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202 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD
The reason for its origin may be obscure, but 5 Why are fossils so rare in the
its consequences are manifest. Sex allows Precambrian?
rapid evolution and diversifi cation of species
because genetic material is swapped and
changes during each reproductive cycle. Further reading
Sexual organisms vary more than asexual Butterfi eld, N.J. 2000. Bangiomorpha pubescens n.
organisms, and they can adapt and specialize gen., n. sp.: implications for the evolution of sex,
more readily. Finally, sexual organisms can be multicellularity, and the Mesoproterozoic/
multicellular. Neoproterozoic radiation of eukaryotes. Paleobiol-
ogy 26, 386–404.
Cavalier-Smith, T., Brasier, M. & Embley, T.M. (eds)
2006. How and when did microbes change the
The Late Neoproterozoic
world? Philosophical Transactions of the Royal
The last 100 myr of the Proterozoic, the Society B 361, 845–1083.
Late Neoproterozoic, is marked by a dra- Cracraft, J. & Donoghue, M.J. (eds) 2004. Assembling
matic increase in fossil diversity. Sexual repro- the Tree of Life. Oxford University Press, Oxford,
duction and multicellularity opened the door UK.
for more complex, and larger, organisms. Hazen, R. 2005. Genesis: The Scientifi c Quest for Life’s
Algal groups, including relatives of plants, Origin. Joseph Henry Press, Washington. http://
darwin.nap.edu/books/0309094321/html/.
appeared. In addition, multicellular animals Knoll, A.H. 1992. The early evolution of eukaryotes: a
or metazoans, also appeared later in the geological perspective. Science 256, 622–7.
Proterozoic, and these included the complex Knoll, A.H. 2003. Life on a Young Planet: The First
Ediacaran animals. Three Billion Years of Evolution on Earth. Princeton
University Press, Princeton, NJ.
Tudge, C.T. 2000. The Variety of Life. Oxford Univer-
Review questions sity Press, Oxford, UK.
1 Find out how many distinct creation myths
you can track down on the internet. References
Arrange them in a classifi cation that links Altermann, W. & Kazmierczak, J.2003. Archean micro-
major features of the myths, and match fossils: a reappraisal of early life on Earth. Research
them to their appropriate religions and in Microbiology 154: 611–17.
time span of general acceptability. Ayala, F.J., Rzhetsky, A.& Ayala, F.J. 1998. Origin of
2 Many claims have been made over the the metazoan phyla: molecular clocks confi rm pale-
years about the oldest fossils of life. Look ontological estimates. Proceedings of the National
back through the literature to fi nd what Academy of Sciences, USA 95, 606–11.
was the oldest acceptable record in 1960, Barghoorn, E.S. & Taylor, S.A. 1965. Microorganisms
1970, 1980, 1990 and 2000. Read about from the Gunfl int Chert. Science 147, 563–77.
why many of these claimed oldest fi nds Baldauf, S.L., Bhattacharya, D., Cockrill, J.,
were eventually doubted or rejected, and Hugenholtz, P., Pawlowski, J. & Simpson, A.C.B.
2004. The tree of life, an overview. In Cracraft, J. &
list the reasons why. Donoghue, M.J. (eds) Assembling the Tree of Life.
3 Read around the debate about the univer- Oxford University Press, Oxford, UK, pp. 43–75.
sal tree of life, and consider whether it will Brasier, M.D., Green, O.R., Jephcoat, A.P. et al. 2002.
ever be possible to determine which Questioning the evidence for earth’s oldest fossils.
branched first – Archaea, Bacteria or Nature 416, 76–81.
Eucarya – and give reasons why some ana- Brocks, J.J., Logan, G.A., Buick, R. & Summons, R.E.
lysts believe that this will never be 1999. Archean molecular fossils and the early rise of
resolved. Eukaryotes. Science 285, 1033–6.
4 What are the advantages and disadvan- Butterfi eld, N.J. 2000. Bangiomorpha pubescens n.
tages of sex and of multicellularity? gen., n. sp.: implications for the evolution of
Catalog as many arguments as you can sex, multicellularity, and the Mesoproterozoic/
Neoproterozoic radiation of eukaryotes. Paleobiol-
fi nd for and against each of these biologi- ogy 26, 386–404.
cal attributes, and describe the possible Catling, D.C. & Claire, M. 2005. How Earth’s atmo-
world today if sex and multicellularity sphere evolved to an oxic state: a status report. Earth
had never arisen. and Planetary Science Letters 237, 1–20.
