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The evolutionary history of testicular externalization and the origin of the scrotum

Journal of Biosciences volume 35, pages 27–37 (2010)Cite this article

Abstract

This paper re-examines the evolution of the scrotum and testicular descent in the context of the recent phylogeny of mammals. The adaptive significance of testicular descent and scrotality is briefly discussed. We mapped four character states reflecting the position of testes and presence of scrotum onto recent mammalian phylogeny. Our results are interpreted as follows: as to the presence of testicondy in Monotremata and most of Atlantogenata, which represent the basal group of all eutherians, we argue that primary testicondy represents a plesiomorphic condition for Eutheria as well as for all mammals. This is in opposition to the previous hypothesis of Werdelin and Nilsonne that the scrotum may have evolved before the origin of mammals and then repeatedly disappeared in many groups including monotremes. We suggest that the scrotum evolved at least twice during the evolutionary history of mammals, within Marsupialia and Boreoeutheria, and has subsequently been lost by many groups; this trend is especially strong in Laurasiatheria. We suggest that the recent diversity in testicular position within mammals is the result of multiple selection pressures stemming from the need to provide conditions suitable for sperm development and storage, or to protect the male gonads from excessive physical and physiological disturbance.

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Abbreviations

AMH:

anti-Mullerian hormone

CSL:

cranial suspensory ligament

DA:

descended ascrotal

DS:

descended scrotal

INSL:

insulin-like factor

M:

marsupial

T:

testicondy

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Authors and Affiliations

  1. Department of Philosophy and History of Science, Charles University, Viničná 7, 128 44, Prague, Czech Republic

    Karel Kleisner & Jaroslav Flegr

  2. School of Molecular and Biomedical Science, University of Adelaide, Adelaide, SA5005, Australia

    Richard Ivell

Authors
  1. Karel Kleisner
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  2. Richard Ivell
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  3. Jaroslav Flegr
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Correspondence to Karel Kleisner.

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Kleisner, K., Ivell, R. & Flegr, J. The evolutionary history of testicular externalization and the origin of the scrotum. J Biosci 35, 27–37 (2010). https://doi.org/10.1007/s12038-010-0005-7

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  • DOI: https://doi.org/10.1007/s12038-010-0005-7

Keywords

  • Evolution
  • function
  • mammals
  • scrotum
  • testicular descent