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This article lists anatomical variations that are not deemed inherently pathological. This list is incomplete ; you can help by adding missing items . ( December 2013 )
Anatomical variations are mainly caused by genetics and may vary considerably between different populations. The rate of variation considerably differs between single organs, particularly in muscles. [2] Knowledge of anatomical variations is important in order to distinguish them from pathological conditions.
Evolutionary physiology is the study of the biological evolution of physiological structures and processes; that is, the manner in which the functional characteristics of organisms have responded to natural selection or sexual selection or changed by random genetic drift across multiple generations during the history of a population or species. [2]
Reconstruction of early Homo sapiens from Jebel Irhoud, Morocco c. 315 000 years BP. Early modern human (EMH), or anatomically modern human (AMH), [1] are terms used to distinguish Homo sapiens (sometimes Homo sapiens sapiens) that are anatomically consistent with the range of phenotypes seen in contemporary humans, from extinct archaic human species (of which some are at times also identified ...
These changes in structure have produced forelimbs adapted for different tasks. [49] The bird and the bat wing are examples of convergent evolution. However, anatomical comparisons can be misleading, as not all anatomical similarities indicate a close relationship.
Ileum, caecum and colon of rabbit, showing Appendix vermiformis on fully functional caecum The human vermiform appendix on the vestigial caecum. The appendix was once believed to be a vestige of a redundant organ that in ancestral species had digestive functions, much as it still does in extant species in which intestinal flora hydrolyze cellulose and similar indigestible plant materials. [10]
Homology thus implies divergent evolution. For example, many insects (such as dragonflies) possess two pairs of flying wings. In beetles, the first pair of wings has evolved into a pair of hard wing covers, [12] while in Dipteran flies the second pair of wings has evolved into small halteres used for balance. [b] [13]
Evolution of fish to tetrapods. The basic body plan has been phylogenetically constrained. Most terrestrial vertebrates have a body plan that consist of four limbs. The phylogenetic inertia hypothesis suggests that this body plan is observed, not because it happens to be optimal, but because tetrapods are derived from a clade of fishes (Sarcopterygii) which also have four limbs.