Biology Chapter 24 Evolution lecture No10 Evidences of evolution Comparative anatomy

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#fscbiology #2ndyearbiology #12classbiology #chapter24 #Evidences of evolution. • Comparative Anatomy: • Anatomical similarities between species grouped in the same taxonomic • category bring another support to the theory of the Descent with • modification. • Following structures provide evidences for evolutionary concept of Darwin. • Homologous structure. • Homologous organs are functionally different but structurally alike. Similarity • in characteristics resulting from common ancestry is known as homology, and • such anatomical signs of evolution are called homologous structures. • Example. Forelimbs of different mammal e.g. the arms of human, forelegs of • cats, flippers of whales, wings of bats, have the same skeletal elements • although these appendages have very different functions. • Divergent evolution. The basic similarity of the structure is the consequence • of the descent of all mammals from a common ancestor and are variations on • a common anatomical theme that has been modified for divergent functions. • Remodeling Process. • Comparative anatomy supports that evolution is a remodeling process in which • ancestral structures that functioned in one capacity become modified as they • take on new functions. • Example. The flower parts of a flowering plant are homologous. They are • considered to have evolved from leaves, to form sepals, petals, stamens and • carpels and adapted different functions • Analogous Structure. • These are functionally alike but structurally different e.g. wings of bat, birds • and insects etc. • Convergent evolution. The same function from different structures may be • related to same habitat. This is convergent evolution.. • Vestigial Structures. • The oldest homologous structures are vestigial organs, rudimentary structures • of marginal, (if any), use to the organism. Vestigial organs are historical • remnants of structures that had important functions in ancestors but are no • longer essential presently. • For instance, the skeletons of whales and some snakes retain vestiges of the • pelvis and leg ones of walking ancestors. Vermiform appendix in carnivores, ear • muscles in man etc.

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