In affluent Western countries, height has a heritability of about 80%. A researcher concludes that environmental interventions to increase height would be ineffective. What is wrong with this reasoning?
ANothing — 80% heritability means genes control most of height, leaving little room for environmental improvement
BHeritability only applies to populations, not individuals, so no conclusion about intervention is possible
CHeritability measures how much of the variation between people in a specific environment is genetic — it does not imply that changing the environment cannot change average height
DThe researcher should use narrow-sense heritability instead, which would give a lower estimate
Heritability measures the proportion of *variance* in a trait associated with genetic differences, within a specific population and environment. When nutrition is uniform and adequate, most remaining height differences are genetic — hence high heritability. But this says nothing about whether changing the average environment would change average height. The Dutch Hunger Winter showed that starvation reduced average height by centimeters in a population with unchanged genes. High heritability coexists with strong environmental malleability.
Question 2 Multiple Choice
Which type of gene-environment correlation best explains why a musically gifted child tends to receive better music instruction than a non-gifted child?
APassive GE correlation — the parents transmit both musical genes and a musical home environment
BActive GE correlation — the child selects a musical environment matching their genetic tendencies
CEvocative GE correlation — the child's genetic characteristics elicit enhanced musical instruction from others
DEpigenetic GE correlation — the musical environment modifies the child's gene expression
Evocative GE correlation occurs when a child's genetically influenced characteristics elicit particular responses from the environment. A musically talented child draws out more investment from teachers responding to displayed ability. Passive GE correlation (option A) would apply if the same musical parents who gave the child music genes also filled the home with instruments — that is about what parents provide, not responses to the child. Active GE correlation emerges more in adolescence when individuals seek out their own environments.
Question 3 True / False
A trait with very high heritability (e.g., 90%) in one population can have low heritability in a different population.
TTrue
FFalse
Answer: True
Heritability is population-specific and environment-specific. If a population is raised in highly variable environments (some with severe malnutrition, some with abundant food), environmental factors account for more variance in height, lowering heritability even with identical gene pools. Conversely, if everyone has near-identical environments, genetic differences explain most remaining variance. Heritability is a statistical property of a population in a context, not a fixed property of a trait.
Question 4 True / False
Because identical twins share 100% of their DNA, any differences between identical twins raised apart should be caused by the environment.
TTrue
FFalse
Answer: False
While environmental experiences do cause differences between identical twins raised apart, other non-environmental factors also contribute. Random developmental noise (stochastic variation in cell division, gene expression timing) creates biological differences even with identical DNA. Epigenetic changes that diverge over a lifetime — methylation patterns, gene expression changes in response to aging — are technically environmental in origin but are not simply caused by differences in upbringing. The logic 'identical DNA + different outcome = environment' is broadly correct but obscures finer-grained developmental mechanisms.
Question 5 Short Answer
What does it mean to say that a gene 'sets a reaction range' rather than 'determining' a trait, and why does this framing matter?
Think about your answer, then reveal below.
Model answer: A reaction range is the set of possible phenotypic outcomes a genotype can produce across the range of environments it might encounter. Rather than specifying a single fixed outcome, genes specify a range of possibilities; the specific environment activates, suppresses, or shifts expression within that range. This framing matters because it explains how high heritability can coexist with meaningful environmental influence: genes constrain but do not dictate, and different environments can produce very different phenotypes from the same genotype.
The reaction range concept directly refutes the heritability-as-immutability fallacy. It shifts the question from 'genes or environment?' to 'what environments amplify or buffer this genetic potential?' A child with high genetic risk for anxiety may never develop an anxiety disorder if raised in a secure environment. The genes are still there — the reaction range is real — but the environment determines where within that range the person lands. This is why interventions can work even for highly heritable traits.