A complex study on various evolutionary peculiarities of the mammalia dispersed 
Alu repeats (Alu repeats of primates and B1 of rodents) has been carried out by 
phylogenetic analysis. A phylogenetic tree, containing the 7SL RNA genes and the 
Alu repeats of primates and rodents has been constructed. It has been shown that 
the branch of the phyletic line leading to the Alu repeats of primates and B1 of 
rodents from the 7SL RNA genes occurred after the divergence of the 7SL RNA 
genes of amphibia and mammalia, but before the divergence of the 7SL RNA genes 
of primates and rodents (250.10 years ago). A statistically reliable slowing 
down in the evolutionary rates of one of two monomers for the human Alu repeats 
has been proved. It may be caused by the functional load of the corresponding 
monomer in connection with the presence of a definit regulatory site in it.