Collenchyma cells

Collenchyma cells are generally elongated cells that have thicker primary walls than parenchyma cells,

Collenchyma cells provide flexible support without restraining growth

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Natural selection was Darwin’s brilliant hypothesis, independently conceived by Wallace, that accounts for adaptations, features that appear “designed” to fit organisms to their environment.

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 Orthogenesis- “Straight-line evolution,” held that the variation that arises is directed toward fixed goals.

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Mutationist- Theories were advanced by some geneticists who observed that discretely different new phenotypes can arise by a process of mutation.

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Ronald A. Fisher, John B. S. Haldane and Sewall Wright- which showed that mutation and natural selection together cause adaptive evolution.

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 Neutral theory of molecular evolution- Developed by Motoo Kimura, who argued that most of the evolution of DNA sequences occurs by chance (genetic drift) rather than by natural selection.

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Theory of recapitulation - Ernst Haeckel
He proposed that the embryonic development of an individual organism (its ontogeny) followed the same path as the evolutionary history of its species (its phylogeny).