Evolution branches off in odd directions
It’s the randomness, which leads to exploring every possible niche and inhabiting those for which an adaptation is possible—and inevitable, given enough time. Melissa Healy reports in the LA Times:
ew way to measure how humans age suggests that Latinos withstand life’s wear and tear better than non-Latino Caucasians, and that they may have their Native American ancestors to thank for their longer lives.
The new findings offer some insight into a longstanding demographic mystery: that despite having higher rates of inflammation and such chronic diseases as obesity and diabetes, Latinos in the United States have a longer average lifespan than do non-Latino whites.
Those findings emerge from an intriguing effort to devise a biological clock — a standard measure of age more revealing than birthdays, walking speed, wrinkled skin or twinkly eyes. By doing so, researchers hope to glean why some people die young while others live long, to understand what chronic diseases have to do with aging, and to predict and increase patients’ lifespans. A reliable measure of biological age could also set a standard by which to judge the effectiveness of anti-aging therapies.
At UCLA, bioinformatician Steve Horvath has devised a measure of aging that reflects the activity level of the epigenome, the set of signals that prompts an individual’s genes to change their function across the lifespan in response to new demands.
Horvath’s “epigenetic clock” captures a key feature of aging: that as we grow older, there are complex but predictable changes in the rate at which our genes are switched on and off by a chemical process called DNA methylation. To arrive at a single measure of a person’s biological age and then compute his or her speed of aging, Horvath has proposed to measure epigenetic activity at 353 sites in a person’s genome.
Earlier efforts to devise an epigenetic clock suggested that biological age, and the speed of aging, not only differ among populations and from person to person: the tissues in each of us may age at different rates. That may explain, for instance, why some organs and tissues are more vulnerable than others to such age-related diseases as cancer.
The new study, published this week in the journal Genome Biology, set out to refine and test that clock. To do so, Horvath and his colleagues analyzed blood, saliva and lymphoblastoid samples collected from 5,162 participants in a wide range of studies.
Those participants included not only black, white and Latino Americans but also Han Chinese, members of the Tsimane Amerindian tribe in South America, and two separate groups of Central Africans: rain-forest-dwelling hunter-gatherers and agrarians living in grasslands and open savannas.
The Tsimane, an indigenous people who forage and cultivate crops in the lowlands of Bolivia, offer an especially good test of the epigenetic clock: constantly bombarded with bacterial, viral and parasitic infections, the Tsimane typically experience high rates of inflammation, which has widely been seen as a marker for aging. But they rarely show risk factors for heart disease or develop type 2 diabetes as they age, and obesity, high blood pressure and problematic cholesterol are virtually nonexistent.
The epigenetic clock found that the Tsimane aged even more slowly than Latinos. The biological clock calculated the age of their blood as two years younger than Latinos and four years younger than Caucasians.
But that finding was despite strong evidence that, over the age of 35, a Tsimane’s immune system was close to exhausted and his inflammation levels “make him look like a 90 year-old,” said Horvath.
“This result sheds light on what is frequently called the Hispanic paradox,” said Horvath. “It suggests that what gives Hispanics their advantage is really their Native American ancestry, because they share ancestry with these indigenous Americans.”
Horvath emphasized that Latinos’ slower aging rate cannot be explained by lifestyle factors such as diet, socioeconomic status, education or obesity, because researchers adjusted such factors.
The study may also shed light on a different demographic oddity: that once African Americans have reached the age of 85, . . .