10 
SAVAGE SUDAN 
there are genera conspicuously indigenous to the northern 
half of the continent. Gazelles, for example, begin at the 
Mediterranean, abound most in Ethiopia, but peter out 
shortly after passing the Equator. The Cob family also 
( Adenota ), together with the little dikdiks, seem typically 
though not quite exclusively Ethiopian. 
While yet busy with these chapters, I find that Darwin 
long ago summed up this matter thus (Origin of Species, 
3rd ed., p. 5):—“Who can explain why one species 
ranges widely and is very numerous, while another allied 
species has a narrow range and- is rare?” Again, at 
p. 411 :*—“ We cannot hope to explain such facts, until we 
can say why . . . one species ranges twice or thrice as far, 
and is twice or thrice as common as another species 
within their own home.” 
Surely after that no more need be said on the subject, 
save only that while fresh material has been accumulating 
during seventy or eighty years, no fresh light has been 
thrown on the problems that puzzled Darwin. 
Bird-Life in detail is described throughout this book. 
The outstanding feature in Sudanese ornithology is that 
the sequence of bird-life throughout the year yet remains 
unascertained—more so, probably, than that of any other 
explored region on earth. No fault attaches to orni¬ 
thologists : the cause lies in local climatic conditions, and 
in those physical obstacles which forbid exploration of 
the interior during spring, summer, and early autumn. 
Those periods, needless to say, normally form the 
seasons of chiefest interest; for it is during their breeding - 
time that birds reveal their secrets and when ornithologists 
garner harvests. In the Sudan no such harvests are 
possible. Nature forbids. In winter we can travel afar 
throughout the country and can see all there is to be 
seen without difficulty. But no sooner has spring come 
than torrential rains and the swollen Nile—quadrupled 
in volume by Abyssinian floods—transform the lower 
levels into one vast swamp, submerged and impassable 
