What makes us who we are?

Nature and Nurture

Based on “Nature via Nurture” by Matt Ridley (2003)

Protein

•Genes code for proteins.•Cells function because of proteins.•Organisms are collections of cells.

Fig 16.10

Protein

The connection between genes and traits is rarely direct.

Fig 16.10

Mostly Nurture-Imprinting:exposure to movement (environment) sets “mother”

Mostly Nature-X/Y chromosomes in humans: genes = traits

XY XX

Your DNA comes in pairs...

X/Y chromosomes in humans:genes = traits

XY XX

Twin studies have been used to determine the heritability of various traits.

Types of twins:

http://pennhealth.com/health_info/pregnancy/000199.htm

Twin studies have been used to determine the heritability of various traits, but there are some caveats:How many twins have been studied?How different are the environments?

Correlation of weight (BMI) %

Identical twins reared together 80

Identical twins reared apart 72

Fraternal twins reared together 43

Biological siblings 34

Parents and children living together 26

Adopted children and parents 4

Unrelated children living together 1

*But food preference shows little genetic correlation

Correlation of weight and relatedness

The nature of environmental influences on weight and obesity: A behavior genetic analysis. Grilo, Carlos M.; Pogue-Geile, Michael F.; Psychological Bulletin, Vol 110(3), Nov 1991. pp. 520-537. And two books by Matt Ridley: Nature via Nurture (2003) and Genome: the Autobiography of a Species in 23 Chapters (1999)

IntelligenceCorrelation of IQ Inheritance :

%

The same person tested twice 87

Identical twins reared together86

Identical twins reared apart76

Fraternal twins reared together55

Biological siblings 47

Parents and children living together40

Parents and children living apart31

Adopted children living together 0

Unrelated people living apart 0

From two books by Matt Ridley: Nature via Nurture (2003) and Genome: the Autobiography of a Species in 23 Chapters (1999)

When the environment is equal (everyone has access to resources), genetic differences are magnified.

When environments are different (only a few have access to

resources), environmental differences are

magnified.

Proof or disproof?Correlation of IQ Inheritance :

%

The same person tested twice 87

Identical twins reared together86

Identical twins reared apart76

Fraternal twins reared together55

Biological siblings 47

Parents and children living together40

Parents and children living apart31

Adopted children living together 0

Unrelated people living apart 0

From two books by Matt Ridley: Nature via Nurture (2003) and Genome: the Autobiography of a Species in 23 Chapters (1999)

Can we see a genetic basis for complex behaviors?

VolesPrairie

• Monogamous

• Both parents care for young

Montane

• Nonmonogamous

• Mother cares for young briefly

Oxytocin(hormone)

Water/salt balance

Contraction of womb and milk production

Encourages bonding between individuals

Hormones are molecules produced in one cell and signal another.

Oxytocin(hormone)

Water/salt balance

Contraction of womb and milk production

Encourages bonding between individuals

VolesPrairie

• Monogamous

• Both parents care for young

Montane

• Nonmonogamous

• Mother cares for young briefly

VolesPrairie

• Monogamous

• Both parents care for young

Montane

• Nonmonogamous

• Mother cares for young briefly

Same levels of oxytocin

Hormones are molecules produced in one cell and signal another.

VolesPrairie

• Monogamous

• Both parents care for young

• More receptors

Montane

• Nonmonogamous

• Mother cares for young briefly

• Less receptorsSame levels of oxytocin

VolesPrairie

• Monogamous

• Both parents care for young

• More receptors

• ?

Montane

• Nonmonogamous

• Mother cares for young briefly

• Less receptors

• ?

Same levels of oxytocin

Inject hormone into brain

VolesPrairie

• Monogamous

• Both parents care for young

• More receptors

• Monogamous

Montane

• Nonmonogamous

• Mother cares for young briefly

• Less receptors

• Nonmonogamous

Same levels of oxytocin

Inject hormone into brain

VolesPrairie

• Monogamous• Both parents care

for young

• More oxytocin receptors

• ?

Montane• Nonmonogamous• Mother cares for

young briefly

• Less oxytocin receptors

• ?

Same levels of oxytocin

Block receptors

VolesPrairie

• Monogamous• Both parents care

for young

• More oxytocin receptors

• Nonmonogamous

Montane• Nonmonogamous• Mother cares for

young briefly

• Less oxytocin receptors

• Nonmonogamous

Same levels of oxytocin

Block receptors

VolesPrairie

• Monogamous• Both parents care

for young

• More oxytocin receptors

• Monogamous

Montane• Nonmonogamous• Mother cares for

young briefly

• Less oxytocin receptors

• Monogamous

Same levels of oxytocin

Increase levels of receptors (genetically) in ventral pallidum

VolesPrairie

• Monogamous

• Both parents care for young

• More receptors

Montane

• Nonmonogamous

• Mother cares for young briefly

• Less receptorsSame levels of oxytocin

Nature and Nurture:

Next...Are traits coded for by genes fixed while traits coded for by the environment are under our control?

Next: Evolution