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Outside the stele lies the endodermis, which is the innermost cell layer of the cortex. The concept of the stele was developed in the late 19th century by French botanists P. E. L. van Tieghem and H. Doultion as a model for understanding the relationship between the shoot and root, and for discussing the evolution of vascular plant morphology. [2]
The notions of time, uplift, slope and drainage density evolution in the erosion cycle have been criticized. [21] Further the validity of some whole concepts associated with the cycle of erosion have been questioned including stream grade , [ 21 ] slope decline , [ D ] base level [ 21 ] and most of all that of peneplains . [ 21 ] [
The word phyletic derives from the Greek φυλετικός phūletikos, which conveys the meaning of a line of descent. [2] Phyletic gradualism contrasts with the theory of punctuated equilibrium, which proposes that most evolution occurs isolated in rare episodes of rapid evolution, when a single species splits into two distinct species, followed by a long period of stasis or non-change.
Two useful introductions to the fundamental theory underlying the unit of selection issue and debate, which also present examples of multi-level selection from the entire range of the biological hierarchy (typically with entities at level N-1 competing for increased representation, i.e., higher frequency, at the immediately higher level N, e.g., organisms in populations or cell lineages in ...
Baal with Thunderbolt or the Baal stele is a white limestone bas-relief stele from the ancient kingdom of Ugarit in northwestern Syria. The stele was discovered in 1932, about 20 metres (66 ft) from the Temple of Baal in the acropolis of Ugarit, during excavations directed by French archaeologist Claude F. A. Schaeffer .
The sloshing bucket model of evolution is a theory in evolutionary biology that describes how environmental disturbances varying in magnitude will affect the species present. [ 1 ] [ 2 ] [ 3 ] The theory emphasizes the causal relationship between environmental factors that impinge and affect genealogical systems, providing an overarching view ...
TimeTree is a free public database developed by S. Blair Hedges and Sudhir Kumar, now at Temple University, for presenting times of divergence in the tree of life. [1] [2] The basic concept has been to produce and present a community consensus of the timetree of life [3] [4] from published studies, and allow easy access to that information on the web or mobile device. [2]
The theory of recapitulation, also called the biogenetic law or embryological parallelism—often expressed using Ernst Haeckel's phrase "ontogeny recapitulates phylogeny"—is a historical hypothesis that the development of the embryo of an animal, from fertilization to gestation or hatching (), goes through stages resembling or representing successive adult stages in the evolution of the ...