The reasons are not far to seek.  The physical conformation of no other continent is so unfavorable for exploration and development.  Africa’s straight coast-lines, affording little shelter to the primitive ships of early mariners, repelled the enterprising Phoenicians and other seafarers in their eager search for new lands worth colonizing.  Nor was it easy for explorers to penetrate into the interior.  In its surface Africa has been compared to an inverted saucer,—­the high plateaus occupying most of the interior descending to the sea by short, abrupt, and steep slopes, so that the wide and peaceful rivers of the plateaus are lashed into foam as they approach the ocean by many series of rapids and cataracts.

In all the other continents rivers have been the lines of least resistance to the advance of man.  Civilization has developed first along the great rivers.  The valleys were first settled, and up these valleys man carried his industries and commerce far inland.  Thus the Euphrates and Tigris of Mesopotamia, the Ganges and Indus of India, and the Hoang and Yangtse of China, were the creators of history; but this is true in Africa only of the Nile.  All the other rivers have been impediments instead of helpful factors in the formidable task of exploration and development.

The trying climate, also, gave Africa odious repute and delayed for centuries the study and utilization of the continent.  When the British expedition under Captain Tuckey attempted to ascend the Congo, in 1816, to see if it were really the lower part of the Niger River, as had been conjectured, nearly all of its members perished miserably among the rapids less than two hundred miles from the sea.  Such tragedies as this paralyzed enterprise in Africa until white men learned that the climate was not so deadly, after all, if they adhered to the manner of life, the hygienic rules, that should be observed in that tropical expanse.

In all the other continents, also, explorers have had the advantage of domestic animals to carry their food and camp equipment; but in large parts of tropical Africa the horse, ox, and mule cannot live.  The bite of the little tsetse fly kills them.  Its sting is hardly so annoying as that of the mosquito, but near the base of its proboscis is a little bag containing the fatal poison.  Camels have been loaded near Zanzibar for the journey to Tanganyika, but they did not live to reach the great lake.  The “ship of the desert” can never be utilized in the humid regions of tropical Africa.

The elephant is found from sea to sea, but he has not proved to be so amenable to domestication as his Asian brother.  He may yet be reduced to useful servitude.  The efforts in this direction in the German and French colonies are somewhat encouraging, though in 1901 only six elephants had thus far been broken to work and were daily used as beasts of burden.  Explorers of tropical Africa have always been compelled to rely upon human porterage, the most expensive and unsatisfactory form of transportation, with the result that nearly all the great lines of exploration have been extended through the continent at enormous cost.