Biological considerations 



Evolution and relationships 



The ancestral stock from which the honey-guides (Indicatoridae) 

 evolved was probably more similar, in a general way, to the non- 

 specialized barbets (Capitonidae) than to any other existing birds, but 

 all connections have long since completely disappeared. While the 

 honej^-guides do seem to have had a common ancestral bond with the 

 barbets, it does not necessaril;y imply that they originated in southern 

 Asia as did the barbets, according to the latest student of that group 

 (Ripley, 1945). Thus, while the honey-guides cannot be looked upon 

 definitely as immigrants into Africa from Asia, it does seem probable 

 that the family dates back at least to the time when the forest faunas 

 of Africa and India were much more closely related and connected 

 than they are at present. Although the family is more richly repre- 

 sented in Africa than in Asia and with greater generic as well as 

 specific diversity — which might be thought to imply an African locus 

 of origin and evolution — the two Asiatic species are by no means very 

 closely related to each other. The Malayan Indicator archipelagicus 

 is more similar to /. indicator of Africa than it is to the Himalayan 

 I. xanthonotus. The last-named species, with its very small, stubby 

 bill and its plumage coloration, is actually quite different from the 

 "typical" species of the genus Indicator and seems to merit the sub- 

 generic distinction given it under the name Pseudofringilla by Hume. 

 This, in turn, suggests considerable antiquity of the group in Asia, 

 making it difficult to infer, from the evidence of present forms and 

 their distribution, whether the family is to be looked upon as originally 

 African or Asiatic. 



In his reconstruction of the history of the development and distri- 

 bution of the African terrestrial vertebrate fauna, Lonnberg (1929) 

 concludes that during the early Tertiary, including the Miocene, 

 Africa had a prevailingly moist climate and was covered by a vast 

 evergreen forest.^ This forest was inhabited by a fauna largely 

 endemic to it, but containing so many types in common with that of 



1 In a paper published after the present manuscript was completed, Moreau 

 (1952) agrees that a continuous pre-Pliocene forest across Africa is a necessary 

 assumption, but considers it doubtful that Africa was suitable for a sylvan con- 

 dition at that time! As in so much evolutionary reasoning we must always remem- 

 ber the uncertainty of conclusions based on assumptions, however necessary they 

 may seem to be. 



8 



