35 



PAST<- 



-+■ PRESENT 



Figure III-4.- Genealogical trees can be deduced from molecular-sequence 

 information. Each box in the figure represents an organism, and the numbers 

 indicate how many of the building blocks of a 200-block-long molecule in the 

 organism are in the same arrangement as this molecule in organism A. Thus, the 

 molecule in question in organism B has many building blocks (190) in an 

 arrangement identical to organism A's molecule. This indicates they diverged 

 from one another relatively recently. Organism D's molecules, on the other 

 hand, has fewer blocks (100) in the same order as organism A 's, indicating that 

 they diverged from one another a long time ago. Organism C exhibits an inter- 

 mediate time of divergence. 



and algae, are generally larger, more complex, and internally differen- 

 tiated (containing several types of internal organelles which them- 

 selves are related to the free-living bacteria). 



The Eukaryotes 



One evolutionary puzzle that has responded to the biochem- 

 ists' scrutiny is that of the origin of the eukaryotic cells (the 

 nucleated cells of all larger forms of life). The currently accepted 



