Meth and the Brain. 1  Meth releases a surge of dopamine, causing an intense rush of pleasure or prolonged sense of euphoria. 2  Over time, meth destroys dopamine receptors, making it impossible to feel pleasure. 3  Although these pleasure centers can heal over time, research suggests that damage to users' cognitive abilities may be permanent.
stabilizing. 1  transitive verb. 2  1 : to make stable, steadfast, or firm. 3  2 : to hold steady: such asa : to maintain the stability of (as an airplane) by means of a stabilizerb : to limit fluctuations of (as prices)c : to establish a minimum price for.  intransitive 1  verb. : to become stable, firm, or steadfast.
On each graph, the x-axis variable is the type of phenotypic trait and the y-axis variable is the amount of organisms. Group A is the original population and Group B is the population after selection. Graph 1 shows directional selection, in which a single extreme phenotype is favored. Graph 2 depicts stabilizing selection, where the intermediate phenotype is favored over the extreme traits. Graph 3 shows disruptive selection, in which the extreme phenotypes are favored over the intermediate. Stabilizing selection (not the same thing as negative selection) is a type of natural selection in which genetic diversity decreases and the population mean stabilizes on a particular trait value.