Explores the differences between the perspectives of embryology and genetics, explaining that the development of molecular biology and the rise of ibodibo in the 1970s led to a convergence of the two disciplines. Going forward, evolutionary biology needs to take an integrative research direction.
The discussion of ‘ontogeny’ is one of the hottest topics in the life sciences, from ancient civilizations to the present day. In particular, the discussion of where and how life came into existence dates back to the time of the ancient Greeks, as evidenced by Aristotle’s De Generatione Animalium, one of his books on biology. At that time, academics made a big deal about the development of animals, mainly through anatomy, and the flexible relationship between biological phylogeny and evolution. This is important because it is a discussion that can serve as the basis for most areas of research in evolutionary biology.
After Darwin published On the Origin of Species, the field of evolution was born, and it merged with other areas of biological research, such as genetics and embryology, to spawn a plethora of discussions. Ironically, however, genetics dominated the discussion of emergence, and embryology was not readily accepted by the academic community. Until the development of molecular biology, embryology was rejected as a discipline based on philosophical discussions because it was difficult to prove mathematically, and the phenomenon of “emergence” could not be scientifically proven.
But is embryology really without scientific value in the discussion of development and evolution? With the advent of molecular biology in the 1970s, along with the development of Ibodibo, the perception of embryology began to change and the direction of research in evolutionary biology began to change. In this article, I will first discuss what information embryology has, and then discuss the rehabilitation of embryology’s reputation and the desirable direction of research in evolutionary biology that occurred with the advent of Ibodibo in the 1970s.
First, let’s look at what makes emergence informative and how emergent processes are controlled. In general, according to most biological texts, the resource that holds the information of development is “genes.” In fact, the academic community studying evolutionary biology has given genes a privileged position in the study of development and made it a major field of research. However, some people interpret that genes cannot be said to hold the information of development because the process of development requires not only genes but also other environments in the cell, such as the organelles in the cell, the proper distribution of chemical concentrations in the cytoplasm, and the methylation of DNA. Furthermore, since these environmental factors are transmitted through generations just like genes, they argue that environmental factors also carry developmental information and play an equal role in the developmental process along with genes. In other words, they argue that it is not only genes that are the unit of evolution and the resource of development, but also the ‘developmental system’ that includes the intracellular environment. On these grounds, arguments have been made since the mid-to-late 20th century to change the tendency of academia to focus exclusively on genes to a more complex study of the developmental system. Given that biology is the study of the interaction of many complex factors, this is a compelling argument. However, embryology failed to emerge as a major field of study in academia and was overshadowed by geneticists. So what are the geneticists’ arguments?
Geneticists argue that the information for development comes from genes rather than external factors such as the surrounding environment. So let’s take a moment to clarify where the information for development comes from by looking at the relationship between genes and phenotype. The relationship between genes and phenotype is quite complex, and can be broken down into four cases. The two extreme cases are that the phenotype depends only on the genotype and the environment has no effect, and that the phenotype depends only on the environment, so that whatever the genotype is, it is only affected by the acquired environment. The other two cases are a compromise: the first is that the environment cannot overcome the difference in genotype, but in the same environment, the phenotype of two individuals with different genotypes will be consistently different, and the second is that the influence of the environment is greater, so that even if the genotypes are different, the influence of the environment can reverse the difference in genotype.
In the real world, most phenotypes in nature appear to be the first of the tradeoffs, or “spurious interactions,” meaning that the relationship between genes and phenotypes is due to interactions between genes rather than other external environmental factors. Other established concepts of phenotypes, such as polygeny and pleiotropy, also support the idea that phenotypes are the result of interactions between genes.
To summarize the arguments of geneticists from the above evidence, we can conclude that genes carry the information about development. Of course, as mentioned earlier, the intracellular environment is used as a resource for normal development, but given that the relationship between genes and phenotypes is determined by the interactions between genes, and that it is genes that control development, it can be said that genes hold the primary information about development. To use an analogy, when analyzing the motion of free fall, physicists consider only gravity without considering other forces, such as air resistance, and so on, so it is possible to explain development by considering only genes.
The differences between embryologists and geneticists were simply a matter of perspective, but as mentioned earlier, genetics was the mainstream field of study in academia, and this contributed to the lack of integrated research in biology, especially in evolutionary biology. However, after the development of molecular biology in the 1970s and 80s, both fields advanced by leaps and bounds, and the direction of research in biology entered a new phase.
At the end of the 20th century, advances in molecular biology led to the discovery of homeoboxes, or genes that control the development of organisms. This had a tremendous impact on the scientific community because, while not true in all cases, one of the homeoboxes, the hox gene, showed remarkable compatibility across distant species. Take the example of the gene that controls the development of the eye: in fruit flies, a gene called eyeless, and in vertebrates, a gene called Pax6. What happens when you cross the eyeless gene into a mouse embryo or the Pax6 gene into a fruit fly embryo? Surprisingly, the mouse embryos develop normal mouse eyes and the fruit fly embryos develop normal fruit fly eyes. This is because genes like Pax6 and eyeless are master control genes, acting as switches to regulate the differentiation of cells early in embryogenesis. These discoveries provide a crucial hint to the most fundamental question of development: why can a single fertilized egg differentiate into many different complex adults?
With the advent of molecular biology, embryology also came into the limelight, as previously there was no scientific basis to explain embryogenesis, but the discovery of embryogenic genes, such as the Hox genes, by molecular biology led to the identification of some mechanisms for embryogenesis. From the 1990s onwards, a new field, Evo-Devo, was created, and embryogenesis was brought into the mainstream of evolutionary biology, attempting to link embryogenesis and evolution. In the early 20th century, when Darwin’s theory of natural selection was in crisis due to the assertion that mutations could not be the cause of evolution, population genetics reasserted the theory of natural selection and led to the integration of natural selection and genetics, the modern integration. With the discovery of ontogeny and the emergence of evo-devo, ontogeny seized the opportunity to be integrated into the modern integration.
Now that we’ve seen that developmental sources of information and advances in molecular biology have led to the convergence of genetics and embryology and the emergence of ibodibo, where does evolutionary biology go from here? Until now, evolutionary biology has focused on the study of genes rather than the study of evolution and development, because, as mentioned earlier, genes hold most of the information about development and the evolutionary process. However, with the discovery of developmental genes and the emergence of ibodibo, it is time to integrate genetics, embryology, natural selection, and other fields without separating them. Not only should genes be studied, but also embryology, which was once criticized as metaphysical and based on philosophical premises, should be studied further through ibodibo. After the modern synthesis of natural selection and genetics, if we complete a synthesis that also incorporates embryology, we may be able to find answers to many of the fundamental puzzles of evolutionary biology.
