D2.Psy.10.9-12: How Nature and Nurture Interact to Shape Behavior

Overview

Lesson Procedure

60-70 minutes of class time across 5 phases.

1. Warm-Up5-10 minutes
2. Direct Instruction20 minutes
3. Guided Practice15 minutes
4. Independent Practice15 minutes
5. Closure5-10 minutes

1. Warm-Up5-10 minutes

   Warm-Up Prompt

   "A friend says: 'My cousin is a great swimmer because swimming runs in her family.' Write down two ways that swimming could 'run in a family' that have nothing to do with genes, and one way that genes could still matter."

   Collect answers. Non-genetic routes usually include a family pool or beach trips, parents who coach, and family expectations. A genetic route might be body build. Then ask: Could genes and the pool both matter, and could each make the other matter more? That question is the lesson.

2. Direct Instruction20 minutes

   Key terms. Nature means inherited biology: the genes a person receives from their parents and the body those genes help build. Nurture means experience in the broadest sense: nutrition, illness, family, schooling, culture and everything learned. Maturation is development that unfolds on a biological timetable, with ordinary experience, but without special training. A sensitive period is a window of time when a particular kind of experience has an especially large effect on development.

   The old phrase "nature versus nurture" suggests that a behavior must come from one or the other. Psychologists today study how the two work together. There are three common patterns:

   • Gene-environment interaction: the effect of a gene depends on the environment, so the same gene can lead to different outcomes.
   • Experience changes how genes are used: chemical tags called the epigenome can switch genes on or off in response to experience.
   • Gene-environment correlation: inherited tendencies affect which experiences a person gets or seeks out. The psychologists Sandra Scarr and Kathleen McCartney built a theory of development around this pattern in a 1983 article in Child Development.

   Read Source 1. Douglas Spalding (about 1841-1877) was a British naturalist who studied young animals; he read this paper at a scientific meeting in 1875.

   1Though the instincts of animals appear and disappear in such seasonable correspondence with their own wants and the wants of their offspring as to be a standing subject of wonder, they have by no means the fixed and unalterable character by which some would distinguish them from the higher faculties of the human race. They vary in the individuals as does their physical structure. Animals can learn what they did not know by instinct and forget the instinctive knowledge which they never learned, while their instincts will often accommodate themselves to considerable changes in the order of external events. [...]

   [...]

   2That the later developments to which I have referred are not acquisitions can be in some instances demonstrated. Birds do not learn to fly. Two years ago I shut up five unfledged swallows in a small box not much larger than the nest from which they were taken. The little box, which had a wire front, was hung on the wall near the nest, and the young swallows were fed by their parents through the wires. In this confinement, where they could not even extend their wings, they were kept until after they were fully fledged. Lord and Lady Amberley liberated the birds and communicated their observations to me, I being in another part of the country at the time. On going to set the prisoners free, one was found dead—they were all alive on the previous day. The remaining four were allowed to escape one at a time. Two of these were perceptibly wavering and unsteady in their flight. [...] The swallows never flew against anything, nor was there, in their avoiding objects, any appreciable difference between them and the old birds. [...]

   Sample warning: the swallow test used five birds, one of which died before release, and had no comparison group of birds raised in the open. Treat it as a striking early observation, not a measured result. Then read Source 3, a current page from the National Library of Medicine. Classic PKU is the page's name for the most severe form of the condition.

   1Phenylketonuria (commonly known as PKU) is an inherited disorder that increases the levels of a substance called phenylalanine in the blood. Phenylalanine is a protein building block (an amino acid) that is obtained from eating certain foods (such as meat, eggs, nuts, and milk) and in some artificial sweeteners. If PKU is not treated, phenylalanine can build up to harmful levels in the body, causing intellectual disability and other serious health problems.

   [...]

   2PKU can often be managed by following a diet that is low in phenylalanine. Since phenylalanine is found in all proteins, the PKU diet consists of avoiding meat, dairy, nuts, tofu, and other foods that are high in protein. [...]

   [...]

   3The occurrence of PKU varies among ethnic groups and across geographic regions worldwide. In the United States, PKU occurs in 1 in 25,000 newborns. Most cases of PKU are detected shortly after birth by newborn screening, and treatment is started promptly. As a result, the severe signs and symptoms of classic PKU are rarely seen.

   [...]

   4Variants (also called mutations) in the PAH gene cause phenylketonuria. The PAH gene provides instructions for making an enzyme called phenylalanine hydroxylase. This enzyme converts the amino acid phenylalanine into other important compounds in the body. PAH gene variants result in the production of altered versions of phenylalanine hydroxylase that cannot process phenylalanine effectively. As a result, this amino acid can build up to toxic levels in the blood and other tissues. Because nerve cells in the brain are particularly sensitive to phenylalanine levels, excessive amounts of this substance can cause brain damage.

   • A deprivation design: Source 1, paragraph 2

     What question was Spalding's swallow test designed to answer, and what does its result suggest about flying?

     Result: The question: does a bird need practice to fly? Keeping the birds where "they could not even extend their wings" removed practice. Because the swallows still avoided objects like "the old birds," flying looks largely like maturation. It still depends on a normal environment, food from their parents, and a body that grew.

   • Gene-environment interaction: Source 3

     Use paragraphs 1 and 2 of Source 3 to explain why PKU is not simply "genetic" or simply "environmental."

     Result: PKU is "an inherited disorder" (nature), but the harm comes from phenylalanine that "is obtained from eating certain foods" (nurture). Paragraph 2 says it "can often be managed by following a diet that is low in phenylalanine." The same gene variants lead to very different outcomes depending on diet.

   • What a heritability number means

     Suppose researchers report that, in one country, about 80 percent of the differences in adult height are linked to genetic differences. Does that mean 80 percent of a 170 cm person's height comes from genes?

     Result: No. Heritability describes how much of the variation among people in a group is linked to genetic variation, in that group and environment. It says nothing about how a single person's height was built, and it can change if the environment changes, for example if some children go hungry.

   • Experience and gene activity

     Source 5 (printed in Independent Practice) says cells in the eye and red blood cells carry "essentially the same genome." How can they be so different?

     Result: Different sets of genes are switched on in each kind of cell. The epigenome, the chemical tags that direct this switching, responds to signals inside the body and, according to Source 5, to outside factors such as diet. Genes are the instructions; the epigenome helps decide which instructions are read.

   • A sensitive period in vision research

     In the 1960s and 1970, David Hubel and Torsten Wiesel reported that closing one eye of a kitten during its first few months sharply reduced the number of cells in the visual cortex that the eye could influence, and that this recovered only a little after the eye was opened again. Closing one eye of an adult cat, even for over a year, had no detectable effect. What does this show?

     Result: The visual brain is built by genes and experience together: inherited wiring needs normal input during a sensitive period. Hubel and Wiesel shared the 1981 Nobel Prize in Physiology or Medicine for their discoveries about how the visual system processes information. Studies like these are reviewed today under federal animal-welfare rules.

   Close the segment by asking which of the three interaction patterns each example fits. Example 2 is gene-environment interaction; Example 4 shows experience acting on gene use; Example 5 is a sensitive period, a timing form of interaction.

3. Guided Practice15 minutes

   Read Source 4 and then Source 6 together. Source 4 is a federal genetics handbook page; Source 6 is an invented study with invented data that follows the logic Source 4 describes.

   1Temperament includes behavioral traits such as sociability (outgoing or shy), emotionality (easy-going or quick to react), activity level (high or low energy), attention level (focused or easily distracted), and persistence (determined or easily discouraged). These examples represent a spectrum of common characteristics, each of which may be advantageous in certain circumstances. Temperament remains fairly consistent, particularly throughout adulthood.

   2Similar temperaments within a family may be attributable to shared genetics and to the environment in which an individual is raised. Studies of identical twins (who share 100 percent of their DNA) and their non-twin siblings (who share about 50 percent of their DNA) show that genetics play a large role. Identical twins typically have very similar temperaments when compared with their other siblings. Even identical twins who were raised apart from one another in separate households share such traits.

   3Scientists estimate that 20 to 60 percent of temperament is determined by genetics. Temperament, however, does not have a clear pattern of inheritance and there are not specific genes that confer specific temperamental traits. Instead, many (perhaps thousands) of common gene variations (polymorphisms) combine to influence individual characteristics of temperament. Other DNA modifications that do not alter DNA sequences (epigenetic changes) also likely contribute to temperament.

   1Invented study summary, written for this page. A research team recruited 60 pairs of identical twins and 60 pairs of same-sex fraternal twins. All the children were 5 years old, lived in one state and were being raised in the same home as their twin. Parents gave written consent, and the children's names were removed from the data.

   2The team measured two behaviors. For sociability, a parent rated how readily each child joins unfamiliar children at a playground, on a scale from 1 (holds back every time) to 10 (joins right away). For team loyalty, a parent named the professional sports team each child cheers for, if any.

   3Results for sociability, as the correlation between the two twins in a pair: identical twins 0.52; fraternal twins 0.28. Results for team loyalty, as the number of pairs in which both twins named the same team or both named none: identical twins 55 of 60 pairs; fraternal twins 54 of 60 pairs.

   4The team's note: "All ratings came from parents, and every family lived in one state, so the results may not hold for other places or for ratings by teachers or observers."

   1. The logic. Identical twins share nearly all their genes; same-sex fraternal twins share about half on average, like other siblings. Both kinds of twins in Source 6 grow up in one home with their twin. If identical twins are more alike than fraternal twins, genes are a likely reason.
   2. A rough estimate. A formula named for the geneticist Douglas Falconer estimates heritability as twice the difference between the two correlations: h² = 2(r_identical - r_fraternal). Students compute it for sociability themselves.
   3. Team loyalty. Compare the two kinds of twins on this behavior. What does it suggest about where the similarity comes from?
   4. Sample warning. 120 pairs from one state, all rated by their own parents, is a limited sample. Parents of identical twins may also expect them to be alike, which could raise their ratings' similarity.
4. Independent Practice15 minutes

   Students read Sources 2, 5 and 7 on their own and use all seven sources for the quiz and homework. Source 2 continues Spalding's paper; Source 5 is a federal fact sheet on the epigenome; Source 7 is an SVHS-written paragraph with deliberate errors. Sample warning for Source 2: Carpenter's evidence is a single case, reported more than forty years after the operation.

   1[...] More than forty years ago Dr. Carpenter took part in an operation performed on a boy three years old for congenital cataract. The operation was successful. In a few days both pupils were almost clear; but though the boy “clearly recognised the direction of a candle or other bright object, he was unable as an infant to apprehend its distance; so that when told to lay hold of a watch he groped at it just as a young child lying in its cradle.” He gradually began to use his eyes; first in places with which he was not familiar, but it was several months before he trusted to them for guidance as other children of his age would do. No one will doubt the accuracy of any of these statements; but I cannot agree with Dr. Carpenter that he had in the case of the boy anything “exactly parallel” to my experiment of hooding chickens at birth and giving them their sight at the end of one or two days. This boy was couched when three years old. Probably sight would have been at first rather puzzling to my chickens, had they not received it until they were six months old. Dr. Carpenter seems to have forgotten for the moment that instincts as well as acquisitions decay through desuetude, and that this is especially true when the faculties in question have never once been started into action and are of the kind which develop through exercise. [...]

   [...]

   2One word as to the origin of instincts. In common with other evolutionists, I have argued that instinct in the present generation may be regarded as the product of the accumulated experiences of past generations. [...]

   1What is the epigenome?

   2The epigenome is a multitude of chemical compounds that can tell the genome what to do. The human genome is the complete assembly of DNA (deoxyribonucleic acid)-about 3 billion base pairs - that makes each individual unique. DNA holds the instructions for building the proteins that carry out a variety of functions in a cell. The epigenome is made up of chemical compounds and proteins that can attach to DNA and direct such actions as turning genes on or off, controlling the production of proteins in particular cells.When epigenomic compounds attach to DNA and modify its function, they are said to have "marked" the genome. These marks do not change the sequence of the DNA. Rather, they change the way cells use the DNA's instructions. The marks are sometimes passed on from cell to cell as cells divide. They also can be passed down from one generation to the next.

   3What does the epigenome do?

   4A human being has trillions of cells, specialized for different functions in muscles, bones and the brain, and each of these cells carries essentially the same genome in its nucleus. The differences among cells are determined by how and when different sets of genes are turned on or off in various kinds of cells. Specialized cells in the eye turn on genes that make proteins that can detect light, while specialized cells in red blood cells make proteins that carry oxygen from the air to the rest of the body. The epigenome controls many of these changes to the genome.

   [...]

   5Can the epigenome change?

   6Although all cells in the body contain essentially the same genome, the DNA marked by chemical tags on the DNA and histones gets rearranged when cells become specialized. The epigenome can also change throughout a person's lifetime.

   7What makes the epigenome change?

   8Lifestyle and environmental factors (such as smoking, diet and infectious disease) can expose a person to pressures that prompt chemical responses. These responses, in turn, often lead to changes in the epigenome, some of which can be damaging. However, the ability of the epigenome to adjust to the pressures of life appears to be required for normal human health. Some human diseases are caused by malfunctions in the proteins that "read" and "write" epigenomic marks.

   1SVHS-written sample interpretation. It contains errors on purpose, for students to find and correct.

   2"Nature has won the nature-nurture debate. Spalding proved in 1875 that animals need no experience at all: his swallows could fly without any practice, so learning plays no part in how animals behave. Modern science agrees. Temperament is 20 to 60 percent genetic, which means that a shy five-year-old was born up to 60 percent shy. Phenylketonuria shows the same thing: if you inherit the gene variants, your fate is sealed. And because the epigenome is fixed before birth, nothing a person experiences can reach their genes."

   Task: in Source 2, paragraph 1, mark the evidence Carpenter offered for nurture and the reply Spalding gave. In two or three sentences, say whether each man explained the boy's case through nature, through nurture or through both, and quote the words that show it.

5. Closure5-10 minutes

   Exit ticket: "Pick one behavior you care about (a sport, a language, an instrument, a temperament trait). In two sentences, describe one way nature and nurture interact in it."

   Teacher notes. (1) Sources 1 and 2 are historical. Spalding's swallow test is a small early observation, not a modern study, and his account of where instincts come from (inherited experience of past generations) is outdated, and students weigh it against Source 5 in the quiz. (2) Spalding confined wild birds and, in passages not printed here, blindfolded newborn pigs. Today, animal research must be reviewed under federal rules, which D2.Psy.4.9-12 covers. (3) Source 3 is general medical information chosen because PKU is a clear case of gene-environment interaction; students never assess anyone's health. If a student has a personal health question, point them to a parent, school nurse or doctor. (4) Sources 6 and 7 are invented for teaching; their data and claims are not real. Source 7's errors are deliberate.

Differentiation Strategies

Assessment Guidance

1. Question 1 of 20 · Multiple Choice

   In Source 1, paragraph 1, what does Spalding say about instincts in individual animals?

   AThey are identical in every animal of the same kind BThey differ among individuals, as bodies do CThey appear only after an animal has been taught DThey disappear as soon as an animal starts to learn

2. Question 2 of 20 · Multiple Choice

   In Source 1, paragraph 2, who released the swallows and reported what they did?

   ASpalding himself, watching with a group of students BDr. Carpenter, who wanted to check the result himself CA newspaper reporter who was visiting the house DLord and Lady Amberley, while Spalding was away

3. Question 3 of 20 · Multiple Choice

   Which detail in Source 1, paragraph 2 counts against the claim that flying needs no practice at all?

   ATwo of the birds were wavering and unsteady in their flight BThe young swallows were fed by their parents through the wires CThe swallows never flew against anything in their path DThe box was hung on the wall near the nest they came from

4. Question 4 of 20 · Multiple Choice

   In Source 2, paragraph 1, what does the boy's case seem to show, from Carpenter's side of the argument?

   AJudging distance by sight is fixed at birth and cannot change BEye surgery in that era usually failed to restore any sight CUsing sight to judge distance has to be learned by experience DChildren who lose their sight never learn to use it again

5. Question 5 of 20 · Multiple Choice

   Why does Spalding say the boy's case is not "exactly parallel" to his experiment with chickens?

   AThe boy was a human being, and human beings have no instincts at all BThe boy got sight at age three, not at one or two days old CThe boy's doctor had no training in experimental science DThe boy was tested in a hospital, not on a farm with animals

6. Question 6 of 20 · Multiple Choice

   Spalding writes in Source 2 that "instincts as well as acquisitions decay through desuetude" when the faculties are "of the kind which develop through exercise." Which idea from the lesson does this anticipate?

   AA sensitive period BRandom assignment CHeritability DGene-environment correlation

7. Question 7 of 20 · Multiple Choice

   According to Source 3, which part of the PKU story is the "nature" side?

   AA diet that is high in protein foods BNewborn screening soon after birth CArtificial sweeteners such as aspartame DVariants in the PAH gene

8. Question 8 of 20 · Multiple Choice

   According to Source 3, paragraph 3, why are the severe signs and symptoms of classic PKU rarely seen in the United States?

   AThe gene variants have nearly vanished from the population BMost families avoid protein foods for cultural reasons CScreening finds most cases at birth and treatment starts promptly DDoctors now use a surgery that replaces the PAH enzyme in newborns

9. Question 9 of 20 · Multiple Choice

   Source 4, paragraph 2 says that "Even identical twins who were raised apart from one another in separate households share such traits." Why is this finding important?

   ATheir shared temperament cannot come from a shared home BIt shows that twins raised apart never meet again as adults CIt proves that homes have no effect on any behavior DIt shows that fraternal twins share all of their DNA

10. Question 10 of 20 · Multiple Choice

    How stable does Source 4, paragraph 1 say temperament is?

    AFixed at birth, and it never changes after that point BFairly consistent, especially throughout adulthood CCompletely different every few years of a life DStable in childhood, but not in adulthood

11. Question 11 of 20 · Multiple Choice

    Use the formula from Guided Practice, h² = 2(r_identical - r_fraternal), with the sociability data in Source 6. What is the estimated heritability?

    A0.24 B0.80 C0.48 D1.04

12. Question 12 of 20 · Multiple Choice

    In Source 6, identical twins matched on team loyalty in 55 of 60 pairs and fraternal twins in 54 of 60. What does this suggest?

    ATeam loyalty is passed on mostly through genes BFraternal twins are raised in different homes CIdentical twins are much more alike in this behavior DThe similarity comes mostly from the shared home

13. Question 13 of 20 · Multiple Choice

    Source 5, paragraph 6 says that the epigenome "can also change throughout a person's lifetime." Which claim in Source 7 does this contradict?

    AThat Spalding's swallows could fly without practice BThat the epigenome is fixed before a person is born CThat temperament is partly linked to genes DThat PKU involves inherited gene variants

14. Question 14 of 20 · Multiple Choice

    A child who inherits a quick, accurate sense of rhythm is praised at music lessons, signs up for band and practices more than classmates. Which pattern from the lesson does this show?

    AGene-environment correlation BGene-environment interaction CA sensitive period DMaturation

15. Question 15 of 20 · Short Answer

    Spalding argued (Source 2, paragraph 2) that instinct "may be regarded as the product of the accumulated experiences of past generations." Source 5, paragraph 2 says epigenetic marks "also can be passed down from one generation to the next." Does Source 5 support Spalding's idea? Explain.

    Show model answer

16. Question 16 of 20 · Short Answer

    Besides its claim about the epigenome, Source 7 contains at least three errors. Identify two of them and correct each one with evidence from a source, quoted with its paragraph number.

    Show model answer

17. Question 17 of 20 · Short Answer

    Invented case: in Town A, every child gets plenty of healthy food. In Town B, some children get plenty and some get much less. Researchers find that the heritability of height is higher in Town A than in Town B. Explain why, and what this shows about heritability.

    Show model answer

18. Question 18 of 20 · Short Answer

    Spalding's swallows (Source 1) flew without practice, but Hubel and Wiesel's kittens (Direct Instruction, Example 5) needed visual experience to develop normal vision. Explain how both results can be true.

    Show model answer

19. Question 19 of 20 · Short Answer

    In Source 6, the sociability correlation for identical twins is 0.52, not 1.0. Explain why this number is evidence that nurture matters, even though identical twins share nearly all their genes and their home.

    Show model answer

20. Question 20 of 20 · Short Answer

    Plan, on paper only, an adoption study that could separate the effects of genes and of the home environment on how much children enjoy reading. Say who you would compare and what result would point to each influence.

    Show model answer

These standards connect to D2.Psy.10.9-12: prerequisites to review first, parallel standards at the same level, and next steps that build on it.

Standard text: National Council for the Social Studies (NCSS), The College, Career, and Civic Life (C3) Framework for Social Studies State Standards: Guidance for Enhancing the Rigor of K-12 Civics, Economics, Geography, and History (Silver Spring, MD: NCSS, 2013). NCSS was not involved in the production of this lesson and does not endorse it.