The idea that brain and brawn are mutually exclusive is fairly well embedded in our culture; the popularity of phrases used to describe weightlifting enthusiasts, like “dumb jock” or “meathead,” make its pervasiveness pretty clear. But is it true? In a word, no. Anyone who’s ever heard Mark Rippetoe assess a novice squatter like a master mechanical engineer, Keith Norris wax poetic about the savage grace of physical culture, or Robb Wolf employ a Battlestar Galactica reference to explain the biochemistry of a glutenous assault on your intestinal tract knows it to be false, but the rest of society tends to lag a bit. Luckily, a few recent studies suggest that resistance training actually promotes neurogenesis – the growth of new neurons in the brain – while another links overtraining to impeded cognitive ability later in life. It may be high time to start disseminating the image of the dumb jogger instead.
A few studies caught my attention this week, not for being all that surprising or groundbreaking or even new, but because they jibed with something I’ve been mulling over: physical activity in old age.
Studies: the first and second. I grouped these together because they largely deal with the same thing. The first, actually a review of a couple dozen separate studies, discusses how basic physical capability seems to predict mortality later in life, while the second focuses entirely on the predictive ability of a person’s walking speed. This is redundant to anyone who’s ever felt a euphoric post-workout rush or the satisfaction of completing a physically taxing task, but judging from the number of people who make endless loops in the parking lot to score that sweet spot by the door and avoid empty staircases in favor of crowded escalators, we are in the minority. Things like grip strength, the time it takes to rise from a chair, the ability to balance on one leg, and walking speed were strong determinants of mortality. The death rate was 1.67 times higher in folks with weak grips, 2 times higher in those who were slowest to rise from the chair, and 2.87 times greater in people who walked at the slowest pace. Most of the studies reviewed were of older subjects, but the physical activity markers were predictive in young people, too. The walking study found that normal gait speed was an indicator of mortality with predictive power similar to BMI, smoking status, blood pressure, and other chronic conditions.
While I think the idea of adult Paleolithic hunter-gatherers regularly dying at age 30 can be laid to rest (sadly, I reckon that particular misconception has an impressive life expectancy), last week’s post on the Gurven-Kaplan paper brings up another question: if the human potential lifespan of 68-78 years, or roughly seven decades, is an evolved, inherent, even genetic trait, what is the evolutionary justification for its selection? Where is the advantage?
The classic Darwinian view is that selection of traits revolves almost entirely around fertility. Once an animal can no longer produce offspring, it has no “reason” to go on living. Since a genes’ survivability ultimately comes down to reproduction, whether an individual can have kids is the primary determinant of viability.
Speculation on ancestral lifespan is fun and potentially illuminating, but I think examining living, albeit imperfect, examples of modern hunter-gatherers offers greater insight. Sure, the environment has changed, wild food sources have shrunk in diversity and availability, and modern civilization has encroached and meddled and disrupted, but the few remaining hunter-gatherer populations exhibiting relatively untouched traditional lifestyles represent the most promising window into what life actually looked like and how long it lasted for our ancestors. Luckily, a couple of researchers – Gurven and Kaplan – had the bright idea to look at ethnographic studies on actual, living HG populations and analyze the available data on actual lifespan and mortality therein. They found some interesting stuff.
It has become an article of faith among, well, basically everyone, that our ancestors lived short, brutal lives. What are they touting as the average lifespan these days – 35 years old or so? I’ve heard anything between 25 and 40 years. The common counter is that infant mortality rates were higher than they are today, thus skewing the average. It’s also often pointed out that a relatively benign accident or illness by today’s standards – a broken arm, a rolled ankle, or a minor infection – could have prematurely ended Grok’s life. And that these cases say nothing about Grok’s potential to live 70+ years. The “short and brutal” meme has wedged itself in the public psyche, and it’s going to take a lot to extract it from its seemingly intractable position.
I’m going to riff a bit on something I’ve been thinking about regarding ancient human bones. This isn’t an official stance or anything; I’m just thinking out loud. Let me know what you think in the comment board.
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