Chapter 5

Biology, Culture and Society

Chapter Outline

Heredity Behavioral Genetics The Growth Revolution Hormones and Behavior DNA and Culture Humans and Other Animals

Genotype and Phenotype

The genotype is the total of the genetic instructions an organism receives from its parents.

The phenotype is what we see when we look at an organism.

Genotype and Phenotype

The genotype is genetic potential. The phenotype is the outcome of the

combination of the genotype and the environment.

The Growth Revolution

Men born in 1956–1962 were 3 times as likely as men born in 1906–1915 to reach a height of 6’ or taller.

1/3 of those born in 1906–1915 were under 5’7”. Fewer than 10% of those born in 1956–1962 were 5’7”.

A century ago, most people did not reach their full adult height until age 25.

Today, most people stop growing by 18.

Trends in the Height of Americans

Year of Birth

1906–1915 1926–1935 1956–1962

Males percent

over 6’ 10.4 14.2 31.8

under 5’7” 29.4 11.4 8.2

Females

over 5’5” 5.4 15.4 25.2

under 5’3” 44.3 27.7 17.8

The Growth Revolution

To ask why humans suddenly began to get so large so fast raises the wrong question.

The right question is, what kept humans so small and delayed their maturation for so long?

This rapid change in the phenotype of human beings reveals the previously unfulfilled potential of the human genotype.

Inadequate Nutrition

Until modern times, most people ate meager diets that were deficient in vitamins and proteins.

Most people lived almost exclusively on bread, mush and soup made from grain.

Their poor diet made people more susceptible to illness and contagious diseases.

Testosterone and Behavior

Men with higher levels of testosterone are more likely to:

Get divorced Physically abuse their wives Engage in extramarital sex Have many sexual partners Have problems with alcoholism

Testosterone and Behavior

Men with higher levels of testosterone are more likely to:

Use drugs Have been punished while in military

service Have been a juvenile delinquent Get in trouble with the law as an adult Be unemployed

Testosterone and Behavior

Men with higher levels of testosterone are less likely to:

Get married Become highly educated Obtain a high-status occupation

Jane Goodall’s Primary Rules of Fieldwork

1. Record everything you notice, always, and file it so you can find it again.

2. After you have drawn a conclusion, search for evidence that you are wrong.

3. Never, ever think you understand everything that’s going on.

Crows and Tool Use

Three Oxford zoologists demonstrated that crows can use tools.

A female crow, captured as a juvenile bird, bent a wire to form a hook and used it to lift food from a vertical plastic pipe.