Recent developments and advances evolutionary theory

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Recent developments and advances evolutionary theory

    VCE BIOLOGY 20062014


    Contemporary studies in biology require students to develop an understanding of evolutionary theory. Students should also be encouraged to consider the future possibilities of research, breakthroughs and any associated community, social or ethical issues.

To assist teachers to implement the VCE Biology Study Design 20062014, the

    following expert paper has been prepared and is of relevance to Units 3 and 4. The paper provides up-to-date information and explanation of important terms and concepts.



    Recent developments and advances in evolutionary theory

    by Stewart Jackel

    In the last few years there have been substantial changes in both biochemical techniques and computer data analysis. The result of this combination has been a revolution in the way in which evolutionary relationships between species are perceived.

    Digital techniques including micro-array data analysis and statistical genetics have revolutionised both genetic techniques such as gene sequencing and the speed at which the huge volumes of data acquired can be processed. Digital data processing now allows the rapid processing of data involving whole genomes.

    At a molecular level, the discovery of microRNA (miRNA) has influenced our understanding of evolution. MiRNA molecules are single stranded lengths of RNA that are typically about 22 nucleotides long. They are encoded in DNA but rather than coding for the more familiar mRNA (and a protein) the genes code for a type of RNA that seems to regulate the expression of other genes. This is thought to be an epigenetic (Greek, epi, around or outside genetics) mechanism that involves heritable changes in the way a gene is regulated without a change in the DNA sequence of the gene. Because miRNAs are involved in the regulation of gene expression as an organism develops, they are important in evolutionary developmental biology (the evolution of development). This science compares the processes in the development of organisms to determine their ancestral relationships.

    MiRNA causes the destruction of coding RNA, or interferes with its activity so the normal protein cannot be produced. This type of RNA apparently affects the expression of many genes ranging from those involved with breast cancer in humans to the synthesis of morphine in opium poppies.

    But a major area of research involves the use of nucleic acid (the genome) and protein sequences (the proteome) of organisms to establish their systematic positions (their relationship with each other) through time. Molecular systematics uses the techniques of molecular biology to investigate the evolutionary relationships of organisms. The data is often processed using cladistics on the assumption that the classification of organisms relates to their evolution and that genotype similarity corresponds to recent divergence (the molecular clock hypothesis).

    Biochemical and fossil data can be used to create two main types of diagram: (taxonomic) cladograms and (evolutionary) phylogenetic trees.

    Cladistics is a philosophy of classification that arranges organisms by taxonomic order. The data used to construct the cladogram can be molecular (such as DNA sequences) biochemical or morpohological. Organisms, that lie at the leaves of the tree are grouped into clades (or branches), share a common ancestor at the point where a branch bifurcates. A cladogram is a hierarchical classification of taxa represented as a tree. Cladograms are often seen as phylogenies.

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    Phylogenetics examines the patterns of genetic relationships between species and higher groups. Phylogenetic trees visually represent the evolutionary history of the groups concerned over the time concerned.

    Research by Kathy Belov at the Australian Museum published in 2001 reveals an explosion of immunoglobulin evolution before the three extant mammalian families diverged. The antibodies found in mammals are IgM, IgA, IgG and IgE. Those in lower vertebrates are different. But those of other higher vertebrate groups also vary. For example, IgM, IgA, IgG and IgE in monotremes are structurally identical to other mammals but are different to birds and reptiles. And the immunoglobulin profile of short-beaked echidnas differs to that of platypuses. Immunoglobulin evidence supports the notion that monotremes separated before the marsupials and therian mammals diverged. In particular, IgM has been shown to be a useful maker in the estimation of the times of mammalian divergences. It is thought that monotremes and placentals last shared a common ancestor about 170 million years before present (BP), marsupials and placentals 130 million years BP and the two monotremes 22 million years BP.

    A more recent investigation involving aspects of physiology revealed an unexpected discovery, that yabbies (Chelax destructor) possess electrosensory perception.

    Echidnas and modern platypuses are able to detect very small electromagnetic fields such as those produced by contracting muscles. The four species of fossil platypus (including Obdurodon dicksoni and the opalised jaw fragment of Steropodon

    galmani) seem to have possessed the same sense. This reinforces the idea of a common ancestor for the Australian and New Guinean echidnas and the modern and ancient platypuses (and perhaps the recently discovered Patagonian platypus).

    Comparison of the skeletal material of modern and ancient platypuses suggests that the modern platypus is much more specialised than its ancestors. It is now found only in rivers in Eastern Australian and its ancestral teeth have been replaced by horny pads. Evolution generally does not favour specialisation.

    The yabby discovery also raises other questions about a common ancestor or multiple evolutions of the trait.

    (Current Biology, Volume 17, Issue 3, 6 February 2007, pages 8384)

    The shallow sea that covered what is now Gogo near the Kimberleys in northwestern Australia in the Late Devonian 380 million years ago, and that now consists of extensive areas of limestone, has revealed dozens of fossilised fish species. One of these, Gogonasus andrewsae, was first described from a snout in 1985 by John Long

    of the Museum of Victoria and from a complete skeleton in 2005. Gogonasus has

    spiracles that are thought to have evolved into the middle ear of land vertebrates. As well, the front fin is similar to that of all tetrapods: it has a well-developed humerus, ulna and radius.

The Wollemi Pine, Wollemia is a new, monotypic genus in the family Araucariaceae,

    was first discovered in the Blue Mountains of NSW in 1994 and is considered to be significant in the study of the evolutionary relationships of flora on the Gondwana continent even though no other species of Wollemia, extant or fossil, have been found.

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    It has characteristics of two related genera, Agathis and Araucaria, but it also has

    features possessed by neither of these. The evolutionary relationships within the Araucariaceae are as yet unknown.

    In 2003, Australian and Indonesian researchers found the fossilised remains of what is generally thought to be a new species of hominid that was much smaller than modern humans. Homo floresiensis lived in caves on the Indonesian island of Flores. The

    species co-existed with modern humans until 18 000 years ago. Initially controversy, now largely settled, was whether the remains belong to a modern human with an underdeveloped brain and short stature (that is, was microcephalic) or a small-stature, dwarf-sized human. Measurements of scores of the skulls of H. floresiensis and

    modern humans support the idea that the individuals belonged to a dwarfed-sized but otherwise normal human. It is also argued that many island species of organisms tend to dwarfism, for example the stegadons that the H. floresiensis hunted. It is also

    suggested that a race consisting only of microcephalics could not have survived up to 95 000 years or 40 000 generations.

    The discovery raises questions about the evolution and extinction of the species. Early evidence discounts the involvement of volcanos in their extinction since examination of ash layers supports the hypothesis that they survived many volcanic eruptions while they lived in the caves of Flores. As well, the discovery of evidence that suggests they made functional tools supports the notion that the species possessed the intellectual ability to both make and use them. This leaves only the likelihood that the species was destroyed by modern humans.

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