The Human Population:The Human Population:Patterns, Processes, and ProblematicsPatterns, Processes, and ProblematicsLecture #7: Lecture #7: Fertility Concepts & MeasurementFertility Concepts & Measurement

Paul SuttonPaul Sutton

psutton@du.edupsutton@du.edu

Department of GeographyDepartment of Geography

University of DenverUniversity of Denver

Keeping our numbers down….

• Control of Human Reproduction is one of the most important and revolutionary changes of modern humans

• This change is comparable in significance to the changes to the death rate

Fertility control is NOT just taking the pill or using a condom• How do we measure fertility?

• Why does fertility vary geographically?

• How do we control fertility?

• Why do we control fertility?

Geographic Variation of Crude Birth Rate

What is Fertility?

• Fertility is about how many children women have

• In a ‘High fertility’ society women have many children

• In a ‘Low fertility’ society women have fewer children

• There are both ‘Biological’ and ‘Social’ components to fertility

Biological Components to Fertility

• Fecundity is a measure of the physical ability to have children

• Fertility is the actual number of children a woman has

• (e.g. my mother had four children, me, my brother and my two sisters so here fertility was 4)

Infertility/Infecundity (for demographers)

• Couples who have tried for 12 months to get pregnant and do not are infecund (infertile to lay people)

1995 this rate was 7% of American couples

1965 this rate was 11% of American couples

Impaired Fecundity• Fecundity does not have to necessarily be

measured on a binary (yes/no) basis

• If….:– A woman believes she can’t get pregnant– Physician recommends a woman not get pregnant for

health reasons– A married couple is married for 3 years, does not use

contraception, and no pregnancy• FECUNDITY is described as “Impaired”• 10% of women have ‘impaired fecundity’

Fecundity and Age• For women, fecundity goes from 0 to non-zero

at the onset of menarch (menstruation)• Female fecundity generally increases to their

mid-20’s and drops to 0 at menopause• Male fecundity goes from 0 to non-zero at

puberty and generally peaks in mid 20’s also• Male fecundity generally drops from mid 20’s

as they age but does not have a definite end point like menopause.

• Male fecundity tends to last longer than female fecundity

Some fecundity Statistics…• 1998 10,000 babies born to women under 15 in U.S.

• 1998 158 babies born to women of age 50-54

• Ruth Kistler oldest natural mother ever– Gave birth to a child at age 57 in 1956

• 63 year old Phillipino woman in 1996 gave birth to an implanted embryo

Astronomical Fertility

A Russian Woman in the

18th Century gave birth to

69 children with ‘only’

27 pregnancies

What is ‘Maximum’ Fertility in absence of any fertility control?

• 1) Assume female fecundity from age 15-49

• 2) Assume 9 months of pregnancy

• 3) Assume 18 months of breast feeding

• Result: 1 child every 2.2 years

• Fertility Rate is 16 children per woman

This is a theoretical maximum for a population (fortunately it does not happen)

No known society has ever attained the theoretical maximum fertility of about 16 children per woman

There are biological reasons for this:

• 1) Pregnancy is dangerous (The ‘risk’ of pregnancy) Many women would die before if not during the delivery of their 16th child

• Not all women are fecund (1/3 of the women in Cameroon are infecund for health/dietary reasons)

• If women don’t eat enough fat they may experience amenorhea (absence of suppression of menstruation and/or anovulatory cycles (egg-free menstruation))

Is Female Menarche (puberty) happening Earlier?

The condition of accelerated puberty in girls is more of ahypothesis than a widely observed phenomenon—in spite of anecdotal reports. Your article seemed to emphasize the vaguepossibility that a host of chemicals, those found in the environmentor in foods, could initiate early puberty. But the only scientificallydocumented cause is the increase in childhood obesity, and thedemonstrated involvement of fat cell-derived leptin in initiatingpubertal events. Next time, I hope you will do your readers a favorby presenting such stories in a more realistic context, rather thanalarming them on the basis of weak scientific evidence.

Ruth Kava, Ph.D., R.D. is Director of Nutrition of the American Council on Science and Health in New York.

What is ‘Natural’ Fertility?

• Definition: The level of reproduction that exists in the absence of deliberate (or at least modern) fertility control

• ‘Natural’ Fertility is much lower than ‘Maximum’ fertility

“The genius of the species has not been to rely on a birth rate so high that it can overcome almost any death rate, no matter how high. The genius of the species is rather to have few offspring and to invest heavily in their care and training, so that the advantages of a cultural adaptation can be realized. Throughout 99% of hominid history, then, fertility was kept as low as it could be, given the current mortality.” (Davis 1981)

Conclusion….

• Social components of Fertility

Much Greater than• Biological Components of Fertility

Studies of twins show that Biological component of fertility only about 25% (same as biological component of mortality)

The Social Components of Fertility

‘Opportunities and Motivations for childbearing vary considerably from one social environment to another’

• Hunter-Gatherers: Space children in time, fertility much lower than ‘natural’ fertility

• Agricultural Societies: High fertility perhaps from demand for people to harvest crops

• Industrial Society: Very low fertility perhaps from the ‘expenses’ associated with raising kids

The Hutterites:A famous ‘High Fertility’ Society

• Anabaptists (opposed to childhood baptism)

• Live in Agrarian communities in NE plains of U.S. and Western provinces of Canada

• 400 came from Russia in late 1800’s

• Doubled Population 6 times in 100 years

• In 1936 the TFR for Hutterite women was 11

Why Hutterite Fertility so High?

• Early age of marriage• A good diet• Good medical care• Belief in Bible’s:“Be Fruitful and Multiply”

• Frequent sex with no contraception

High fertility is not rocket science

What happened to the Hutterites?

Population growth has slowed• Communes grow to about 130 and divide

• New land needs to be purchased

• Canada passed laws specifically aimed at preventing Hutterites from buying land

• Technology changed farming and fertility.

Other ‘High Fertility’ Societies• Shipibo Indians from Eastern

Amazon of Peru-Avg Age at Marriage 14

-Avg Age at 1st Child 15.6

- Total Fertility Rate ~ 11

Hmong Refugees to U.S. in 1980’s

same deal: Marry Early, impregnate often

Total Fertility Rate ~ 11

Age Specific Fertility

Rate

Fertility obviously varies in space and time…To understand why, 2 questions must be asked

How do people control fertility?

Why do people want to control fertility?

How is fertility controlled?

• 11 intermediate variables (how’s)

through which any social factors (why’s)

must operate. (See table on next slide)

• 3 Phases of Fertility Control

1) Intercourse 2) Conception 3) Gestation

‘ProximateDeterminants’

or ‘IntermediateVariables’

controllingfertility