Journal of Biosciences

, Volume 35, Issue 1, pp 27–37 | Cite as

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

  • Karel Kleisner
  • Richard Ivell
  • Jaroslav Flegr


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.


Evolution function mammals scrotum testicular descent 

Abbreviations used


anti-Mullerian hormone


cranial suspensory ligament


descended ascrotal


descended scrotal


insulin-like factor






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Copyright information

© Indian Academy of Sciences 2010

Authors and Affiliations

  1. 1.Department of Philosophy and History of ScienceCharles UniversityPragueCzech Republic
  2. 2.School of Molecular and Biomedical ScienceUniversity of AdelaideAdelaideAustralia

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