Developmental biology including embryology is proposed as "the stem cell of biological disciplines. Moreover, developmental biology continues to roll on, budding off more disciplines, while retaining its own identity.
While its descendant disciplines differentiate into sciences with a restricted set of paradigms, examples, and techniques, developmental biology remains vigorous, pluripotent, and relatively undifferentiated. In many disciplines, especially in evolutionary biology and oncology, the developmental perspective is being reasserted as an important research program.
Citation: Gilbert SF Developmental biology, the stem cell of biological disciplines. PLoS Biol 15 12 : e This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: As the author of a developmental biology textbook, I acknowledge that I desire courses in developmental biology to be mandatory for all biology majors and pre-meds. Citation lists are political documents, I had argued. Furthermore, a history of a new field should explain why the field arose. It might even have a mythos, a narrative theme for its origin story.
The student asked if my account of the history of evolutionary developmental biology had an underlying narrative and, if so, what it was. But genetics arose out of embryology, and eventually, evolution came to be seen as a proper subset of population genetics. Genetics displaced development as the way to study evolution.
In my narrative, evo-devo represents the return of developmental biology to its rightful place as the means to study evolution. Nobel Prizes and other awards for discoveries in developmental biology are often cast even in scientific journals as breakthroughs in genetics or in stem cell biology. As should be clear by now, I have indeed wondered why developmental biology has been overlooked and am playing with a hypothesis to explain why. I propose that developmental biology and its parent discipline, embryology has been the stem cell of biological disciplines.
Developmental biology, it should be noted, is a twice-named discipline. In the s, the term was coined by Paul Weiss and N.
Berrill to include the parent discipline, embryology, as well as the study of adult stem cells and nonembryonic development, such as budding and regeneration. This was the impetus for the journal Developmental Biology. It was named again in the s, for the annual series, Current Topics in Developmental Biology , where it was seen as the molecular approach to embryology. So, let us begin with the cell theory. In the mids, the study of embryos gave rise to various theories of cell formation. But where do these cells form?
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By the turn of that century, Eli Metchnikoff and other embryologists, looking for the sources and roles of the mesoderm the middle cell layer of embryonic embryo , formulated the first approaches to immunology. Metchnikoff had found that the mesodermal cells of the starfish embryo budded off from the gut-producing endoderm and were capable of their own intracellular digestion, phagocytizing foreign bodies inserted into the larvae.
His discovery led to the first hypotheses of cellular immunity [ 8 ]. Thus, by , embryology had already given rise to cell biology and immunology. Shortly thereafter, the gene theory was constructed by embryologists who had been embroiled in debates over what part of the embryo—the nucleus or the cytoplasm—controlled development. In the early s, embryologists Theodor Boveri and E. Wilson believed that the nucleus, especially the nuclear chromosomes, carried the instructions for organismal development.
In contrast, embryologist Thomas Hunt Morgan who had written a monograph on the embryology of the frog egg favored the cytoplasm [ 9 ]. By , Morgan [ 10 ] inadvertently obtained the evidence that chromosomal genes were necessary for the production of inherited traits. He had hoped to prove otherwise.
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As a student of both biology and religion in college, it struck me how the rise and separation of genetics from embryology, and the disparagement of the parent discipline by some of the acolytes of the new discipline, echoed the supersessionist rhetoric of Christianity as it separated from Judaism. Even more interestingly, some of the founders and critics of early genetics seemed to think so, too [ 12 ]. Genetics was to replace embryology.
There were many reasons for the dominance of genetics during the 20th century, not the least of which were the destruction of the Continental European laboratories during the two World Wars and the fear of mutations caused by the detonation and testing of atomic bombs [ 14 , 15 ].
As English replaced German as the language of science, so genetics replaced physiology and development, including theories of development as the motor of evolution. In fact, Darwin explicitly viewed plant biodiversity as being predicated by alterations of floral development [ 18 ]. He also noted that natural selection could not produce the variations that provided the raw material for natural selection [ 18 — 20 ]. Evolutionary biologists such as Huxley and Herbert Spencer were greatly influenced by embryologist K.
That view shifted with the advent of genetics. This was important because it would quiet both the Creationists in America and those scientists who favored Lysenko, the leader of Soviet biology, who embraced a Lamarckian theory of acquired heritability [ 27 ]. Embryology had given rise to the first mechanistic theories of evolution, only to be usurped by its rebellious child, genetics. Evolutionary developmental biology is now emphasizing that the emergence of new phenotypes occurs during embryonic development, and that developmental regulatory genes are crucial for evolution.
Evolutionary biology cannot explain evolution by population genetics, alone. Knowledge of development is critical in explaining the origins of species. And this, as I explained to the graduate student, is the return of the rightful sovereign. Neurobiology similarly has an embryological pedigree, and in the early s, one of its biggest concerns was whether the axon was really a cellular process that extended meters in the body.
In the s and s, those embryonic laws were beginning to be explained by morphogenetic fields, and as early as , C. Waddington [ 32 ] claimed that cancers could be studied as derangements of morphological fields established in the embryo. Tumors were seen as recapitulations of or truncated stages of normal development, and oncology emerged from the work of developmental biologists studying how misregulation leads to aberrant growth.
During the mid-to-late 20th century, there was a fascinating reciprocal interaction between the two disciplines, as developmental biology provided mechanisms for cancer growth and cancer biology became a niche in which developmental biology could be nourished i. Scientists such as T. Boveri, G. Pierce, and R. Auerbach used embryological means to study tumors and used tumors to study embryology.
The breakthroughs in cloning were done on cancer grants to study gene regulation [ 35 ]. Yet, genetics soon assumed dominance over the field of cancer research just as it had with evolutionary biology whose paradigms cancer biologists often propose for their own field. The founding document of the genetic somatic mutation theory of cancer appears to be that of Boveri [ 36 ].
Boveri was very much a cytologist and an embryologist, and he related the anomalies of cancer to those developmental anomalies caused by polyspermy and by chromosome elimination during nematode development, noting that such chromosomal rearrangements might be the cause of cancer. This was a later addition, probably by Morgan. The somatic mutation theory SMT still holds sway, claiming that cancer was due to mutations in the premalignant cell. This failure to gain traction for a developmental approach to cancer is more likely due to the inability of the target to respond.
But things may be changing. The basis for the allele-oriented SMT has recently been questioned [ 39 — 41 ], and the relevance of embryonic fields to cancer has been re-established [ 38 — 44 ].
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Alterations in paracrine factor signaling in both the target and producer cells have been seen to initiate cancer formation, and embryonic processes such as epithelial-mesenchymal transformation are now seen as critical in metastasis. It is without question, though, that developmental biology helped establish oncology and has continued to help mold it. The rightful sovereign returns. Having generated cell biology, immunology, genetics, neurobiology, and oncology, developmental biology still seems to be budding off new disciplines.
Evolutionary developmental biology sees evolution as Huxley did, as changes in development rather than changes in allele frequency and focuses on the arrival of the fittest. Ecological developmental biology sees the environment as having instructive as well as permissive agency in normal development. Systems biology, which began with embryologically oriented philosophers such as Woodger and von Bertalanffy [ 45 — 47 ], attempts to fuse developmental biology, ecology, and physiology into an integrative science of becoming.
And other new disciplines are struggling to form an identity separate from their developmental parent discipline.
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Stem cell biology has its own meetings, its own journals, and its own professional societies, different from those of developmental biology. When Irving Weismann, one of the founders of the International Society for Stem Cell Research, became president of that organization, he threw down the gauntlet to developmental biology, saying [ 48 ],. Like anything new, we are a threat to the established order, and at every kind of educational and research institution, to thrive, we must be recognized as entities, not as divisions of old entities. But it is not yet a truly independent field, as it has yet to propose anything different from developmental biology.
All the articles in Stem Cell Reports are papers that would find a home in journals of developmental biology.
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At the moment, stem cell biology is a political, rather than an intellectual, bud from developmental biology, and it is performing important services in creating science-based educational accessibility and political guidelines, which the developmental biology societies have not done. Whether it becomes more than a medical aspect of developmental biology remains to be seen.
There are three main messages of this essay. The first is that developmental biology is not a confined, specified discipline—such as genetics, cell biology, immunology, oncology, neurobiology, and so forth. Developmental biology is not confined to any level of organization in that genes, cells, tissues, organs, organisms, and ecosystems can each be studied developmentally.
It can be studied in any species, organ system, or biome. Developmental biology remains pluripotent.
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The descendants of developmental biology—cell biology, genetics, immunology, neurobiology—are more differentiated and their potency much more restricted. They have boundaries. Surely, developmental biology has its own set of questions, perhaps the best questions of any science—How does the brain form?