Review of
Disputed Inheritance: The Battle over Mendel and the
Future of Biology. By Gregory Radick. Chicago: University of Chicago Press.
2023. xii+ 630 pp. ISBN 978-0-226-82272-3 (paper).
How We Get Mendel Wrong, and Why It Matters. By Kostas
Kampourakis. Boca Raton: CRC Press. 2024. xxi + 226 pp. ISBN 978-1-032-45690-4
(paper).
I
am a reformed Mendelian. I left the cult when I came to realize that Mendel
himself never had two laws called Segregation and Independent Assortment. That
was Thomas Hunt Morgan’s reframing of Mendel. Prior to Morgan, the first
decade-and-a-half of Mendelians referred to something nebulous and singular,
Mendel’s Law. It generally went something like this: A trait is controlled by a
pair of elements, only one of which is passed on to offspring, and one element
of a pair can sometimes suppress the effect of the other.
But
that leaves out chromosomes, polygenic inheritance, crossing-over,
co-dominance, pleiotropy, epistasis, developmental plasticity, mtDNA, epigenetics,
microbiomes, indeed most of genetics. Which in turn raises the question, are
Mendel’s Laws the rule or the exception? The attempt to make Mendel seem
relevant to an understanding of human genetics has indeed always proved vexing.
There are genes making enzymes and blood antigens, but having B-negative blood
or the ability to taste phenylthiocarbamide seem unlikely to have been major
factors in the adaptive divergence of the hominin lineage, much less in the
extinction of Neanderthals. Of course, there are also genes causing rare genetic
diseases, but they are less relevant to a general understanding of human
heredity simply by virtue of being rare. In 1940, infamously, the fruitfly
geneticist Alfred Sturtevant suggested that the ability to roll one’s human tongue
was a Mendelian trait. By 1956, he
acknowledged being embarrassed by it, but it proved too pedagogically valuable
to discard so readily. The Mendelian gene, for all its heuristic value, is
surprisingly elusive in human biology.
Gregory
Radick is a historian of biology, whose excellent 2016 book on early studies of
ape cognition, The Simian Tongue, is
itself of considerable interest to readers of this journal. Radick wants to
call our attention to W. F. R. (Raphael) Weldon, a geneticist at the base of
the Mendelian intellectual tree, who maintained that the emerging concept of a
gene was meaningless, for a gene (whatever it may be) is actually a complex and
context-dependent unit. Weldon’s untimely death in 1906, argues Radick, left
the more complex gene without a defender, and left subsequent Mendelian
discourse on a much more simplistic (and conveniently easily politicized)
track. That track was defined by William Bateson, who was so into Gregor Mendel
that he named his first son (who later became an eminent anthropologist) after
him.
Convergently,
philosopher and biology educator Kostas Kampourakis has written several books
on genetics and evolution, and trains his sights on Mendelism as well. As a
historian, Radick is more focused on the past; Kampourakis, on the other hand,
is more interested in the future. Both books are at pains to dismantle the myth
of Mendel. The founding myth of genetics is that of the solitary genius,
working to discover the basis of heredity in the cloistered confines of his
monastery, disconnected from mainstream science; then deducing the rules of
particulate genetic transmission by quantifying his results; and summarizing
them in two Laws, Segregation and Independent Assortment (Dagher 2014). He understood before anyone else that a
genetic factor is responsible for a visible character, and it enters the next
generation probabilistically. Alas, his work went unnoticed and thus
unappreciated until 35 years later, when it was noticed, and belatedly
constituted the foundation of our understanding of heredity – albeit with most
of our understanding of heredity as exceptions. There have been, naturally,
some geneticists who have pushed back in various ways against the reductive
Mendelian fallacies at the center of 20th century genetics: notably,
from center-left to far-left: Sewall Wright at Chicago, Conrad Waddington at
Edinburgh, Richard Lewontin at Harvard, and Trofim D. Lysenko in Moscow.
Kampourakis
highlights Mendel’s education and connectedness within the community of
scholars, especially with Carl Nägeli, a Swiss experimental botanist. Mendel
himself was interested in genetics only insofar as it related to hybridization,
and he knew that his results were not particularly generalizable. Moreover, the
20th century was well underway before anyone at all was talking
about two laws, Segregation and Independent Assortment. Kampourakis also paints
with broader strokes than Radick, whose book is primary research in the history
of science, with the depth and focus that comes with that territory. Both books
are readable, and tell familiar and unfamiliar stories in readily
understandable ways. Radick’s book is devoted in nearly its entirety to the
machinations of William Bateson in promoting and elevating a particular vision
of Mendel’s work. Radick’s denouement is
an experiment in counterfactual science history: What if Raphael Weldon hadn’t
died in 1906, but had lived to challenge Bateson’s binary, essentialist
“Mendelian gene” with a more fluid concept – a “Mendelian gene” that could be
upregulated and downregulated, interact with other genes, and whose products
could engage in a complex set of cellular, physiological, and ontogenetic
processes, eventually resulting in a phenotype?
Much
has been written on just why Mendel’s work was ignored. It focused exclusively
on heredity, when biologists still combined heredity and development, which
later became disengaged after the development of the cell theory. It was also a
paper about hybridization, not genetics. He didn’t follow it up. It was in
German. And it was about peas. Today we casually accept (and teach) that
reproduction in peas is the same as it is in humans, but that is actually only
true from the perspective of cells. And even then, only very abstractly.
Moreover, if you try to show your students videos of both species reproducing,
you may well find the perspective of lawyers, in which reproduction in peas and
people is very different, more important than the perspective of cells.
When
I was in graduate school, some people followed an old rumor in questioning
whether Brother Gregor fudged his data, on the grounds that his reported
numbers were somehow too close to the ratios he was deducing. I always thought
that was a weird argument; but to me what was weirder was that Mendel reported
on seven traits, each of which turned out to be on a different one of the seven
pea chromosomes. God must have really wanted him to come up with a Law of
Independent Assortment.
Whatever
laws he may have discovered, and whatever he may have done to discover them,
the fact remains that Mendel was adopted as an icon by the fledgling field of
genetics early in the 20th century. Students of heredity brandished
him as their standard-bearer and mythic founder in much the same way as their
recent precursors in natural history had adopted Darwin (Meloni 2016). Their
main difference would be that Darwin’s insight was recognized in his time,
while Mendel’s was not. A more sinister convergence is that both sets of
theories were readily appropriated in ways that we identify retrospectively as
evil: Social Darwinism (Hofstadter 1944) and social Mendelism (Teicher 2022).
We
don’t talk as much about social Mendelism. But the tunnel vision of seeing the
world from the perspective of cells and meiosis and fertilization eventually
led Mendelism to accumulate a lot of baggage over the course of the 20th
century. The gene for wrinkled seeds had hardly a fraction of the effect on
people’s lives that the gene for feeblemindedness had. The Mendelian gene for
beta-globin (dysfunctional in sickle-cell anemia) and the gene for
hexosaminidase A (dysfunctional in Tay-Sachs Disease), which are both very
real, lie on one side of the ledger. On
the other side are the genes for intelligence, altruism, and xenophobia, which
aren’t real, or at least aren’t real in the same way.
A
British geneticist named David Heron put it this way in 1912, critical of the
American genetical obsession with a gene for this and a gene for that,
especially when it came to psychological traits: “Mendel defectiveness
seems for these American investigators to be a far more serious problem than mental defectiveness!” (p. 54, emphasis
in original).
Obviously
we don’t want to throw out the baby with the bathwater. So what is at stake
with baby Gregor? On one side of the moral ledger are Mendel and his laws. On
the other side of the ledger is the take-home lesson from the very first
English textbook on the subject, called Mendelism:
namely, that education is bunk, and “the creature is not made, but born”
(Punnett 1905:60). On that same side is
the “unit-character fallacy,” identified by cautious geneticists a century ago
as the problem of mapping a single gene onto a single noun – such as
thalassophilia, an ostensibly genetic explanation for the Phoenicians’ love of
the sea, by an incautious but nevertheless very influential geneticist. On that
same side is also the idea that somehow you are, or are built from, nothing but
the summation of your genes, the intellectual stimulus that eventually got the
Human Genome Project rolling in the 1990s. And on that side as well is the idea
that people can be naturally sorted into discrete binaries, like wrinkled and
round peas.
So
maybe taken as a whole, Mendelism wasn’t that great of a way to think about
biological heredity in the first place, has run its course, and should be
re-thought for the 21st century. Maybe binary Mendelian genes are
simply special cases in a real world of chromosomes, RNA, pleiotropy, and
epigenetics that sometimes even manages to mimic Lamarckism. Both books
converge on a common theme: How can we teach human genetics differently and
better? For a human genetics seminar, a science studies class, or just to
rethink some of those undergraduate lectures, the two books will pair very
well.
What
might replace the Mendelian genes as units of inheritance? The physical
elements that actually do the cellular work of segregating and recombining –
namely, the chromosomes. There aren’t 20,000 independently segregating genetic
elements in a human cell, only 23. The segregating units aren’t the genes, but
blocks of genes. And within those segregating and recombining units lie units
of transcription, embedded within complex patterns of DNA, whose products may
themselves be biochemically active (i.e., as RNA), or may help produce other
biochemically active molecules in turn (i.e, as proteins). The biochemical
activity can be upregulated or downregulated by direct interaction with the
environment (i.e., epigenetically) or by mutation. And out of this often
qualitative cellular business somehow emerge quantitative phenotypes, for
phenotypes are problematic, not automatic. And what gets downplayed in such a
treatment? Those bits of phenotypic difference that automatically represent
genotypic difference – that is to say, genes for things. Those rare diseases,
like the pea examples, which are special cases.
Together,
what these books demonstrate is that there is a major change in the offing
about how we should teach the most basic facts about heredity, from centering
abstract binary elements to instead centering the actual cellular and biological
systems involved in genetic transmission. Viva la revolución!
References
Dagher, Zoubeida R. (2014) The relevance
of history of biology to teaching and learning in the life sciences: The case of
Mendel’s laws. Interchange 45: 205–216.
https://doi.org/10.1007/s10780-015-9241-y.
Heron, David. (1913) Mendelism and the
Problem of Mental Defect. I. A Criticism of Recent American Work. London:
Dulau.
Hofstadter, Richard (1944) Social
Darwinism in American Thought. Philadelphia: University of Pennsylvania
Press.
Meloni, Maurizio. (2016) Political Biology:
Science and Social Values in Human Heredity from Eugenics to Epigenetics.
London: Palgrave Macmillan.
Punnett, Reginald C. (1905) Mendelism.
London: Macmillan.
Sturtevant, A. H. (1940) A new inherited
character in man. Proceedings of the National Academy of Sciences, USA
26: 100-102.
Sturtevant, A. H. (1965) A History of
Genetics. New York: Harper and Row.
Teicher, Amir (2020) Social Mendelism: Genetics and the Politics of Race in Germany, 1900–1948. New York: Cambridge University Press.
