Journal of Molecular Evolution

, Volume 48, Issue 6, pp 779–783

The First Sexual Lineage and the Relevance of Facultative Sex

  • Joel  Dacks
  • Andrew J.  Roger

DOI: 10.1007/PL00013156

Cite this article as:
Dacks, J. & Roger, A. J Mol Evol (1999) 48: 779. doi:10.1007/PL00013156


Models for the origin of the sex incorporate either obligate or facultative sexual cycles. The relevance of each assumption to the ancestral sexual population can be examined by surveying the sexual cycles of eukaryotes, and by determining the first lineage to diverge after sexuality evolved. Two protistan groups, the parabasalids and the oxymonads, have been suggested to be early-branching sexual lineages. A maximum-likelihood analysis of elongation factor-1α sequences shows that the parabasalids diverged prior to the oxymonads and thus represent the earliest sexual lineage of eukaryotes. Since both of these protist lineages and most other eukaryotes are facultatively sexual, it is likely that the common ancestor of all known eukaryotes was facultatively sexual as well. This finding has important implications for the ``Best-Man hypothesis'' and other models for the origin of sex.

Key words: Oxymonad — Parabasalid — Eukaryote phylogeny — Melosis — Origin of sex 

Copyright information

© Springer-Verlag New York Inc. 1999

Authors and Affiliations

  • Joel  Dacks
    • 1
  • Andrew J.  Roger
    • 1
  1. 1.Department of Biochemistry, Dalhousie University, Halifax, N.S., Canada, B3H 4H7CA

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