Running Head: Nature Versus
Nurture
Nature versus Nurture: Does it have to be all or nothing?
Nichole V. Greer
Graduate Student
Liberty University
NATURE VERSUS NURTURE 2
Abstract
Human behavior and its origins are a long-debated subject in many settings, from the family
dinner table to scholarly researcher’s desks. After hundreds of years, we seem no closer to
answering the age-old question: what determines our behavior? Although no definitive answer to
this question has been discovered, this in no way implies that major contributions in the field
have not been made. Developmental systems theorists argue that no behavior can be exclusively
attributed to genes, but those behaviors that seem instinctive should be analyzed to determine
what motivates their appearance. Many of the studies conducted involved the cooperation of both
monozygotic and dizygotic twins, as well as full biologically related siblings. This is a look into
the role both genetics and environment play in the life-span development process.
Keywords: Nature versus nurture, heredity and environment, genetics, behavior, how is
behavior determined, what role do genes play in human behavior, behavioral theory,
psychoanalytic theory
NATURE VERSUS NURTURE 3
Nature versus Nurture: Does it have to be all or nothing?
For hundreds of years, the debate between nature and nurture regarding life-span
development has been contentious at best. Researchers have spent countless hours examining the
role that genetics and environment play in our cognitive growth. What if geneticists and
behavioralists are both correct. What if the role heredity and environment play are equally
important in life-span development. The way researchers look at cognitive processes and how
they evolve seems to be on the rise. This study focuses on both nature and nurture as equal parts
in life-span development. Nature versus nurture, genetics versus environment, however you
choose to label it are all studies of what the driving force of human behavior is and its roots.
The focus of one such study was on nature and nurture of intelligence and specific
cognitive abilities. Kees-Jan Kan, Jelte Wicherts, Conor Dolan, Han Van Der Maas (2013,
para. 1) “scrutinized how heritability coefficients vary across specific cognitive abilities both
theoretically and empirically” using data from 23 twin studies. They found in adult samples
“culture-loaded subtests tend to demonstrate greater heritability coefficients than do culture-
reduced subtests” (Kan et al, 2013, para. 1). Finding that genetic aptitudes are the most culture-
dependent.
Evaluations of the empirical data was completed with the use of mainstream g theory and
fluid-crystallized theory. Both g theory and fluid-crystallized theories state, intelligence is a
genetically fixed source of individual differences in Intelligence Quotient. Sources of individual
differences in cognitive processing was seen either directly, in fluid tests, or indirectly, in
crystallized tests. Further research into genotype-environment covariance and how cognitive
abilities are differentiated by their hereditability coefficients could further explain the culture-
loaded and culture-reduced cognitive processing abilities (Kan et al, 2013). Additional
NATURE VERSUS NURTURE 4
information can be gathered on intelligence from Exploring how nature and nurture affect the
development of reading: An analysis of the Florida Twin Project on Reading.
A longitudinal study conducted using the sample group from the Florida Twin Project on
Reading discusses genetic and environmental influences on reading development. This sample
group consisted of first through fifth grade twins with data collected from the 2003-2004 to
2008-2009 school year. The participants consisted of 824 monozygotic twins, of which 419
were female to female pairs and 405 were male to male pairs, 1,546 dizygotic twins, 369 were
female to female pairs, 399 were male to male pairs, and 778 opposite-sex pairs. Of the
participants,
19% reported their race or ethnicity as African American, 24% Hispanic, 50% Caucasian, and
the rest of mixed race. No twin families were excluded from the sample group, including those
who recognized English as a second language. This statistic encompassed 20% of the sample
group.
Twins had a mean age of seven beginning grade one. Because the study and data collection
procedures were cross-sequential, not all information was available at all points in time during
the investigation (Hart, Logan, Soden-Hensler, Kershaw, Taylor, and Schatzschneider, 2013).
Logan and associates (2013) took race/ethnicity into account when analyzing the data to
consider a diverse population. Genetic effects can be anecdotal within the twin intraclass
correlations where monozygotic intraclass correlations are greater than dizygotic intraclass
correlations for both same-sex and opposite sex twins. “In general, estimates across both
intraclass correlations and structural equation modeling suggested a pattern of high and
significant estimates of heritability and low estimates of the shared environment for the whole
sample” (Logan et al, 2013). Less than half the difference between monozygotic and dizygotic
intraclass correlations can be attributed to environmental effects that make family more similar.
NATURE VERSUS NURTURE 5
Throughout the analysis any change in score was minimal and the pattern of significance was
unchanging (Logan et al, 2013).
A research study conducted by Plomin, Shakeshaft, McMillan, and Trzaskowski, focused
on the differences between expert readers and normal readers and how genetics and environment
effected their level of intelligence in reading comprehension. Plomin and associates in 2013 said,
“The issue is not nature versus nurture, but rather nature and nurture because both are important,
which suggests that the way forward is to develop strategies that bring nature and nurture
together to help us understand the development of complex traits.” Behavioral patterns are
influenced by development over generations. Just like we see with evolution, we can see patterns
of behavior modified to benefit the physical and psychological needs of a person where they are
in time.
This way of thinking has changed drastically with the average lay person, as ninety
percent of parents and teachers believe the development of behavioral traits are impacted equally
from heredity and environment (Plomin et al. 2013). Intelligence, learning disabilities,
personality, and even mental illness are all effected by behavioral traits passed down from
generation to generation. It is the origin of these behavioral traits that still eludes us to this day.
To further examine this phenomenon, Plomin and his associates conducted a quantitative
research study on normal readers and expert readers at the age of 12. A sample group of 10,000
twins, or 5,000 twin pairs, allowed them to use only the top five percent for analysis. An
adaptation of the Peabody Individual Achievement test, which assesses comprehension of
sentences, was the source of data collection. The children were shown a sentence and had to
choose the best corresponding picture out of four to go with the sentence they had read. The
children started with the same sentences and pictures, however as they progressed an adaptive
NATURE VERSUS NURTURE 6
algorithm would modify the item order or discontinue the test based on performance (Plomin et
al, 2013).
To adequately analyze the results of the test, three twin analyses were utilized; the
standard univariate twin model-fitting analysis, the liability-threshold model-fitting analysis, and
the DeFries-Fulker extremes analysis. “The goal of our study is to test the reasonable hypothesis
that expert reading performance is due solely to environmental factors, or whether genetic factors
also contribute to reading expertise” (Plomin et al, 2013).
Regardless of how the data was analyzed, over half of the difference between normal
readers and expert readers can be attributed to genetic factors. While, shared environmental
factors, such as growing up in the same family or attending the same schools, accounted for less
than a fifth of the difference between expert readers and the rest of the population. This
includes the difference between monozygotic and dizygotic twins, different sexes, and family
resemblance.
In Nature, Nurture, and Expertise: A Response to Ericsson, Ericsson criticizes the work
of Plomin and his associates by rejecting the “handful” of individuals claimed to be superior
readers as irrelevant but does not use the same definition of superior that Plomin does (2013).
Ericsson also limits his expertise to adults, whereas Plomin’s research focused on 12-year-old
twins. In addition, Ericsson focused on “beginners,” but failed in his definition of these
“beginners,” because they were competing in national level competitions. So, how could a
beginner be competing at such high levels. Ericsson states also, that the age of the sample group
in Plomin’s study cannot be relevant as reading ability is still increasing at this age. Plomin
(2013) argues that the annual rate of reading performance, by age 12, slows significantly. There
seem to be several arguments between researchers and what is considered common knowledge in
regards to
NATURE VERSUS NURTURE 7
defining specific words and when the reading performance stops growing. Plomin and his
associates (2013) claim their research in no way asserts that practice in the development of
intelligence is unnecessary or that environment is irrelevant. In fact, they emphasize the
acknowledgement, rather than denial, of inherited influences on expert performance.
Emphasizing the contributions of genes, environment, and epigenetic factors on
developmental processes is the Developmental Systems theory. Developmental systems theory
or DST states, both biological and behavioral phenotypes “emerge spontaneously from the
mechanical interactions of a large number of factors that together constitute a single complex
system” (Moore, 2016, p. 2). This system includes such things as DNA, cell membranes and
their proteins, hormones, neurotransmitters, and actual physical features of the environment.
Because this systems view is that contextual factors play an essential role in phenotype
development, genes cannot be considered the prime elements of any phenotype (Moore, 2016).
DST recognizes development as epigenetic and probabilistic rather than predetermined.
Because of this, “DST reject(s), as inherently flawed, the traditional view that nature and nurture
can contribute in independent ways to development” (Moore, 2016). Theorists who recognize
developmental systems theory distinguish that traits that appear innate, just like behaviors,
require investigation to discover what influences and mechanisms bring them about.
Because of the conclusions drawn by both DST proponents and behaviorists, a natural
partnership should be built (Moore, 2016). Both believe in the importance of contextual factors
as an integral part of their research, and the need for a historical analysis of behavioral
characteristics. An alliance between the two could only be beneficial to developing further
insights into human behavior.
NATURE VERSUS NURTURE 8
A qualitative research study using the Interpretative Phenomenological Approach
intended to evaluate parent’s perspective on personality differences between their children.
Twelve participants, both parents from one family, engaged in the study reported personality
differences in their child to be both biological and psychosocial in nature. This study focused on
collecting attitudes, feelings, vocal and facial expressions, as well as other behaviors and how
they relate to the parent’s perception of their child’s personality (Kamran, 2016).
The sample group of 12 participants had to meet the following criteria to contribute;
parent’s of at least two children, between the ages of two and twelve, and with no greater than a
five-year age difference. This study did exclude any single parent households. Parents,
interviewed separately of one another, were questioned in their home for 30-40 minutes by the
researcher with a set of semi-structured but open-ended questions in an informal, conversational
style gathering.
The analysis of the study provided information that parents tend to view their children
from the “ideal child” perspective rather than based on their own observation of the child’s
personality. One parent stated, “a whole heap of trouble...that's how I'd describe them...well they
are good kids in their own way” (Kamran, 2016, para. 21). Based on this and the views of other
participant’s, a trend on the “ideal child” was found. Parent’s also cited both genetic and
environmental factors as creating their child’s personality. Night and day differences were
attributed to how much of the child’s genes were inherited from one parent over the other. And,
rationalizing objectionable behavior by blaming age and gender rather than personality.
The Affective Neuroscience Personality Scales study was used to collect and analyze
data regarding primary emotionality in humans. The importance of this research is for
psychological well-being and psychopathologies. Using affective neuroscience by Jaak
Panksepp, Montag and
NATURE VERSUS NURTURE 9
Hahn (2016) looked at the four positive emotions; SEEKING, LUST, CARE, and PLAY as well
as the three negative emotions of RAGE, FEAR, and PANIC to measure individual differences
in the primary emotional systems. The participants contributed data by means of the German
version of the Affective Neuroscience Personality Scale questionnaire.
The sample group participating in this research study consisted of 795 individuals; 303
monozygotic twins, 172 dizygotic twins, 267 non-twin siblings, and 53 individuals with
unknown zygosity. This sample group was determined based on who had participated in
previous voluntary German twin studies and non-twin sibling internet and online-game behavior
study of cohabitation (Montag et al, 2016).
Results of an analysis of variance show, “monozygotic twin correlations exceeded those
of the dizygotic twin and non-twin sibling pairs in all cases. For FEAR, ANGER, PLAY and
SADNESS, monozygotic twin correlations were over double the dizygotic correlations
suggesting genetic dominance influences to be especially important. Regarding SEEK CARE
and Spirituality, twin correlations rather pointed to shared environmental influences. Apart from
the pattern of twin similarities, relatively high resemblances within non-twin siblings rather
indicated shared environmental influences for all ANPS dimension except SEEK and
SADNESS” (Montag et al, 2016, para. 14). Overall results from the Affective Neuroscience
Personality Scale questionnaire showed all are influenced by genetics, but by varying degrees
and the remaining part of change is described by effects of non-shared environmental factors.
In the last 100 years, theories of human development have swayed from nurture back to
nature, and yet again back to nurture, with this last development focusing more on equal parts
significant in human development. While behaviorism was on the rise, neuroscience exploded
with new techniques for viewing the living human brain. The development of MRI’s and PET
NATURE VERSUS NURTURE 10
scans allowed for more research on the nature of human development. This time also brought
about the use of twin studies used to evaluate the degree of similarities between monozygotic
and dizygotic twins brought up in the same home. Intelligence, height, aggressive behavior could
all be measured and attributed to genetic and environmental influences. These behavioral
variables almost always shown to have contributed a 50/50 split in terms of importance (Rettew,
2017).
Even with increasing knowledge in both psychology and biology, the two fields were
kept independent of one another. Most likely reasoning for this came from the notion that,
“automatic ‘wiring’ of the brain that was generally driven by genes and beyond the influence of
environmental factors” (Rettew, 2013, para. 11). With this continued advancement in biology
and psychology, there is no question that both genetics and environment effect human behavior.
As science continues to evolve and more testing becomes readily available, we will need to bear
in mind that of which we have already discovered in relation to nature and nurture and the
effects on human behavior.
There have been many research studies conducted on how both genetics and the environment
affect human behavior. Some studies focus on how genetics alone influence behavior while
others focus solely on how our environment inspires behavior. Of the studies conducted, not one
alone has been able to fully synthesis what determines human behavior. With recent ground-
breaking advances in genetics, the argument for nature being more important than nurture may
be on the upswing. However, until such evidence is available we will continue to argue the
importance of each. Leading theorists are pushing for a more unified approach to researching
acquired behaviors from both genetically inherited traits and environmental factors. A new
appreciation for the
NATURE VERSUS NURTURE 11
necessity of both heredity and environment and the roles they play in human development is on
the horizon.
NATURE VERSUS NURTURE 12
References
Elam, K. K., Harold, G. T., Neiderhiser, J. M., Reiss, D., Shaw, D. S., Natsuaki, M. N., . . .
Leve,
L. D. (2014). Adoptive parent hostility and children’s peer behavior problems:
Examining the role of genetically informed child attributes on adoptive parent
behavior. Developmental Psychology,50(5), 1543-1552. doi:10.1037/a0035470
Hart, S. A., Logan, J. A., Soden-Hensler, B., Kershaw, S., Taylor, J., & Schatschneider, C.
(2013). Exploring how nature and nurture affect the development of reading: An analysis
of the Florida Twin Project on Reading. Developmental Psychology,49(10), 1971-1981.
doi:10.1037/a0031348
Kamran, F. (2016). Are Siblings Different as 'Day and Night'? Parents' Perceptions of Nature vs.
Nurture. Journal of Behavioural Sciences,26(2), 95-115. Retrieved from https://search-
proquest-com.ezproxy.liberty.edu/docview/1864042019?pq-
origsite=summon&accountid=12085.
Kan, K., Wicherts, J. M., Dolan, C. V., & Han L. J. Van Der Maas. (2013). On the Nature and
Nurture of Intelligence and Specific Cognitive Abilities. Psychological
Science,24(12), 2420-2428. doi:10.1177/0956797613493292
Montag, C., Hahn, E., Reuter, M., Spinath, F. M., Davis, K., & Panksepp, J. (2016). The Role
of Nature and Nurture for Individual Differences in Primary Emotional Systems:
Evidence from a Twin Study. Plos One,11(3). doi:10.1371/journal.pone.0151405
Moore, D. S. (2016). The Developmental Systems Approach and the Analysis of Behavior.
The Behavior Analyst,39(2), 243-258. doi:10.1007/s40614-016-0068-3
Plomin, R., Shakeshaft, N. G., Mcmillan, A., & Trzaskowski, M. (2014). Nature, nurture,
and expertise. Intelligence,45, 46-59. doi:10.1016/j.intell.2013.06.008
NATURE VERSUS NURTURE 13
Plomin, R., Shakeshaft, N. G., Mcmillan, A., & Trzaskowski, M. (2014). Nature, nurture, and
expertise: Response to Ericsson. Intelligence,45, 115-117.
doi:10.1016/j.intell.2014.01.003
Rettew, D. C. (2017, October). Nature vs. nurture: 50 years of a popular debate. Pediatric
News, 51(10), 1+. Retrieved from
http://link.galegroup.com.ezproxy.liberty.edu/apps/doc/A513010313/ITOF?
u=vic_liberty&sid=ITOF&xid=73968f7e.
