It’s hard to overstate just how brilliant and huge an idea Charles Darwin’s theory of evolution by natural selection was and continues to be. It absolutely rocked Victorian England, to the extent that stuffy old Victorian England could be rocked past people just barely raising their voices in polite protest. But some folks, particularly highly religious types, weren’t too happy with the idea that nature can run perfectly fine on its own, without the guiding hand of a higher power. Not happy in the least bit.
But contrary to popular belief today, scientists were kicking around the idea of evolution before Darwin—even Charles' grandpa, Erasmus, alluded to it in verse, like a true OG. Charles' contribution was specifically the natural selection bit, that organisms vary, and these variations can better suit individuals to their environment, thus boosting their chances of passing down these traits to future generations. (Weirdly, Darwin's friend, the brilliant naturalist Alfred Russel Wallace, had arrived at the same idea independently at around the same time. The two presented their preliminary findings to the Linnean Society of London, before Darwin blew the lid off the whole thing with On the Origin of Species.)
There was a bit of a problem with all of this natural selection stuff, though: Darwin didn’t know how it, uh, worked. Offspring had a mix of their parents’ features, sure. But how? What was going on at the moment of conception? It was a huge hole in Darwin’s theory of evolution. So in 1868, almost a decade after he published On the Origin of Species, Darwin tried to plug that hole with the theory of “pangenesis,” a wildly wrong idea that goes a little something like this:
Every cell in our bodies sheds tiny particles called gemmules, “which are dispersed throughout the whole system,” Darwin wrote, and “these, when supplied with proper nutriment, multiply by self-division, and are ultimately developed into units like those from which they were originally derived.” Gemmules are, in essence, seeds of cells. “They are collected from all parts of the system to constitute the sexual elements, and their development in the next generation forms a new being.”
Because both parents contribute these cell seeds, offspring end up blending the features of mom and dad. But what about a child exhibiting more features of one parent than the other? This comes about when “the gemmules in the fertilized germ are superabundant in number,” where the gemmules “derived from one parent may have some advantage in number, affinity, or vigor over those derived from the other parent.” In other words, they kinda just put more effort into it.
Gemmules must develop in the proper order to build a healthy organism. When something glitches along the way, though, you get birth defects. “According to the doctrine of pangenesis,” Darwin wrote, “the gemmules of the transposed organs become developed in the wrong place, from uniting with wrong cells or aggregates of cells during their nascent state.”
But most important of all, Darwin’s theory of pangenesis could finally explain variations among organisms—the raw fuel of evolution. This has two causes. First, "fluctuating variability" comes from “the deficiency, superabundance, and transposition of gemmules, and the redevelopment of those which have long been dormant." In other words, they're expressed in a grandchild after skipping a generation, though the gemmules themselves haven't "undergone any modification."
>Darwin’s theory of pangenesis could finally explain variations among organisms—the raw fuel of evolution.
The second touches on a now discredited theory of Lamarckism, which argued that traits an organism acquires during its lifetime, perhaps because of environmental factors, can then be inherited by its young. Darwin believed gemmules could be altered during an organism's lifetime, and these newly altered gemmules could multiply and supplant the old ones. (Lamarckism is dead, but some modern scientists argue that because behaviors like your language are acquired, this represents nongenetic inheritance that can change the course of an organism’s evolution. But it’s still quite a controversial subject that we needn't get into here. Those interested should read this good primer on the topic.)
So to sum up: Gemmules are seeds of cells that you get when your parents conceive you. They must form in the proper order to build a healthy organism, and the way they mix results in variations. Some gemmules can lie dormant, resulting in traits that skip generations, or change over an organism's lifetime, resulting in offspring inheriting traits that their parents had developed due to environmental factors.
Any theory needs a solid experiment, and that fell to Darwin’s cousin, Francis Galton. To prove gemmules induce variation, he took the blood of one rabbit and injected it into another, with the idea that the offspring of the latter would show traits of the former. In his essay “Darwin and Heredity: The Evolution of His Hypothesis of Pangenesis,” Gerald Geison writes: “These experiments, like all that followed, failed utterly to confirm Darwin's view; and when, in addition, the idea of the inheritance of acquired characters became discredited, Pangenesis was rapidly swept out of court by more satisfying explanations.”
“As a result,” Geison adds, “Pangenesis has often been looked upon as one of those mysterious and inexplicable failures of genius. Perhaps because they wish to present only Darwin's genius, several of his biographers fail to mention Pangenesis at all.”
I’ve said it before in this column and I’ll say it again: Being wildly wrong is perfectly healthy in science, because when someone comes along to prove that you’re wrong, that’s progress. Somewhat embarrassing progress for the person being corrected, sure, but progress nonetheless.
The real logic behind genetics was first discovered, oddly enough, by a monk and his pea plants in the 1850s, just as Darwin was preparing On the Origin of Species. By breeding these plants and recording how traits get passed down from generation to generation, Gregor Mendel noticed that offspring weren’t simply a blend of their two parents, as biologists had reckoned at that time. The offspring of a plant with smooth peas and another with wrinkled peas, for instance, wouldn’t itself have kinda-wrinkled peas, but either full-blown smooth or wrinkled peas. This is what we now refer to as dominant and recessive alleles, or versions of a particular gene: If you have blue eyes, for instance, you’re expressing a recessive allele, and if you have brown eyes, it’s the dominant trait. This happens because you get two copies of each gene, one from your mother and another from your father.
“Hey dudes, I found this cool thing here,” Mendel may have said, to the deafening sound of crickets. No one gave a hoot about his work. It wasn’t until 1900 that his research was rediscovered by botanists, kicking off the age of genetics. Soon scientists had figured out that it was DNA that held the information that gives you your many traits, and in 1953 Watson, Crick, and colleagues finally gave it a shape: the famous double helix.
We now know that inheriting traits has nothing to do with gemmules mixing together. We of course get our DNA, which contains genes, from both our mother and father. But these are combined in unique ways at each conception, leading to variations even among siblings. Variation can also come from mutations: When our cells divide they frequently make copies of their DNA that don’t always come out perfect (you probably have a whole lot of mutations that you don’t even notice). So these mutations, combined with genetic shuffling at birth, drive variations and therefore evolution: Some individuals are born with traits that may suit them better to their environment, which boosts their chances of surviving and breeding and passing those genes to future generations.
Darwin took a swing at the problem of inheritance and missed, sure, but let’s keep in mind that he was also responsible for what is arguably the greatest theory ever: evolution by natural selection. He just didn’t live long enough to see the final piece, genetics, fall into place (well, the final giant piece, I should say—we still have much to learn about evolution).
And isn't it at least a little bit comforting to be reminded that even the greatest minds in history can muck things up? It sure is for me, considering that up until recently I didn't know that avocados were fruits. I mean, who saw that coming?
References:
Darwin, C. (1868) "Provisional Hypothesis of Pangenesis." The Variation of Animals and Plants Under Domestication. London: John Murray
Geison, G. (1969) "Darwin and Heredity: The Evolution of His Hypothesis of Pangenesis." Journal of the History of Medicine and Allied Sciences. (4):375-411
