return to SALMON
"Does inclusive fitness theory predict grandparents' investment in their grandchildren?"

A Psychological Research Methods and Critical Thinking Exercise

Author Paul Kenyon

Lecture #1

 

Inclusive fitness: examples from everyday life

Inclusive fitness theory

Genes and kin selection theory

Levels of certainty in paternity: maternal certainty and paternal uncertainty

Generation effects

The "Grandmother Hypothesis"

References

Workshop Activities

 

Lecture #2

 

Workshop feedback

Results file

Interpreting your results

 

 


Inclusive fitness: examples from everyday life

 LIFE FOR BABY KILLER


27 November 2004

A Whitleigh man who battered a six-month-old baby to death was today beginning a life sentence for the killing.

A Plymouth Crown Court jury delivered a unanimous guilty verdict after hearing how Jeffrey George Newton smashed Jack Graham's skull against a wall or bunk-bed and then hit him so hard he left an imprint of his ring on his head.

After the verdict, Jack's mother Gemma Graham branded her baby's murderer 'scum', saying he had turned her life into a living hell.

Newton, 32, was ashen-faced and visibly shocked as judge Mr Justice Owen told him he would serve a minimum of 13 years in prison before being considered for parole.


Inclusive fitness theory

Evolutionary psychology holds that the human mind contains specialized modules that have evolved to increase inclusive fitness. Inclusive fitness refers to the propagation of genes into future generations, either directly by mating and caring for offspring, or indirectly by helping relatives (kin) survive and reproduce. Grandparents can increase their own inclusive fitness by helping their grandchildren survive and reproduce.

 

Genes and kin selection theory

Identical twins share 100% of their genes with each other. A parent shares 50% of their genes with each of their children. A grandparent shares 25% of their genes with each of their grandchildren. According to kin selection theory, parents and grandparents will invest time and effort into children and grandchildren.



Kin selection theory explains nepotism - the tendency to behave altruistically towards blood relatives - kin. Altruism involves a donor, a recipient, and a cost to the donor and benefit to the recipient. An altruistic act involves the donor giving something of benefit to the recipient that will enable them to survive and reproduce. According to kin selection theory, altruism increases as genetic relatedness increases. Hamilton (see Buss, pp223) formulated a rule to predict altruism between relatives. Basically Hamilton's rule predicts that we will favour close relatives over more distant ones for any given act of helping.

 

We all have four grandparents who can be classified as follows:

 

·         Father's father - FaFa

·         Father's mothers - FaMo

·         Mother's father - MoFa

·         Mother's mother - MoMo

 

 

Euler and Weitzel (1996) found those grandparents on the father's side of the family (paternal grandparents - FaMo and FaFa) provided less care for their grandchildren than grandparents on the mother's side of the family (maternal grandparents - MoMo and MoFa).

 

euler weitzel results

 

 

Levels of certainty in paternity: maternal certainty and paternal uncertainty

One explanation for this effect involves parental certainty. Women know with absolute certainty that they are the mothers of their own children (maternal certainty). On the other hand - because of the possibility of female infidelity - men can never be completely certain that they are the fathers of their children (paternal uncertainty).

 

In the case of a grandfather there are potentially two opportunities for the genetic link between himself and his grandchildren to become severed:

·         Because of female infidelity, the grandfather may not be the biological parent of his son or daughter

·         And - because of female infidelity - his son may not be the biological parent of his own children

This is called the 'double whammy' effect.

 

On the other hand, grandmothers:

·         Are certain that they gave birth to their sons and daughters

·         Are certain that they are biologically related to their daughter's children

·         But - because of female infidelity - a grandmother may not be genetically related to her son's children

 

According to inclusive fitness theory the level of certainty in paternity should influence investment in grandchildren in the following way:

MoMo - absolute certainty of paternity and thus certain of genetic relatedness - therefore this grandparent provides the most investment in grandchildren

MoFa - generation effects may operate here (see below)

FaMo - generation effects may operate here (see below)

FaFa - greatest uncertainty of paternity and thus degree of genetic relatedness - thus this grandparent provides the least investment in grandchildren

Generation effects

Generation effects refer to the possibility that grandparents may be sensitive to changes in rates of infidelity across generations in allocating their resources. Today's grandparents may believe that the rate of infidelity is greater in their children's generation than in their own generation. Thus FaMo may believe that her son is at greater risk of being the victim of his partner's infidelity than a man in her generation. In contrast, MoFa may believe that he was at less risk of infidelity and that therefore he really is the father of the grandchild's mother. Consequently MoFa is more certain of his genetic relatedness to his grandchildren whereas FaMo is relatively less certain of her genetic relatedness to her grandchildren.

 

The "Grandmother Hypothesis"

The "Grandmother Hypothesis" refers to the possibility that menopause evolved as a way of investing in children and grandchildren (Barrett, Dunbar and Lycett, 2002, pp164-169; Hill & Hurtando, 1991)

 


References

 Barrett,L., Dunbar, R. and Lycett,J. (2002). Human Evolutionary Psychology. Basingstoke: Palgrave.

 

Buss, D.M. (1999). Evolutionary Psychology: The New Science of the Mind (pp237-239). Boston, MA: Allyn and Bacon.

 

DeKay, W.T. (1995) cited in Buss, D.M. Evolutionary Psychology: The New Science of the Mind (pp237-239). Boston, MA: Allyn and Bacon.

 

Euler, H.A., & Weitzel, B. (1996). Discriminative grandparental solicitude as reproductive strategy. Human Nature, 7, 39-59.

 

Gaulin, S.J.C. McBurney, D., & Brakemann-Wartell, S. (1997). Matrilateral biases in the investment of aunts and uncles: A consequence and measure of paternity uncertainty. Human Nature, 8, 139-151.

 

Hill, K.,  & Hurtando, A.M. (1991) the evolution of premature reproductive senescence and menopause in human females. Human Nature, 2, 313-350.

 

Lancaster, J.B., & King, B.J. (1985). An evolutionary perspective on menopause. In J.K. Brown & V. Kern (Eds.) In her prime: A new view of middle-aged women (pp13-20). Boston, MA: Bergin & Carvey.

 

Slater, P.J.B. (1995) Kinship and altruism. In P.J.B. Slater and T.R. Halliday (Eds) Behaviour and Evolution (pp193-222). Cambridge: Cambridge University Press.

 

Smith, M.S. (1998). Research in developmental sociobiology: Parenting and family behavior. In K.B. MacDonald (Ed.), Sociobiological perspectives in human development (pp. 271-292). New York: Springer-Verlag.

 

Smith, P.K. Grandparents & grandchildren, The Psychologist, 18/11 684-687, 2005

 


Workshop Activities

Practical Psychological Research: Evolutionary Psychology

 

"Does inclusive fitness theory predict grandparents' investment in their grandchildren?"

The workshop activities set out below will help you to become familiar with some of the issues in this type of research.

1. Construct a brief that would ensure full informed consent from participants.

2. How would you explain the distinction between maternal and paternal grandparents to participants in this study?

3. Design a question which rank orders each grandparent in terms of the time they spent with the participant whilst they grew up,

 and a question which rank orders each grandparent in terms of how emotionally close they were to the participant whilst they grew up.

4. How and why would you control for ‘order effects’ in the presentation of these questions?


Workshop feedback - here are some ideas put forward by workshop participants. Are they good or bad ideas?
Q1: Construct a brief that would ensure full informed consent from participants
Good ideas ?Good ideas? ?Bad ideas?
"This study is investigating the closeness you feel to your grandparents" "Study based on family relationships" - a bit too vague "The study is a questionnaire on grandparents and grandchildren" - not fully informed. Brief should contain reference to emotional content i.e. your relationships
Q2: How would you explain the distinction between maternal and paternal grandparents to participants in the study?
Good ideas ?Good ideas? ?Bad ideas?
Ask them to give the name of each of their grandparents. Use this information to explain the terms 'maternal' and paternal'. "Draw diagram i.e. family tree" - possibly confusing "Maternal grandparents are the biological parents of your biological mother" - 'biological' may confuse
Q3. Design a question which rank orders each grandparent in terms of the time they spent with the participant whilst they grew up, and a question which rank orders each grandparent in terms of how emotionally close they were to the participant whilst they grew up.
Good ideas ?Good ideas? ?Bad ideas?
"Rank order each grandparent in order of whom the most time has been spent. 1st being the most time and 4th the least time"

"Rank order each grandparent in order of with whom you feel most emotionally attached.. 1st being the most, 4th the least "

This 'forced-choice' ranking is the procedure we will adopt

 Likert scale with 1='very little time spent with grandparent' to 5="very often".

OK, but end points of scale may mean different things and several grandparents may get same score - i.e. not forced to rank order grandparents.

"How close are you to both grandparents?"

Vague, what would you record to produce a number that could be statistically analysed? Does not distinguish between each of the 4 grandparents.

"Who you have the most vivid memorys with as a child - good or bad?"

Vague, what would you record to produce a number for each of the 4 grandparents that could be statistically analysed?

Q4. How and why would you control for ‘order effects’ in the presentation of these questions?
Good ideas ?Good ideas? ?Bad ideas?
"Have half the participants be presented with Q1 first then Q2 and vice versa for the other half"

"Change order of presentation of questions around, so the participants response is not biased"

"control it by not having all the yes questions together" - this would control for 'response bias' not 'order effects' per se. "Alternate the rating or something every question" - this would not control for order effects in question presentation.

"Ask more emotionally based questions last " - assumes you know which questions are emotionally charged.

 

 


Results file

 

You can download  the results (in an Excel spreadsheet) from the study carried out in December 2005. You can use this data to prepare histograms that address a number of specific questions.


 

 

Interpreting your results

 

Here is a series of questions, and examples of the histograms you can construct from data in the results file to seek answers to the questions. You should include a table of results and histograms in your report.


 

What percentage of participants have maternal and paternal grandparents alive today?

Are more grandmothers rather than grandfathers alive today? What is a likely explanation for this finding?

 

 


What percentage of grandparents died before the participants were seven years old? What is the impact of this pattern of results for the interpretation of our study?

 

 

 


Which grandparent did most of the participants spend most time with when growing up?

There are several possible outcomes to our study:

The following histograms illustrate each of these possibilities. You need to discuss if the pattern of results is consistent or inconsistent with inclusive fitness theory.

 

 

 





Which grandparent did most of the participants spend least time with when growing up?


Which grandparent did the participants feel most emotionally close to when growing up?


Which grandparent did the participants feel least emotionally close to when growing up?


Did maternal and paternal grandparents send a birthday card?

 


 

Did maternal and paternal grandparents send a birthday present?



Yahoo! Music Unlimited Find a job at Yahoo! HotJobs Yahoo! Personals

SALMON materials copyright Dr Paul Kenyon 1994-2007