As infants, we depend physically and emotionally on adult caregivers. As children, we learn to get along with others and to abide by the rules and norms of society. As adolescents, we begin to explore romantic relationships and consider how we will take our place in the adult world. As adults, we assume responsibility for the care and support of others and contribute, through work, to the broader society.

The bond between infant and parent is promoted by innate tendencies: the infant to cry and the parent to help. Infants prefer their caregivers and react to their caregivers and in that way, the infants take an active role in building emotional bonds between themselves and those on whom they most directly depend. Attachment refers to emotional bonds.

The experiments of Harlow with monkeys provided a lot of evidence for the contact comfort theory, in which the bond between mother and infant is promoted by the warmth and comfort of the mother. Bowlby’s evolutionary explanation of the fact that infants between 8 months and 3 years old are distressed when their caregivers are out of sight is that infants who were in their mother's sight were an evolutionary advantage in the past. Evidence for this comes from the fact that similar behaviours occur in all human cultures and in other species of mammals.

There are four types of attachment and this can be assessed by the strange situation test, in which the mother suddenly leaves the room leaving the child either by itself or with a stranger.

1. Secure attachment (60%)
   These infants actively explore the environment with their mothers present and become distressed when their mother leaves.
2. Insecure-resistant attachment (10%)
   These infants appear anxious even with their mothers present and don’t explore much. They become very distressed when their mother leaves, but display anger towards the mother upon return.
3. Insecure-avoidant attachment (15%)
   These infants appear anxious even with their mothers present and don’t explore much. They show little distress when the mother leaves and when the mother returns they avoid contact.
4. Disorganized/disoriented attachment (15%)
   These infants don’t fit the other categories and have mixed reactions to either the departure or the reunion of the mother.

Sensitive care is the behaviour in which the infant’s signals of distress are responded to promptly and the infants receive regular contact comfort and interact with the infant in an emotionally synchronous manner. Sensitive care correlates with secure attachment and the children that are securely attached were more likeable people later in life, as well as better at problem-solving and emotionally healthier. Children that have a certain homozygous gene are less affected by environmental experiences.

There are three successive stages in a child from age 1 – 12: autonomy, initiative and industry. Prosocial behaviour is voluntary behaviour intended to benefit other people. There are three aspects of young children’s prosocial behaviour:

1. Helping
   An infant from about 12 months old will randomly start to give out objects in games of give-and-take, will help the adults any way they can and they always want to help.
2. Comforting
   An infant will start to cry when other infants are crying. Until the age of 15 months, the infant’s distress when others are distressed is referred to as egocentric distress because they look for comforting themselves. At about 15 months the infant will respond to distress by attempting to comfort them.
3. Sharing
   The extent to which children share increases with age. Sharing in young children is especially common in situations in which they need to collaborate to achieve a goal.

The development of empathy causes prosocial behaviour to be based on the understanding of and concern for other’s needs and feelings. Children of about age 2 and younger frequently engage in emulation, using different means to achieve the same goal. Later in life, they start with imitation, copying actions exactly and start with overimitation, copying all actions exactly, even if some actions are irrelevant. Preschool children do not often deliberately teach a skill to another child. It is more common for a child to happen to see the outcome of another child’s actions.

Parenting styles are described in terms of two dimensions: the degree of warmth a parent shows toward a child, reflected by being loving and attentive to children and their needs and the degree of control a parent attempts to exert over a child’s behaviour. Parenting style can be divided into four general types depending on where a parent falls on these two dimensions:

1. Authoritarian (low warmth, high control)
   There is extensive use of power
2. Authoritative (high warmth, high control)
   The reason for the desired behaviour is explained. If the reason is not effective, use force.
3. Permissive (high warmth, low control)
   Little correction of undesired behaviour
4. Uninvolved (low warmth, low control)
   Not asking for anything, not giving anything.

Research found that the children of authoritative parents exhibited the most positive qualities. Evidence that parenting style influence children’s development comes from experiments that modify, through training, the styles of one group of parents and then compare their offspring to those of otherwise similar parents.

The evolutionary explanation that a child’s focus on peers is mostly because of future reproduction. Children across all cultures play and this play is mostly gender-segregated. Play serves as a possibility to develop skills. It also serves the function of learning an advanced understanding of rules, social roles and greater self-control. It also helps with the learning and understanding of society’s morals.

There is a difference between play between children that have a similar age and play between children that have a range of ages. Play between children that have a similar age is very competitive and this is not the case with play between children that have a range of ages. Younger children learn from older children through play and older children practice their nurturing skills through play with younger children. It also helps older children consolidate some of their knowledge by helping younger children.

There are gender differences between infants. Newborn boys are more irritable and less responsive to caregiver’s voices and faces than newborn girls. Boys from 6 months old also show anger more often than girls. By 13 to 15 months girls are more obedient than boys and this stays this way. By 17 months, boys show significantly more physical aggression than girls.

These differences could be explained by the way boys and girls are treated. The differences in treatment start at birth. By the age of 4 or 5, most children have learned strong cultural stereotypes for males and females. By this age, they also develop a gender identity, an understanding that they are one gender and will always be this gender. Young children often overgeneralize gender differences, with this being more extreme in boys than in girls. Children prefer to play with children of their own sex, although this preference is stronger in boys than in girls. In the segregated playgroups, boys often practice what they perceive to be masculine activities of their culture and the girls do it the other way around. Children sometimes reinforce gender segregation by ridiculing those who cross gender lines.

Girls and boys tend to play differently as well as separately. The world of boys has been characterized as consisting of relatively large, hierarchically organized groups in which individuals or coalitions attempt to prove their superiority through competitive games, teasing and boasting. The world of girls has been characterized as consisting of smaller, more intimate groups, in which cooperative forms of play predominate and competition is more subtle. Boys and girls play together more often in age-mixed groups.

Adolescence is the transition period from childhood to adulthood. It starts with puberty and ends when society deems the person an adult. In the stage of development emerging adulthood, a person has the independence of an adult but does not see himself like one yet.

The teenage rebellion typically occurs over immediate control that the parent still has over the teenager. Adolescence is often marked by conflicts centring parental authority. Children go to their parents for emotional support and this gradually declines. Adolescents mostly go to their peers for emotional support. Adolescents take more risks in life than any other age group. There are several theories for this:

1. Moffit’s theory
   The reason that adolescents take more risks is that adolescents are biologically adults and want to enter the adult world in any way available and crimes, sex and drugs is a way for them.
2. Harris’ theory
   This theory states that this risk-taking is not to join the adult world, but to set themselves apart from it.
3. Steinberg’s theory
   There is a competition between two developing brain systems, the cognitive-control network and the socioemotional network. The socioemotional network becomes dominant under conditions of emotional or social arousal or when in the presence of peers.

The increased risk-taking in mostly adolescent males is also called the young-male syndrome. There is a possible evolutionary explanation for this. In our species’ history, males who took risks to achieve higher status among their peers may well have produced more offspring, so genes that promoted this tendency have been passed along more.

Adolescence is also a period of rapid growth in the sophistication of moral reasoning and a time in which many people develop moral self-images that guide their actions. Kohlberg states that there are several stages of moral reasoning:

1. Obedience and punishment orientation
   Reasoners in this stage focus on direct consequences to themselves.
2. Self-interested exchanges
   Reasoners in this stage understand that different people have different self-interests, which sometimes come into conflict. To get what you want, you have to make a bargain.
3. Interpersonal accord and conformity
   Reasoners in this stage try to live up with the expectations of others who are important to them.
4. Law-and-order morality
   Reasoners in this stage argue that to maintain social order, each person should resist personal pressures and feel duty-bound to follow the laws and conventions of the larger society.
5. Human-rights and social-welfare morality
   Reasoners in this stage balance their respect for laws with ethical principles that transcend specific laws.

Moral reasoning is not the same as moral action. In adolescence there is a development of sexual attraction and a sexual-minority development; people start to identify their sexuality. Also, sexually transmitted diseases and pregnancy are relatively high in adolescence, compared to other age groups. Males are more eager to have sexual intercourse without a long-term commitment and this can be explained in terms of parental-investment.

Natural selection may have predisposed humans to be sensitive to cues in the childhood that predict whether one or the other sexual strategy (restraint vs. promiscuity) will be more successful. One such cue may be the presence or the absence of a caring father at home.

People in love typically experience distress when the other leaves, either temporarily or permanently. When an individual’s partner leaves, an individual typically experiences intense anxiety, depression and feelings of loneliness and emptiness that is not relieved even by highly supportive friends and active social life. The attachment that adults form with romantic partners can be classified as secure, anxious and avoidant. Bowlby's theory states that people form mental models of close relationships based on their early experiences with their primary caregivers and then carry those models into their adult relationships.

There are some relationship patterns that can be changed for the better if the couple is willing to work on them:

1. Positive style of talking and resolving arguments (e.g: avoid yelling and name-calling).
2. An effort to communicate when you disagree (e.g: don’t give the silent treatment).
3. Handle disagreements as a team (e.g: capitalize on each other’s strengths to resolve conflicts).
4. Honesty with self and partner

Jobs are perceived as the least stressful if they are:

1. Complex, rather than simple
2. Varied, rather than routine
3. Not closely supervised

The paradox of old age is the following. Objectively, life looks worse in old age, subjectively, it feels better. The socioemotional selectivity theory states that older people shift their attention to the present moment, instead of the future, and this causes older people to enjoy life more, despite the losses that old age brings. Older people attend to more positive emotional stimuli than negative emotional stimuli. This is called the positivity bias.

Terminally ill people will generally go through five stages upon hearing the news:

1. Denial
2. Anger
3. Bargaining
4. Depression
5. Acceptance