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PERSPECTIVES
T. H. Morgans resistance to the chromosome theory
Keith R. Benson
The history of science often emphasizes the great discoveries, but neglects to mention that many aspects of these discoveries were frequently known in advance. Such was the case for the chromosome theory of inheritance. Although the behaviour of the chromosome in fertilization and cell development was known before Thomas Hunt Morgans work, its role in the inheritance of particulate traits was not appreciated. Morgans relationship with the chromosome theory of inheritance provides a good case study to illustrate how theoretical issues can both impede and facilitate science.
Thomas Hunt Morgans acceptance, in 1910, of the chromosome as the carrier of heritable traits has been hailed as one of the most important scientific discoveries of the twentieth century1. But historical accounts of Morgans contributions to the emerging discipline of genetics often omit the reason it took biologists so long to appreciate the role of chromosomes in inheritance. After all, chromatin material had been identified over 30 years before Morgans work on Drosophila, the behaviour of the chromosomes in mitosis and meiosis had been well researched, and the association of the so-called accessory (sex) chromosomes with sexual dimorphism had been described. But many descriptions of Morgans work have neglected the historical context of the period from 1880 to 1910, making the development of chromosome theory seem inevitable.A much more satisfactory history is obtained by critically evaluating not
only the growing empirical evidence for the role of chromosomes in inheritance, but also by examining the theoretical milieu in which the empirical studies were embedded. In this manner, we can appreciate the powerful hold of theory over scientific practice, as well as the important conceptual shift that accompanied Morgans seminal work.
Blending inheritance and variation
Like so many new scientific ideas, the chromosome theory of Mendelian heredity had to overcome well-entrenched conceptual obstacles. That is, for all of the nineteenth century, ideas of inheritance and variation (the two concepts were inextricably bound together during the 1800s) depended on the notion that whatever was passed from parent to offspring had to be contained in the (male and female) seminal material2. The offspring, accordingly, was the result of the mixture of these blended materials. This idea, referred to as...