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Hox clusters

Size doesn't matter

Nature volume 399, pages 730–731 (1999)Cite this article

Molecular biology has had a huge effect on our ability to understand the evolution of biological diversity. As we learn more about how embryos develop at the molecular level, we hope to be able to reconstruct the transitions in developmental programmes that lead to new forms. We need to know, for example, which organisms are most closely related to which others; what features these organisms have inherited from a common ancestor; at which critical junctures new innovations appeared; and, finally, how the genetic machinery could allow such transitions. But before we can determine the direction of evolutionary change, we need to sort out the natural evolutionary relationships of living animals. This is the subject of a report by de Rosa et al.1 on page 772of this issue.</

Our understanding of the relationships between metazoan (multicellular) animals comes mainly from detailed examinations of how different animals are put together — the kinds of tissues and organs they possess, and the extent to which their embryonic development is shared. Animals that have a common anatomical organization, or ‘body plan’, are grouped into ‘phyla’. Crustaceans and insects, for example, are invertebrates grouped in the same phylum (Arthropoda). This is in part because all have individual body segments covered in a hard exoskeleton. Phyla are often then grouped into larger categories, or taxonomic units, such as the ‘Articulata’ (invertebrate animals with sequential body segments). But these taxonomic units are intellectual constructs, which may or may not reflect features of common ancestry. Even defining concepts such as ‘body plan’ are difficult to agree on. Instead, an accurate representation of evolution must identify true clades of animals (groups derived from a common evolutionary ancestor).

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Figure 1: The main evolutionary relationships and higher-level taxonomic groupings of multicellular animals (metazoans).

References

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Authors and Affiliations

  1. Kewalo Marine Laboratory, Pacific Biomedical Research Center, University of Hawaii, Honolulu, 96813, Hawaii, USA

    Mark Q. Martindale

  2. Department of Organismal Biology and Anatomy, University of Chicago, Chicago, 60637, Illinois, USA

    Matthew J. Kourakis

Authors
  1. Mark Q. Martindale
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  2. Matthew J. Kourakis
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Martindale, M., Kourakis, M. Size doesn't matter. Nature 399, 730–731 (1999). https://doi.org/10.1038/21530

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