Authors: Frans de Waal, Richard Byrne, Robin Dunbar, William C. McGrew, Anne Pusey, Charles Snowdon, Craig Stanford, Karen B. Strier, and Richard W. Wrangham
BOOK SUMMARY
Tree of Origin: What Primate Behaviour Can Tell Us About Human Social Evolution
Image: edited to show Pan species, a chimpanzee (left) next to a bonobo (right)
Introduction
Purpose of Comparative Biology
"Depending on whether the main objective is to confirm human identity or to stress the common thread that runs through all forms of life"
1. Separating humans from animals
In anthropology, trying to define humanity, determining if a behaviour is exclusive to our species
2. Integrating humans with animals
As in the Darwinin approach, evolution, natural selection and behavioural origins/similarities
3. Understand human social evolution BY comparison to primates
Using observations of social organisation, communication, learned habits, subsistence, reproduction and cognition
4. Understand human behavioural evolution BY comparison to primates
Tool use etc.
Influential Factors
"All behaviour in all primates, including our own species, derives from a combination of evolved tendencies, environmental modification, development, learning, and cognition"
Behaviour is influenced by genetic and environmental factors
Kin selection, competition and cooperation, and food distribution important in determining affects on social behaviours
Comparisons & Beginnings
Pioneering comparisons of primate and human behaviour:
1967 Desmond Morris's 'The Naked Ape'
1971 Jane Goodall's 'In the Shadow of Man'
Reconsider culture, language etc.
Origins of politics, warfare, morality seen in primates
Image: credit from the book itself, 'Tree of Origin', showing the evolutionary primate tree
1.
Of Genes and Apes: Chimpanzee Social Organisation and Reproduction
by Anne E. Pusey
Social structure: Patterns of kinship, residence, philopatry and mating
Influence: Patterns of cooperation and social behaviour
Observing Chimpanzees:
Typically difficult to observe wild
Provisioning use to be used to habituate chimpanzees
1960 Jane Goodall, Gombe National Park: banana provisioning
1965: Toshidada Nishida, Mahle Mountains: sugar cane provisioning
Adv: make close observations, habituate shy chimpanzees, follow individuals easily
Dis Adv: effect behaviour unnaturally, less valid results
1970-1980: non-provisioned
Communities:
Jane Goodall: chimpanzees move alone/small temporary parties, any gender/age, only sometimes gather in large communities, only mother and offspring stable group
Toshidada Nishida: chimpanzees rarely all together, live in large "unit groups" (communities), several adult males and more/same females and offspring
Now: chimpanzee communities 20-120 individuals
Fission-fusion society:
Individuals of a community spend time alone and time in temporary sub-groups
Females 50% time alone, males 18% time alone
Females localised but do visit all ranges, males large 8-15km range
Unusual among primates
Due to female receptivity
Sexual receptivity cycles by swellings lasting 13 days in a 36-day cycle
5.2 year Gombe/7 year Kibale interbirth intervals
Swellings: females over large range/outgoing
No swellings: feed alone accompanied by dependent offspring over small range
Females distributed SO Males range over wide area in groups to protect access to receptive females
Due to feeding behaviour
Richard Wrangham: diet consists of seasonal/sparse fruits which cannot suit large groups, females minimise competition and maximise efficiency and reproductive success by feeding alone
Violence:
1960s Gombe: no evidence of lethal aggression
1970s Gombe: habituated communities at feeding stations split into sub-groups, these groups became extreme separate communities, Kaesekela North and Kahamana South and they stopped travelling into the other range, patrolling boundaries and violent group attacks observed
Male chimpanzees participate in intergroup hostility
Why?
Feeding territory protection
Female access protection
Female access increase by expanding territory
Philopatry and dispersal:
Nishida: males and females belong to set particular group
Wrangham: male-only groups with female crossing both groups so male groups compete for territory with more females
BUT males attack both opposition/foreign community males and females
Goodall: 20 different strange females at Gombe attacked, 15/20 had infants
Females sensitive to community borders and expand core range with groups range
SO female group spatial allegiance means males don't gain more females by expanding range
So true dynamic: Male territoriality repel males and females of other communities
Males remain with kin and females disperse
Due to feeding
Goodall, Williams, Pusey: Males defend community feeding territory
Small range: smaller core area of females, chimpanzee density higher, lower body weight, longer interbirth interval
Expanding range: increase reproductive success and rates
Due to avoiding interbreeding
Male chimpanzees return to birth group from mothers stay within kin community range
Females mate with natal community and then disperse to avoid interbreeding with kin
Females show less sexual receptivity to male relatives, and scream to avoid them
This behaviour and social structure prevents interbreeding, reduced viability and fertility of offspring
Philopatry-dispersal of opposite sexes observed in many animals as interbreeding avoidance mechanism
Common pattern is for female philopatry and male dispersal
Chimpanzees have male philopatry and female dispersal
Due to kin selection
Male philopatry: cooperate with kin, genetics are passed on via relatives
Female dispersal: male kin remain for kin selection, so females must disperse to avoid interbreeding
Evidence: Gombe individuals shared mitochondrial DNA with individuals several km away which proves extensive female migration
Group dynamics and behaviour:
Friendlier behaviour towards relatives
Bonobos: females (which show philopatry in bonobos) have strict dominance hierarchy, with relatives and dominant females showing most support for one another and males have hierarchies with tense relationships and do not groom
Chimpanzees: male hierarchies depend on alliances with other males, many aggressive interaction but also more friendly male relationships, rival males groom and cooperate against external male threats, female rank has effect on reproductive success, offspring mature younger as they gain better access to food
But is it due to relatedness/kinship?
Mitochondrial DNA shows the most genetically related chimpanzees did not have close relationships
Chimpanzees with close behaviour relationships, cooperation and grooming were not maternally related
Relationships are opportunistic and not kinship related, for advantage of power
Philopatry-dispersal may have initially evolved for kinship
Levels of relatedness reduced by individual strategies and mating choice
Mating patterns and reproduction:
Female swell to advertise readiness to mate
Swollen females are centre of attention and subject to attack, wounding, less feeding time, infection
IMO: Though not advantages to the female. This feature is retained perhaps as it is those who have it who are more likely to reproduce and pass it on
Females can mate multiple times per day when receptive
Due to infanticide prevention
Infanticide is frequent but mating with many males confuses relation
Males will not want to kill their own offspring
By confusing who the father is, any male who has mated with the female will not kill the offspring, thus mating with more males offers greater protection from infanticide
Sarah Hrdy: Male primates taking over another group kill group infants so females return to receptivity
Mating with many males, even when pregnant, helps confuse paternity
e.g. Mahle: males kill boy offspring from newly immigrated females, though these males had mated with the females the fact that the females' ranging pattern was close to the border of their old group proved that infants were of dubious paternity, eventually females spend more time with the infanticidal males
Due to female gain
Females may mate with many males for personal gain
Males are more likely to protect and share food with females they have mated with
Due to genetic gain
Females mating with many males increase chance of high quality genes
More likely chance of high-quality male fertilisation
Increases male competition so more high-quality males mate with females
Male behaviour
Generally competition for female is low
Towards end of ovulation when fertilisation more likely high-ranking males become possessive of females
In large groups, high-ranking males work together to guard female and share copulation
Male may take female to edge of community range for long period, but the single pair at risk of neighbouring attacks
IMO: this last one sounds similar to human partnership behaviour
Males may also force females by attack to mate, or they may go willingly
Sexual dimorphism
Males much larger than female chimpanzees
Darwin: males compete aggressively over females
Male chimpanzees have large testes compared to other apes
As females mate with many males and house multiple male gametes, males who deposit more sperm are more likely to fertilise the female gamete
Paternity - who is the father?
Consortships high in chimpanzees (conceptions range from 50% Tutin and McGinnis, to 25% Goodall and Wallis)
Goodall: unlikely rank relates to paternity, even though alpha males may be possessive, females still mate with many males when likelihood of fertilisation high, so chance of paternity is varies
Other studies show rank and paternity correlation is strong but not absolute
Due to these mating patterns relatedness is rare, and few offspring are actually full siblings from the same parents
Human and Chimpanzee social structures
Similarities
Hunter-gatherer bands consist of 150 members similar to chimpanzees
Female-biased dispersal and male philopatry (in agricultural, 2/3 hunter-gatherers)
Intergroup hostility
Patrolling
Kinship importance
Male philopatry- female dispersal so rare but occurs in chimps, bonobos and humans suggests it was also seen in our common ancestor
Sexual dimorphism with larger males
Differences
Human hostility is organised warfare and pitched battles with many opponents unlike chimpanzees
Kin bonds elaborated beyond group boundaries to extent of marriage in humans
Human copulations private unlike primates
Humans form conjugal marriage bonds, monogamy or man with many female partners unlike chimpanzees where females not bound and have multiple mates
Humans mate over more of total life span
Human mating occurs at lower frequencies, but at any time
Lower sexual dimorphism in humans (15%) than chimpanzees (25%)
Humans do not show cyclic changes to advertise ovulation
Why do humans form pair bonds and forgo high promiscuity?
Labour division: females gather vegetables and males hunt so the sexes share, infant dependency increased as brain size increased so males help protect and care for infant
Female benefits: Smuts suggests females gain protection by male partners and a male has increased mating opportunity, Wrangham proposes that after invention of cooking females needed males to guard their food
2.
Apes from Venus: Bonobos and Human Social Evolution
by Frans B. M. de Waal
Use Bonobos and Chimpanzees as models
Bonobos as valuable as chimpanzees in studying human behaviour
Historically: Chimpanzee violence/male dominance means we adopt it as a model of the origins of human social behaviour and Bonobos more peaceful/female importance means they have been overlooked
Exaggerated idea: Chimpanzees not completely violent, Bonobos not completely peaceful
Use both as model: not wishful to compare to peaceful bonobo, or staying traditional to chimpanzee human social similarity
Biology
Bonobo changed very little since human-pan common ancestor
Chimpanzee adapted to semi-open woodlands
Bonobo stay adapted to equatorial regions
Chimpanzees adapted to new environment, bonobo similar environment to common ancestor = Bonobo model of the common ancestor?
Examples
Bonobos often walk upright (e.g. carrying food), with straight back more than other apes = very humanlike
Harold Coolidge state 1933 that bonobos "may approach more closely to the common ancestor of chimpanzees and man than does any living chimpanzee." = bonobo generalised anatomy as model of evolution, bridge gap between human and chimpanzee differences
Adrienne Zihlman measured body-weight distribution = bonobos resemble australopithecines (early hominid)
Image: credit Frans de Waal from the book itself, 'Tree of Origin', showing bonobos standing upright
Behaviour
3.
Beyond the Apes: Reasons to Consider the Entire Primate Order
by Karen B. Strier
4.
The Ape's Gift: Meat-eating, Meat-sharing, and Human Evolution
by Craig B. Stanford
5.
Out of the Pan, Into the Fire: How Our Ancestors' Evolution Depended on What They Ate
by Richard W. Wrangham
6.
by Richard W. Byrne
How did our cognition and intellectual capacities evolve?
Role of Comparative Biology
Behaviour of ancient ancestors hardly preserved archaeology
Behaviour of modern living species can provide an insight
We can look at:
What form does a particular behaviour take?
The functions of a particular behaviour now?
Under what conditions is a particular behaviour seen?
How is the behaviour related to the environment?
How does the behaviour vary?
Relatives have evolved as much as we have since divergence
Modern primates they are not perfect prehistoric ape replicas
Two popular but wrong theories of using comparative biology:
19th Century: Great Chain of Being
Belief that studying modern primate is direct way our ancestors were like
View that monkeys evolved into apes evolved into humans
Ontogeny recapitulates phylogeny
20th Century: Radical Behaviourism
Belief that all species equal so rat can be used to compare with humans rather than ape
But if all species equal why need comparison
Claims that language sets humans apart
BUT
Both theories are overly simplistic
Language cannot be acquired suddenly, it is so complex it must have roots in other animal cognition
Capacities of all animals are not equal:
Monkeys show more complex behaviour than most mammals
This ability results from an enlarged neocortex that allows rapid learning
Great apes demonstrate some understanding of intentions and causes.
This comprehension is based on an ability to perceive, and to build, complex novel behaviour
What do we need to consider to answer evolutionary questions?
1. Function of evolved trait
Selection pressure = environmental challenge
Environmental challenge met by aptitude
How challenge increased inclusive fitness in carriers of allele/trait
How did those with trait produce more offspring with trait than those without the trait
Example: Cognition
"What environmental challenge caused ancestors to gain a fitness advantage from the cognitive adaption?"
The challenge may not have related to the function of cognition at the time
Are the challenges which cognition helps with today the same as the ones which led to its evolution, or does intelligence have new functions?
2. Form of evolved trait
Specific abilities for one use?
Multiple uses?
If intelligence is modular its function may have been the same
3. Chronology of trait
a) Sociocultural variation
Modern: cross-cultural variation
Evolutionary variety between cultures
Understand modern human psychology - individual and social environments
Recent evolution of trait
b) Evolution since divergence
Ancient: Evolutionary changes since divergence from last ancestor
Change in biological potential seen via archaeology, knowledge modern humans and last common ancestor
Behaviour leaves little material trace so archaeology rooted in past environment is more accurate
c) Evolution before divergence
Adaptions in our last ancestor with the potential for intelligence
Roots of intelligence have own evolutionary origins (challenges in past)
Presence and cause of intellect of the common ancestor can only seen via comparative study
Overall:
As humans and chimpanzees/bonobos are more closely related to each other than any of them are to gorillas and orangutans, our last common ancestor is only 4.5m years old. This is too short a time span for any intellectual development. We need to look at its roots before our divergence. Modern comparative studies of animals shows wide intellectual differences, this provides evidence of the stages of intellectual development in human past.
Evolutionary Reconstruction
Evolutionary reconstruction uses comparative evidence to reconstruct the human past
The distribution of the characteristic in the living members is used to reconstruct its origin in the past
We can reconstruct the earliest phases of human behavioural evolution without fossil evidence
Similar to a family tree we use the phylogeny of primate relatives
Each biological branch on this family tree is a common ancestor
Existence of ancestors reliable from modern studies
Fossils/bones hard to attribute as lineage may have died out quickly
Phylogeny based on molecular and DNA similarities
Change occurs at constant rate overtime
So we can roughly calculate dates of ancestor
Traits shared with certain animals show its evolutionary origins:
All monkeys = early evolutionary origin (approx. 25-30m ya)
Great apes = trait evolves12-25m years ago
Chimpanzees = trait evolves 4.5-6m years ago
No species share trait = trait evolves after 4.5m years
Where trait is developed by convergent evolution (independently in different species) this cannot tell us how it evolved in humans but perhaps its function
Primate comparison allows time-frame for human behaviour
Complex Primate Behaviour
Social Support:
Monkeys and apes interact in third parties
Rely more on alliances to give power in competition
Alliances form among kin and non-kin
Grooming:
Important trade in alliances
Repaid by support in fights/tolerance at feeding site
Socially complex:
When major alliance threatened by minor argument, even opponents will reconcile
Obligation and influence of relationships key
Analysis of Social Rankings:
Socially knowledgable
Monkeys attacked by dominant animals react to assert their power
Attacked monkeys redirect aggression to weaker parties (like bullying)
Attack young relatives/subordinate females to gain power
Choice of victim shows awareness of social rank, opponents, dominant members and alliances
Calls and responses to monkeys shows they are aware of:
Other kinships
Dominance and social rank of other members
Membership of groups they were never part of
Deception and Dominance:
Monkeys and apes use social knowledge for manipulative tactics (deception to get what they want)
Example:
Dominant male stops female gorillas from mating with subordinates
So she 'gets left' to be out of site to copulate
Invite subordinates and copulate quietly
Whiten and Byrne Survey of Deception:
Primatologists rarely publish 'anecdotes' of deception
Survey done to see cases of deception
Results suggest tactics varied but deception is used by primates
Example:
Young baboon screamed as if hurt when saw adult with food
Mother scare off 'aggressor'
Young gets food
AND Young aware of:
Ensuring this is when mother out of sight
Mother's rank is higher than adult
Not reusing tactic often on same person
Why do primates have social complexity?
Quick at remembering socially relevant info
It is a species typical principle based on genetics
Trial and Error learning:
Because primates have fast social learning and connect social facts to environmental circumstances, they can quickly learn from situations
Example:
1. Event happens (Baboon attacked by adult)
2. Events follow (Mother protects young and gets food)
3. Application (Use situation is deceptive way next time)
OR
Learn based off observing others
Ability to Learn:
Based off size of neocortex
Ratio neocortex linked to larger brains
Dunbar: ratio also linked to size of group/social complexity
Size neocortex may also be related to recognition (social or environmental - such as fruits)
Apes have brain x2 size of mammal of same body mass
Feedback Loop:
Increasing social complexity may select for brain size
Increasing brain size affects behavioural complexity
(neocortex ratio affect frequency of deception)
Theory:
Larger brains evolved in response to a need for social skills, this increased brain size allowed for rapid learning which underlies the social sophistication of apes
Inability to understand mental state:
Tempting to assume animals using deception understand the situation
BUT comprehension of deceit and situation is not necessary
Rapid learning based off observation and application rather than understanding
Dorothy Cheney and Robert Seyfarth Experiment
Mother approached by "predator" when infant
a) can see threat
b) cannot see threat
In both circumstance mother alerted child of threat
Unaware of infants mental state of seeing or not
This explains why animals who are manipulated by deception do not understand what is happening
BUT Chimpanzees and apes show knowledge of intention:
Sarah Boysen Experiment
Chimpanzee approached by "predator" when friend
a) can see threat
b) cannot see threat
When chimpanzee realises its friend cannot see a call is raised and it acts to "protect"
When chimpanzee realises its friend can see there is no call raised
Chimpanzees can distinguish mental states
In the wild only chimpanzees teach offspring in a way that is aware of infants ignorance
Ability to understand mental state is unique to Great Apes:
Chimpanzees aware of when being deceived e.g. annoyed at a "look behind you" trick when there is nothing there
Cercopithecine monkeys use deceptive tactics more frequently than great apes
BUT the ways the apes use tactics imply awareness of what they were doing
Chimpanzees must have intentional social manoeuvring (e.g. switch allegiances)
Example:
Frans De Waal observe in Chimpanzee Politics:
Male who did not have qualities to become top ranked himself
Male used clever switches of allegiance to gain more effective power than held by either of the two males he supported
Once they began to solidify position with his support he defected to the other
Reasons behind social manoeuvring:
Males who require powerful ally to hold top rank were always vulnerable
A male who gradually built up a broad base of support among weaker males and females males was able to hold tenure far longer
Self-recognition:
Gordon Gallup notice chimpanzees, but not monkeys, show self-recognition
E.g. Looking in the mirror to examine hidden areas of their bodies such as teeth and gums, or making repeated, exaggerated gestures while watching their reflections
Complex understanding:
Few Old World monkeys regularly make/use tools
Chimpanzees in West Africa use two rocks as hammer and anvil to break nuts
Chimpanzees in East Africa use tools and bimanual coordination to capture ants
Manipulation of tools and techniques:
Capuchins use tools but in simplified situation - obvious visibility of hole of an open termite mound
Chimpanzees can termite fish with less clear mound, without a hole, and delicately guide tool - more abilities beyond use of tools
Planning:
Chimpanzees can plan their tactics driven by knowledge not immediate stimuli and show awareness of possible outcomes
Examples:
No suitable plant for fishing grows near termite mound, chimpanzees plan to make tools in advance to bring to site
No suitable rocks near nuts, chimpanzees carry a hammer-stone before they get to tree
Cultural Variation:
McGrew shows local traditions in chimpanzee tool use as in human cultures:
Some discard frayed tools
Some rotate tools to use less worn end
Some 'resharpen' tool
The use of inefficient methods shows social learning by imitation
Trial-and-error requires progression towards optimal technique and cannot pin point inefficiency if there is no more efficient method attempted to compare to
Elaborate series of actions:
Tool manipulation and planning is a great ape trait
Example:
Gorilla diet is mainly of plants which use stings/hard castings/mechanics which make it hard to it
Gorillas use techniques to minimise stings from nettles
Remove leaf blades in gathered bunch by using half-open hand to strip stem
Remove stems/petioles with worst stings
Folds leaf bundle so only one leaf sting side is exposed
Why are great apes cognitively superior?
Efficient Skill Learning Mechanism: Imitation
Gorilla: population consistent techniques and individual variation at detail
Chimps: inter-population tool use differences not explained by ecology
Orangutan: copy human traditions (e.g. building fire)
Comprehend objects and events - mental states and tool behaviour
Monkeys cannot acquire complex novel behaviour by observation and imitation
Great ape ancestor had cognitive potential to plan, imitate and understand others
Not due to further neocortex size (neocortex affects learning speed) so something else affect ape mental complexity (maybe structure?)
Selection Pressure:
Complex Social interaction
30m years ago: monkey and ape ancestor develop rapid learning and larger brain
Due to: Need for larger permanent groupings
Monkey vs Ape Competition
12m years ago: apes and human ancestor develop ability to take account of others' behaviour and understanding
Due to: Large size of apes adapted to brachiation (for trees) mean walk in awkward gait on knuckles
Old World monkeys have adv of eating unripe fruit
SO apes develop cognitive abilities such as foraging and planning to survive intense competition with monkeys
What cognitive skills were we left with?
A causal understanding of complex behaviour, enabling novel schedules of actions to be put together and allowing the behaviour of others to be used as a source of ideas for new action schedules; in other words, nonverbal planning and skill learning by imitation
A degree of understanding of the intentions of others-what they want, know, and think; in other words, possession of a theory of mind
Evolution of language would be impossible in a species in which individuals could not imagine that other individuals know things that they do not know themselves.
Language is acquired by imitation - not by direct copying
Children do not parrot our parents' words
Child "imitates" a word, the actual sounds are quite different and the use of the word is individual
An understanding of a novel behaviour is gained so an individual can express it in their way
7.
Dunbar Brains on Two Legs: Group Size and the Evolution of Intelligence
by Robin I. M. Dunbar
Group size is a possible measure of social complexity
Social complexity then drives intelligence and neocortex size
The evolution of language allowed these large group sizes and brain advances
8.
by Charles T. Snowdon
9.
The Nature of Culture: Prospects and Pitfalls of Cultural Primatology
by William C. McGrew
My Reflections
What makes us human?
One would think our genes, looks, tools and intelligence makes us human but even those can be seen elsewhere.
It cannot be complex social structures, constructions, verbal communication and cultural material production, because we were human long before any of these.
Perhaps abstract thought and art? But I'm sure other species display that too.
Distinguishing us as a species by genetics?
We are Homo Sapiens based on our unique DNA - the genetic species theory.
However, what actually makes us human, humanity?
This has actually become harder to define as we learn more, as we compare humans with animals.
Rather than finding ways to distinguish ourselves from animals - as perhaps was the initial intention behind comparative biology - we find our behaviours and biology are identifiable in a wide variety of species.
From species close to us (primates) to even distantly related animals (dolphins), humans and not separate from nature, we are, like all animals, products of evolution and natural selection and thereby hold an equal place among all species.
Comments