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Development may also occur as a result of human nature and of human ability to learn from the environment. There are various definitions of the periods in a child's development, since each period is a continuum with individual differences regarding starting and ending.
Physical development. By this age, infants may have doubled their birth weights. They typically grow about 0.8 inches (2.0 cm) and gain about 1 to 1.5 pounds (450 to 680 g) during this month. [28] Fat rolls ("Baby Fat") begin to appear on thighs, upper arms and neck. Motor development. May be able to roll from front to back. [29]
Human embryology is the study of this development during the first eight weeks after fertilization. The normal period of gestation (pregnancy) is about nine months or 36 weeks. The germinal stage refers to the time from fertilization through the development of the early embryo until implantation is completed in the uterus.
In biological terms, human development entails growth from a one-celled zygote to an adult human being. Fertilization occurs when the sperm cell successfully enters and fuses with an egg cell . [2] The genetic material of the sperm and egg then combine to form a single cell called a zygote and the germinal stage of prenatal development commences.
Early childhood development is the period of rapid physical, psychological and social growth and change that begins before birth and extends into early childhood. [1] While early childhood is not well defined, one source asserts that the early years begin in utero and last until 3 years of age.
In human pregnancy, prenatal development is also called antenatal development. The development of the human embryo follows fertilization, and continues as fetal development. By the end of the tenth week of gestational age, the embryo has acquired its basic form and is referred to as a fetus. The next period is that of fetal development where ...
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])
The embryonic period varies from species to species. In human development, the term fetus is used instead of embryo after the ninth week after conception, [19] whereas in zebrafish, embryonic development is considered finished when a bone called the cleithrum becomes visible. [20]