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originally posted by: Soylent Green Is People
Another question would be "is intelligence necessarily a 'height' of evolution?"
originally posted by: Kashai
'the way evolution works, every creature living today is at the height of evolution of its particular species."
Why are you assuming that we have today reached a point where we can no longer evolve
It is generally accepted that the chief role of the environment is to act as sieve, favouring suitable genetic combinations and rejecting the less suitable ones. In view of these roles of the environment, which are actually two aspects of the same process, WADDINGTON 1957 alludes it to dual effect of environmental pressure and has also emphasized the fact that it is not the environment alone that plays the role of selection, the individuals particularly animals, also have a choice to select their environment. In the case of non-motile plants, which have to depend upon extrinsic agencies for their dispersal (through seeds etc.), the concept of the choice of the environment by the individual cannot be applied in the same sense. Further it is also established that the environmental natural selection not only results in the elimination of certain combinations, but the environment also induces certain adaptive changes (physiologic or morphologic) to enable the individual to survive in a particular type of set up. Presently, it seems that enough data has accumulated to make it possible to attribute yet another role to environment i. e. its role in the production of variability by affecting the mutational frequencies or by acting on various components of recombination system and gene flow.
©Verlag Ferdinand Berger & Söhne Ges.m.b.H., Horn, Austria, download unter www.biologiezentrum.at
3. Mutation It is generally accepted that the basic source of variability, that is so essential for evolution, is mutation. Mutation can be considered at three different levels (1) gene (2) chromosome (3) chromosome set or genome.
3.1. Mutagenic agents Under normal conditions genes mutate at a certain frequency, which is known as the spontaneous mutation rate. The mutation rate is generally increased when the organism is exposed to x-rays, ultraviolet light, mustard gas and some ionizing radiations (GRANT 1963). Treatment with certain chemicals, fertilization with "stale" pollen, mutilation, and the use of long dormant seeds, also increases the mutation rate (TLTRRILL 1940). NICHOLAS 1941 and D'AMATO 1963 have also shown that decrease in germinability with increasing age of seeds is accompanied by progressive increase in chromosome abberations and mutation frequency. Heat definitely increases mutation rate; some types of mutations increase towards extreme low temperatures also (SRB & OWEN 1952).STEFFENSON 1953, 1955 has shown that in Tradescantia, spontaneous breakages increase when medium is deficient in Calcium and Magnesium. Translocation in flowering plants can be produced by means of puterscin, a product of natural decay from oil seeds. ABRAHAM 1965 has shown that decaying organic substances, like compost, cow dung and oil cakes can cause chromosomal and genie changes. Similar changes are also induced by substances like ammonium sulphate, ammonium nitrate, ammonium phosphate and potassium chloride. It is extremely significant that these substances are normally used in agricultural practices and are components of the natural environment.
3.2. Genotypic control of mutation Mutations may be gene controlled (BEADLE 1922, IVES 1950, MCCLINTOCK 1950, 1953). "The genotypic control of mutability would account for some of the characteristic differences that have been found in the spontaneous mutation rates of some of the organisms" (GRANT 1963). MCCLINTOCK 1956 demonstrated the presence of mutation and gene action controlling elements, situated on the chromosome in maize and suggested that "controlling elements are normal components of chromosome complement and that they are responsible for controlling, differentially, the time and type of activity of individual genes". It has been argued that the higher organisms do not normally encounter mustard gas and other mutagenic chemicals in their natural external environment, and the radiation to which they are exposed naturally, is not enough to explain the frequency of mutation. GRANT 1963 has suggested that these organisms "do perhaps come in contact with chemical mutagens of their own making in the internal milieu of the cell".
©Verlag Ferdinand Berger & Söhne Ges.m.b.H., Horn, Austria, download unter www.biologiezentrum
Animal behaviorists have started to have a larger variety of options to influence unwanted pet behaviors by using synthetic pheromones. Pheromones are chemical substances produced by an animal to serve as a stimulus for behavioral responses in others of the same species. Pheromones are secreted by glands (including anal sacs) and are found in saliva, feces, and urine. Their purpose is to induce specific reactions (behavioral and emotional), including sexual behaviors, aggression, fear-related behaviors, and avoidance reactions.
Koko the gorilla is best known for a lifelong study to teach her a silent form of communication, American Sign Language. But some of the simple sounds she has learned may change the perception that humans are the only primates with the capacity for speech.