Changes

The human [[biological life cycle|life cycle]] is similar to that of other [[placenta]]l mammals. New humans develop [[vivipary|viviparously]] from [[fertilization|conception]]. An [[ovum|egg]] is usually fertilized inside the female by [[spermatozoon|sperm]] from the male through [[sexual intercourse]], though the recent technology of [[in vitro fertilization]] is occasionally used. The fertilized egg, called a [[zygote]], divides inside the female's [[uterus]] to become an [[embryo]], which over a period of thirty-eight weeks (9 months) of [[gestation]] becomes a human [[fetus]]. After this span of time, the fully-grown fetus is expelled from the female's body and breathes independently as an [[infant]] for the first time. At this point, most modern cultures recognize the baby as a [[person]] entitled to the full protection of the law, though some jurisdictions extend personhood to human fetuses while they remain in the uterus.

The human [[biological life cycle|life cycle]] is similar to that of other [[placenta]]l mammals. New humans develop [[vivipary|viviparously]] from [[fertilization|conception]]. An [[ovum|egg]] is usually fertilized inside the female by [[spermatozoon|sperm]] from the male through [[sexual intercourse]], though the recent technology of [[in vitro fertilization]] is occasionally used. The fertilized egg, called a [[zygote]], divides inside the female's [[uterus]] to become an [[embryo]], which over a period of thirty-eight weeks (9 months) of [[gestation]] becomes a human [[fetus]]. After this span of time, the fully-grown fetus is expelled from the female's body and breathes independently as an [[infant]] for the first time. At this point, most modern cultures recognize the baby as a [[person]] entitled to the full protection of the law, though some jurisdictions extend personhood to human fetuses while they remain in the uterus.

Compared with that of other species, human [[childbirth]] is dangerous. Painful labors lasting twenty-four hours or more are not uncommon, and may result in injury, or even death, to the child and/or mother. This is because of both the relatively large fetal head circumference (for housing the brain) and the mother's relatively narrow [[pelvis]] (a trait required for successful bipedalism, by way of natural selection).<ref>{{cite journal | author = LaVelle M | title = Natural selection and developmental sexual variation in the human pelvis | journal = Am J Phys Anthropol | volume = 98 | issue = 1 | pages = 59-72 | year = 1995 | id = PMID 8579191}}</ref><ref>{{cite journal | author = Correia H, Balseiro S, De Areia M | title = Sexual dimorphism in the human pelvis: testing a new hypothesis | journal = Homo | volume = 56 | issue = 2 | pages = 153-60 | year = 2005 | id = PMID 16130838}}</ref> The chances of a successful labor increased significantly during the 20th century in wealthier countries with the advent of new medical technologies. In contrast, pregnancy and [[natural childbirth]] remain relatively hazardous ordeals in developing regions of the world, with maternal death rates approximately 100 times more common than in developed countries.<ref>{{cite journal | author = Rush D | title = Nutrition and maternal mortality in the developing world. | journal = Am J Clin Nutr | volume = 72 | issue = 1 Suppl | pages = 212 S-240 S | year = 2000 | id = PMID 10871588}}</ref>

Compared with that of other species, human [[childbirth]] is dangerous. Painful labors lasting twenty-four hours or more are not uncommon, and may result in injury, or even death, to the child and/or mother. This is because of both the relatively large fetal head circumference (for housing the brain) and the mother's relatively narrow [[pelvis]] (a trait required for successful bipedalism, by way of natural selection).<ref>{{cite journal | author = LaVelle M | title = Natural selection and developmental sexual variation in the human pelvis | journal = Am J Phys Anthropol | volume = 98 | issue = 1 | pages = 59-72 | year = 1995 | id = PMID 8579191}}</ref><ref>{{cite journal | author = Correia H, Balseiro S, De Areia M | title = Sexual dimorphism in the human pelvis: testing a new hypothesis | journal = Homo | volume = 56 | issue = 2 | pages = 153-60 | year = 2005 | id = PMID 16130838}}</ref> The chances of a successful labor increased significantly during the 20th century in wealthier countries with the advent of new medical technologies. In contrast, pregnancy and [[natural childbirth]] remain relatively hazardous ordeals in developing regions of the world, with maternal death rates approximately 100 times more common than in developed countries.<ref>{{cite journal | author = Rush D | title = Nutrition and maternal mortality in the developing world. | journal = Am J Clin Nutr | volume = 72 | issue = 1 Suppl | pages = 212 S-240 S | year = 2000 | id = PMID 10871588}}</ref>