The view that abilities become more refined or differentiated with age. Being a very general hypothesis, it has found applications in studying, for example, the development of both language and perception, and with regard to the formation of social identity in the context of intergroup relations, the latter being referred to as the identity-differentiation hypothesis …
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Differentiation (general)
According to Waddington, in his book The evolution of an evolutionist (1975), this term was borrowed by embryology from psychology. In developmental biology, it refers to the fact that cells not only increase in number during development, but also change in structure and function, and become different in their specializations from their earlier forms and …
Differentiation (embryology)
Literally, the development of differences, it is the process by which cells become increasingly different and specialized, giving rise to more complex structures that serve particular functions in the adult organism (e.g., embryonic cells develop into bone, muscle and nerve cells). See Cytokines, Dependent differentiation, Determination, Development, Developmental biology, Differentiation (general), Differentiation (specific), Ectoderm, Entoderm …
Differential equation
In differential calculus, an equation in which the rate of change of a set of variables is a function of the current values of the variables. Solutions of differential equations are time courses of all variables. These time courses are uniquely determined given the initial values of the variables. The order of a differential equation …
Differential parenting
Differences in parents’ treatment of their various children (e.g., favoritism), and which may be evident with identical twins in order to accentuate their differences (e.g., by dressing them differently). Parents who act as ‘differentiators’ in this sense are contrasted with ‘twinners’ or ‘egalitarians’ that try to treat twins as a single unit. This distinction appears …
Diencephalon
The basal cell mass of the paired posterior or caudal parts of the forebrain or prosencephalon that contain the thalamus (dorsal thalamus, epithalamus, sub-thalamus or ventral thalamus) and hypothalamus. The dorsal part consists of the epithalamus and dorsal thalamus, and the ventral part the sub-thalamus and hypothalamus. It connects the mesencephalon (midbrain) of the brain …
Diarthrodial joints
The largest number of movable joints in the body having a joint or synovial capsule filled with synovial membrane that secretes a viscous fluid called synovia containing glycoprotein, which serves to lubricate the smooth cartilage (articular) surfaces making contact with the two bones. Hence, it is sometimes referred to as a synovial joint. The classification …
Diagraph
A pair of letters that operate together to represent a single sound (e.g., clown, chin). In a vowel digraph, a pair of vowel letters operate together to represent a single vowel sound (e.g., ow, ee, oo), and a pair of consonants (e.g., ch, th, sh) to give a consonant digraph. See Alphabet, Consonants, Grapheme, Vowel-to-consonant …
Diaphysis
The central shaft of a long tubular bone (e.g., tibia) lying between the epiphyses (the extremities of the bone). It is the first to ossify and contains an extended ossification centre (see figure below). It has a hollow middle (medullary cavity) containing bone marrow that is red in children, and which changes with age to …
Diagnosis (or diacrisis)
Determining the cause or causes of a congenital defect, injury or illness and accounting for its symptoms and signs. Diagnosis implies that a causative mechanism for the condition is known. Three broad categories of diagnosis can be identified: clinical diagnosis (based on signs and) symptoms, diagnosis by exclusion (ruling out all but one disease thought to …