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During the formation of these materials, as they cool from the melt, carbides precipitate, and at even lower temperatures γ' phase precipitates. [11] [12] Gamma prime (γ'): This phase constitutes the precipitate used to strengthen the alloy. It is an intermetallic phase based on Ni 3 (Ti,Al) which have an ordered FCC L1 2 structure. [10]
In utero development and malformations were correlated in severity. [14] Freiston and Galis look at the development of ribs, digits, and mammalian asymmetry. They argue that this construction is relevant for the study of disease, the consistency in evolution of body plans, and understanding of developmental constraints. [15]
Multiregional evolution holds that the human species first arose around two million years ago and subsequent human evolution has been within a single, continuous human species. This species encompasses all archaic human forms such as Homo erectus , Denisovans , and Neanderthals as well as modern forms, and evolved worldwide to the diverse ...
The evidence on which scientific accounts of human evolution are based comes from many fields of natural science. The main source of knowledge about the evolutionary process has traditionally been the fossil record, but since the development of genetics beginning in the 1970s, DNA analysis has come to occupy a place of comparable importance.
Human evolution is the evolutionary process that led to the emergence of anatomically modern humans, beginning with the evolutionary history of primates – in particular genus Homo – and leading to the emergence of Homo sapiens as a distinct species of the hominid family, the great apes.
Earliest development of bilateral symmetry, mesoderm, head (anterior cephalization) and various gut muscles (and thus peristalsis) and, in the Nephrozoa, nephridia (kidney precursors), coelom (or maybe pseudocoelom), distinct mouth and anus (evolution of through-gut), and possibly even nerve cords and blood vessels. [8]
The March of Progress, [1] [2] [3] originally titled The Road to Homo Sapiens, is an illustration that presents 25 million years of human evolution. It was created for the Early Man volume of the Life Nature Library , published in 1965, and drawn by the artist Rudolph Zallinger .
The Rare Earth hypothesis argues that planets with complex life, like Earth, are exceptionally rare.. In planetary astronomy and astrobiology, the Rare Earth hypothesis argues that the origin of life and the evolution of biological complexity, such as sexually reproducing, multicellular organisms on Earth, and subsequently human intelligence, required an improbable combination of astrophysical ...