Step 1: Read Katherine Gibson’s article “Epigenesis, Brain Plasticity, and Behavioral Versatility:
Alternatives to Standard Evolutionary Psychology Models.” In Complexities: Beyond Nature and Nurture
(2005), pp. 23‐33 and 37 bottom-38 (excerpt of a longer chapter; difficult) Step 2: As you read, pay attention to the following terms and make sure you understand them: 1. Environment of evolutionary adaptation (EEA) 2. Standard evolutionary psychology models (SEPMs) – these are misconceptions Gibson refutes 3. Epigenesis 4. Pleiotropy 5. Neural plasticity Step 3: Write one sentence summarizing the ideas Gibson is criticizing (these are the SEPMs). Step 4: Make a bullet-pointed list of the key pieces of evidence Gibson provides to support her own
argument that the EEA was highly variable rather than stable, and that its variability indicates the
importance of brain plasticity in the evolution of modern homo sapiens. Aim for 5+ bullet points. Step 5: What does Gibson mean when she writes that “brains are also epigenetic organs in the
anatomical sense” (p. 31)? Write two sentences explaining this. Is her information consistent with, or does
it contradict, the arguments you read about previously in Mahler and Twilley?
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excerpt for Anth 2120
32
KATHLEEN R. GIBSON
Garraghty, and Mishkin 1988; Pons et al. 1991). Cortical reorganizations in
adult humans and primates can also follow small behavioral changes or
small environmental insults. For example, in monkeys, temporary immobi
lization of the hand or arm may lead to functional reorganization of the mo
tor cortex within days (Nudo et al. 1996), and in humans several days of
practicing the piano can lead to enlargement of the pertinent cortical re
gions (Grabowki and Damasio 2000).
Adult neural plasticity reflects different anatomical processes than the
selective pruning of neurons and connections evident during maturation.
Adult mammals remain capable of forming new cortical synapses in re
sponse to learning, and they c;::m generate new neurons in a subcortical neu
ral structure, the hippocampus (Gould et al. 1999). Also, some synapses and
neurons are thought to survive the early pruning but to exhibit minimal ac
tivity until unmasked by an environmental insult that inhibits or destroys
other, more dominant pathways or until stimulated by new behaviors and
experiences (Greenough, Black ;ind Wallace 1987; Hallett 2000). Phantom
limb pain. may provide an example of this latter phenomenon. Subsequent
to amputation, humans often experience pain in tht’ nonexistent limb. In
these instances, lightly brushing other body parts can result in sensation
perceived to originate in the amputated limb. This pain can sometimes be
relieved by a form of visual therapy in which the patient is supplied with a
mirror box that reflects the image of the nonarnputated limb, thereby creat
ing the illusion that the amputated limb is in the box and moving in coor
dination with the normal limb (Ramachandran, Rogers-Ramachandran,
and Cobb 1995). Phantom limb pain is thought to reflect an unmasking of
neural. connections that already exist in the brain (Ramachandran, Stewart,
and Rogers-Ramachandran 1992; Ramachandran, Rogers-Ramachandran,
and Cobb 1995).
The findings that normal brain development is a functionally plastic
epigenetic process and that some functional plasticity remains throughout
life have significant implications for modern human behavior. Just as epige
netic processes allow apes reared with humans to acquire language facilities
not normally manifest in the wild, they allow humans to acquire functional
modifications of their brains that permit the acquisition of skills, such as
reading, writing, typing, and playing computer games, that are not part of
our evolutionary heritage. If, in contrast, our cognitive and behavioral ca
pacities were primarily controlled by innate, predetermined “neural mod
ules” designed to solve specific problems encountered during the Pleis
tocene, we would lack this behavioral flexibility. Our brains may look the
. same as those of our Pleistocene hunter-gatherer ancestors, but in some re-
EP!GENESIS, BRAIN PLASflC!TY, AND BEHAVIORAL VERSATILITY
33
spects they may be functionally quite different, because environmental in
puts during the developmental process a�e now_ quite different:
We can only speculate about what ep1genes1s may mean with regard to
social behavior, morality, and other complex behavioral systems of specific
interest to evolutionary psychologists such as theory of mind, reciprocal al
truism, and the detection of cheaters. In contrast to neuroscientists, SEPM
theorists rarely attempt actually to identify the neural regions that subserve
the behaviors and cognitive capacities of interest to them, and some of them
explicitly deny the potential relevance of developmental studies (F� dor
_
1983; Cosmides and Tooby 1992). Rather, they assume that if a potentially
adaptive mental capacity can be identified in adult humans, it must be con
trolled by an innate neural module dedicated to that capacity. For example,
.SEPM theorists use the ability of human adults to detect cheaters as evi
dence for the existence of a specific, genetically determined, neural cheater
detector module. However, they never actually identify any area in the brain
that functions specifically to detect cheating and have never found any part
0[ the genome that appears to relate in any way to detecting cheaters. They
justify this methodology by calling it reverse engineering an� li�ening i� to
the dismantling of mechanical equipment in order to determine its function
and means of manufacture. In actuality, this methodology amounts to in
appropriate generalization from behavioral phenotype to genotype. The
clear evidence of the epigenetic nature of brain development invalidates this
methodology. Even if at some future date adult brains were found to contain
regions dedicated to cheater detection or reciprocal altruism, that would be
insufficient evidence to draw sweeping conclusions about their genetic or
developmental determination.
[ANTH 2120 excerpt: skip to concluding passage on p. 37:]
Summary
Over the last decades, some evolutionary psychologists and linguists have
argued that the human mind consists of numerous, specialized, innate neu
ral modules designed to meet specific problems encountered in the Pleis-
38
KATHLEEN R. GIBSON
tocene hunter-gatherer environment. This chapter argues, in contrast, that
there has never been a single environment of evolutionary adaptation.
Rather, modem humans and their earlier hominid ancestors encounter(ed)
and successfully adapt(ed) to highly varied environments. This human
adaptability reflects the neural plasticity and epigenetic processes that shape
the maturing human brain. It also reflects a basic intellectual process
mental construction–that allows humans to combine and recombine ac
tions and concepts to create novel solutions to novel problems. This model
has distinct advantages over SEPMs in that it is compatible with our under
standings of minimal genetic change between humans and apes and with
our understandings that most genes affect multiple traits and exert their ef
fects through epigenetic processes.
The existence of mental constructional processes indicates that the hu
man brain is not only an epigenetic and functionally plastic organ. The
brain also endows our species with mental capacities that allow humans to
create a seemingly infinite numbt:r of linguistic, terhnical, artistic, social,
musical, ar d motor constructs and, hence, to adapt to changing and novel
environments. Given that humans have exploited variable environments for
millennia, it is likely that the major selective pressures throughout all of ho
minid evolution up to the present day have acted in favor of the mental cre
ativity and flexibility that the human mental constructional process pro
vides rather than in favor of functionally dedicated neural modules to meet
the very specific environmental demands of a given time and place.
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