Chapter 2 - Biological Beginnings

Question 1

NATURAL SELECTION and ADAPTIVE BEHAVIOUR

Answer 1

NATURAL SELECTION is the evolutionary process by which those individuals of a species that are best adapted are the ones that survive and reproduce. In On the Origin of Species, DARWIN argued that, in the struggle for life, those organisms that survive are better adapted to their world than are the non-survivors.

ADAPTIVE BEHAVIOUR is behavior that promotes an organism’s survival in the natural habitat - for example, attachment between a caregiver and a baby for it ensures caretaking and protection.

Question 2

EVOLUTIONARY PSYCHOLOGY

Answer 2

EVOLUTIONARY PSYCHOLOGY emphasises the importance of adaptation, reproduction, and “survival of the fittest” in shaping behavior - “fit” is the behaviour that ensures the ability to bear offspring that survive long enough to bear offspring of their own.

DAVID BUSS is one of the leading researchers in evolutionary psychology - he has been especially influential in stimulating interest in how evolution can shape behaviour. He reasons that evolution pervasively influences how we make decisions, how aggressive we are, our fears, and our mating patterns.

Evolutionary psychology has limitations - some scholars acknowledge the important influence of evolution on human adaptation, still reject the idea that behavior is strictly the product of evolved biology. According to this view, evolution gave us biological potentialities, but it does not dictate behavior. Evolutionary theories are difficult to test or refute because evolution is on a time scale that does not lend itself to empirical study.

Question 3

EVOLUTIONARY DEVELOPMENTAL PSYCHOLOGY

Answer 3

Recently interest has grown in using the concepts of evolutionary psychology to understand human development. Some ideas proposed by EVOLUTIONARY DEVELOPMENTAL PSYCHOLOGISTS are:

1) an extended childhood period in humans might have evolved because humans require time to develop a large brain and learn the complexity of human societies;
2) many of our evolved psychological mechanisms are domain-specific - as our ancestors dealt with certain recurring problems, specialised modules that process information related to those problems evolved. For example, such specialised modules might include a module for mathematical knowledge for trading, and a module for language to communicate.

Question 4

GENETIC FOUNDATIONS of DEVELOPMENT

Answer 4

The nucleus of each human cell contains CHROMOSOMES, threadlike structures made up of deoxyribonucleic acid - or DNA - and proteins which contain genetic information. GENES are short segments of DNA which guide protein production and promote cell reproduction - proteins are the building blocks of cells.

A) Genes are COLLABORATIVE: whether a gene is turned “on,” working to assemble proteins, depends on environmental influences. Internal events - such as hormone flow - and external events - such as stress, radiation, and temperature - can excite or inhibit gene expression. Hormone flow is strongly influenced by external events, such as light, day length, nutrition, and behavior.

B) Genes are ENDURING: they are passed from generation to generation, thanks to two mechanisms:
1) Every cell except sperm and egg cells has 46 chromosomes arranged in 23 pairs - they reproduce through MITOSIS, in which the cell’s nucleus duplicates creating two identical daughter cells.
2) Sperm and egg cells contain 23 unpaired chromosomes - they are produced through MEIOSIS, in which a cell’s nucleus duplicates but then divides twice, thus forming four cells, each of which has only half of the genetic material of the parent cell.
During FERTILISATION, an egg and a sperm fuse to create a single cell, called a ZYGOTE, which has 46 chromosomes. Each chromosome in the pair contains varying forms of the same genes, at the same location on the chromosome.

Question 5

SOURCES of GENETIC VARIABILITY

Answer 5

Combining the genes of two parents in their offspring increases GENETIC VARIABILITY in the population by creating several sources of variability:

1) the chromosomes in the zygote are not exact copies of those in the mother’s ovaries and the father’s testes - during meiosis which chromosome in the pair goes to the gamete is a matter of chance;
2) in a phenomenon known as CROSSING-OVER, during meiosis, before the pairs separate, pieces of the two chromosomes in each pair are exchanged, creating a new combination of genes on each chromosome;
3) chance events - such as flaws in cellular mechanisms - produce MUTATED GENES, which are permanently altered segments of DNA.
4) For each GENOTYPE - a person’s genetic makeup - a range of PHENOTYPES - the set of observable characteristics -can be expressed.

Question 6

GENETIC PRINCIPLES that regulate the relation between GENOTYPE and PHENOTYPE

Answer 6

Several principles determine how a genotype is expressed to create a particular phenotype:

1) DOMINANT-RECESSIVE genes principle:
A DOMINANT gene always exerts its effects overriding the potential influence of the other gene, called the RECESSIVE gene. RECESSIVE genes exert their influence only if the two genes of a pair are both recessive.

2) SEX-LINKED genes principle:
Most mutated genes are recessive. When a mutated gene is carried on the X chromosome, the result is called X-linked inheritance. If there is a disease-relevant gene on the X chromosome, males have no “backup” copy to counter the harmful gene and therefore may develop an X-linked disease.

3) GENETIC IMPRINTING principle:
Genetic imprinting occurs when genes have differing effects depending on whether they are inherited from the mother or the father - a chemical process randomly “silences” one member of the gene pair.

4) GENE-GENE INTERACTION principle:
many genes are interdependent in determining a phenotypical characteristic - characteristics that are determined by the interaction of many different genes are said to be POLYGENICALLY DETERMINED.

Question 7

CHROMOSOMAL ABNORMALITIES

Answer 7

CHROMOSOMAL ABNORMALITIES result from the formation of a gamete which does not have the typical set of 23 chromosomes. The most important abnormalities result in:

A) DOWN SYNDROME, which consists in disabilities involving motor and intellectual development caused by the presence of an extra copy of chromosome 21;

B) SEX-LINKED CHROMOSOMAL ABNORMALITIES, such as:

1) KLINEFELTER SYNDROME, a chromosomal disorder in which males have an extra X chromosome, making them XXY. Males with this disorder have undeveloped testes, and they usually have enlarged breasts and become tall;
2) FRAGILE X SYNDROME, that results from an abnormality in the X chromosome which often produces mental deficiency - it is more frequent in males than in females, possibly because the second X chromosome in females balances the effects of the abnormal X chromosome;
3) TURNER SYNDROME, a chromosomal disorder in females in which an X chromosome is either partially or completely missing. Females with Turner syndrome are short in stature and have a webbed neck;
4) XYY SYNDROME, a chromosomal disorder in which the male has an extra Y chromosome.

Question 8

GENE-LINKED ABNORMALITIES

Answer 8

GENE-LINKED ABNORMALITIES are produced by harmful genes:

1) PHENYLKETONURIA (PKU) is a genetic disorder in which the individual cannot properly metabolise phenylalanine - if left untreated, excess phenylalanine builds up in the child, producing intellectual disability and hyperactivity. It results from a recessive gene - it is easily detected, and it is treated by a diet that prevents an excess accumulation of phenylalanine.
2) SICKLE-CELL ANEMIA is a genetic disorder that impairs the functioning of the body’s red blood cells. Red blood cells carry oxygen to the body’s other cells and are usually shaped like a disk - a recessive gene causes the red blood cell to become a hook-shaped “sickle” that cannot carry oxygen properly and dies quickly, which results in the body’s cells not receiving adequate oxygen, causing early death.

Question 9

PRENATAL DIAGNOSTIC TESTS

Answer 9

A number of PRENATAL DIAGNOSTIC TESTS can indicate whether a fetus is developing normally:

1) ULTRASOUND TOMOGRAPHY;
2) FETAL MRI;
3) CHORIONIC VILLUS SAMPLING;
4) AMNIOCENTESIS;
5) MATERNAL BLOOD SCREENING;
6) NONINVASIVE PRENATAL DIAGNOSIS.

Question 10

ULTRASOUND TOMOGRAPHY

Answer 10

ULTRASOUND TOMOGRAPHY is a prenatal medical procedure in which high-frequency sound waves are directed into the pregnant woman’s abdomen. The echo from the sounds is transformed into a visual representation of the fetus’s inner structures - it can also give clues about the baby’s sex. This technique poses virtually no risk to the woman or the fetus.

Question 11

FETAL MRI

Answer 11

FETAL MRI makes use of a powerful magnet and radio images to generate detailed images of the body’s organs and structure - it can provide more detailed images than ultrasound. Generally, ultrasound will indicate a possible abnormality and then fetal MRI will be used to obtain a clearer, more detailed image.

Question 12

CHORIONIC VILLUS SAMPLING and AMNIOCENTESIS

Answer 12

CHORIONIC VILLUS SAMPLING, in which a small sample of the placenta is removed, may be used to detect genetic defects and chromosomal abnormalities. It can be used between 10 and 14 weeks after conception, and there is a small risk of limb deformity when CVS is used.

AMNIOCENTESIS is a prenatal medical procedure in which a sample of amniotic fluid is withdrawn by syringe and tested for chromosomal or metabolic disorders. The amniotic fluid is found within the amnion, a thin sac in which the embryo is suspended. Ultrasound tomography is often used during amniocentesis so that the syringe can be placed precisely. It must be performed between the 14th and 20th weeks of pregnancy - it brings a small risk of miscarriage.

Both amniocentesis and chorionic villus sampling provide valuable information about the presence of birth defects, but they also raise difficult issues for parents about whether an abortion should be obtained if birth defects are present .

Question 13

MATERNAL BLOOD SCREENING

Answer 13

MATERNAL BLOOD SCREENING identifies pregnancies that have an elevated risk for birth defects such as spina bifida and Down syndrome. The current blood test is called the TRIPLE SCREEN because it measures three substances in the mother’s blood.

Question 14

NONINVASIVE PRENATAL DIAGNOSIS

Answer 14

NONINVASIVE PRENATAL DIAGNOSIS represents an alternative to procedures such as chorionic villus sampling and amniocentesis. It focuses on brain imaging techniques and the isolation and examination of fetal cells circulating in the mother’s blood.

Question 15

INFERTILITY AND REPRODUCTIVE

TECHNOLOGY

Answer 15

INFERTILITY is defined as the inability to conceive a child after 12 months of regular intercourse without contraception. The cause of infertility can rest with the woman or the man - the woman may not be ovulating, she may be producing abnormal ova or her fallopian tubes may be blocked, whereas the man may produce too few sperm or the sperm may lack the ability to move.

Infertility can be overcome with:

1) SURGERY;
2) HORMONE THERAPY;
3) ASSISTED REPRODUCTION TECHNOLOGY (ART), such as IN VITRO FERTILISATION, in which eggs and sperm are combined in a laboratory dish, and then transferred into the woman’s uterus. Success rate for IVF depends on the mother’s age, and one result of fertility treatments is an increase in multiple births. No significant differences were found between the children from the in vitro fertilisation and the spontaneously conceived children.

Question 16

ADOPTION

Answer 16

ADOPTION is the social and legal process by which a parent-child relationship is established between persons unrelated at birth. Children who are adopted very early in their lives are more likely to have positive outcomes than children adopted later in life - still, a majority of adopted children and adolescents adjust effectively. Studies have shown no differences in the self-esteem of adopted and non-adopted children and adolescents, as well as no differences between transracial and same-race adoptees.

A number of changes have characterized adoptive children and adoptive parents in the last three to four decades - couples started to adopt a much wider diversity of children such as children from other countries, other ethnic groups, with motor or mental disabilities or abused children. In recent decades increased diversity has characterized adoptive parents as well, and many adoption agencies today have no income requirements and permit adults from a wide range of background to adopt.

Parents of adopted children face some unique circumstance - they need to recognise the differences involved in adoptive family life, communicate about these differences, show respect for the birth family, and support the child’s search for self and identity.
In INFANCY few differences in attachment have been found between adopted and non-adopted children, whereas in EARLY CHILDHOOD many adopted children begin to ask where they came from. This is a natural time to begin to talk in simple ways to children about their adoption status - secrecy can create psychological risks if the child later finds out about the adoption. As they grow older, children might question their parent’s explanation - during ADOLESCENCE, the stage in which individuals develop person al identities, problems might arise as adolescents might reflect on their adoptive status in more complex ways, such as focusing on the physical differences between themselves and their adoptive parents.

Question 17

BEHAVIOR GENETICS and related RESEARCH DESIGNS

Answer 17

BEHAVIOR GENETICS seeks to discover the influence of heredity and environment on individual differences in human traits and development.

To study the influence of heredity on behavior, behavior geneticists often use either:

1) TWIN STUDIES, in which the behavioural similarity of identical twins - who are genetically identical - is compared with the behavioural similarity of fraternal twins - who only share similar environments. Several issues complicate interpretation of twin studies - perhaps the environments of identical twins are more similar than the environments of fraternal twins, for genes may influence the type of environment an individual is exposed to;
2) ADOPTION STUDIES, in which investigators seek to discover whether the behavior and psychological characteristics of adopted children are more like those of their adoptive parents, who have provided a home environment, or more like those of their biological parents, who have contributed their heredity.

To understand the environment’s role in differences between people, we should distinguish between SHARED ENVIRONMENTAL EXPERIENCES - siblings’ common experiences, such as their parents’ personalities or intellectual orientation, the family’s socioeconomic status, and the neighbourhood in which they live - and NONSHARED ENVIRONMENTAL EXPERIENCES - a child’s unique experiences.

Question 18

3 HEREDITY-ENVIRONMENT CORRELATIONS

Answer 18

Individuals’ genes may influence the types of environments to which they are exposed by providing “environmental propensities”. Behavior geneticist SCARR described three ways that heredity and environment are correlated:

1) PASSIVE GENOTYPE-ENVIRONMENT correlations: children inherit genetic tendencies from their parents, and parents also provide an environment that matches their own genetic tendencies (musically inclined parents provide musical tendencies and environments);
2) EVOCATIVE GENOTYPE-ENVIRONMENT correlations: children’s genetic tendencies elicit stimulation from the environment that supports a particular trait - thus, genes evoke environmental support (outgoing children elicits friendly responses from others);
3) ACTIVE GENOTYPE-ENVIRONMENT correlations: children actively seek out environments that reflect their own interests and talents and are thus in accord with their genotype (musically inclined children seek musical environments in which they can employ and practice their abilities).

The emerging view is that complex behaviors are influenced by genes in a way that gives people a propensity for a particular developmental trajectory.

Question 19

The EPIGENETIC VIEW and the GENE X ENVIRONMENT INTERACTION

Answer 19

The EPIGENETIC VIEW states that development is the result of an ongoing, bidirectional interchange between heredity and the environment. Epigenetic mechanisms involve molecular modification of the DNA strand as result of environmental inputs in ways that alter genetic functioning. Epigenetic modifications change the likelihood of genetic expression but they do not change the genetic sequence. The standard definition of epigenetic requires these alterations to be heritable.

This interaction between environmental input and changes in genetic expression is called GENE X ENVIRONMENT INTERACTION - epigenetic studies focus on the interaction of a specific, measured variation in DNA and a specific, measured aspect of the environment. Research involving interaction between genes and environmental experience has focused on attachment, parenting and predisposition to depression. It has been found that some genes are a risk factor for psychological disorders only if an individual has also experienced early adversities, such as physical abuse.