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CHAPTER 5 - SEXUAL DIMORPHISMS

Published online by Cambridge University Press:  05 August 2012

Lewis I. Held, Jr
Affiliation:
Texas Tech University
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Summary

The key lesson from the previous chapter is that no member of a meristic series (finger, tooth, vertebra, etc.) can deviate appreciably in its anatomy until it acquires a distinctive identity. Identities are conferred by the ON/OFF states of selector genes that encode transcription factors.

Once a member(s) of an array does come under the jurisdiction of its own selector gene(s), a new “compartment” can form within the genome. If the selector gene later captures a target gene(s) that affects local growth, then this body part can attain a unique size and shape (cf. Fig. 4.2).

Why do men and women differ in size and shape?

From the standpoint of our genome, the states of the system that we call Man and Woman are operationally no different from Thumb, Canine, or Sacrum. They're just other compartments [885, 1392, 1393] without the meristic trappings [151]. In short, men and women differ in anatomy for the same reasons that our thumb differs from our forefinger: (1) they employ different selector genes, and (2) those regulatory genes control different sets of downstream genes that directly affect size and shape.

The sexual equivalent of the “grotesque mosaicism” seen in some meristic patterns (cf. Figs. 4.1–4.7) would be a disparity so dramatic that the two sexes look as if they belong to separate species. Gorillas are a good example within the primates [1361, 1667], and it is not hard to find similar cases in most animal groups [71, 962, 1315, 2079, 2370].

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Quirks of Human Anatomy
An Evo-Devo Look at the Human Body
, pp. 75 - 104
Publisher: Cambridge University Press
Print publication year: 2009

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  • SEXUAL DIMORPHISMS
  • Lewis I. Held, Jr, Texas Tech University
  • Book: Quirks of Human Anatomy
  • Online publication: 05 August 2012
  • Chapter DOI: https://doi.org/10.1017/CBO9780511626890.006
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  • SEXUAL DIMORPHISMS
  • Lewis I. Held, Jr, Texas Tech University
  • Book: Quirks of Human Anatomy
  • Online publication: 05 August 2012
  • Chapter DOI: https://doi.org/10.1017/CBO9780511626890.006
Available formats
×

Send book to Google Drive

To send content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about sending content to Google Drive.

  • SEXUAL DIMORPHISMS
  • Lewis I. Held, Jr, Texas Tech University
  • Book: Quirks of Human Anatomy
  • Online publication: 05 August 2012
  • Chapter DOI: https://doi.org/10.1017/CBO9780511626890.006
Available formats
×