EXTREME SELECTION IN HUMANS AGAINST HOMEOTIC TRANSFORMATIONS OF CERVICAL VERTEBRAE

Why do all mammals, except for sloths and manatees, have exactly seven cervical vertebrae? In other vertebrates and other regions, the vertebral number varies considerably. We investigated whether natural selection constrains the number of cervical vertebrae in humans. To this end, we determined the...

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Bibliographic Details
Published inEvolution Vol. 60; no. 12; pp. 2643 - 2654
Main Authors Galis, Frietson, Van Dooren, Tom J. M, Feuth, Johan D, Metz, Johan A. J, Witkam, Andrea, Ruinard, Sebastiaan, Steigenga, Marc J, Wijnaendts, Liliane C. D
Format Journal Article
LanguageEnglish
Published United States Society for the Study of Evolution 01.12.2006
Oxford University Press
Subjects
Adult
Cervical vertebrae
Cervical Vertebrae - abnormalities
Cervical Vertebrae - diagnostic imaging
Developmental constraint
Evolution
evolutionary medicine
Female
Fetus
Fetus - abnormalities
Fetus - diagnostic imaging
Genes, Homeobox
Genetics
Hox genes
Humans
Infant
Infants
left-right asymmetry
Male
Mammals
Mesoderm
modularity
Musculoskeletal Abnormalities - epidemiology
Mutation
phylotypic stage
pleiotropy
Pregnancy
Prevalence
Radiography
Ribs
Selection, Genetic
Spine
Thoracic vertebrae
Thoracic Vertebrae - abnormalities
Thoracic Vertebrae - diagnostic imaging
Vertebrates
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Summary:Why do all mammals, except for sloths and manatees, have exactly seven cervical vertebrae? In other vertebrates and other regions, the vertebral number varies considerably. We investigated whether natural selection constrains the number of cervical vertebrae in humans. To this end, we determined the incidence of cervical ribs and other homeotic vertebral changes in radiographs of deceased human fetuses and infants, and analyzed several existing datasets on the incidence in infants and adults. Our data show that homeotic transformations that change the number of cervical vertebrae are extremely common in humans, but are strongly selected against: almost all individuals die before reproduction. Selection is most probably indirect, caused by a strong coupling of such changes with major congenital abnormalities. Changes in the number of thoracic vertebrae appear to be subject to weaker selection, in good correspondence with the weaker evolutionary constraint on these numbers. Our analysis highlights the role of prenatal selection in the conservation of our common body plan.
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ISSN:0014-3820
1558-5646
DOI:10.1554/06-064.1