Child Development

Child development, the growth of perceptual, emotional, intellectual, and behavioral capabilities and functioning during childhood. The term childhood denotes that period in the human lifespan from the acquisition of language at one or two years to the onset of adolescence at 12 or 13 years.

A brief treatment of child development follows. For full treatment, see human behaviour: Theories of development. The physical growth of children is treated in human development.The end of infancy and the onset of childhood are marked by the emergence of speech at one to two years of age. Children make enormous progress in language acquisition in their second year and demonstrate a continually growing vocabulary, an increasing use of words in combinations, and a dawning understanding of the rules of grammar and syntax. By their third year children tend to use sentences containing five or even six words, and by the fourth year they can converse in adultlike sentences. Five- and six-year-olds demonstrate a mastery of complex rules of grammar and meaning.

Early childhood (two to seven years) is also the time in which children learn to use symbolic thought and language to manipulate their environment. They learn to perform various mental operations using symbols, concepts, and ideas to transform information they gather about the world around them. The beginnings of logic, involving the classification of ideas and an understanding of time and number, emerge in later childhood (7 to 12 years). Children’s memory capacity also advances continually during childhood and underpins many other cognitive advances they make at that time. As both short-term and long-term memory improve, children demonstrate an increasing speed of recall and can search their memory for information more quickly and efficiently.

Young children’s growing awareness of their own emotional states, characteristics, and abilities leads to empathy—i.e., the ability to appreciate the feelings and perspectives of others. Empathy and other forms of social awareness are in turn important in the development of a moral sense. The basis of morality in children may be said to progress from a simple fear of punishment and pain to a concern for maintaining the approval of one’s parents. Another important aspect of children’s emotional development is the formation of their self-concept, or identity—i.e., their sense of who they are and what their relation to other people is. Sex-role identity, based on gender, is probably the most important category of self-awareness and usually appears by the age of three.

The onset of the physical and emotional changes of puberty and the acquisition of the logical processes of adults mark the end of childhood and the start of adolescence.

embryo

human and animal

Embryo, the early developmental stage of an animal while it is in the egg or within the uterus of the mother. In humans the term is applied to the unborn child until the end of the seventh week following conception; from the eighth week the unborn child is called a fetus.

A brief treatment of embryonic development follows. For full treatment, see morphology: Embryology.

In organisms that reproduce sexually, the union of an ovum with a sperm results in a zygote, or fertilized egg, which undergoes a series of divisions called cleavages as it passes down the fallopian tube. After several cleavages have taken place, the cells form a hollow ball called a blastula. In most mammals the blastula attaches itself to the uterine lining, thus stimulating the formation of a placenta, which will transfer nutrients from the mother to the growing embryo. In lower animals the embryo is nourished by the yolk.

By the process of gastrulation, the embryo differentiates into three types of tissue: the ectoderm, producing the skin and nervous system; the mesoderm, from which develop connective tissues, the circulatory system, muscles, and bones; and the endoderm, which forms the digestive system, lungs, and urinary system. Mesodermal cells migrate from the surface of the embryo to fill the space between the other two tissues through an elongated depression known as the primitive streak. As the embryo develops, the cell layers fold over so that the endoderm forms a long tube surrounded by mesoderm, with an ectodermal layer around the whole.

Nutrients pass from the placenta through the umbilical cord, and the amnion, a fluid-filled membrane, surrounds and protects the embryo. The division of the body into head and trunk becomes apparent, and the brain, spinal cord, and internal organs begin to develop. All of these changes are completed early in embryonic development, by about the fourth week, in humans.

Between the head and the heart, a series of branchial arches, cartilaginous structures that support the gills of fishes and larval amphibians, begin to form. In higher vertebrates these structures form part of the jaw and ear. Limb buds also appear, and by the end of the embryonic stage, the embryo is distinguishable as a representative of its species.