Since the invention of the telescope, humankind has been faced with the overwhelming notion that the universe is vastly larger than our own little world. This also brought the exhilarating but terrifying question: Are we alone or has life emerged on other planets as well? Even more interesting is the question: If life does exist elsewhere, does it look anything like what we see on earth? Two new books, each in their own way, provide interesting insight into this question and point us to some surprising answers.
In his new masterpiece, The Equations of Life: How Physics Shapes Evolution, Charles S. Cockell wades with admirable fortitude into the waters of how the laws of physics and mathematics place constraints – and offer solutions – to the great challenges of survival. How inevitable was it that life would land on DNA as the repository of genetic information? Why have the vast majority of animal and plant species settled on two biological sexes? What’s so special about phospholipids that all living cells use them for their membranes? How do ladybugs regulate their temperature? These are just a few of the incredibly complicated biological questions that actually have quite simple mathematical answers, as Cockell demonstrates.
On what would seem to be the opposite end of the spectrum, Kenneth R. Miller tackles questions no smaller than the human intellect itself in his fourth book, The Human Instinct: How We Evolved to Have Reason, Consciousness, and Free Will. In it, Miller gives a brief but comprehensive summary of the most important scientific and philosophical work aimed at explaining if and how humans have a true and autonomous inner self. As Miller astutely acknowledges, even the words we use to try to debate this question – words like autonomy, individual, thought, perception, intention, awareness, and conscience – cannot be taken for granted. If these words are to have any meaning whatsoever, that meaning must be created in the very instrument they are meant to describe, the human mind. It is not difficult to tie oneself into rhetorical knots while attempting to discuss the nature of consciousness, yet Miller nimbly walks us through the minefield.
If The Equations of Life attempts to provide simple answers to complicated questions, The Human Instinct does the opposite, helping us see just how complicated these questions really are and how divergent the answers could be. These books pair together perfectly because they both strike blows against the prevailing notion that human beings are the most unlikely of species. As Cockell explains, “there is nothing uncanny about life’s ability to land on the same solutions.” While anyone with basic knowledge of biology is aware of the many examples of convergent evolution, Cockell seasons those examples by deriving the mathematical relationships that underlie the convergence. Even if things like building a cell, storing genetic information, and swarming towards food might be easily reduced to physical forces, surely reason and consciousness are in a different realm altogether. Hardly, says Miller. Channeling the eminent paleontologist Simon Conway Morris, among others, Miller aggressively defends the claim that, “It is possible, perhaps even likely, that the appearance of humanlike intelligence is part of the deep structure of nature probed again and again by the evolutionary process.”
In The Equations of Life, Cockell introduces us to a unique pedagogical exercise that he has utilized for many years at the University of Edinburgh. Each semester, he challenges teams of students to explore biological processes or life forms and derive the physical equations that underpin them. Of course, he brings his own expertise to the exercise as he and his students unite the fields of classical physics and modern biology. His fascinating book is the result of many years of engaging students in this way. This should serve as inspiration to all of us in the academy charged with not only teaching science, but encouraging students to appreciate what it can and should do for our society.
The striking unity of life has long been considered to be one of the most compelling arguments for common ancestry, and for good reason. Cells could have utilized any number of molecules to store genetic information. What are the odds that all life would have ended up with DNA for our genes if we hadn’t inherited it from a common ancestor? Our basic biochemical energy metabolism, with pyruvate, glucose, and glutathione in such crucial positions, seems incredibly arbitrary. Why would these pathways be so strictly conserved were all living cells not related to one another?
The great Stephen J. Gould taught us that if we were to wind back the tape of history and then let it run again, life would play out on earth differently every time and the organisms we’d find would be unrecognizable to us today. Cockell stunningly concludes the very opposite. From phospholipid membranes that solve “the problem of dilution” to pyruvate as the central node of biochemical energy conversions, the solutions life came up with are anything but arbitrary. Like an electron settling into its lowest energy state, the trillions upon trillions of cells on early earth toyed around with all feasible solutions to life’s great challenges. Pyruvate wasn’t an arbitrary choice. If we replayed the tape, we’d almost certainly end up with pyruvate again.
Far from undercutting the unity of life, our common physics binds us even more tightly together. For example, the genesis of spots, whether on ladybugs, leopards, or Dalmatians, follows a very simple equation involving just two physical factors, pigments and inhibitors. This equation operates independently of the precise molecular mechanisms, which are of course quite different in those three animals. As Cockell explains, the pigment-inhibitor gradient phenomenon is a Turing pattern. From striking simplicity springs breathtaking complexity requiring little more than overlapping gradients. Whether those gradients are made of molecules, organisms, weather fronts, or solar systems, we get spots, vegetation patterns, storms, or the spiral arms of galaxies.
Cockell does not limit his interrogation to why things are, but also why some things aren’t. For example, the wheel is a human invention that made so much physical and mathematical sense that it transformed every culture it touched. So why didn’t life come up with a wheel with all its many advantages over other means of locomotion? As Cockell explains, indeed it has! The bacterial flagellum turns very much like an axle and crankshaft, with all the efficiency those innovations bring. However, that efficiency breaks down rapidly when brought to larger scales because gravity takes over for buoyancy as the dominant force. When eukaryotic cells, hundreds of times larger than prokaryotic ones, developed their own flagellum, there is a reason they opted to extend and flex their cytoskeleton rather than employing the crankshaft design. Each type of flagellum performs well for its scale and they aren’t interchangeable. Also, as Cockell reminds us, wheels are only useful if you first pave smooth surfaces for them to run on.
Roads and wheels did emerge on earth. They just required human ingenuity to emerge first. In The Human Instinct, we turn our gaze inward and ask how humanity could have evolved such incredible intellectual capacities. As one who often writes about the continuity of human and animal minds, this book was a great reminder for me of the truly remarkable leaps our species has made. Miller takes us through a tour of recent research on the uniqueness of human nature, and does so humbly and with an objective distance that makes it hard to know what his own position is, or if he even has one. I recently sat on a panel with Miller at the Boston Public Library on the evolution of human nature. When challenged on his claims of human exceptionalism, Miller conceded, quoting Henry Gee from The Accidental Species, “It’s easy to come in first when we’re the one awarding the prizes.”
But, humans are indeed unique if for no other reason than we can think about our uniqueness. No other species can do that, even those we have exhaustively taught to communicate through sign language. The contemplation and introspection that Carl Sagan famously referred to as “a way for the cosmos to know itself,” cannot simply be dismissed as anthropocentric self-congratulation. Miller elegantly expands upon this point by reminding us that, on the evolutionary tree of life, “one branch, and one alone, produced a creature with the potential… to reconstruct the very tree of which it is a part.”
Miller goes beyond musing about whether or not we are special and asks if we are improbable, as so many have said we are. While Gould insisted that it’s hard to imagine anything like Homo sapiens emerging even if we “replay the tape a million times,” Miller asks more poignantly whether something as intelligent as us would emerge, even if we didn’t. He makes a very strong case that something would.
Self-awareness, as defined by versions of the mirror test, has been documented in countless species, as has rudimentary metacognition. Many lineages have evolved perspective-taking and empathy, and many use true referential communication using sounds or gestures in a representational way. It appears that some animals really are aware of their own mental contents and that of others.
Consider how long multicellularity took to emerge after the first cells first appeared on earth: 2.5 billion years. Now consider that vertebrates with a true brain have existed for only one-fifth of that time and yet, here we are. Clearly, the jump from one cell to many cells was more improbable than the jump from no brain at all to the publication of string theory. Human beings have been on a unique evolutionary path, distinct from other extant animals, for a mere 7 millions years. That seems to have been plenty of time for hominids such as Barbara McClintock and Neil de Grasse Tyson to evolve from otherwise run-of-the-mill primates. Quoting Robert Wright, Miller implores the likes of Gould and Gee to “have some patience.”
The Human Instinct opens with a concise but erudite defense of evolution, that is, the scientific claim that Homo sapiens evolved from ape ancestors over the last few million years. Miller has no doubt honed his airtight arguments through years of sparring with creationists since the Dover, PA “intelligent design trial,” at which he was a key witness. In the final chapters, however, Miller courageously takes on the subject of free will and determinism. Understandably, Miller’s writing posture is a defensive one in these sections, as he is fully aware that the notion of free will is currently facing considerable headwinds among scientists. Nevertheless, Miller argues that the claim that our universe and the common human experience is fully deterministic undermines the scientific process itself and implies that all the great strides we’ve made to examine, probe, and describe our universe were pre-destined, as was the rejection of scientific evidence by too many. Like Stephen Hawking before him, Miller finds this conclusion not only incongruous but self-defeating.
One important lesson taught equally by The Equations of Life and The Human Instinct is that when you have billions of years and trillions of trials, fantastically unlikely events become not just possible, but inevitable. For so long, popular science writing has underscored the assumption that life is ultimately improbable and that human beings are the most unlikely creatures of all. Maybe not. Though they would seem to hail from separate magsiteria, as it were, both of these books come to the rather surprising conclusion that life and humanity, as we know them, may not be so implausible after all. Many of the strange quirks of our world really aren’t so strange.
A common trope in science fiction is to depict extraterrestrial sentient life as basically humanoid, right down to two eyes, ten fingers, and one narrow tube for eating and breathing. Many of the aliens encountered by the various incarnations of the USS Enterprise can even interbreed. Mr. Spock, arguably the first extraterrestrial that Western culture became intimately familiar with, was just such a hybrid. Here on 21st century earth, contrarian scientists like myself reliably (and pedantically) respond that life on other planets would likely have evolved to be radically different, possibly to the point of being incomprehensible to us. Everything we find familiar is arbitrary, we would say, and life on other planets could be altogether unrecognizable to our subjective sensibilities.
Cockell and Miller teach us that, in fact, if we ever encounter extraterrestrials, they might not be so different than the life forms we find familiar here on earth. The common animal body plan – meaning eyes, paired limbs, guts with polarity and unidirectional flow, and sensory-perception cephalization at one end of the body – is so advantageous that multicellular creatures are likely to evolve that way anywhere, just as they have multiple times here on earth. And as long as eating, surviving, and reproducing are important to a species, selecting for advanced cognition seems inevitable as well.
Science fictions writers may be correct after all. Extraterrestrial life may be strikingly similar to terrestrial life. In fact, I would further argue that alien species are sure to have their own versions of the quirks and flaws I describe in Human Errors. Cockell even takes down the Horta, one of the few examples of truly “alien” life from the Star Trek franchise, featured in Devil in the Dark, one of the best episodes from the original 1960s series. The Horta are a species with silicon- instead of carbon-based chemistry. However, as similar to carbon as silicon is, the covalent bonds it forms are weaker, making impossible the kinds of large complex biomolecules necessary for cellular life.
Similarly, Miller argues that the mental abilities we know as human reasoning are also not arbitrary, or at least, they are no more arbitrary than mathematics itself. Humans didn’t invent arithmetic, algebra, trigonometry, or even calculus. We discovered them. While the scientific method is a purely human endeavor, at least on earth, it does not follow that science is a construct the way that literature or the arts are constructs.
We know that science is more than just a human invention because it works independently of us. Certain principles are elevated as “logic” because they are objectively unassailable. There cannot be a world, at least not in this universe, where a species evolves to understand that two plus two is five. As Cockell demonstrates, from something as simple as two plus two can emerge the forces that propel a dolphin through the water or a naked mole-rat through the earth. It can hardly be any other way. And creatures that learn to carefully observe their surroundings will one day attempt to understand them. How else will they test their understanding but by making predictions and testing them through observation?
If his goal is to show how the beauty and complexity of life spring from the logic and simplicity of math, Cockell succeeds enormously. If you agree with Miller, as I do, that science is the ultimate expression of human reason, logic, and curiosity, you will find The Human Instinct and The Equations of Life to be scholarly, delightful, and utterly satisfying. Perhaps they were pre-determined to be so by the laws of physics.