Ying-Xue Sun, Ji-Wang Chen, Ji-Ming Chen
China Animal Health and Epidemiology Center, Qingdao, 266032, China (Ji-Ming Chen, Ying-Xue Sun); Department of Medicine, Section of Pulmonary, Critical Care, Sleep and Allergy Medicine, University of Illinois at Chicago, Chicago, IL60612, USA (Ji-Wang Chen)
Ji-Ming Chen (E-mail: email@example.com; firstname.lastname@example.org)
Anatomy; Behavior; Ecology; Evolution; Genetics; Molecular & cellular biology; Paleontology; Theoretical biology; Zoology
The origin of the striking height of the giraffe has intrigued many biologists and non-scientists, and it has been a subject of debate for centuries. In this study, we provided a systematic review of the past debates on this topic, as well as presenting some novel views by synthesizing data from anatomy, behavior, dynamics, genetics, paleontology, and physiology. First, different from previous hypotheses which all emphasized a single factor, we proposed that the striking height of the giraffe possibly resulted from and is maintained by the interaction between sexual and non-sexual selection constraints. Possibly after the animal’s stature reached a considerable height, non-sexual selection constraints began to inhibit further increases in the height, whereas sexual selection constraints further increased the height to a striking degree. Second, as extrapolated by recent genetic studies of human height, giraffe height is probably determined by many loci located on autosomes; thus, although adult female giraffes are significantly shorter than adult male giraffes, they are also very tall as a by-product of sexual selection. Third, we explained why absences of certain gender differences, which have been used to refute the effect of sexual selection on giraffe height, are insufficient in genetics and physiology to disprove the effect. Fourth, the interaction between sexual and non-sexual selection constraints could lead to a punctuated equilibrium in the giraffe’s evolution, i.e., the height changed very slowly for most of their geological history, but rather rapidly in a relatively short geological period. Fifth, through genomic sequences, the origin of giraffe height probably involved many small phenotypic and genetic variations, although great phenotypic and genetic variations could not be excluded. These novel views answer more questions than previous hypotheses about the origin of giraffe height, as well as providing new insights into natural selection and biological evolution.
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