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Novel Synthesis on the Origin of Giraffe Height

Ying-Xue Sun, Ji-Wang Chen, Ji-Ming Chen
Author Affiliation(s)
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)
Corresponding Author(s)
Ji-Ming Chen (E-mail:;
Subject Areas
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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  • Comments #7      2016-02-07 10:00:23    
    Although, this article claims that the browsing selection hypothesis originally proposed by Darwin is likely wrong, it has strengthened the effect of natural selection on biological evolution which is the soul of Darwinism, to a higher level. People usually think that a biological trait is due to the selection of a single factor, and a trait without much changes for a long period is not under selection, while this article claims that many biological traits are due to interactions of various selection constraints, and a trait without much changes for a long period can be also under strong selection constraints which offset the effect of each other.
  • Comments #6      2016-02-07 09:48:47    
    Respond to 2016-02-07 09:29:56 The origin of giraffe neck was debated between two research groups which favored the traditional browsing selection hypothesis and the novel sexual selection hypothesis, respectively. These two groups did not realize that the selection likely acted on giraffe height rather than only giraffe necks, and they did not utilize genetic data to support their hypothesis. This article claimed that the selection likely acted on giraffe height, and utilized genetic data to support the novel sexual selection hypothesis. Therefore, it is similar to the scenario that 1+1+1=2 as calculated by previous studies, while this article claimed that 1+1+1=3 even without new measurements.
  • Comments #5      2016-02-07 09:29:56    
    A "new" synthesis is not built on old analysis. What new anatomical, physiological, ecological, or paleontological measurements have been made by the authors to support their "new" synthesis?
  • Comments #4      2016-02-01 10:02:59    
    This preprint was revised on 31 Jan 2016.
  • Comments #3      2016-01-29 14:30:51    
    To 2016-01-17 13:34:16 That is right you did not rate this preprint if you think it is beyond your knowledge.
  • Comments #2      2016-01-17 13:34:16    
    I can not rate this article because it is beyond my knowledge.
  • Comments #1      2016-01-11 18:53:04    
    This preprint is being proofread in grammar by International Science Editing.

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