TABLE 1.

Summary of romantic love using Tinbergen’s (1963) framework.

Causes	Key question	Summary of answer
Proximate
Mechanisms	What are the mechanisms that cause romantic love?	Romantic love is associated with social mechanisms, psychological mate choice mechanisms, and the expression of specific genes. The cognitive, emotional, and behavioral features of romantic love result from neural activity associated with reward and motivation, emotions, sexual desire and arousal, and social cognition as well as endocrine activity associated with sex hormones, serotonin, dopamine, oxytocin, cortisol, and nerve growth factor. Research into psychopathology, cognitive biases, and animal models can inform our understanding of the mechanisms regulating romantic love.
Ontogeny	How does romantic love develop over the lifetime of an individual?	Romantic love first develops in childhood, manifests at all ages, usually lasts months or years, but can exist for many years or decades. It is influenced by a range of internal and external factors, is cross-cultural, and may be influenced by the modern environment.
Ultimate
Functions	What are the fitness-relevant functions of romantic love?	Romantic love has a number of fitness-relevant benefits and costs that relate to four interrelated functions: mate choice, courtship, sex, and pair-bonding. There is a small amount of evidence about the health benefits and costs of romantic love. Theories exist about selective pressures that led to the evolution of romantic love. Romantic love is a complex suite of adaptations and by-products and can be either adaptive or maladaptive.
Phylogeny	What is the evolutionary history of romantic love?	The antecedents to romantic love existed in mammals before romantic love evolved. Its evolutionary history was probably coupled with the emergence of pair-bonds sometime recently in human evolution. There may be ethnic or geographic variation in romantic love and culture has influenced romantic love’s effect on human evolution in recent times.