Biological Beginnings of Development

 Much of the early (pre-natal) human development is characterized by biological changes, while some psychological (cognitive and social) abilities (such as hearing) begin before birth, most develop after birth.

In considering influences on who we are and how we develop, there are some basic features that we can review before examining prenatal (before birth) development.

The Nature -Nurture debate

Consider the relative influences of genetics (nature) and experience (nurtture) on who we are and how we develop. Historically psychologists have taken various opinions on this debate such as nativists like Sir Francis Galton suggest that our genetics are all important and environmentalists like John B. Watson suggest that our circumstances and experiences are all important.

Natural Selection

is a process hypothesized by Charles Darwin to be the central mechanism for the evolutionary development of species and the creation of new species from other ones.

The major components of this theory are the contribution of genetic inheritance in terms of traits that vary within and between species and the environmental pressures that "select" traits for survival .

The essential components for Darwin's theory are that the environment "selects" organisms with some traits to survive while others die out, what this means is that those who survive are best "fit" for their environments.

Other often present Darwin as saying that " survival of the fittest" means those who can be more competitive with their neighbours and are more fit (aggressive or otherwise) than their competitors.

Others, such as Richard Dawkins on Natural Selection ( part 2 ) discusses the "Selfish Gene" whereby we are seen as prisoners of our genes, they (our genes) work to selfishly replicate themselves and and our behaviour is merely at the service of our genes.

Dawkins also describes the importance of the social transmission of ideas that enhance adaptation which he called memes .

Hence survival of the fittest mean the genes' fitness, not the body's

As such, altruism or pro-social behaviour is merely in appearance when our genes are acting in self-interest since we tend to share the same genes with those around us.

Evolutionary Development Propositions


Basic Concepts

Chromosomes are the basic structural units of heredity which are composed of DNA, normal humans have 23 pairs of chromosomes with the last pair being the sex chromosomes ( XX-female; XY-male).


Genes are the basic functional units of heredity which are located on chromosomes.

Genome is the complete set of genetic information that makes up an organism. Fig 3.1

99% of the genomes of all humans are identical, thus only 1% of genetics gives rise to differences found among us all. 

Genotype - involves the total genetic material for a given individual

Phenotype - observable expression of physical and psychological characteristics, (height, weight, hair colour, personality & intelligence) 

The nature of Gene expression is based upon dominant and recessive genes where Dominant Genes will be expressed over their Recessive counterparts (e.g., Brown vs blue eye colour). Most mutant genes are recessive.

Sex-linked Genes occur on the X or Y chromosomes where genetically women have two X genes in their pair. If one X gene mutates, there is still a backup copy. Males have only 1 Y and 1 X gene, so if there is a mutation there is no backup.



Polygenetic Inheritance is where phenotype characteristics are determined by the interaction of many genes.


Epigenetics - Proteins surrounding the genome are sensitive to environmental conditions and turn on or off specific genes

Epigenetics twins


Stages of Prenatal Development

Conception to Birth - First the human starts out as a zygotes (0-2 weeks) then forms into an embryo (3 to 8 weeks) ( 40, 45, 60, 120 days ) then into a fetus (9 to 39 weeks).

Three trimesters of pregnancy:


Variations in development

Prenatal development is sensitive to the infleunce of genetic variabilites, hormones and other chemicals.

Hormones and other chemicals that pass through the placenta will potentially have an impact on the growing fetus. 

E.g., Testosterone may be secreted during this stage to provide the second stage of gender identity development.

Teratogens are substances that are toxic to the embryo or fetus and may lead to developmental deficiencies.  critical periods

E.g., Thalidomide was given to pregnant mothers for morning sickness from 1957 to 1961. It was soon found to cause birth defects such as phocomelia - limb deformities (hands without arms).

Rubella (German Measles) if mother contracts it prior 11 th week can cause mental retardation, blindness and deafness, and heart problems.

Cat feces contain a unicellular parasite, toxoplasmosis, that can cause hydrocephalus (a condition in which the brain swells), intellectual deficiencies and anemia -3 rd trimester.

Fetal Alcohol Syndrome - occurs when the mother consume large amounts of alcohol during (early) pregnancy. Symptoms are: stunted growth, facial deformities , & intellectual deficiencies.

Even for mothers who only have 2-3 drinks a day may have children who have deficits in: balance, dexterity & intelligence, attention, memory & math ability.

Stress & Development

Stress can alter our hormones and immune system functioning and can have an impact on t e developing fetus.

Studies suggest an a increased risk of the child later developing ADHD, emotional and language problems.

Given the impact of epigenetics there is also the possibility of Intergenerational trauma being passed on in such a fashion.

Nurturing low birth weight and preterm infants

Teen mothers or others who many have experienced malnutirion, smoking, or other stressful conditions may give birth to low birth weight infants.

Preterm infants (born 3 + weeks before full term) also may be born due to medical conditions of the mothers that don't allow ful term pregnancy.
The infants may be premature - before 37 weeks of pregnancy, Low birth weight - of less than 2.3 kg, Very low birth weight - of 1.4 kg., or Extremely low birthweight - of under 0.9 kg.

Complications form such conditions may include the development of learning disabilities, ADHD, Autism Spectrum Disorders, or breathing problems like asthma.

Treatment for such infants may involve isolation in incubators and the use of many medical (machine) interventions, where by they don't recieve the contact comform that most "normal" infants recieve.

Kangaroo  Care involes holding he infant skin to skin by their mothers for 2 - 3 hours per day to foster growth and well being. Just adults and children need to be touched and "cuddled" these treatments can reduce mortality, sever illness, infection and length of stay in hospital as well.

Social development of emotional bond and regulation also begins at this stage of life, where such "contact comfort" gives rise to secure attachment (see later sections).