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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]
The earliest evidence for life on Earth includes: 3.8 billion-year-old biogenic hematite in a banded iron formation of the Nuvvuagittuq Greenstone Belt in Canada; [30] graphite in 3.7 billion-year-old metasedimentary rocks in western Greenland; [31] and microbial mat fossils in 3.48 billion-year-old sandstone in Western Australia.
The brain divides into 5 vesicles, including the early telencephalon. Leg buds form and hands form as flat paddles on the arms. Rudimentary blood moves through primitive vessels connecting to the yolk sac and chorionic membranes. The metanephros, precursor of the definitive kidney, starts to develop. The initial stomach differentiation begins. [5]
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 ...
The history of life on Earth traces the processes by which living and extinct organisms evolved, from the earliest emergence of life to the present day. Earth formed about 4.5 billion years ago (abbreviated as Ga, for gigaannum) and evidence suggests that life emerged prior to 3.7 Ga. [1] [2] [3] The similarities among all known present-day species indicate that they have diverged through the ...
In 1944, Reginald Ernest Moreau suggested that in more seasonal environments or higher latitudes, fecundity depends on high mortality. [11] David Lack suggested in 1954 that differential food availability and management across latitudes play a role in offspring and parental fitness. [12]
The timeline of human evolution outlines the major events in the evolutionary lineage of the modern human species, Homo sapiens, throughout the history of life, beginning some 4 billion years ago down to recent evolution within H. sapiens during and since the Last Glacial Period.
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 ...