6 I DOING SCIENCE A 127 



Some MBL embryologists, such as Whitman, were intrigued by the sort 

 of quasi-predeterminism that German biologist August Weismann sug- 

 gested in his chromosome theory of heredity, with its collection of deter- 

 minants, ids, and idants. They found equally intriguing Weismann' s and 

 Wilhelm Roux's mosaic theory of development, according to which the 

 various pieces of the developing organism act as separate bits of of a mosaic, 

 each predestined by heredity to become a particular body part. Yet they still 

 sought an in-between, essentially epigenetic viewpoint; extreme predeter- 

 minism remained a horror to most MBL scientists. Morgan, for example, 

 saw as anathema Weismann's idea that inherited germinal material (or 

 germplasm) might actually determine, in some mechanistic and prepro- 

 grammed way, how an organism develops. Such an idea is not true science, 

 he suggested, but just pushes the question of how development occurs back 

 to a "shadowy, ancestral past." Others at the MBL declared that Weismann's 

 speculations seemed as futile as "sorting snou^akes with a hot spoon " and 

 could not possibly explain how development occurs. Still others condemned 

 such predeterministic ideas as a "scientific misdemeanor." 



To the MBL researchers, it seemed obvious that the internal organi- 

 zation of the egg itself and its response to environmental stimuli direct 

 development. Inherited nature plays a role in development, of course, but 

 so does nurture — as biologists a bit later would have put it. Problems of 

 development and heredity reigned in the first years at the MBL. DNA 

 changed the picture that nineteenth-century researchers had had of the 

 undifferentiated egg, of course, and made it seem more predetermined. Yet 

 many MBL biologists today would still stress, along with Wilson, Conklin, 

 Morgan, Loeb, and others, that development is every bit as important as 

 predetermined heredity in guiding the differentiation process that turns the 

 germ into an adult. 



For the first half-century of MBL researchers the question, "does each 

 organism develop epigenetically or by preformation?" could have been 

 rephrased as: does the egg in some way already possess the organization 

 that the adult then assumes? In particular, how much is cell division of the 

 fertilized egg determinate, or fixed, and how much is indeterminate, or 

 subject to change as conditions vary? Cell biologists today pursue similar 

 questions. The laboratory of Raymond Stevens, for example, explores the 

 biochemistry of microtubules, asking what role they play in cell division and 

 cell processes. Shinya Inoue explores in detail the process of mitosis and cell 

 morphogenesis, looking at each morphological bit of the cell. Richard 

 Whittaker's group excimines the way in which the genes control cell differ- 

 entiation. Others at the MBL have extended cell lineage study to other 

 organisms, such as the nematodes, to discover exactly what each cell does 

 at each stage of the developmental process. Each of these laboratory 



