Blogging the Human Genome: How genetics nearly killed off Darwinism.

How genetics—and a very dirty diaper—nearly killed off Darwinism.

Chromosome 3

Illustration by Andrew Morgan

Human genetics started with a black diaper. Around 1900, the English doctor Archibald Garrod began studying cases of alkaptonuria, a disorder that turns people’s urine black when exposed to air. Garrod noticed clusters of alkaptonuria in certain families, and assumed something in their environment or diet caused it. Then, in 1901, a mother brought in her newborn baby, whose diapers looked like an octopus had used them. Garrod realized that someone so young had almost certainly inherited alkaptonuria. Further digging revealed that the child’s parents were first cousins. Certain he was onto something—but unsure of what—Garrod published his findings. He soon got a letter from English biologist William Bateson.

The year before, three biologists had rediscovered Gregor Mendel. Mendel, a monk, had uncovered the first hints of genes (in pea plants) in the 1860s, but had died unappreciated—better known for his showdowns with local sheriffs than his science. Bateson had not been among the trio to rediscover Mendel, but he made up for that by becoming the most zealous “Mendelist” in Europe. He preached the monk’s doctrines tirelessly, and even took up cigars and chess because Mendel liked them.

Bateson’s letter explained to Garrod that alkaptonuria fit the pattern for recessive genetic disorders, which are caused by inheriting two defective copies of a gene. Like almost all creatures, human beings have two copies of each gene (one from mom, one from dad), so if one of the pair sputters, you have a backup.* Only if both crap out are you in trouble. Thankfully, inheriting two bum copies isn’t common—unless, Bateson explained, your parents are closely related. Garrod’s clinical observations dovetailed beautifully with Bateson’s theoretical insight, and the alkaptonuria gene became the first gene identified in humans. Scientists have since traced the culprit to chromosome 3.

Inspired by this discovery, Garrod went on to identify albinism and other recessive disorders in humans. The work also roused Bateson, but for different, darker reasons. It’s almost forgotten today, but early-20th-century biology suffered through a period of massive confusion regarding evolution. While most biologists at the time agreed that evolution occurred, they disparaged Charles Darwin’s theory for how evolution occurred: natural selection. Indeed, Bateson and others had long been working to undermine Darwinism, and felt emboldened by the alkaptonuria finding.

These biologists had some sound scientific reasons for disliking Darwin. Most important was a disagreement about the pace of evolution. Darwin had always emphasized the similarity among most creatures in a population. All that separated A from B was a few inches, or a few IQ points. Darwin nevertheless argued that natural selection, when compounded over many generations, could stretch those tiny differences into large ones and eventually produce new species. Other biologists didn’t buy that. They favored leaps—new species emerging all at once. How else to explain how men evolved from monkeys?

Darwinism also had something else working against it: emotion. People hated the idea. Starvation and death seemed to be of paramount importance, with superior types always crushing the weak. Darwinism violated the progressive ethos of the young century, and even by 1904, one German biologist could cackle, “We are standing at the deathbed of Darwinism, and making ready to send the friends of the patient a little money, to ensure a decent burial.”

In this context, genetics—a term coined by Bateson in 1906—seemed far more important than natural selection, because it better explained where new, potentially advantageous traits came from. As one wag said, natural selection might explain the survival, but not the arrival of the fittest. Mendel’s work did explain the arrival: So-called mutations (whatever those were) changed genes and caused new traits to emerge. Moreover, Mendel’s peas had shown signs of big leaps—he found only tall or short stalks, yellow or green peas, nothing in between. Many biologists believed that these leaps might cause new species to emerge instantly, and this theory therefore sidestepped all the murder and starvation that Darwin seemed to require. Happily, the alkaptonuria work proved that the same laws of genetics applied to humans.

This period became known as the eclipse of Darwinism, and with every year that passed, Darwin had fewer defenders. About his only champions were a group of mathematically minded biologists called biometricians, who believed in Darwin’s slow-but-steady version of evolution. But Bateson—who could be a nasty SOB—soon went to work on them. One biometrician, Walter Weldon, had actually been Bateson’s mentor once, but Bateson showed his gratitude by joining a scientific society that funded biology work, then cutting Weldon off. When Weldon died in 1906, his widow publicly blamed Bateson’s rancor for the death, even though Weldon died from a heart attack while riding a bicycle. Meanwhile, a Weldon ally, Karl Pearson, blocked Bateson’s papers from appearing in journals, and also attacked Bateson in his (Pearson’s) house organ, the journal Biometrika. When Pearson refused Bateson the courtesy of responding in print, Bateson printed up fake copies of Biometrika, inserted his response inside, and distributed them to libraries and universities without any indication they were fraudulent. A limerick current at the time ran, “Karl Pearson is a biometrician/ and this, I think, is his position./ Bateson and co./ hope they may go/ to monosyllabic perdition.”

Bateson and co. relished the idea of banishing Darwin to the same historical obscurity that Gregor Mendel had once known. Of course, that never happened, thanks largely to a group of biologists at Columbia University, who put some overripe bananas on a windowsill one day in 1907 and started the most productive period in genetics history by capturing a few fruit flies. As I explain in The Violinist’s Thumb, the leader of this fruit fly group—Thomas Hunt Morgan—was probably the most unlikely savior Darwin could have hoped for. Morgan in fact thought that both natural selection and genetics sounded like bunk. But almost against his will, Morgan and his disciples proved that the small differences Darwin had championed, when combined with genetic insights from Mendel, could indeed create men from monkeys.

Geneticists had threatened Darwin with everything they had, but their challenge ultimately made Darwinism stronger. And within a few decades of discovering that first human gene on chromosome 3, geneticists had laid down the bedrock of modern biology.

Correction, July 23, 2012: The article originally stated that all creatures are have two copies of each gene. This is not always the case. (Return to the corrected sentence.)