Deserts and Limitations

Lessons from Prehistoric Desert Dwellers

Living in the desert is challenging. We spent the week after Christmas in Baja, California, camping on the beach. Fortunately, our tents were comfortable and meals were cooked for us. But Pedro, a Baja native, gave us a glimpse into a very different past.

Pericú women, part of the indigenous tribe of southern Baja in California.© George Shelvocke

The afternoon was cool with sun shining through broken clouds and a rare rain in the offing. As we climbed up the steep, rock-strewn path we were careful to watch our step. Although vegetation is sparse, most of the plants wear spines or thorns for protection. A little stumble could result in a painful jab. Despite their armor, many desert plants are edible. Pedro assured us that the common prickly-pear cactus fruit tastes good, and even the pads are edible—after removing the spines.

We reached a cave that had been the winter home for a band of Pericü people, the extinct indigenous tribe of southern Baja. A small red ochre pictograph decorated the cave. We imagined a dozen people huddled in the chill admonishing their toddlers to stay away from the edge. A pile of shells lay below, showing that the Pericü enjoyed the ocean’s bounty.

On top of the mesa we found their summer home. There was little to mark it except for another heap of shells and four round depressions in the rock. Grinding holes, Pedro commented. He then explained that there is a type of manna—the pitahaya fruit—that ripens in late summer. It grows on the organ pipe cactus (pitahaya dulce) that resembles a clump of spiny fingers pointing skyward. The size of a tennis ball, pitahaya fruit has the color and a bit of the flavor of watermelon. Although rich in energy, the tiny seeds pass through without being digested.

European missionaries recorded that the indigenous peoples were hungry except during the brief pitahaya season—perhaps wishful thinking on the Europeans" part. Lacking any means of preserving fruit, how could people prolong this short season of plenty? Baja natives came up with an unlikely solution.

The indigenous people developed a system to harvest the nutrition in pitahaya seeds that disgusted missionaries. While enjoying the abundance of the harvest, people collected their poop in special places. When it had dried, the seeds were separated, washed, and then pulverized in those circular rock depressions. After grinding they make an edible paste high in fat. Their "recycling" of calorie-rich pitahaya seeds illustrates how desperate they must have been to get enough nutrition.

Baja, California is a desert peninsula: the sun is brilliant, the growing season long and vacant land plentiful. What is lacking is enough fresh water. Not much grows with only five inches of rain a year. Without plentiful seafood this place could not support humans.

Every living system has limits to the number of plants or animals it can sustain. Biologists call it "carrying capacity"—the number of plants, animals or people that an area can support given the quality of the natural environment. Ingenuity can extend the environment’s ability to support people, but not forever. We are subject to biological and other limits.

When a habitat’s carrying capacity is exceeded, it becomes degraded and the population will be forced to decrease. Carrying capacity in the desert is dictated by the supply of water. Many people think that the ultimate limitation here in the arid Southwest will be water, just as it was for the Pericü.

We have exploited the resources of our planet for so long, and found so many ingenious ways to increase its productivity, that we often forget about limits. The desert reminds us of the finiteness of biological systems.

Humans are cleverer than most animals in cultivating nature. There is no evidence that the Pericü had formal agriculture. Nevertheless, some seeds must have escaped from the pitahaya gatherers and landed near their habitations, thus increasing future harvests. Accidental seeding may have been one of the ways that agriculture got started in other parts of the world.

Planting seeds and controlling water are two of the first steps to growing crops. Agriculture freed people from spending so much time producing food, and eventually led to our abundant lives. We must not lose track of our dependence on water, however, nor forget that the earth can support only a finite number of people.

RICHARD GROSSMAN is an obstetrician-gynecologist who has been helping women plan their families for over 30 years. He chose this medical specialty because of concern about human population growth, and can be reached at