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Large mammals develop at an absolute slower rate compared to small mammals. Thus, the large mammal tend have longer gestation periods than small mammal as they tend to produce larger neonate. [18] Large mammals require a longer period of time to attain any proportion of adult mass compared to small mammals. [19]
Ligon (1999) suggested with Vehrencamp (2000) that male incubation existed first and later gave way to shared and finally female only incubation. A possible evolutionary timeline by Kavanau suggests that basal theropod dinosaurs evolved into birds that evolved unique bi-parental care, after which avian birds evolved homeothermy and flight.
Gestation, called pregnancy in humans, is the period of time during which the fetus develops, dividing via mitosis inside the female. During this time, the fetus receives all of its nutrition and oxygenated blood from the female, filtered through the placenta , which is attached to the fetus' abdomen via an umbilical cord .
For mammals, the gestation period is the time in which a fetus develops, beginning with fertilization and ending at birth. [1] The duration of this period varies between species. For most species, the amount a fetus grows before birth determines the length of the gestation period. Smaller species normally have a shorter gestation period than ...
The fetal origins hypothesis (differentiated from the Developmental Origins of Health and Disease hypothesis, which emphasizes environmental conditions both before and immediately after birth) proposes that the period of gestation has significant impacts on the developmental health and wellbeing outcomes for an individual ranging from infancy to adulthood.
Gestation is the period of development during the carrying of an embryo, and later fetus, inside viviparous animals (the embryo develops within the parent). [1] It is typical for mammals, but also occurs for some non-mammals. Mammals during pregnancy can have one or more gestations at the same time, for example in a multiple birth. [2]
Only 1 in 14 million of the ejaculated sperm will reach the fallopian tube. The egg simultaneously moves through the fallopian tube away from the ovary. One of the sperm encounters, penetrates and fertilizes the ovum, creating a zygote. Upon fertilization and implantation, gestation of the fetus then occurs within the uterus. [11] [12] [13] [14]
The WHO defines the perinatal period as "The perinatal period commences at 22 completed weeks (154 days) of gestation and ends seven completed days after birth." [26] Perinatal mortality is the death of fetuses or neonates during the perinatal period. A 2013 study found that "While only a small proportion of births occur before 24 completed ...