Posts tagged evolution
There are many mechanisms that underlie exactly how and why sexual selection takes place- one is the ‘handicap’ /’costly honest signal‘ theory according to which a trait that is actually disadvantageous or a handicap for the host evolves to signal exactly that fact- that despite this handicap I am able to function well and must therefore be of better genetic quality; the most common example being the evolution of peacocks tail which is a handicap and makes the male peacock carrying a big tail more vulnerable for predation, but also is attractive to females and preferred by them. Another theory is that of ‘runaway selection’ i.e . a trait may evolve in a direction due to some genetic drift and the preference for it may also evolve in tandem such that there is a slight leaning or preference towards that trait. Now, in a competition, those, typically males, who have that trait will be selected by the females and their progeny will have an advantage as they are more likely to display that trait and be favored by subsequent generations; thus an arbitrary trait may get fixed by this runaway selection where all members of the species want to be part of the new fashion/club in town. I know I am drawing very loose analogy, but just to give an idea. Nakedness or loss of hairs in humans is predicted to have followed this pattern.
Of course sexual selection also differs on whether it is largely intrasexual, driven by competition (selection pressure) between males for eg having big antlers to defeat and subjugate another male; or is driven by mate preferences and has intersexual selection dynamics- like the peacocks tail.
What the authors of this paper hypothesized was that sexual selection is behind the evolution of altruism or selfless concern with non-kin and that this being the case and this sexual selection dynamics being driven by inetrsexual dynamics, there are bound to be genetic underpinnings to both the trait altruism as measured in males/females and the mate preferences for altruistic trait in both females as well as males. The reason they didn’t anticipate any differences in male sand females was that parental investment, as per them, is roughly equal in case of humans and so both males and females exert equally strong sexual selection pressure son each others traits and ‘choose’ their mates equally.
However, in this study they looked only at females and their genetic basis for altruistic traits as well as mate preference for altruism. The altruistic traits and mate preferential weer measured using self-report instruments. the genetic components underlying these were estimated using classical twin studies paradigm where correlation between mono-zygotic twins and di-zygotic twins are compared to estimate the genetic contribution. They also calculated the phenotypic correlation between mate preference for altruism and altruistic trait in individuals and tried to calculate how much of this correlation again was genetic in nature or in other words was a result of mating between those who had the trait and those who preferred the trait. . They hypothesized that in the ancestral environmental this type of mating for trait altruism would have taken place and thus these would be genetically correlated.
This is exactly what they found; they found that both altruistic personality and mate preference for altruism had genetic components and that they both co-varied and that covariance again had genetic component. the pare itself is full text open access and is written very well, so go ahead and read it yourself. this is an important paper that has come timely when the whole kin-selection paradigm for evolution of eusociallity is being challenged by E o Wilson and team and provides a fresh and alternative perspective of why altruism may have evolved.
Here is a tit-bit from the discussion:
We believe that the sexual selection hypothesis for the evolution of human altruistic traits should now be considered alongside other more established theory (Bshary & Bergmu¨ller, 2008; Lehmann & Keller, 2006), particularly as there is the possibility that multiple mechanisms might underlie a complex behaviour such as altruism. Empirical testing of contrasting theories might even be possible. For example, reciprocal altruism (Trivers, 1971) does not strictly predict the genetic correlation between MPAT and ‘altruistic personality’ found here as ongoing reciprocation towards others would not necessarily result in such a selective process. Indirect reciprocity (Leimar & Hammerstein, 2001) concerns reputation directed towards all other group members while the sexual selection hypothesis focuses solely on altruistic displays that can be evaluated by potential mates (Phillips et al., 2008). A study that examined ‘costly signalling’ of altruistic behaviour through personal donation to a children’s charity found a significant effect on male behaviour when witnessed by a female observer while no such effect was found when male participants were observed by same sex others (Iredale et al., 2008), a finding that could be seen to be at odds with indirect reciprocity. Additional studies could further elucidate the effects of altruistic reputation when directed towards same sex others as opposed to potential mates, thus testing the relative claims of indirect reciprocity against the sexual selection hypothesis.
Tim Phillips1, Eamonn Ferguson2, & Fruhling Rijsdijk (2010). A link between altruism and sexual selection: Genetic influence on altruistic behaviour and mate preference towards it British Journal of Psychology DOI: 10.1348/000712610X493494
I’ve touched upon life history theory earlier, in an oblique fashion, while discussing evolutionary perspectives on personality.
Life History theory posits that an individual’s life efforts can be subsumed under two headings- somatic life efforts
and reproductive life efforts. The latter relates to selection due to being able to successfully replicate one-self; the former relates to the ability of an organism to survive and thus act as a vehicle for genes that can be replicated at a later date. To elaborate more on the life history theory I quote:
Life History Theory is a mid-level theory from evolutionary biology that describes the strategic allocation of bioenergetic and material resources among different components of fitness (e.g., calories and nutrients devoted to growth vs. reproduction). Somatic Effort anchors one end of the first dimension of this trade-off whereas Reproductive Effort anchors the other. Somatic Effort refers to resources devoted to continued survival of the individual organism whereas Reproductive Effort refers to resources devoted to production of new organisms as vehicles for survival of the individual’s genes. The second dimension of this trade-oV further partitions Reproductive Effort. Mating Effort anchors one end of this continuum whereas Parental Effort and Nepotistic Effort jointly anchor the other. Mating Effort refers to resources devoted to obtaining and retaining sexual partners whereas Parental/Nepotistic Effort refers to resources devoted to enhancing the survival of existing offspring and other genetic relatives. Thus, a life-history strategy allocates an individual’s bioenergetic and material resources among the competing demands of survival and reproduction.
I break the somatic effort into five different functions:
- Survival– each organism needs to survive and maintain its body integrity
- Growth – each organism needs to consume energy and grow
- Maintenance– each organism needs to maintain the body it accumulates as a result of previous efforts
- Development– there is developmental unfolding and stages where different needs are met at different times
- Differentiation/specialization– the organism makes efforts to create an environmental niche for itself
I agree with the authors that reproductive effort can be broken into 3 parts:
- Mating effort– effort to find and retain a mate.
- Parental effort– efforts devoted to nurture offspring
- Nepotistic efforts– efforts devoted to helping close genetic kins.
The first three stages/efforts are related to energy balance while the next two are timing related. Finally the final three are efforts proper, thus completing the eight stage model.
The life history theory says that one has limited energy, time and efforts and needs to invest these limited resources wisely- between current and future reproduction; between quantity and quality of offspring; and between self and offspring.
Let me elaborate.
Current and future reproductive trade-offs can be conceptualized as a giant trade-off between somatic effort and reproductive effort. If I reproduce now, I do not invest in my growth, maintenance, survival etc and thus have lowered future chances of being able to survive and reproduce. On the other hand if I do not reproduce now, I can invest the excess energy in somatic efforts- granting me future reproductive benefits, but incurring the opportunity cost of not reproducing now.
Quality and quantity of offspring trade-off can be conceptualized as how best to allocate resources, once I have decided to reproduce, amongst a litter- the size of litter (no. of offsprings), the size of individual baby at birth and the quality or survivability of offspring at birth. All these are orthogonal to each other and involve trade-offs.
The final traditional trade-off is between self and offspring- the parent-offspring conflict. Given that I am reproducing some offsprings now, what resources should I invest in them now, such that my future reproductive costs are not sky-high and I can survive and reproduce later and invest in later offsprings too. Here the two sexes have different incentives when a baby is gestating- for mother later offsprings will also be hers; for father later offsprings may not be his; thus father wants the baby to consume as many resources now as possible; while mother wants to spread resources more evenly- the genomic imprinting conflict theory.
Here it is instructive to pause and note the cost of reproductive (to mother)-
- future survival (death in childbirth – for mammals important)
- future energy capture (pregnancy, lactation and nursing resulting in less loco mobility and foraging)
- future reproduction (lowered fecundity as a result of prior child birth)
The avid reader will note that the three trade-offs refrred to above relate to the three stages of reproductiuve effort – mating (now/future), parenting (one/many child) and nepotism (future related babies/unrelated babies)
There do exist of course tradeoff between somatic and reproductive efforts and it has been shown time and gain that they are inversely related; however more interesting is the fact that somatic efforts themselves are multi-dimensional; thus forgoing reproduction may not simply lead to longer lifespan; it may just result in more growth and heavier bodies.
Also important to note the concept of r and K strategies.
Let us now look at some of the life history variables and again present them is a stage fashion, with special focus on r-K strategy and how these have antagonistic and opposite effects on variables under consideration:
- Mortality rate (survival)- low in r , high in K
- Body size (growth) -low in r, high in K
- Metabolic activity related lifespan (maintenance)- low in r , high in K
- Age of sexual maturity (developmental) – early in r, later in K
- Age of first reproduction (differentiation/specialization)- early in r, later in K
- duration of gestation/pregnancy (mating) – lesser in r, greater in K
- no. and size of offspring in a litter (parenting)- more number and lesser size in r, smaller no. and bigger size in K
- no. of reproductive events (nepotism)- semelparous or one reproductive event only in many r; iteraparous or multiple reproductive events in most K
Another way of parsing the data is to link these to developmental and evolutionary tasks and personality traits, as I had done earlier:
- Foes: Survival
- Food: Growth
- Friends: Maintenance
- Maturity: Development
- Mate selection: specialization/differentiations (displays of creativity etc)
- Mate retention: mating long term for future reproductive benefits
- Parenting: parental efforts for ensuring well being of offsprings
- Nepotism /altruism: favoring kin/ non-kin to ensure inclusive fitness
The last three are generally referred to as dilemmas of parental investment- balancing reproduction, well being of offsprings and inclusive fitness via nepotism with somatic or self fitness.
Its also instructive to note that many ecological variables affect the somatic as well as reproductive effort distribution (the r and K strategy are under ecological constraints to an extent).
For ex, changes in ecology like Mortality hazard (foe related) , food availability (food related) , density of con-specifics (friends related) , shortage of food during critical developmental window( maturity related) or differential habitats leading to different genetic variants (niche related) all lead to changes in these life history variables sometime affecting growth, sometimes reproduction, sometime lifespan etc etc. For eg caloric restriction may lead to increased lifespan etc etc
The above life history analysis was applied to organisms, but the same can be extended to brains and neurons-the following processes are involved in neuronal life history (neural Darwinism)
- Neuronal survival
- Neuronal growth
- Neuronal maintenance
- Neuronal developmental and
- Neuronal specialization/differentiation.
In all of the above neurotropins or growth factors are instrumental and drive these processes. Whether or not this applies to neuronal level, but to organism level life history theory makes a lot of sense. What do you make of it and its fit with the 8 stage evolutionary theory?
Graf, M., Cellerino, A., & Englert, C. (2010). Gender Separation Increases Somatic Growth in Females but Does Not Affect Lifespan in Nothobranchius furzeri PLoS ONE, 5 (8) DOI: 10.1371/journal.pone.0011958
FIGUEREDO, A., VASQUEZ, G., BRUMBACH, B., SCHNEIDER, S., SEFCEK, J., TAL, I., HILL, D., WENNER, C., & JACOBS, W. (2006). Consilience and Life History Theory: From genes to brain to reproductive strategy Developmental Review, 26 (2), 243-275 DOI: 10.1016/j.dr.2006.02.002
In my last post I had mentioned how Seligman and Peterson have tried to correlate their structure of human virtues/character strengths with work of other researchers like the universal dimensions of human mate preferences discovered by Buss et al. Today I wish to discuss in detail the universal dimensions of human mate preferences discovered by Buss et al.
Buss et al looked at data , using an 18 item preference ratings archival database, of about ten thousand people, from various cultures across the globe, and used the analysis strategy outlined by Bond to take care of different sample size from different cultures. they then applied the Principal component analysis to the refined data so obtained to determine the underlying structure of the mate preferences.
Their PCA analysis led to discovery of four dimensions all of which could be quantified as bipolar dimensions with one pole representing a different construct and another representing a sort-of-but-not-really opposed construct. For eg.,the first factor included loadings from ‘‘good financial prospects’’ (-0.65), ‘‘favorable social status or ratings’’ (-0.62), and ‘‘ambition and industriousness’’ (-0.41), each of which loaded negatively. The component also included ‘‘mutual attraction—love’’ (0.49), which loaded positively. They thus labeled this component ‘‘Love vs. Status/Resources.’’
Similarly the 3 other components were labeled “Dependable/Stable vs. Good Looks/Health”; “Education/Intelligence vs. Desire for Home/Children”; and “Sociability vs. Similar Religion”.
To my naive mind all of these bipolar dimensions seem to be separate constructs in themselves and I cannot fathom why dependable/stable should be taken as opposed to good looks/health. to me they seem sort of independent constructs. I would rather view the findings as eight separate poles than 4 bipolar dimensions with each dimension conflating two constructs/factors.
The paper immediately drew to my mind this paper, by Haslam et al, that while finding the underlying structure of positive characteristics, found three consistent bipolar dimensions using multi dimensional scaling. However, when the same data was subjected to cluster analysis, 6 factors were or clusters were apparent , each cluster being the pole of a single bipolar dimension. These 6 factors were “self-control,” “love,” “wisdom,” “drive,” “vivacity,” and “collaboration” which to my mind seems to map onto the virtues of self-restraint/temperance strengths, interpersonal or humanity strengths, intellectual or wisdom strengths, courage or emotional strengths , activity or vitality strengths and justice or civic strengths. Of course I think their MDS missed a fourth dimension which would have led to 8 clusters , the 2 remaining being religious and transcendence strengths.
Returning back to our current paper on universal mate preferences, I would like to break up the 4 dimensions into 8 factors and present them in a staged developmental order. It would be worthwhile to note that the two opposed dimensions are usually two adjacent stages following each other and may indeed reflect some conflict in mind of people as to which stage of mate preference to prefer based on their evolved natures . Here goes:
- first stage: Physical/biological : good looks/health
- second stage: will, restraint and control: dependable/stable.
- third stage: dominance/hierarchy, friends and foes: status/ resources.
- fourth stage: interpersonal: Love
- fifth stage: cognitive: education/ intelligence
- sixth stage: intimacy: desire for home/children.
- seventh stage: communicative/ generative: sociability
- eights stage: integrity, ingroup/outgroup: similar vs dissimilar religion.
Of course this is not the first time I have tried to put Buss’s findings in a 8 stage model; earlier I had tried to put his views on personality in a eight fold structure- whereby the last three stages of reproduction/evolution may be now characterized as biological, linguistic and cultural evolution. Anyway getting back to universal mate preferences, I can see that eight fold structure is found in the mate preferences too depending on which stage of preferences you have evolved/developed.
SHACKELFORD, T., SCHMITT, D., & BUSS, D. (2005). Universal dimensions of human mate preferences Personality and Individual Differences, 39 (2), 447-458 DOI: 10.1016/j.paid.2005.01.023
Haslam, N., Bain, P., & Neal, D. (2004). The Implicit Structure of Positive Characteristics Personality and Social Psychology Bulletin, 30 (4), 529-541 DOI: 10.1177/0146167203261893