Evolution And History

36 CHAPTER 2 | Genetics and Evolution

known genes, also replicates. Mistakes can occur in the

replication process, adding or subtracting repeats of the

four bases: A, C, G, and T. This happens with some fre-

quency and differently in every individual. As these “mis-

takes” accumulate over time, each person develops his or

her unique DNA fingerprint.

Cell Division

In order to grow and maintain good health, the cells of

an organism must divide and produce new cells. Cell

division is initiated when the chromosomes replicate,

forming a second pair that duplicates the original pair of

chromosomes in the nucleus. To do this, the DNA “un-

zips” between the base pairs—adenine from thymine and

these stretches of DNA are metaphorically snipped out
and left on the cutting room floor.
Some of this seemingly useless, noncoding DNA (of-
ten called junk DNA) has been inserted by retroviruses.
Retroviruses are some of the most diverse and widespread
infectious entities of vertebrates—responsible for AIDS,
hepatitis, anemias, and some neurological disorders.^5
Other junk DNA consists of decaying hulks of once-useful
but now functionless genes: damaged genes that have been
“turned off.” As cells divide and reproduce, junk DNA, like

(^5) Amábile-Cuevas, C. F., & Chicurel, M. E. (1993). Horizontal gene transfer.
American Scientist 81, 338.
Biocultural Connection

The Social Impact of Genetics on Reproduction

While pregnancy and childbirth have

been traditional subjects for cultural an-

thropology, the advances in genetics are

raising new questions for the biocultural

study of reproduction. At first glance,

the genetics revolution has simply

expanded biological knowledge. Indi-

viduals today, compared to a hundred

years ago, can see their own genetic

makeup, even down to the base-pair

sequence level. But this new biological

knowledge also has the capacity to pro-

foundly transform cultures, and in many

places new genetic information has

dramatically affected the social experi-

ence of pregnancy and childbirth.

New reproductive technologies allow

for the genetic assessment of fertilized

eggs and embryos (the earliest stage of

animal development), with far-reaching

social consequences. These technologies

have also become of interest to cultural

anthropologists who are studying the

social impact of biological knowledge.

For nearly twenty-five years, anthropolo-

gist Rayna Rapp has examined the social

influence of prenatal genetic testing in

North America.a Her work illustrates that

biological facts pertaining to reproduc-

tion do not exist outside of an interpre-

tive framework provided by the culture.

Prenatal genetic testing is conducted

most frequently through amniocentesis,

a technique developed in the 1960s

through which fluid, containing cells

from the developing embryo, is drawn

from the womb of a pregnant woman.

The chromosomes and specific genes

are then analyzed for abnormalities.

Rapp has traced the development of am-

niocentesis from an experimental proce-

dure to one routinely used in pregnancy

in North America. For example, today

pregnant women over the age of 35 rou-

tinely undergo this test because certain

genetic conditions are associated with

older maternal age. Trisomy 21 or Down

syndrome, in which individuals have an

extra 21st chromosome, can be easily

identified through amniocentesis.

Through ethnographic study, Rapp

has shown that a biological fact (such

as an extra 21st chromosome) is open

to diverse interpretations and reproduc-

tive choices by “potential parents.” She

also illustrates how genetic testing may

lead to the labeling of certain people as

“undesirable,” pitting women’s repro-

ductive rights against the rights of the

disabled—born or unborn. Generally,

during the first two trimesters, women

in the United States have a constitution-

ally protected right to decide whether to

terminate or continue a pregnancy for

any reason at all, including the diagno-

sis of a genetic anomaly. Following this

window, federal law protects the rights

of disabled individuals with these same

anomalies.

Individual women must negotiate a

terrain in which few rules exist to guide

them. New reproductive technology,

which reveals genetic anomalies, has

created an utterly novel social situation.

Rapp’s anthropological investigation

of the social impact of amniocentesis

illustrates the complex interplay be-

tween biological knowledge and cultural

practices.

BIOCULTURAL QUESTION

What do you think about prenatal ge-

netic testing for diseases? Would you

like to know if you carry the recessive

allele for a harmful condition?

aRapp, R. (1999). Testing women,

testing the fetus: The social impact of

amniocentesis in America. New York:

Routledge.

Medical anthropologist Rayna Rapp

has conducted fieldwork in genetics

laboratories and genetic counseling centers

as part of her ethnographic study of the

social impact of genetic testing.

Courtesy of Rayna Rapp