Triggers of humanity

Theories of human evolution usually select a trait that is unique or distinctive in humans, and build a theory explaining how this trait underlies others, and was the ‘cause’ of human evolutionary success. There are many contenders –

Trait Benefits in human evolution Proponent
Hunting Provides high quality food and enhances cognitive skills for planning and social co-operation. Dart
Aquatic Resources Provides high quality food especially for brain development, and reduces high residential mobility. Crawford
Cooking Enhances nutritional value of food through reduced digestion/chewing, and enhances social cooperation. Wrangham
Food sharing Enables foraging specialisation (men hunt, women gather) and reduces ecological risk and enhances sociality. Isaac
Bipedalism Allows for more efficient terrestrial foraging or frees the hands for tool making.  Darwin
Social brain Large brains allow individuals to cope with social complexity, the benefits of which enhanced human cognition, culture and behaviour. Dunbar
Language Language is the basis for complex, abstract thought, for communication, for social bonding, and organisationand planning.
Culture Culture – the social transmission of information and behaviour – is the basis for all human activities
Communal breeding The successful development of a human child is heavily dependent upon communal investment (i.e. beyond the mother), and this improves survivorship and enhances co-operation Hrdy
Tool-making (Stone) tool-making made for much greater extractive efficiency of resources, required social communication for learning, and also advanced cognitive skills.

The structure of most of these trigger or driving force theories is to identify a trait found in humans but not in apes (or better still, in rudimentary form in apes), and show how this trait is a foundation to other traits. This principle runs through Darwin’s Descent of Man, in which he discusses key human traits, and seeks their potential antecedants. Raymond Dart was among the first to link a major causal theory of human evolution to the empirical evidence of the fossil record. For example, Richard Wrangham has argued that cooking provides the basis for reduction in dentition, reduction in the size of guts, increased digestive efficiency (and so more energy available for activity and especially reproduction), changes in life history (reduced infant mortality, early weaning, etc.), and greater levels of sharing, co-operation and social cohesion. This is then traced through the archaeological and fossil evidnece – for example, the first evidence for fire or changes in the size of the human rib cage (evidence for reduced gut size). Another example is Kristen Hawkes and Jim O’Connell’s model of the central role of grandmothers in human evolution, leading to , among other things, the evolution of the menopause. Trigger theories have given rise to a multitude of books called the something ape.

Desmond Morris's The Naked Ape started a trend of similarly titled books

Desmond Morris’s The Naked Ape started a trend of similarly titled books

The length of time human evolution took, the complexity of changes, and the chronological evidence of the fossil record make most of these trigger models unlikely, and most theories will explore the relationships between several factors.