-but-efficient construction of our body. She wants the news of evolution to make us glad. While glad is not my general reaction, there is at least one pleasant consequence to taking evolution personally. It fosters healthy disregard for the many prescriptions foisted upon us on (sketchy) evolutionary grounds. The “way we were made” or “what we are hardwired to do” often are employed to shame us into certain behaviors: exercise programs telling us to move like our spear-hunting ancestors, and run shoeless; paleo diets that prioritize meat, nuts, and plants as our natural nutriments; contrasting excuses permitting us salty, sweet, and fatty foods we are “hardwired” to prefer. Roberts’s sense of us as evolved beings suggests we need not be adapted to caveman conditions, any more than we should feel obligated to climb trees and nosh on leaves.

But might not evolution indicate that our bodies don’t mean anything? That they simply are, and are ours for staying alive and reproducing, case closed? Roberts tries to push readers past that disenchantment and resignation. Instead, she wants this knowledge, of the process and of the human body, to breed wonder and delight.

Seeing ourselves as connected to everything else, indeed as blooming from the primordial stuff of the earth, should fuel our satisfaction in a way not unlike Carl Sagan’s pronouncement that we are “star stuff.”

Amplifying joyous amazement at our evolved selves is the title attribute, the “unlikeliness” of it all. Repeatedly she admits that the process of embryo development is so complex that things easily could go wrong, and sometimes do. But each of us matters so little in the evolutionary scheme of things that the clay can hardly talk back to the potter. Reckoning with our low origins, a hairless ape who is kin to a hagfish, we might be blown away with the sheer dumb luck that we exist at all. All those points in evolutionary history when things could have gone differently, plus all those other sperm that could have fertilized the egg and made somebody else, mean “the chances of your conception are vanishingly small.” So we should be glad because we are “lucky to be alive.” Further, our being lays on us the “heavy burden” of “weighty responsibility,” to use our big brains to understand and communicate, to direct the global impact of our actions “informed by the investigative urge we call science.”

That fails to satisfy. If it is unlikely that I exist, but I do, philosophy and theology help me find my place better than does that “investigative urge” alone. Scripture and experience teach that we come from dust and return, but also that the way we are made is fearful and wonderful. It may not be possible to tell what the human being is, even by looking microscopically at embryos or through the lens of evolution, but God is mindful of us.

Agnes R. Howard is Assistant Professor of History at Gordon College in Wenham, Massachusetts.