2.1 Unit Overview: Human development from conception to birth

Lesson Objectives:

* What roles do nature and nurture play in the development of a fetus?
* How do the various domains influence development during the prenatal stage?
* What are the sociocultural influences on prenatal development?

What roles do nature and nurture play in the development of a fetus?

Both genes and environment are necessary for a person to exist. Without genes, there is no person; without environment, there is no person (Scarr and Weinberg, 1980). Heredity and environment operate together, or cooperate, to produce a person’s intelligence, temperament, height, weight, abilities, and so on. The emerging view is that many complex behaviours likely have some genetic loading that gives people a propensity for a particular developmental trajectory. But the actual development requires more - an environment. And that environment is complex, just like the mixture of genes we inherit. Environmental influences range from the things we lump together under “nurture” (such as parenting, family dynamics, schooling, and neighbourhood quality) to biological encounters (such as viruses, birth complications, and even biological events in cells) (Santrock, 1999, p. 83).

How do the various domains influence development during the prenatal development stage?

Physical Development:

* The germinal period is the first two weeks of development. This period is characterized by rapid cell division, the beginning of cell differentiation, and implantation of the blastocyst into the uterine wall. By approximately one week after conception, the zygote is composed of 100 to 150 cells. The differentiation of cells commences and the zygote becomes differentiated into two layers: The blastocyst is the inner layer of cells that later develop into the embryo; the trophoblast is the outer layers of cells that later provides nutrition and support for the embryo. Implantation of the zygote into the uterine wall takes place about 10 days after conception (Santrock, 1999, p. 103).
* The embryonic period is the period of prenatal development that occurs from two to eight weeks after conception. The embryo's endoderm, the inner layer or cells, primarily produces internal body parts such as the respiratory and digestive systems. The middle layer of cells, called the mesoderm, will become the circulatory system, bones, muscle, excretory system, and reproductive system. The outer layer of cells, the ectoderm, will become the nervous system, the sensory receptors (eyes, nose, ears), and skin. As the embryo develops so too does the placenta, the umbilical cord and the amnion (fluid-filled sac) (Santrock, 1999, p. 103).
* The fetal period is the period of development that begins two months after conception and lasts for seven months, on the average. Three months after conception the fetus is 10 centimetres long and weighs approximately 60 grams. It has become active, moving its arms and legs, opening and closing its mouth, and moving its head. The face, forehead, eyelids, nose, and chin are all distinguishable, as are the arms, hands and legs. At four months, a growth spurt occurs in the fetus' lower parts. By the end of the fifth month the toenails and fingernails have formed and the fetus is more active. By the end of the sixth month the eyes and eyelids have completely formed, a grasping reflex is present and irregular breathing occurs. In the last two months, fatty tissues develop and the functioning of various organs such as the heart and kidneys steps up (Santrock, 1999, p. 103).

Cognitive Development:

* Some simple aspects of the functioning of the human nervous system appear very early. Indeed the blood circulation system and the nervous system are the first to function in embryonic life, with heartbeat commencing in the third week following conception. By the second month, an avoidance reaction, the withdrawal of the hand region by contraction of the neck muscles, occurs if an unpleasant stimulus is applied to the embryonic upper lip. These developments imply that simple arc reflexes are already differentiated at this stage, with appropriate synaptic connections and interneuronal activity being brought into play in order to coordinate muscular movements (Rose, 1989, p. 192).

Temperament/Personality Development:

* Every individual is born with a distinct, genetically-based set of psychological tendencies, or dispositions. These tendencies, which together are called temperament, affect and shape virtually every aspect of the individual's developing personality. Temperament, and therefore personality, is not merely genetic: it begins in the multitude of genetic instructions that guide the development of the brain and then is affected by the prenatal environment (Berger, 2000, p. 219).