Evolutionary Psychology

“In the distant future . . . psychology will be

based on a new foundation, that of the

necessary acquirement of each

mental power and capacity by gradation.”

--Charles Darwin, 1859

What is evolutionary psychology?

• The study of the psychological adaptations of humans to the changing physical and social environment, especially of changes in brain structure, cognitive mechanisms, and behavioral differences among individuals.

Evolutionary Biology + Cognitive Psychology

= Evolutionary Psychology

The goal of evolutionary psychology is to understand

behavior from an evolutionary perspective

Origins of Modern Humans

• Homo Erectus– Migrated from Africa to Asia (1.8 MYA)

Milestones in the Origins of Modern Humans

Increases in brain size during evolution

ardipithecus

brain size: 300 ccs

Australopithe-cus

brain size: 310-530 ccs

homo habilis

brain size: 580-752 ccs

homo erectus

brain size: 775-1225 ccs

Neandertal

brain size: 1200-1450 ccs

modern human

brain size: 1350 ccs

What are the two major theories of the origins of complex adaptive mechanisms?

1. Creationism

2. Evolution by natural selection

Darwin’s Theory of Natural Selection

• The explanatory challenge:

1. why change takes place

2. how new species emerge

3. what the functions are of parts

The key to natural selection: Differential reproductive success because of heritable variants; everyone has ancestors, but not

everyone leaves descendants

Natural selection provided 3 key answers

• Explained change over time: descent with modification

• Explained the apparent purpose quality of component parts: adaptive function

• United all species into one grand tree of descent: including humans (this is the one creationists don’t like!)

Darwin was deeply troubled by facts that could not be explained

by natural selection.Hence, the need to explain the tremendous importance of the

theory of sexual selection

Illustrative Thought Experiment:Mission Impossible

• What would you do if you were a gene?

• Your Mission: to increase your replicative success

Sexual Selection

Evolutionary theorists argue that physical attractiveness reliably conveys biological information about a person's genetic quality, health, and reproductive potential.

Being able to judge these attributes reliably would have enabled people in Stone Age environments to select healthy mates and be reproductively successful, as healthy mates would be better providers and protractors for the family unit.

“Evolutionary Theory of Female Physical Attractiveness” Singh (2006)

Sexual Selection Components

• Intrasexual Competition

“Adaptations in humans for assessing physical strength from the voice”

Sell et al (2010)

Recent research has shown that humans, like many other animals, have a specialization for assessing fighting ability from visual cues.

Because it is probable that the voice contains cues of strength and formidability that are not available visually, we predicted that selection has also equipped humans with the ability to estimate physical strength from the voice.

We found that subjects accurately assessed upper-body strength in voices taken from eight samples across four distinct populations and language groups: the Tsimane of Bolivia, Andean herder-horticulturalists and United States and Romanian college students.

Regardless of whether raters were told to assess height, weight, strength or fighting ability, they produced similar ratings that tracked upper-body strength independent of height and weight.

Male voices were more accurately assessed than female voices, which is consistent with ethnographic data showing a greater tendency among males to engage in violent aggression.

Raters extracted information about strength from the voice that was not supplied from visual cues, and were accurate with both familiar and unfamiliar languages.

These results provide, to our knowledge, the first direct evidence that both men and women can accurately assess men’s physical strength from the voice, and suggest that estimates of strength are used to assess fighting ability.

Core Tenets of Evolutionary Psychology

• 1. All behavior is a function of psychological mechanisms + input to those mechanisms

“Disgust as an adaptive system for disease avoidance behaviour”

Curtis et al (2011)

Disgust is an evolved psychological system for protecting organisms from infection through disease avoidant behaviour. This ‘behavioural immune system’, presents in a diverse array of species and exhibits universal features that orchestrate hygienic behaviour in response to cues of risk.

Disgust is also a dynamic adaptive system.

Specialized learning mechanisms modify the disgust response.

Hygiene behaviour is influenced at the group level through social learning and cultural norms

Core Tenets of Evolutionary Psychology

• 2. All psychological mechanisms, at some basic level, originate from evolutionary processes

Core Tenets of Evolutionary Psychology

• 3. Natural and sexual selection are the most important evolutionary processes responsible for creating psychological mechanisms

Core Tenets of Evolutionary Psychology

• 4. Evolved psychological mechanisms become part of the brain (remember Maguire?).

Core Tenets of Evolutionary Psychology

• 5. Evolved psychological mechanisms are functional: Designed to solve statistically recurrent adaptive problems

Evolved Sex Differences Exist

Men and Women Differ in Domains Where they Have Recurrently

Faced Different Adaptive Problems Over Human

Evolutionary History