Free She Has Her Mother's Laugh: The Powers, Perversions, and Potential of Heredity by Carl Zimmer
Authors: Carl Zimmer
described himself in 1857 as a “wretched contemptible invalid.” Three of Darwin’s ten children died young, and the others suffered from bouts of poor health.
“It is the great drawback to my happiness, that they are not very robust,” he wrote to a friend in 1858. “Some of them seem to have inherited my detestable constitution.”
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Darwin put only a little of his research on heredity in The Origin of Species. Instead,he saved that profound matter for a book of its own. When he began focusing his thoughts on heredity, however, he decided that all the details he had been collecting about pigeons and insanity would not be enough. He would also have to figure out the physical process that accounted for allthe strange ways in which animals and plants reproduced.
At the time, Mendel was raising pea plants and hawkweed, but Darwin—like most scientists of his day—didn’t even know who Mendel was. Instead, Darwin drew his inspiration from other biologists who had made a profound discovery of their own: that all of life is made of cells.
To Darwin, the central question of inheritance was what sort of substances the cells of parents transmitted to an embryo so that its cells came to resemble theirs. Whatever made muscles strong was stored in muscle cells. Whatever made brains wise or defective must be stored in brain cells.
Perhaps, Darwin thought, the cells throughout the body cast off “minute granules or atoms.” He dubbed these imaginary specks gemmules.Once released by cells, gemmules coursed through the body, gradually piling up in the sexual organs. When the gemmules from both parents combined in a fertilized egg, they enabled it to develop into a blend of cells from both parents.
Darwin wanted a catchy name for this imaginary process. Maybesomething that combined cells with genesis. Darwin asked his son George, then a student at the University of Cambridge, to ask classics professors there for a name. George came back with outlandish suggestions like atomo-genesis and cyttarogenesis . Darwin settled on pangenesis .
Pangenesis set Darwin apart from most naturalists of his day. They explained heredity as a blending of traits—akin to mixing blue and yellow paint to produce green. Darwin looked at heredity instead as the result of distinct particles. They never fused and never lost their separate identities. Darwin readily admitted that pangenesis was “merely a provisional hypothesis or speculation.” Yet it offered Darwin great powers of explanation. “It has thrown a flood of light on my mind in regard to a great series of complex phenomena,” he said.
Darwin could explain why children sometimes resembled one parent more than the other with pangenesis: Some gemmules were stronger than others. The gemmules that gave rise to newborn babies were a mixture of particles that had accumulated over generations, from parents, grandparents, and on back through time. A gemmule might be overshadowed by stronger ones for thousands of years, only to leap forward and revive some ancient feature. And as experiences altered cells, they would also alter their gemmules. As a result, a trait acquired in life could be passed down to future generations.
On that last point, Darwin was simply following in a tradition that reached back over two thousand years to the writings of Hippocrates. Earlier in the nineteenth century, Darwin’s predecessor, the French naturalist Jean-Baptiste Lamarck, had offered the first detailed theory of evolution, and he had made the inheritance of acquired characteristics a crucial part. A giraffe striving to reach leaves on a high branch would force a vital fluid into its neck, stretching it. Its offspring would then be born with that longerneck, and over many generations this stretching produced the neck of the giraffes we see today.
Darwin saw gemmules as acting like Lamarck’s vital fluid. In his research, Darwin discovered thatimproved breeds of cattle grew small lungs and
“It is the great drawback to my happiness, that they are not very robust,” he wrote to a friend in 1858. “Some of them seem to have inherited my detestable constitution.”
----
—
Darwin put only a little of his research on heredity in The Origin of Species. Instead,he saved that profound matter for a book of its own. When he began focusing his thoughts on heredity, however, he decided that all the details he had been collecting about pigeons and insanity would not be enough. He would also have to figure out the physical process that accounted for allthe strange ways in which animals and plants reproduced.
At the time, Mendel was raising pea plants and hawkweed, but Darwin—like most scientists of his day—didn’t even know who Mendel was. Instead, Darwin drew his inspiration from other biologists who had made a profound discovery of their own: that all of life is made of cells.
To Darwin, the central question of inheritance was what sort of substances the cells of parents transmitted to an embryo so that its cells came to resemble theirs. Whatever made muscles strong was stored in muscle cells. Whatever made brains wise or defective must be stored in brain cells.
Perhaps, Darwin thought, the cells throughout the body cast off “minute granules or atoms.” He dubbed these imaginary specks gemmules.Once released by cells, gemmules coursed through the body, gradually piling up in the sexual organs. When the gemmules from both parents combined in a fertilized egg, they enabled it to develop into a blend of cells from both parents.
Darwin wanted a catchy name for this imaginary process. Maybesomething that combined cells with genesis. Darwin asked his son George, then a student at the University of Cambridge, to ask classics professors there for a name. George came back with outlandish suggestions like atomo-genesis and cyttarogenesis . Darwin settled on pangenesis .
Pangenesis set Darwin apart from most naturalists of his day. They explained heredity as a blending of traits—akin to mixing blue and yellow paint to produce green. Darwin looked at heredity instead as the result of distinct particles. They never fused and never lost their separate identities. Darwin readily admitted that pangenesis was “merely a provisional hypothesis or speculation.” Yet it offered Darwin great powers of explanation. “It has thrown a flood of light on my mind in regard to a great series of complex phenomena,” he said.
Darwin could explain why children sometimes resembled one parent more than the other with pangenesis: Some gemmules were stronger than others. The gemmules that gave rise to newborn babies were a mixture of particles that had accumulated over generations, from parents, grandparents, and on back through time. A gemmule might be overshadowed by stronger ones for thousands of years, only to leap forward and revive some ancient feature. And as experiences altered cells, they would also alter their gemmules. As a result, a trait acquired in life could be passed down to future generations.
On that last point, Darwin was simply following in a tradition that reached back over two thousand years to the writings of Hippocrates. Earlier in the nineteenth century, Darwin’s predecessor, the French naturalist Jean-Baptiste Lamarck, had offered the first detailed theory of evolution, and he had made the inheritance of acquired characteristics a crucial part. A giraffe striving to reach leaves on a high branch would force a vital fluid into its neck, stretching it. Its offspring would then be born with that longerneck, and over many generations this stretching produced the neck of the giraffes we see today.
Darwin saw gemmules as acting like Lamarck’s vital fluid. In his research, Darwin discovered thatimproved breeds of cattle grew small lungs and