In popular discourse, the theory of evolution has become a victim of its own success, reduced to sound-bites such as “survival of the fittest”. Biologists will of course quickly point out that this is an oversimplification, though philosopher Daniel S. Milo takes things a few steps further. Good Enough is a thought-provoking critique of the dominance of adaptationist explanations. He argues that, while natural selection is important, it is not the only, possibly not even the default mechanism, in evolution. No, Milo claims, the mediocre also survive and thrive.
First order of business to take care of is the obvious danger of misappropriation. We scientists love critical academic discussion, but are also wary of how eagerly and uncritically creationists will misappropriate and misrepresent *any* discussion of evolution: “See? See!?! I told you so, evolution is a theory in crisis!!!”. So, for all the biologists who are frantically waving at Milo to say: “Pssst, hey, don’t feed the creationists!”, do not worry, Milo takes care of that right off the bat.
Good Enough is a book in three parts. Without disrespecting Darwin’s legacy, Milo critically examines the history of evolutionary theory to explain how today’s thinking originated, offers alternative explanations, and provides sharp observations on how evolutionary thinking pervades many aspects of human society.
Darwin’s original sin, says Milo, was his obsession with domestication. Given that he was writing in the 1850s for an audience unprepared for the concepts of evolution and natural selection it is only understandable that he turned to this familiar analogy. Animal and plant breeding was something everyone understood. Next to farm animals, dog breeding was particularly popular at this time (see The Invention of the Modern Dog: Breed and Blood in Victorian Britain). So, both On the Origin of Species and the subsequent The Variation of Animals and Plants under Domestication leaned heavily on domestication as a model of evolution. This led to the idea that natural selection is as relentless as breeders are, to which Milo outlines several objections, arguing that all that matters is that organisms are good enough to reproduce and survive.
“Milo outlines several objections to the idea that natural selection is as relentless as breeders are, all that matters is that organisms are good enough to reproduce and survive”
In the process he takes aim at several icons of evolution, including the giraffe’s long neck, the Galápagos finches (see 40 Years of Evolution: Darwin’s Finches on Daphne Major Island, a true but atypical case of natural selection that should not be extrapolated to all of nature), and human brain size and complexity, which leveled off long before the advent of agriculture and the concomitant population explosion.
The second part is where Milo offers his explanation. The history of the theory of evolution has led to a near-myopic focus on natural selection. In the process, scientists often ignore anomalies or try and find adaptive explanations – biologists, it seems, just cannot resist the temptation. In a conceptual move that parallels Brandon & McShea’s Zero-Force Evolutionary Law (see my recent review of Biology’s First Law: The Tendency for Diversity & Complexity to Increase in Evolutionary Systems), Milo argues for a change in perspective. Rather than assuming function to be the default, neutrality is. A lot of traits are simply not selected for and vary randomly.
There are two noteworthy examples Milo discusses. One, the messy organisation of genetic material: many genomes are unnecessarily large and riddled with non-coding sequences. Already back in 1968, Motoo Kimura argued that most genetic variability is neutral and of no evolutionary consequence (see The Neutral Theory of Molecular Evolution and Population Genetics, Molecular Evolution, and the Neutral Theory: Selected Papers, but see also Junk DNA: A Journey Through the Dark Matter of the Genome). Two, wide ranges in phenotypic trait values. Phenotypic polymorphisms (e.g. eye colour) can easily be brushed off as irrelevant when they are equally costly. But where traits differ, sometimes dramatically, in number or size there are energetic costs to their production (e.g. sperm count, or the bizarre headgear of treehoppers, pictured right). Such variation is often taken to be the substrate for evolution to proceed by leaps and bounds. Though clearly, says Milo, such traits are not under strict natural selection themselves, they are not being optimized. And they are far too numerous to ignore.
“For traits that need to be present without needing to be optimized, excess and wastefulness are the safer options; “better to be inefficient than to be dead”
Milo patiently considers and disarms the usual adaptive explanations and then proposes several mechanisms explaining this bias towards excess. Invoking “conserved core components and processes” (widely shared and conserved features of organisms such as DNA replication, see The Plausibility of Life: Resolving Darwin’s Dilemma) and Pareto’s 80/20 rule, he argues that a small number (the proverbial 20%) of optimized traits are under strong natural selection and contribute most (the proverbial 80%) to survival. This leaves many traits that need to be present without needing to be optimized. For those, excess and wastefulness are the safer options; “better to be inefficient than to be dead”.
So far, so fascinating. I have often questioned why “no selection” is not considered more often as an explanation, so I find this argument appealing. That, of course, does not mean it is not worthwhile to look for adaptive explanations (Milo says as much). My main criticism here is that Milo might be perceived to conflate two concepts. He argues that many traits are selectively neutral and evolve randomly, something that others have done before him (see e.g. Randomness in Evolution). But he couches this in language that still sounds adaptationist. Saying that the mediocre also survive, that merely being good enough is sufficient, still implies selective pressures, albeit weaker ones.
The third part of the book is equally fascinating. Here, Milo looks at human society and offers some of his most incisive and sharp-witted observations. What sets humans apart evolutionarily is that we can perceive of a future, and with that came a seed of restlessness, of wanting to improve our lot. Through cooperation, delegation, and specialization we have created societies where we care for each other’s needs. The drive for excess led to imaginative brains that became very successful in ensuring survival for all through technology, agriculture, and health care.
“”our bored neurons crave action”. So we construct problems for ourselves to solve […] for without it “we would succumb to boredom and despair””
We have achieved this now, but the drive persists, “our bored neurons crave action”. So we construct problems for ourselves to solve, endless diversions to lose ourselves in. Politics, sports, cuisine, art, fashion, science, work – all our culture, all our questing for athletic, emotional, and spiritual goals. They are all but exercises, endless loops, to give our lives meaning. Even though we have never had it so good, we continue to compete as if our lives depend on it, for without it “we would succumb to boredom and despair”. It may sound bleak, but for all those who ever wondered what the point of it all is… Now, says Milo, contrast that with the tales we tell ourselves. Our economies are steeped in Darwinian metaphors of relentless optimization and cut-throat competition, and we continue to educate our children to excel. We have taken Darwin’s good ideas and extrapolated them to many other fields where they just do not apply.
Good Enough is nicely produced with numerous carefully designed colour illustrations. On the biological details, Milo is clearly not alone (neutral selection has been mooted by others), but his application of it to human affairs is both insightful and unsettling. His ideas are thought-provoking, no doubt controversial to some, and I look forward to pushback from evolutionary biologists. But a fun and accessible read like this is suitable for a wide audience. What a fantastic book!
Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.
Good Enough hardback, ebook, audiobook or audio CD
Other recommended books mentioned in this review:
Kimura & Takahata’s Population Genetics, Molecular Evolution, and the Neutral Theory paperback or hardback