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Altricial mammals needs less time to gestate compare to the precocial (well-developed neonate) mammal. A typical precocial mammal has a gestation period almost four times longer than a typical altricial mammal of the same body size. [20] Precocial mammal species generally have greater adult body weights than altricial mammals as precocial ...
In the case of mammals, it has been suggested that large, hearty adult body sizes favor the production of large, precocious young, which develop with a longer gestation period. Large young may be associated with migratory behavior, extended reproductive period, and reduced litter size.
Primates are precocial at birth, with the exception of humans. [42] The duration of gestation in placental mammals varies from 18 days in jumping mice to 23 months in elephants. [43] Generally speaking, fetuses of larger land mammals require longer gestation periods. [43] Fetal stage of a porpoise
Fertilization of the ovum to form a new human organism, the human zygote. (day 1 of fertilization [1]) The zygote undergoes mitotic cellular divisions, but does not increase in size. This mitosis is also known as cleavage. A hollow cavity forms marking the blastocyst stage. (day 1.5–3 of fertilization. [1])
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]
Humans usually produce a single offspring at a time. The mother's body is prepared for birth by hormones produced by the pituitary gland, the ovary and the placenta. [2] The total gestation period from fertilization to birth is normally about 38 weeks (birth usually occurring 40 weeks after the last menstrual period). The normal process of ...
Ethnicity in humans is also a factor that may lengthen or shorten gestation. [4] In dogs, there is a positive correlation between a longer gestation time and fewer members of the litter. [5] The duration of gestation is usually longer in placental mammals than in marsupials. [6]
The smaller birth canal became a limiting factor to brain size increases in early humans and prompted a shorter gestation period leading to the relative immaturity of human offspring, who are unable to walk much before 12 months and have greater neoteny, compared to other primates, who are mobile at a much earlier age. [125]