Major transitions in evolution: understanding the fossil evidence

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The evolution of life on Earth has seen a series of major transitions in the way genetic information is organised and transmitted between generations. These transitions involve shifts in the level of selection. For example, in the case of the transition from single-celled to multicellular organisms selection shifted from acting on single cells to acting on a group of cells. Such shifts opened up new opportunities that, in this case, include the possibility of division of labour between cells, or the specialization of certain cells for specific tasks. As a result the major transitions make it possible for organisms with greater degrees of complexity to evolve.My research focuses on the important early evolutionary transitions that took place in the Precambrian. These include the origin of compartmentalized cells, the origin of eukaryotes (organisms with nuclei), the origin of multicellular organisms and the origin of animals. I will both reappraise the fossil evidence for the transitions and also test previous suggestions of mechanisms responsible for driving them. This will be critical for understanding the relationship between biology and environment on the early Earth. It will also provide important information for scientists attempting to identify evidence of life on other planets.The only way that these early transitions can be directly studied is through the Precambrian fossil record. A number of Precambrian fossils have been proposed as being important in understanding these transitions, but they have often been controversial and the claims made about them have frequently been challenged. A key problem is that many of the diagnostic structures are relatively simple. As a result, it can be difficult to distinguish between genuine biological features that have been fossilized and artefacts that result either from decay or from crystal growth that occurs during and after fossilization. My research aims to tease apart genuine biology from artefact by using two complimentary approaches that will enable a much-needed reappraisal of the Precambrian fossil record. Firstly, a range of organisms, as well as non-biological structures that have been suggested to have a role in the origin of life, will be decayed under experimental conditions. This will enable me to determine whether structures such as nuclei and other subcellular structures can feasibly be preserved. It will also enable me to determine the effects of decay on features of organic walls that are vital in identifying fossil eukaryotes and animal resting stages. I will also test the preservation potential of lipid vesicles, which can be generated in the absence of life and have been proposed to play a role in the origin of cells. However, if preserved in the rock record, lipid vesicles would also have the potential to be mistaken for true cells. This research will determine whether the preservation of lipid vesicles is feasible, which will have important implications for understanding the earliest fossil record as well as potential life from other planets.Secondly, a range of cutting edge analyses will be applied to Precambrian fossils. These aim to characterize the texture and chemistry of (a) preserved biological tissue; and (b) artefacts caused by later mineral growth. Once the characteristics of each style of mineral growth have been established in uncontroversial fossils, the information can be used to interpret more contentious material.The findings from these two lines of evidence will be used to critically reappraise the Precambrian fossil record. This reappraisal will improve our understanding of major transitions in early evolution. This information will be used in an analysis to test proposed driving mechanisms for major transitions. For example, it has been suggested that increased oxygen levels drove switches to multicellularity in a number of groups. The analysis will use new techniques that enable proposals such as this to be tested.