The origin of sex
The arctic Canadian island of Somerset, located close to the Qikiqtaaluk Region of Nunavut, has some rocks containing fossils of red algae deposited approximately 1200 million years ago during the Mesoproterozoic Era. Because the fossils are very well preserved, it has been possible to identify the algae as Bangiomorpha pubescens and to study the cell-division patterns of the multicellular filaments in the geologic record.
The spore/gamete formation shows that the algae had been sexually reproducing, and this is the oldest reported occurrence in fossils.[1] Eukaryotes, which are organisms whose cells contain a distinct membrane-bound nucleus, appeared around 1600 million years ago and became successful because sex provided the advantages of genetic recombination and it allowed complex multicellularity. The first appearance of sexual reproduction is associated with the first stratigraphic occurrence of complex multiple-cell organisms. Eukaryotic multicellularity is the innovation that established organism morphology as a significant factor in biological evolution.
[1] Nicholas J. Butterfield, Bangiomorpha pubescens n. gen., n. sp.: implications for the evolution of sex, multicellularity, and the Mesoproterozoic/Neoproterozoic radiation of eukaryotes, Paleobiology; September 2000; v. 26; no. 3; p. 386-404.
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