36 The Nature of Biological Diversity 



nitrogen, and oxygen atoms in such a chain. Figure 11 shows how the 

 helical structure can take on visible order. The upper photograph is 

 an electron micrograph of single filaments of protein which is a com- 

 ponent of collagen. When the protein filaments aggregate, as shown 

 in the lower photograph, they do so in a specific ordered array be- 

 cause of the particular arrangement of amino acids in the proteins. 

 Here you can begin to see the appearance of the visible order that 

 must be generated to create mitochondria, chloroplasts, and other 

 subcellular particles. This generation of order is, of course, common 

 to all living things and is not unique to photosynthesis. One can gen- 



FIG. 11. Electron micrograph of collagen filaments, (a) Filaments of collagen, a 

 protein which is usually found in long fibrils, were dispersed by placing them in 

 dilute acetic acid. This electron micrograph, which enlarges the filament 75,000 

 times, was made by Jerome Gross of the Harvard Medical School, (b) Fibrils of 

 collagen formed spontaneously out of filaments such as those shown above when 

 1 per cent of sodium chloride was added to the dilute acetic acid. These long 

 fibrils are identical in appearance with those of collagen before dispersion. 



erate order, beginning from the primitive molecules of the early 

 earth's atmosphere (Fig. 8), through proteins (Figs. 10 and 11) into 

 the subcellular material itself (Fig. 4) . 





Development of Rudimentary Catalysts 



Let us now turn to the question of the generation of the porphyrins, 

 which seem to be central not only to the capture of light as repre- 

 sented by chlorophyll but to the appearance of adenosine triphos- 



