Search results
Results from the WOW.Com Content Network
Less than 5% of breech babies have their heads in the "star-gazing" position, the face looking straight upwards and the back of the head resting against the back of the neck. Caesarean delivery is absolutely necessary because vaginal birth with the baby's head in this position confers a high risk of spinal cord trauma and death. [28]
It has been assumed that parents of fewer offspring, with a high probability of adult survival, should permit less risk to themselves. Even though this compromises their young, the overall fitness of their offspring is reduced, which is a strategy to invest in producing more offspring in the future.
Established traits are not immutable; traits that have high fitness in one environmental context may be much less fit if environmental conditions change. In the absence of natural selection to preserve such a trait, it becomes more variable and deteriorate over time, possibly resulting in a vestigial manifestation of the trait, also called ...
Rapid environmental changes typically cause extinctions. [28] Of all species that have existed on Earth, 99.9 percent are now extinct. [29] Since life began on Earth, five major mass extinctions have led to large and sudden drops in the variety of species. The most recent, the Cretaceous–Paleogene extinction event, occurred 66 million years ...
Early obstetric ultrasound, comparing the size of an embryo or fetus to that of a reference group of pregnancies of known gestational age (such as calculated from last menstrual periods) and using the mean gestational age of other embryos or fetuses of the same size. If the gestational age as calculated from an early ultrasound is contradictory ...
Survivorship curves can be constructed for a given cohort (a group of individuals of roughly the same age) based on a life table. There are three generalized types of survivorship curves: [ 1 ] Type I or convex curves are characterized by high age-specific survival probability in early and middle life, followed by a rapid decline in survival in ...
The use of a sequence of experiments, where the design of each may depend on the results of previous experiments, including the possible decision to stop experimenting, is within the scope of sequential analysis, a field that was pioneered [12] by Abraham Wald in the context of sequential tests of statistical hypotheses. [13]
Ernst Haeckel supposed that embryonic development recapitulated an animal's phylogeny, and introduced heterochrony as an exception for individual organs. Modern biology agrees instead with Karl Ernst von Baer's view that development itself varies, such as by changing the timing of different processes, to cause a branching phylogeny.