Explanation​:
Kin selection theory explains that altruistic behaviours are influenced by the desire to promote the survival of one's genes. This is an evolutionary explanation for prosocial behaviour, focusing on helping behaviour targeted at younger/healthy kin likely to reproduce. It says that it is evolutionarily beneficial to help individuals with similar genes, helping a twin or sibling because it will lead to the passing of one's genes to the next generations.

Explanation​:
Conformity involves the process of changing/altering one's behaviour/attitudes/opinions to match it with the social group. It focuses on the pressure created by a group/society on an individual.

Conformity is directly related to bystanderism because bystanders are a social group who implicitly agree not to take action in a specific situation. They are individuals who $\text{‘}$watch' the situation unfold without intervening/helping.

It highlights the conforming behaviour of an individual not to act because the group around is not taking action in a situation.

Explanation​:
De Dreu et al. (2010) have discovered that oxytocin, also called the love hormone, can lead humans to sacrifice themselves for the sake of their in-group members. Individuals were likely to self-sacrifice for the benefit of their in-group in a competition against the out-group.

The results showed that oxytocin was linked to in-group trust and cooperation, and aggression towards the members of the out-group.

Explanation​:
Modelling is one of the most effective ways of promoting prosocial behaviour in people. When people observe others being helpful or kind, they pick on those qualities and behave similarly.

Prosocial behaviours are intended to benefit others. For example, acts of kindness, cooperation, empathy, and altruism.

Explanation​:
When positive and constructive strategies are used to maintain a relationship, it is called accommodation.

Communication strategies used to maintain relationships are categorised as active/passive and constructive/destructive. Depending on the conflict an individual is in, people resort to these communication strategies.

Explanation​:
Studies on culture and interpersonal relationships often rely on self-reporting questionnaires as $\text{‘}$happiness', $\text{‘}$cultural norms' and $\text{‘}$satisfaction' is subjective and cannot be accurately measured by a third party. It may also be that members of collectivistic cultures are less likely to share negative feelings regarding their marriage/relationships because of the fear of society.

Explanation​:
The attraction$\text{–}$similarity model states that we are attracted to those we perceive to be similar to us. This is often observed in ethnicity, age, culture, and social class. This similarity is also seen in research on physical traits, personality, attitudes and beliefs.

Explanation​:
The jigsaw classroom technique for conflict reduction was developed by Elliott Aronson. This technique mainly divides the tasks equally among group members to ensure that the only way to achieve success is to cooperate. It has been used in the school setting for creating cooperative learning groups in classrooms.

Explanation​:
The reciprocal altruism theory defines altruism as prosocial behaviour between genetically distant or unrelated individuals, which may incur some cost or detriment on the helper's side. An example of this behaviour is helping to save a stranger's life by putting one's life in danger.

This theory was proposed by Robert Trivers in 1971.

Explanation​:
The sociocultural approach to understanding human behaviour explains the development of prosocial behaviour through Lev Vygotsky's research on the influence of social and cultural factors on human development. Cultural norms and values may shape prosocial behaviour. Primary and secondary socialization helps to learn prosocial behaviour in the early years.

Explanation​:
According to Gottman's Four Horsemen, stonewalling is when an individual withdraws from a conversation and refuses to acknowledge the other individual.

In this process, a person refuses to communicate with their partner, resulting in one-way communication.

In support of this, research done by Collins, Miller and Steinberg (1994) and Huang (2016) found that self-disclosure may be an essential element in forming and maintaining relationships.

Popov, A., Parker, L., & Seath, D. (2017). Psychology course companion (2nd ed.). Oxford University Press.

Explanation​:
Gottman & Gottman (2017) conducted longitudinal research using data and method triangulation. To understand the natural principles of love, their research used both qualitative and quantitative methods to collect detailed data. Observation method, biometric data, audio/video data, polygraphs and electrocardiograms, interviews and questionnaires were used.

Explanation​:
The by-products of the categorisation process that lead to prejudice and discrimination are in-group favouritism and out-group discrimination. The same can be observed in the Robbers Cave experiment by Tajfel, where members of the same group favoured their group members while showing hostility towards members of the other group.

Explanation​:
The realistic group conflict theory was studied by Campbell in 1965.

The theory states that inter-group conflict mostly arises when groups (in-group and out-group) have opposing goals and are competing for limited resources.

Explanation​:
Empathy-altruism hypothesis focuses on the role of empathy and pro-social behaviour in promoting cooperation among individuals.

The hypothesis was proposed by Daniel Batson, who believed that people act out of empathy and genuine concern for the well-being of other people.

Explanation​:
Daniel Batson designed the empathy-escape paradigm to differentiate between two types of helping motivation. The assumption is that empathy can be generated for a sufferer. For example, individuals told to imagine another person's stress are likely to experience more intense physiological arousal, as a result of which they are likely to help the person in need even though escape in that situation is easier.

Explanation​:
Vasopressin has been found to play a role in stable, long-term pair bonding in prairie voles. Prairie voles are rodents who actively select mates, are monogamous, share parenting and are characterised by long-term pair bonds.

These social characteristics found in them, along with similar brain structures and neurochemical make-up, make them a perfect sample to study social behaviour in humans.

Popov, A., Parker, L., & Seath, D. (2017). Psychology course companion (2nd ed.). Oxford University Press.

Explanation​:
The social dominance theory explains the existence and persistence of social hierarchies, as well as the intergroup dynamics and discrimination that occurs within those. It focuses on the belief that for one group to succeed in society, another group must fail.