Human Behaviour

Question 1

Themes of Lecture

Answer 1

1. Why study behaviour?
   Function drives form: behaviour “drives” anatomy
2. Levels of control of behaviour (timing, plasticity)
3. Variation in human behaviour (plasticity)
4. Evolutionary perspective on behaviour: many behaviours are adaptations (result from natural selection in particular environments)

Natural selection of behaviour (survival & reproduction)

Sexual selection of behaviour: (e.g. aspects of human mate choice & mating competition)

Question 2

Why is behaviour of interest?

Answer 2

Behaviour is the interface of the organism with its environment and as such precedes the evolution of many anatomical and physiological features.

ex. Locomotion and changes in femurs and pelves in Australopithecus & Homo

Behaviour is part of our interactions with one another. We are constantly behaving and interpreting the behaviour of others

Question 3

Human behaviour: function & evolution

Answer 3

Proximate explanations:

What controls, elicits, or modifies the expression of a behaviour and what is the outcome within the life time of an individual?

Genetics, physiology, development, ecology

Ultimate explanations:

How does a behaviour increase survival and reproduction?

What is the selective advantage that has resulted in the evolution of
this behaviour?

How?

*Comparative analyses of behaviour use naturally occurring variations and measure survival and reproductive success.

Repeated correlations of behaviour with environmental variables

Question 4

Behaviour occurs in a context

Answer 4

Physical environment (forest canopy, woodland floor…) cold response

Biological environment (Food substances, Predators, Conspecifics)

PROXIMATE: What triggers the behaviour within the individual?
(e.g. hunger => food search and ingestion)

ULTIMATE : What was the selective pressure that resulted in this
variant predominating (over others)?
if nutrients (energy) too low, organism dies or can’t repro empty gut => hunger=> food search behaviour => energy intake

How did the behaviour contribute to SURVIVAL andREPRODUCTION in the INDIVIDUAL ACTOR?

Selective advantage of a behaviour is context dependent.

Question 5

Ultimate and Proximate explanations are NOT alternatives.

Answer 5

1. There will be ultimate AND
   proximate explanations possible for every behaviour.

how does it work?
what did it contribute to & repro?
https://www.birdspot.co.uk/bird-reproduction/ courtship-behaviour-in-birds selection pressures (under what conditions?)

2. The mechanisms of control and expression of a behaviour can tell us something about its evolution.
   examples: courtship rituals
   (feed intended mate)

Question 6

“Controls” of behaviour

Answer 6

Proximate (how & when):
Immediate (fast response)

Neuronal
CNS
Reflexes

Intermediate (expression, thresholds, likelihood)

Development (early psychosocial stress changes repro patterns)

Hormonal
CNS
Cognitive / Learning
Ultimate (why)

Environment through natural selection shapes level of control as well as the behaviour itself

How fast must the response occur to increase (survival/repro) ?

Question 7

General questions about human behaviour?

Answer 7

Human universals

what is true of all humans and different from other species? (derived species trait)

Human diversity
what is true of some humans and not others?
(popn, sex, culture….)

Human plasticity
how does developmental context shape human behaviours?
physical environment (altitude)
social environment (father absence, # bros)

Question 8

Individual (natural) Selection

Answer 8

Survival:

Recognizing and avoiding predators, parasites

Efficient foraging (obtaining energy)

Allocating energy

Cooperating and competing with conspecifics (learning)

Reproduction:

Recognizing and accessing mates

Appropriate levels of care of offspring
selection for investment, infanticide, neglect ?
learning

Reminder of natural selection definition in appendix

Question 9

Reflex behaviours: Involuntary responses

Answer 9

Primitive reflexes (low plasticity)
behaviour that is not volitional (that is automatic)

Rooting (turns to cheek side stimulation), plantar (curl of foot at stimulation), grasping
https://www.youtube.com/watch?v=0vrdkzOnGgo
startle

“Fight or flight” adrenalin response
Pupil dilation low light
pleasing sight

These are behaviours with little plasticity !!

UNLIKE many species, much of human behaviour has MUCH plasticity.

Question 10

Mammalian males and females

Answer 10

General mammalian case:

Mammalian females invest more in offspring (gestation and lactation) and so usually increase their fitness more by
obtaining better quality mates.

Mammalian males invest less in offspring and so usually
increase their fitness more by
obtaining a greater number of mates obtain more mates by out-contesting competitors

Question 11

Mammalian Repro: Contributions to offspring differ between sexes

Answer 11

Question 12

Sexual selection

Answer 12

“Increased individual fitness through obtaining a larger number of mates
OR better quality mates”

Different roles and time commitments by males and females to offspring =>
different selection pressures acting on 2 sexes of one
species

behaviour morphology psychology

Question 13

Selection for: Human mate preferences

Answer 13

Answer 14

Question 14

Waist to Hip Ratio
Preference

Answer 14

Sexually selected trait is the preference in males,

NOT the ratio itself.
The ratio has to do with natural selection on fat storage for female reproduction
Think about this!

Answer 15

Question 15

Symmetry

Answer 15

Both sexes show preference for symmetry over asymmetry
(experimental)

Both sexes able to assess symmetry

Male preference trait for symmetry may be greater

Symmetry indicative of developmental robustness in face of environmental challenges while in-utero (genetic quality??

Question 16

summary

Answer 16

Behavioural traits that we are NOT aware of (not consciously performing)

Reflexes

Preference traits

Selection can act differently on males and females

Results in diferences within species of the two sexes

Understand how natural selection can result in a trait that underpins sexual selection of a preference trait

Understand sexual selection and why and how it differs in
males and females

How might a preference trait then further result in sexual selection for the original naturally selected trait (think about whr)

Question 17

Social Behaviour and Kin selection

Answer 17

Kin selection for seemingly “altruistic” behaviour (an additional explanatory model for the evolution of “helping” behaviour)

Reciprocity a further development in social behaviour (altruism moderated by repayment)

Social learning
Brains and Learning
Social living

Question 18

Primates

Answer 18

Lived in complex and changing environments

Almost all live in social groups

Many very complex social groups

In social groups: at least one sex was surrounded by relatives (one sex emigrates)

Had relatively long and overlapping life spans

Conditions conducive to selection for social learning

Conditions conducive to selection for “altruistic” acts

Answer 19

Altruistic behaviour : behaviour that conveys an individual fitness cost to the actor and a
fitness benefit to the recipient

Altruistic behaviour is NOT expected to evolve through natural selection at the individual level
(expect to help offspring only)

WHY?

How do we explain apparently altruistic behaviour?

Must live in (social) group (with relatives?)

Benefits of social acts

Question 20

When can natural selection favor an “altruistic” allele?

Answer 20

Think in terms of individual natural selection

Costs of the trait in a given environment (development, energy,
opportunity costs) relative to alternative trait

Benefits of trait in environment relative to alternative

Translate costs to units of reproduction (fitness costs)

Think of the benefits of the trait (as above) and translate to units of reproduction (fitness benefits)

Traits can evolve through natural selection if B > C

How to explain traits where the Cost to individual reproduction
looks bigger than the Benefit to reproduction ??

Question 21

Living in social groups

Answer 21

Living in groups involves competition and cooperation

Can cooperation that has a cost to the individual evolve?

The kind of behaviour that we think we see every day in humans woman throws herself into ocean to try and rescue her son person rushes into street to grab a child from being run over fireman runs into burning building

Are these altruistic?

Answer 22

Answer 23

Question 24

Kin selection provides an explanatory model to understand the evolution of:

Answer 24

Food sharing Cooperative care of young by other than parents Delayed reproduction and care of siblings Group defence against predators Cooperative behaviour

Question 24

Kin Selection and Inclusive fitness

Answer 24

Inclusive fitness = Sum individual fitness + Additional fitness (copies of genes) increased in next generation through individual's influence on his/her relatives' reproduction.

Question 25

2nd explanatory model: Reciprocity expands the constraint function to include "repayment"

Answer 25

The immediate cost of an altruistic behaviour may also be beneficial to an individual's individual fitness IF it is likely to be returned at a later time when its benefit will be greater. This is less dependent on relatedness (r) Because cost is reduced if repaid But note: cost is now, benefit later so not guaranteed (probability function)

Question 26

Reciprocity in Hunter-gatherers

Answer 26

Hunter - gathering peoples often share food items Gathered foods (plants) are usually shared with immediate family only A hunter does not get a large prey item very often and very large prey items cannot be efficiently stored Hunted foods (large meat items) are often shared more widely in the group (Hadza, Ache, !Kung, Efe etc) Everyone eats better more often if share when they get an item

Question 27

What facilitates reciprocity?

Answer 27

Living in social groups Overlapping generations Individual recognition Complex environment with variance in resources available to individual Living with kin ?? .. brains. Environments that are also associated with larger

Question 28

Correlates of enlarged brain size

Answer 28

climate cooling Increases in brain size in 4/7 clades occurs during or just post major climate cooling (decrease in oceanic surface temperature) Primates brain size correlated with diet: fruit and animal eaters >> leaf eaters both brain and gut tissue are "expensive" tissues. Large brain requires high quality food group size: larger groups >> larger brain for body size

Answer 29

Answer 30

Question 31

Evolution of Large Brains

Answer 31

Primates have larger brains for their body size than mammals in general Humans have VERY large brains for body size Selection for ecological problem solving? And/or Selection for tracking complex social environment

Question 32

Learning

Answer 32

Individual learning allows individual to respond to the environment s/he experiences experience = change or reinforce behaviour many species do this Social learning allows individual to respond without the potential cost of individual learning observing other's experience => change or reinforce one's behaviour

Question 33

Human Behavioural Plasticity

Answer 33

Homo spread over the world into a variety of habitats because they had a generalized diet and an ability to acclimate rapidly to change. Part of this ability to acclimate is due to the ability to learn to learn from others

Question 34

Human Sociality

Answer 34

Homo brains and behavioural plasticity Learning as an adaptation to changing environments Individual learning (own experience) Social learning (others' experiences; Culture) Cooperative and "helping" behaviour Kin selection (benefit through related fitness of individuals) Reciprocity (benefit through later receipt of at least equal "goods")

Question 35

Living in cooperative social groups also resulted in the evolution of social learning

Answer 35

Genetic adaptation is slow Rapid environmental change cannot be tracked genetically Most or all Primates have individual learning Some Primates have social learning - Japanese macaques, potato washing - Chimps termite fishing, hunting Humans are excellent social learners...... More on topics covered relative to these 2 lectures in ANHB 2215: Human Variation (evolution of life history, ecology, development, genetics, culture)

Question 36

Summary

Answer 36

Ability to learn is an adaptation to rapidly changing environments and/or living in social groups Cooperative behaviours evolve in kin groups through kin selection according to Hamilton's Rule Kin groups facilitate selection for reciprocity but are not required (think about this carefully) Evolution of cooperative behaviours in kin context facilitates living in "super-social groups" Social living precedes social learning Social learning can lessen the cost of individual learning