Necks-for-sex or competing browsers? A critique of ideas on the evolution of giraffe

摘要: Recent years have witnessed a resurgence in tests of the evolution and origin great height long neck giraffe Giraffa camelopardalis. The two main hypotheses are (1) necks evolved through competition with other browsers allowing to feed above them (‘competing browsers’ hypothesis); or (2) for direct use intra-sexual combat gain access oestrous females (‘necks-for-sex’ hypothesis). Here, we review recent developments their relative contribution explaining evolution. Trends from Zimbabwean giraffes show positive allometry male isometry female body mass, while comparative analyses cervical versus total vertebral column giraffe, okapi fossil suggest selection specifically on length rather than overall height. Both support necks-for-sex idea. Neither study, however, allows us refute one ideas. We new approaches quantifying importance hypotheses. A analysis pressure via survival reproduction should clarify mechanism maintaining trait, predict that short robust ossicones arisen concurrently incipient elongation if sexual was selective driver. challenge competing browser hypothesis is explain why remained about 2 m taller tallest competitors over 1 Myr, whereas cannot provide an adaptive explanation giraffe. conclude probably both mechanisms contributed maintenance neck, can be clarified further.