2.4
Inferences Pertinent To Mammalian Sociality Can Be Drawn From
West-Eberhard (1975)
West-Eberhard’s
(1975) summary of general models of social evolution reducible to
mechanisms dependent upon inclusive-fitness maximizing is useful as a
reminder that Hamilton’s rule is manifested in several ways,
dependent upon local condition, sex, role (e.g., reproductive or
helper), and lineage. It is noteworthy that each of the six
strategies (1a – 3b) is, in one manner or another, applicable to
social mammals and to mammalian females living mutualistically or
cooperatively in groups. In insects and most mammals, olfaction is
the primary mechanism of communication. Thus, coordination and
control of conspecifics is expected to be constrained by the
spatiotemporal dynamics of chemical properties (rapid delivery,
relatively rapid decay, pheromonal repression of selfishness).
Despite interspecific similarities, it is possible to derive
inferences from West-Eberhard’s (2005) outline that may pertain,
especially, to social mammals.
Inference
1: Because the variance on reproductive success is lower among
females than among males, ceteris
paribus
(Trivers 1972), mammalian females will be more closely related, on
average, to other females in their group or population than will
males be, on average, to each other, to group or population females,
and to each other’s offspring. For the same reasons, a mammalian
population is likely to include more females than males, and females
are more likely to exhibit sociality.
Inference
2: Trivers’ (1972) model, fundamentally, concerns differential
energetic investments by males and females and the life-history
trajectories deriving from polymorphic allocation patterns. Thus,
because female “fitness budgets” are more constrained
energetically that those of males, the reproductive female component
of a group or population is expected to be more stable,
spatiotemporally, than the dispersion of males in the same
population. For the same reason, on average, female turnover is
likely to be lower, female survivorship higher, female emigration
rates lower than for males.
Verbal
Model I was advanced by Trivers (1972) and was not, originally,
presented as a general model of social evolution. However, this
author predicts that social evolution will be biased by initial
reproductive allocations or energetic investments (Schoener, 1971).
This verbal model is not limited to evolution by sex, encompasses all
conditions in which organisms make (“Hebbian”) “decisions”,
including, decisions to join (group-formation), or, remain in
(group-maintenance), groups, and has the potential to be developed,
qualitatively, and, expressed, quantitatively, as a synthetic
formulation.
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Inference
3: On average, since females are “energy-maximizers”,
“inclusive-fitness maximizing” is expected to mitigate energy
losses, and, on average, females should benefit from transferring
some component “fitness budget” to others. Thus, females and
their female offspring are likely to be the major donors and
beneficiaries of the benefits of cooperation and altruism, and,
relative to males in her population, an adult female has more to gain
in her reproductive lifetime from facilitation.
Inference
4: Since males, “time-minimizers”, are expected to favor direct
over indirect reproduction, “inclusive-fitness maximizing”, a
relatively time-intense strategy, is unlikely to characterize
reproductive males, on average.
Inference
4: Ceteris
paribus,
and, depending upon threshold reproductive effects relative to
ecological conditions, where males cannot discriminate their own
young, they should be indiscriminately selfish, concentrating on
mating allocation strategies rather than facilitation of
conspecifics.
Inference
5: It follows from “parental manipulation” and “maternal
control” models that females can discriminate their mothers and,
there own offspring, where females are not “promiscuous” and do
not express “favoritism” of a single male during an estrus cycle.
On the other hand, cortical circuitry may be favored, permitting
females to make “decisions” based on likelihoods of paternity.
In order for this neurophysiological strategy to be favored by
selection, losses from error must not, on average, compromise
relative reproductive success (of the pertinent genotype). It is
important to note that “decisions” based on kinship may yield
lower group sizes than those based on selfish strategies (Hamilton
1964); thus, the Malthusian optimum for a reproductive female may not
concord with idealized mean fitness of her population.
Inference
6: Following from previous inferences, a reproductive female, on
average, is expected to lose less from probabilistic tactics and
strategies than will a reproductive male of the same population.
Related to the previous inference, “inclusive-fitness maximizing”
is expected to mitigate the maternal investment : ageing tradeoff for
tactical and strategic females, on average, possibly explaining the
reproductive advantage of extended post-reproductive lifespan in
humans and killer whales: ////.
The
previous discussion of West-Eberhard’s (1975) classification
(1a-3b) suggests that “inclusive-fitness maximizing” should be
more characteristic of reproductive females, on average, than of
reproductive males in the same conditions. It is hypothesized that
this condition obtains since, theoretically, females are expected to
be “energy-maximizers”. The latter life-history strategy should
privilege time-intense (“non-damaging”) rather than
energy-intense (“damaging”) strategies, theoretically,
characteristic of males. Should the aforementioned allocation
(thermal) trajectories withstand quantitative, including,
experimental, testing, each of them will yield information pertinent
to the evolution of mammalian sociality. In particular, on average,
each reproductive morph in the same population will respond
differentially to density effects that are expected to impact
“energy-maximizers” to a greater degree than “time-minimizers”
since an increase in population density should correlate positively,
ceteris
paribus,
with increased intensities of competition. Under these regimes,
reproductive females should “switch” to or increase dependence
upon, time-intense, energy-saving, helper tactics and strategies,
including, in some regimes, self- (suicide, “give-up” points) or
offspring-elimination (foetal resorbtion, abortion).