April 2007
Written by Holly Pyhtila

Tags: Health, genetics, animal models, evolution

Are genes that once helped people survive starvation, now making them sick?
Have you ever stopped to notice how some creatures have adapted to their surroundings?
A hummingbird’s beak is long and thin to extract nectar from deep in a flower. A camel stores enough energy in its hump (in the form of fat – not water!) to last weeks in the desert.

Even the majestic antlers of an elk are necessary for mating rituals and defence – aren’t these all examples of adaptations to the environment?
Are We Humans Badly Adapted?

Do you ever look at other humans and wonder how we’ve adapted for survival? A recent genetic theory suggests some humans have adaptations that may not be well suited to our current environment. It’s called the “thrifty gene theory” and was suggested in 1962 by American geneticist Dr. James Neel to explain why some people gain weight and develop type II diabetes easily.

Neel believed that indigenous people had genes that helped them survive their feast-to-famine history. Native North Americans lived a hunter-gatherer lifestyle not that long ago, and food was often hard to find. South Pacific islanders endured near starvation while paddling long distances between islands.

Alternating between food scarcity and abundance also affected the Australian Aborigines, native Hawaiians, New Zealand Maoris, Mongolians, and others.

The theory suggests that “thrifty genes” gave these people an evolutionary advantage, until the typical Western lifestyle was adopted. With less physical activity, a high fat diet, and access to a constant supply of calories, their bodies continued to store calories in preparation for a famine that didn’t arrive.

Geneticists studying Neel’s theory have discovered certain genes and mutations (like mt16189, PSARL in chromosome 3q27, Pro12Ala in PPAR_2, and leptin- STAT3) that affect insulin levels and stored glucose. Normally, the body uses the hormone insulin to control the level of glucose (sugar) in the blood, but in diabetes mellitus, this process is altered.

Type I diabetics have less insulin available and must replace it with injections. Type II diabetics don’t usually respond to insulin, so injections don’t work. Type II is most common, affecting 90% of diabetics. Type I often affects children where type II generally affects adults, especially those who are inactive and obese.

Diabetes is serious and costly. It can lead to blindness, heart attacks, nerve damage, amputations, and death. The World Health Organization says six people in the world die every minute from the disease; and it’ll soon become one of the world’s biggest health problems. Epidemics of obesity and type II diabetes are now threatening the lives of hundreds of millions of people. Ten percent of North Americans will develop diabetes, with rates many times higher in aboriginal populations. Indigenous groups in Fiji, Hawaii, and Australia are reporting skyrocketing rates of type II diabetes, where just a generation ago this disease was unheard of.

Thrifty Gene Theory Controversy
Some people don’t agree entirely with the “thrifty gene” theory – saying that poverty, stress due to racism, and poor nutrition (especially during pregnancy) also result in children being born predisposed to diabetes. Most experts agree that genetics alone does not determine the risk factor of obesity; but research does suggest that “thrifty genes” predispose people to hold on to food (sugars), making them more likely to develop type II diabetes. It is also common for indigenous groups to be poorer and have less access to healthy foods than the general population, so it is difficult to separate genetic from environmental factors.

The Good News
The good news is that having “thrifty genes” isn’t a guarantee that you’ll become obese or develop type II diabetes; and the disease is treatable and preventable with changes in diet, exercise, and other lifestyle factors. There is however, a lot of evidence to suggest that genetics plays a role in predisposing some people to diabetes, even those with healthy lifestyles, and researchers are continuing to uncover the genes that affect both whether a person may develop type II diabetes, and how severe that disease may turn out to be.