evolution and behaviour

Evolution and Behaviour

Session 21

Presentations due for Fridays session Needs to include a mind map/plan of a model

exam response 5% deduction for late submissions

Quick Reminder!

Evolution is the changing in the inherited traits of a species over time.

What is evolution?

Based on the assumption that living organisms face environmental challenges.

Organisms that adapt the best have a greater chance of passing there genes to the next generations.

Organisms with specific genetic traits that enhance survival are said to be naturally selected.

They are more likely to survive and pass those traits on.

Many of the traits that you have been passed down to you to help you survive.

Darwin’s theory of evolution

A principle of evolutionary psychology is that as genes mutate, those that are advantageous are passed down through a process of natural selection. This is derived from Charles Darwin's theory of evolution.

Evolutionary psychologists attempt to explain how certain human behaviours show how humans have developed over time. Certain behaviours can be explained by examining their evolutionary origins and their identifying their ability to enhance survival.

What is evolutionary psychology?

I am going to show you 14 images

For each picture I am going to ask you to write down the first emotion you feel when you look at the image

You may find some of these pictures unpleasant. You have the right to withdraw at any time

Activity

How does this image make you feel?

What did you notice?

What emotion do you think these people are experiencing? How do

you know?

◦ Model Answer Intro In this essay the behaviour which will be

examined in terms of an evolutionary explanation of behaviour is the study of emotions, in particular disgust.

Disgust: Noun A feeling of revulsion or profound disapproval

aroused by something unpleasant or offensive.

Disgust: what the dictionary says...

A universal emotion?

•Ekman (1972), found facial expression for disgust was identical in different cultures across the globe. •Facial expression also produced in blind individuals and is correctly interpreted by individuals born deaf.•This evidence indicates an innate biological basis for the expression and recognition of disgust. The recognition of disgust is also important among species as it has been found that when an individual sees another person looking disgusted after tasting a particular food, he or she automatically infers that the food is bad and should not be eaten.• This evidence suggests that disgust is experienced and recognized almost universally and strongly implicates its evolutionary significance.

The face of disgust

“Yuck!”

Curtis (2004) has even claimed that disgust could have been one of the first words uttered by humans. "The word 'yuck' is similar in languages all over the world. It seems

to be a proto-word," says Curtis.

Fessler’s (2006) study of an evolutionary basis for disgust in pregnant women

Aim:To investigate whether the ‘morning sickness’ experienced by

pregnant women has an evolutionary basis.

Investigated women's experiences of nausea during pregnancy (resulting in morning sickness).

During the first trimester, hormones suppress the immune system in order to accustom the body to the foreign genetic material growing in the womb.

He hypothesised that the heightened sense of disgust experienced by women during this time was the body's way of compensating for the lacking immune system.


Procedure:A sample of 496 healthy pregnant women aged between

18 and 50 years old was used. The women were asked to consider 32 stomach churning

scenarios such as: - Walking barefoot and stepping on an earthworm- Someone accidently sticking a fishhook through their

finger- Maggots on a piece of meat in a outdoor trashcan Before asking the women to rank how disgusting they

found the scenarios (using a survey), Fessler posed a series of questions, designed to determine whether they were experiencing morning sickness.


Findings & Conclusions: Women in the first trimester of their pregnancy scored much higher on scores across the board on disgust sensitivity than their counterparts in the second and third trimester. They found the scenarios involving food most disgusting. As many of the most harmful diseases are food-borne,

Fessler concluded that a heightened sense of disgust was advantageous to our ancestors and allowed them to survive long enough to produce offspring, who passed on the same sensitivities.

It would have helped compensate for the increase susceptibility to disease during early pregnancy, which is a risky period due to the suppressed immune system, by increasing the urge to be picky abut food.


Evaluation This study supports the role of disgust in aiding

reproduction, and thus, as an evolutionary behaviour. The data was collected through questionnaires. Self

reports may not be a great way of measuring disgust. It would have been better to confront them with real

disgust-eliciting objects. The effect was big (but not hugely significant when

using statistical significance).

Fessler’s study supports that disgust may be an evolutionary behaviour as it may assist reproduction of offspring and protection against disease, thus having a greater chance of surviving or living a longer life, having children passing on genes to their offspring.

Links back to the question

Curtis et al. (2004) Internet survey on disgust responses

Aim: AimTo carry out research on the Internet to test

whether there were patterns in people’s disgust responses.


Aim: Procedure:Used an online survey in which participants were shown

20 images. Participants were asked to rank their level of disgust. Among the 20 images were seven pairs in which one

was infectious or potentially harmful to the immune system, and the other was visually similar but non-infectious—for example, one pair was a plate of bodily fluids and a plate of blue viscous liquid.

There were 77 000 participants from 165 countries.

Curtis et al (2004) results

Disgust reaction was most strongly elicited for those images which threaten one’s immune system. ◦ Natural selection may have helped human ancestors to be

more disgusted at things which threatened the immune system to avoid things that could potentially lead to diseases.

Women had higher disgust reactions than men.◦ As women are carriers for offspring, they have a stronger

disgust reaction so as not to threaten the lives of unborn offspring.

The disgust reaction also decreased with age. The decrease of disgust with age may be explained by the fact

that the older a member of a species, the less likely they are to reproduce.


Evaluation

Curtis used 77 000 participants from 165 countries. Large sample size and cross cultural = generalisable

Provides support for Fessler et al (2005) and vice versa

Self report measures of disgust = subjective


Curtis (2004) study supports the role of disgust in aiding reproduction, and thus, as an evolutionary behaviour.

Links back to question

But we can override the disgust response. People find family less disgusting than strangers. And when it comes to sex, we compromise

between our instinctive avoidance of disease and our urge to reproduce.

But do we find everything disgusting?

Recent research has also suggested that sensitivity to disgust is related to ethnocentrism (Navarrete & Fessler, 2006) as well as various politically conservative issues including abortion, immigration, homosexual marriage and stem-cell research, as well as prejudice toward homosexuals.

Disgust sensitivity has also been found to be correlated with other variables such as right-wing authoritarianism, religious fundamentalism (Terrizzi & Ventis, 2006) and religious obsessions (Olatunji, Tolin, Huppert & Lohr, 2005).

*Ethnocentrism is judging another culture solely by the values and standards of one's own culture.

Other factors influencing disgust

Evaluative points for evolutionary theoryIn spite of such evidence, there are some things to consider

when examining an evolutionary argument. The theories are speculative – its difficult to carry out

experiments to clearly prove the theories

• Since it may be difficult to test empirically some evolution-based theories, researchers may be susceptible to confirmation bias— that is, they see what they expect to see. The researcher Hayes (2005) states that there is a tendency to ignore findings that don’t fit in with the theory confirmation bias

• Little is known about the behaviour of early Homo sapiens, so statements about how humans used to be are hypothetical.

• Evolutionary arguments often underestimate the role of culture/nurture/the present environmental influences in shaping behavior.

There is some evidence to support evolutionary explanation of disgust

◦ Fessler (2006) showed that disgust may be an evolutionary behaviour as it may assist reproduction of offspring by compensating for a suppressed immune system.

◦ Curtis et al. (2004) found that the disgust reaction may help to prevent sicknesses. Research suggests that disgust aids the survival of the

human species and is therefore an evolutionary behaviour.

Also need to consider other factors such as the environment

Conclusions?

Want to take part in some online disgust research?

http://www.yourmorals.org/explore.php

Disgust Scale

evolution and behaviour

Documents

particular disgust

recognition of disgust

face of disgust

behaviour evolution

evolutionary psychologists

evolutionary origins

evolutionary significance

facial expression