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Stabilizing selection (not to be confused with negative or purifying selection [1] [2]) is a type of natural selection in which the population mean stabilizes on a particular non-extreme trait value. This is thought to be the most common mechanism of action for natural selection because most traits do not appear to change drastically over time ...
A preterm birth, also known as premature birth, is defined as babies born alive before 37 weeks of pregnancy are completed. [40] There are three types of preterm births: extremely preterm (less than 28 weeks), very preterm (28 to 32 weeks) and moderate to late preterm (32 to 37 weeks). [40]
The first and most common function to estimate fitness of a trait is linear ω =α +βz, which represents directional selection. [1] [10] The slope of the linear regression line (β) is the selection gradient, ω is the fitness of a trait value z, and α is the y-intercept of the fitness function.
In 2008 the rate of low birth weight was the highest in babies born to women younger than 15 years old (12.4%). [23] Women aged 40–54 had a rate of low birth weight at 11.8 percent. The lowest rates of low birth weight happened among babies whose mothers were between the ages of 25–29 years (4.4%) and 30–34 years (7.6%). [23]
The K a /K s ratio is used to infer the direction and magnitude of natural selection acting on protein coding genes. A ratio greater than 1 implies positive or Darwinian selection (driving change); less than 1 implies purifying or stabilizing selection (acting against change); and a ratio of exactly 1 indicates neutral (i.e. no) selection.
This maneuver should yield the opposite information and validate the findings of the first maneuver. If the woman enters labor, this is the part which will most likely come first in a vaginal birth. If it is the head and is not actively engaged in the birthing process, it may be gently pushed back and forth.
Fecundity selection, also known as fertility selection, is the fitness advantage resulting from selection on traits that increases the number of offspring (i.e. fecundity). [1] Charles Darwin formulated the theory of fecundity selection between 1871 and 1874 to explain the widespread evolution of female-biased sexual size dimorphism (SSD ...
Measurement of the belly being performed by a pregnant woman during her pregnancy. The amount of healthy weight gain during a pregnancy varies. [102] Weight gain is related to the weight of the baby, the placenta, extra circulatory fluid, larger tissues, and fat and protein stores. [16] Most needed weight gain occurs later in pregnancy. [103]