Patterns of EvolutionPatterns of EvolutionA tree that represents an estimate (hypothesis) of evolutionary ld i hlrelatedness is a phylogenyClassifications can be based on groupings within a phylogenygpg pygyGroupings can be categorized•monophyletic-a group that includes all of the descendants ofmonophyletica group that includes all of the descendants of a single common ancestor• paraphyletic - a group that includes some, but not all, of the ddtfil tdescendants of a single common ancestor• polyphyletic - a group that is not based on common ancestryTraditional classifications were often based on branching df l i Thi fpatterns andapparent amounts of evolution. This often creates paraphyletic groupings (e.g. Class Reptilia). Modern classifications tend to be constructed using monophyleticmonophyletic groups and reflect only the branching patternbranching pattern of the phylogeny.Once the hl fphylogeny of a group is known other inferences about evolutionary history can behistory can be made:•Segmentation ghas evolved twice.• Sight has evolved multiple timestimes.Did the ancestor of humans and chimps have opposable toes?If not then opposable toes must have evolved again in theIf not, then opposable toes must have evolved again in the chimp lineage.If so, then opposable toes were lost in the human lineage.If so, then opposable toes were lost in the human lineage.The simpler answer is usually preferred.Important inferences are made from analysis of phylogeniesFeatures of an organism almost always evolve from a preFeatures of an organism almost always evolve from a pre-existing feature present in their ancestors - complex characters don’t evolve de novo.Wings evolved from forelimbs at least 3 times in vertebrates (birds, bats, pterodactyls)Wings and forelimbs are homologous characters - they arise from the same embryonic structures and their development is controlled by the same genesby the same genes.Homology is established by•correspondence of position•correspondence of position• correspondence of structure•correspondence in developmentcorrespondence in development• continuity from an inferred ancestor in a phylogenyHomoplasy (multiple origins of the same character state) is common.Independent evolution of similar characteristics insimilar characteristics in homologous structures is called parallel evolution -tfhla type of homoplasy.Independent evolution of similar characters through differentIndependent evolution of similar characters through different developmental pathways is called convergent evolution -another type of homoplasyConvergent and parallel evolution are often due to independent adaptation to similar environmentsadaptation to similar environments.ElilTh l fEvolutionary reversals are common. The ancestral state of a character can re-evolve. The jawless fishes were the first to evolve boneasThe jawless fishes were the first to evolve bone -as protective armor over the outside of their body.Modern descendants of the early jawless fishes have bodies lacking bone entirely.bod es c g bo e e e y.Mosaic evolution is common. Species characteristics often lid dlf hhevolve independently of each other. Every organism has a mix of ancestral and derived character states Slow evolving characters are calledconservativestates. Slow evolving characters are called conservative characters. They are retained even though other characters change. In terrestrial vertebrates, walking on four legs is a conservative character. Having 5 digits on the appendages is also ti H i i i i th d l j iconservative. Having incisors in the upper and lower jaws is conservative character.Change in form is often related to a change in function.Evolution is usually gradual (gradualism)Intermediates are often seen in the fossil recordfossil record.Living organisms often exhibit gradual variation in gform.Species similarity changes during ontogeny.von Baer’s Law: Development proceeds from the general to the ifiDi b ispecific. -During embryonic development, the characteristics of the broader taxonomic categories are seen in the embryo before the characteristics of the morecharacteristics of the more specific taxonomic category.The biogenetic law: “ontogeny recapitulates phylogeny” is not literally true. Organisms do not develop by progressing th h th b d t f th i tthrough the body types of their ancestors.Developmental processes underlie some patterns of morphological evolutionevolution.IndividualizationIndividualization -the taking on of specific forms and functions in a serially repeating character.Heterochrony - an evolutionary change in the timing or rate of dl ldevelopmental events.Paedomorphosis - the retention of larval or juvenile characteristics after the attainment of sexual maturitydue tocharacteristics after the attainment of sexual maturity -due to the relative increase in the rate of maturation of the gonadsPeromorphosis - the delaying of sexual maturation and prolonging of the juvenile period in a way that results in greater development of gpsome adult features - e.g. an increase in cranium volume.Allometry - differences in growth rate among different parts or di i f idimensions of an organism.Although throughout evolutionary history there has been trend of increasing complexity decreases in complexity are also commonincreasing complexity, decreases in complexity are also common.Vertebrate evolution is characterized by many examples of simplification of structuressimplification of structuresAdaptive radiation - the diversification of a genetic lineage into many species with many different adaptations to different aspectsmany species with many different adaptations to different aspects of the environment - is common in some groups.One of the most dramatic examples of adaptive radiation is that of the cichlid fishes of the Great Lakes of Africa In the largest 3the cichlid fishes of the Great Lakes of Africa. In the largest 3 lakes (Victoria, Tanganyika, and Malawi), speciation and adaptation has resulted in “species flocks” that fill different ecological niches. It happened independently in each lake, but has given rise to species with similar habits and a similar range of morphological