Evolution And History

292 CHAPTER 12 | Modern Human Diversity: Race and Racism

Biocultural Connection

Beans, Enzymes, and Adaptation to Malaria

Some human adaptations to the deadly

malarial parasite are biological while

others are strictly tied to cultural practices

such as local cuisine. The phenotype

of the sickle-cell allele, for example,

manifests specifically in red blood cells.

Biological and dietary adaptations to ma-

laria converge with the interaction between

one form of the glucose-6-phosphate-

dehydrogenase (G-6-PD) enzyme and fava

bean consumption.

The fava bean is a broad flat bean

(Vivia faba) that is a dietary staple

in malaria-endemic areas along the

Mediterranean coast. G-6-PD is an

enzyme that serves to reduce one

sugar, glucose-6-phosphate, to an-

other sugar—in the process releas-

ing an energy-rich molecule. The

malaria parasite lives in red blood

cells off of energy produced via G-

6-PD. Individuals with a mutation in

the G-6-PD gene, so-called G-6-PD-

deficiency, produce energy by an alter-

nate pathway not involving this enzyme

that the parasite cannot use. Further-

more, G-6-PD-deficient red blood cells

seem to turn over more quickly, thus al-

lowing less time for the parasite to grow

and multiply. While a different form

of G-6-PD deficiency is also found in

some sub- Saharan African populations,

the form found in Mediterranean popu-

lations is at odds with an adaptation

embedded in the cuisine of the region.

Enzymes naturally occurring in fava

beans also contain substances that

interfere with the development of the

malarial parasite. In cultures around

the Mediterranean Sea, where malaria

is common, fava beans are incorporated

into the diet through foods eaten at the

height of the malaria season. However,

if an individual with G-6-PD deficiency

eats fava beans, the result is that the

substances toxic to the parasite become

toxic to humans. With G-6-PD defi-

ciency, fava bean consumption leads to

hemolytic crisis (Latin for “breaking of

red blood cells”) and a series of chemi-

cal reactions that release free radicals

and hydrogen peroxide into the blood

stream. This condition is known as

favism.

The toxic effect of fava bean con-

sumption in G-6-PD individuals has

prompted a rich folklore around this

simple food, including the ancient

Greek belief that fava beans contain

the souls of the dead. The link between

favism and G-6-PD deficiency has led

parents of children with this condition

to limit consumption of this favorite

dietary staple.

Unfortunately, this has sometimes

become a generalized elimination

of many excellent sources of protein

such as peanuts, lentils, chickpeas,

soy beans, and nuts. Another biocul-

tural connection is again at the root

of this unnecessary deprivation. The

Arabic name for fava beans is foul

(pronounced “fool”), while the soy

beans are called foul-al-Soya, and

peanuts are foul-al-Soudani; in other

words, the plants are linked linguisti-

cally even though they are unrelated

biologically.a

An environmental stressor as po-

tent as malaria has led to a number

of human adaptations. In the case of

fava beans and G-6-PD deficiency,

these adaptations can work at cross

purposes. Cultural knowledge of the

biochemistry of these interactions will

allow humans to adapt, regardless of

their genotype.

BIOCULTURAL QUESTION

How does what you have learned from

this chapter about the falsehood of the

biological category of race relate to the

way the varied adaptations to malaria

described here work against one

another?

aBabiker, M. A., et al. (1996). Unneces-

sary deprivation of common food items

in glucose-6-phosphate dehydrogenase

deficiency. Annals of Saudi Arabia

16 (4), 462–463.

Fava beans, a dietary staple in the coun-

tries around the Mediterranean Sea, also

provide some protection against malaria.

However, in individuals with G-6-PD defi-

ciency, the protective aspects of fava beans

turn deadly. This dual role has led to a rich

folklore surrounding fava beans.

© Charles O. Cecil/Alamy

consequence, when they are introduced to Western-style
diets (characterized by abundance, particularly of foods
high in sugar content), the incidence of obesity and dia-
betes skyrockets. This chapter’s Biocultural Connection
describes another example of genetic and cultural adapta-
tions working at cross purposes.

Skin Color: A Case Study in Adaptation

Generally, the notion of race is most commonly equated

with skin color. Skin color is subject to great variation and

is attributed to several key factors: the transparency or

thickness of the skin; a copper-colored pigment called car-

otene; reflected color from the blood vessels (responsible

for the rosy color of lightly pigmented people); and, most

significantly, the amount of melanin (from melas, a Greek

word meaning “black”)—a dark pigment in the skin’s outer

layer. People with dark skin have more melanin-producing

melanin The chemical responsible for dark skin pigmentation

that helps protect against damage from ultraviolet radiation.