Development across the Life Span 313Table 8.1 A Comparison of Three Developmental Research Designs
Cross-Sectional Design
Different participants of various
ages are compared at one
point in time to determine age-
related differences.Group One: 20-year-old participants
Group Two: 40-year-old participants
Group Three: 60-year-old participantsResearch done in 2014Longitudinal Design
The same participants are
studied at various ages to
determine age-related changes.Study One: 20-year-old participants
Study Two: Same participants at
40 years old
Study Three: Same participants are
now 60 years oldResearch done in 1974
Research done in 1994Research done in 2014Cross-Sequential Design
Different participants of various
ages are compared at several
points in time to determine
both age-related differences
and age-related changes.Study One:
Group One: 20-year-old participants
Group Two: 40-year-old participants
Study Two:
Group One: Participants will be 25
years old
Group Two: Participants will be 45
years oldResearch done in 2014Research to be done
in 2019surroundings, economic factors, and anything that can have an influence on develop-
ment that does not come from within the person.
So is a person like Hitler born that way, or did something happen
to make him the person he was?How much of a person’s personality and behavior is determined by nature and
how much is determined by nurture? This is a key question, and the answer is quite
complicated. It is also quite important: Are people like Hitler or Dzhokhar Tsarnaev
(the youngest of the two brothers responsible for the bombings at the 2013 Boston
Marathon) the result of bad genes, bad parenting, or life-altering experiences in child-
hood? How much of Stephen Hawking’s genius is due to his genetic inheritance?
What part did the parenting choices of his family play? Or are his cognitive abilities
the unique combination of both hereditary and environmental influences? After many
years of scientific research, most developmental psychologists now agree that the last
possibility is the most likely explanation for most of human development: All that
people are and all that people become is the product of an interaction between nature
and nurture (Davis et al., 2012; Insel & Wang, 2010; Polderman et al., 2015; Ridley,
1999; Sternberg & Grigorenko, 2006). This does not mean that the nature versus nur-
ture controversy no longer exists; for example, intelligence is still a “hot topic” with
regard to how much is inherited and how much is learned. Some researchers and the-
orists assume a large genetic influence (Bouchard & Segal, 1985; Herrnstein & Murray,
1994; Jensen, 1969; Johnson et al., 2007; Kristensen & Bjerkedal, 2007), whereas many
others believe that culture, economics, nutrition in early childhood, and educational
opportunities have a greater impact (Gardner et al., 1996; Gould, 1996; Rose et al.,
1984; Wahlsten, 1997).
Behavioral genetics is a field of study in which researchers try to determine how
much of behavior is the result of genetic inheritance and how much is due to a person’s
experiences. As the video Family and Twin Studies explains, behavioral geneticists use a
variety of methods to determine this, including family, twin, and adoption studies.