Science & Tech

Heredity and Our Fascination with It

A new book traces the history and science of a concept that resonates deeply.

Today, for less than $100, an American consumer can purchase a home DNA test kit that tells them their ancestry down to the most minute detail, matches them up with “relatives” in a database of millions, and outlines their disease susceptibilities. Though such tests are a product of our modern technological society, the impulses behind them are ancient. The first book of the Bible is Genesis, and much of it is taken up with the genealogy of the patriarchs who loom large in the Abrahamic religions. Our interest in heredity is testament to a deep human concern with generations past, and those yet to come.

Carl Zimmer’s She Has Her Mother’s Laugh: The Powers, Perversions, and Potential of Heredity tackles this vast and important topic. Zimmer’s background as a science journalist might lead many to assume that when he refers to “heredity” he means genetics. But one of the surprises of She Has Her Mother’s Laugh is that it explores the social and cultural relevance of heredity as much the genetic aspect.

The story begins with the author’s own family, a mix of Irish, English, and Jewish, and moves forward to his reflections on the birth of his daughter and the generations to come. But then Zimmer proceeds to deftly interleave his stories, both personal and political, with the development of the science of heredity.

These threads come together in Zimmer’s recounting of the importance of Henry Goddard’s 1912 book The Kallikak Family: A Study in the Heredity of Feeble-Mindedness. Goddard purported to show the pattern of inheritance of feeble-mindedness across the generations in the pedigree of this family, beginning with a young woman in his institution, given the pseudonym “Deborah Kallikak.” It traces her lineage back to one Martin, who was married to an upstanding Quaker woman but also had a dalliance with a “feeble-minded barmaid.” He went on to sire two distinct lines of descendants. Those who descended from the upstanding Quaker woman were in their own turn pillars of the community. Those who descended from the barmaid were disreputable characters. This was a morality tale garbed in heredity science.

The Kallikak Family was a very influential book. Published just six years after the science of genetics was given its name by William Bateson, it lent a scholarly sheen to the cultural currents ascendant in the United States in the early 20th century, which supported eugenics. Goddard’s work would be used to support eugenics legislation in 1914, which would eventually be held constitutional in 1927 in Buck v. Bell. This is the famous case in which Oliver Wendell Holmes Jr. concluded the majority opinion by asserting that “Three generations of imbeciles are enough.”

But there is far more, and less, to the story than what Goddard told in his book. Deborah Kallikak’s real name was Emma Wolverton. There is a fair amount of evidence that Wolverton was in fact in the normal range of intelligence; she apparently came to Goddard’s attention because of her willful personality and behavior. Further analysis of the pedigree reconstruction in The Kallikak Family also uncovered gross errors, which undercut the conclusions of heritable feeble-mindedness. In later years Goddard himself stepped back from these results, aware of the shortcomings in the science. But by then the book had already made its mark on American policy and culture.

Even before the flaws in Goddard’s science became apparent, however, cultural currents were arguably far more important in driving the debate over eugenics. During these decades, the field of genetics was discovering its very fundamentals. Where heredity has been a human concern since time immemorial, the Mendelian framework of genetic units of inheritance approached maturity only in the 20th century. Concepts we take for granted today — chromosomes, genetic recombination, and sex-linked traits — were still to be elucidated in detail.

Human genetics specifically was a little-understood topic for decades, despite the aura of rationality that it imparted to eugenic legislation. For many decades in the 20th century geneticists knew little more than the inheritance of the ABO blood groups. Even as late as the 1990s our knowledge was limited to hundreds of markers. Today we have mapped all human genes — about 19,000 of them.

Despite its horrifying conclusion, in a way Oliver Wendell Holmes Jr.’s opinion in Buck v. Bell reflected a faith in progress and rationality. The early 20th century saw the final shift of human civilization away from its pastoral and primal roots, to an age girded in metal and driven by the motive forces of electricity and oil. These engineering marvels transformed American society and were based in science. Not surprisingly, many believed that American society itself could be transformed and engineered based on the latest science. These thinkers failed to understand not only that genetic science was a primitive basis upon which to make any decisions, but also that social and ethical systems could not be improved upon in the same manner as a car improved upon the horse.

Notably, the Supreme Court’s single dissenter in Buck v. Bell was a devout Roman Catholic. Eugenic legislation often faced vociferous resistance from the Catholic Church, which as an institution did not keep up with the times.

But 2018 is not 1918. As She Has Her Mother’s Laugh moves forward to the present, and tackles the enormous complexities of heredity and biology slowly emerging before our eyes, we are confronted by too much rather than too little knowledge. Goddard’s attempts to ascertain patterns of feeble-mindedness in his pedigrees were laughable, but researchers such as Ian Deary at the University of Edinburgh are now zeroing in on numerous genes responsible for variations in intelligence. The development of a cheap and powerful genetic-engineering technique, CRISPR, opens the possibility that some disease risks might be fixed this way.

He plumbs the depths of startlingly new landscapes exposed by the latest in genetic science, all the while excavating the social and cultural landscape of a century gone by.

Where 20th-century Mendelian genetics modified our understanding of heredity, 21st-century genomics adds nuance and texture to the elegant simplicity of our previous knowledge. Some of the most bizarre and fascinating sections of She Has Her Mother’s Laugh concern genetic chimeras, individuals who are a mosaic of genetic patterns. There was the case of a woman who was not genetically related to her putative biological children, and accused of fraud and kidnapping by the authorities. As it happened, different portions of the woman’s body had different genetic signatures, and the cells that transformed into eggs were different from those that produced blood.

Even more strangely, cells of the children women bore in the past can remain present in their bodies for decades. Many women carry cells not only of their surviving children, but also from pregnancies that were miscarried. The genetic ghosts of children who never were persist in the blood of these women.

Across more than 600 pages, Zimmer covers a shockingly diverse range of topics. He plumbs the depths of startlingly new landscapes exposed by the latest in genetic science, all the while excavating the social and cultural landscape of a century gone by.

She Has Her Mother’s Laugh is a chronicle of timeless values, and the permanent importance of bonds of kinship and the passing of generations in human culture. It is also a stark caution against human hubris, as the early decades of hereditary science show just how much damage science can cause when it’s poorly done and unethically applied. Finally, it is a wondrous exposé of the rapid-fire results and advances being made in 21st-century genetics, and the social and cultural consequences that they might unleash.

Razib Khan — Razib Khan is a geneticist. His blog is Gene Expression (

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