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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.
Biological constraints are factors which make populations resistant to evolutionary change. One proposed definition of constraint is "A property of a trait that, although possibly adaptive in the environment in which it originally evolved, acts to place limits on the production of new phenotypic variants."
Recent molecular phylogenetic reconstruction of the internal relationships of choanoflagellates allows the polarization of character evolution within the clade. Large fragments of the nuclear SSU and LSU ribosomal RNA , alpha tubulin , and heat-shock protein 90 coding genes were used to resolve the internal relationships and character polarity ...
Phylogenetic bracketing is a method of inference used in biological sciences. It is used to infer the likelihood of unknown traits in organisms based on their position in a phylogenetic tree. One of the main applications of phylogenetic bracketing is on extinct organisms, known only from fossils, going back to the last universal common ancestor ...
The larval form is not capable of feeding, though it may have a rudimentary digestive system, [53] and is only a dispersal mechanism. Many physical changes occur to the tunicate's body during metamorphosis , one of the most significant being the reduction of the cerebral ganglion, which controls movement and is the equivalent of the vertebrate ...
Both of the major vessels, especially the upper one, can pump blood by contracting. In some annelids the forward end of the upper blood vessel is enlarged with muscles to form a heart, while in the forward ends of many earthworms some of the vessels that connect the upper and lower main vessels function as hearts. Species with poorly developed ...
Phylogenetic comparative methods (PCMs) use information on the historical relationships of lineages (phylogenies) to test evolutionary hypotheses. The comparative method has a long history in evolutionary biology; indeed, Charles Darwin used differences and similarities between species as a major source of evidence in The Origin of Species .
Evolutionary progress as a tree of life. Ernst Haeckel, 1866 Lamarck's two-factor theory involves 1) a complexifying force that drives animal body plans towards higher levels (orthogenesis) creating a ladder of phyla, and 2) an adaptive force that causes animals with a given body plan to adapt to circumstances (use and disuse, inheritance of acquired characteristics), creating a diversity of ...