Many of the most common slime moulds are brightly coloured, with yellow or orange ones being most conspicuous. What we see of a slime mould is in fact a mass of microscopic protists, but yet amazingly at one stage in their life cycle they are capable of coordinated amoeba-like movement across decaying wood or plants. There are, for example, fungus-like protists known as Myxomycota or slime moulds they are capable of absorbing nutrients from other living or dead plants, just as fungi and animals do. Algae live either in freshwater or in sea water and are capable of creating their own food by photosynthesis, but not all protists are able to synthesise their food. Protists are minute organisms, such as protozoa and algae. (There is some evidence that the Eukaryota may have evolved not just by mutations from primitive single-celled organisms but as new organisms created by the fusion of material from Bacteria and Archaea - suggesting tree branches that are able to rejoin.)įor our purposes here, we will ignore the Bacteria and Archaea but look in some detail at the third domain, the Eukaryota, because nearly all of the life forms that we can see, comprising four Kingdoms: the plants, animals, fungi and protists. At some time in the past these separations must have stemmed from single-celled, very primitive types of life form more akin to the Archaea than anything else known today. Recent genetic research based on RNA has led to a general acceptance of top-level domain groupings that separate out Bacteria, Archaea and Eukaryotes. DNA sequencing data have resulted in revisions that align these groupings with Darwin's theory of common descendants - the theory of evolution - but in essence Linnaean classification is still used today.Ĭharles Darwin arranged all life forms into just two Kingdoms, the plants (Plantae) and the animals (Animalia). Modern biological classification is based on pioneering work by Swedish Botanist Carolus Linnaeus, who grouped species with similar physical characteristics. Cladistics has already raised questions about many accepted classifications, several of which have indeed been found to be incorrect and have had to be revised. Nodes cannot be observed today, of course, as they are a hypothetical diverging event - a viable mutation - in the distant past nevertheless, DNA and RNA sequencing data and special computer programs are helping scientists to create cladograms with increasing confidence.īecause we have so few fossil records to help date the branching nodes on plant cladograms, and given the computational limitations of even the most powerful computers available today, cladistics cannot yet unravel all of Life's evolutionary mysteries however, allied with traditional taxonomy this new science is certainly helping to improve our understanding of the evolutionary process that produced the biodiversity of species found on Earth today. In some of the resulting trees, called cladograms, the branch length from a branching node, representing the most recent common ancestor of two or more successors, is a measure of time. Cladistic trees - a 20th century concept - focus on evolutionary changes rather than current similarities between extant species. Not all trees use the same convention, however. Taxonomy is another term for the study of the physical or morphological relationships, and taxa (the singular is a taxon) are the various kinds of living things that are organised into hierarchical groupings based on the degree of similarity of various features, or 'characters'. The tree of life, reproduced from Darwin’s On the Origin of Species by Natural Selection, published in 1859 The traditional way of illustrating such relationships is a tree, where the branches stem from a common origin, splitting again and again until twigs terminate either in an extinct species or one existing today (an extant species). In biology, the term systematics refers to the scientific study of life on Earth, how it has evolved, and the relationships, physical and genetic similarities and differences between organisms existing now and those that existed in the past. Systematics, Evolution, and the Relationships between Living Organisms
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