52 AFRICAN GAME ANIMALS 



from that of the lower zones, and is closely allied to that 

 of the north temperate zone, from which source it has evi- 

 dently been derived. The heaths, hypericums, alchemillas, 

 junipers, and brambles are the chief groups of northern 

 derivation. It is possible that some of these reached East 

 Africa from the Mediterranean region by way of the ranges 

 flanking the Red Sea and the Abyssinian highlands. The 

 region, however, is widely isolated from such a source, being 

 without connecting mountain chains and having the great 

 barrier of the Sahara Desert between. These northern 

 species have, no doubt, reached central Africa at various 

 times as strays, wind-borne, or by migratory birds or oth- 

 erwise. It is scarcely conceivable that they could reach 

 the region by progress through the lowlands at some time 

 when the climate may have approximated that of southern 

 Europe. Moreover, we have no evidence of the climate 

 having been any colder to any considerable degree during 

 any past period in tropical Africa. A small element of the 

 alpine flora has ascended the mountains from the plains 

 below. The groundsels, lobelias, bamboos, and grasses are 

 examples of this sort. A strong argument of the accidental 

 acquiring of the present flora is the fact that not a single 

 northern type of mammal exists on the high mountains. 

 This is not likely to have been the case had northern plants 

 been able to reach the region by way of the lowlands. The 

 species of mammals which occur at high altitudes have all 

 been derived from the lower levels. None of these show 

 more than a slight amount of specialization, notwithstand- 

 ing the great climatic and environmental changes to which 

 they are now subject. It is evident that the lack of any 

 marked physical characteristics in the mammals of the 



