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.
Now, bones are notoriously confusing, especially when we’re trying to figure out the age of the individual who died. We learn a lot from studying them, but only to a point. Just how do forensic anthropologists determine the age of death of a particular skeleton’s former owner?
For skeletons of infants, children, adolescents, and young adults, fossil analysis yields accurate age of death estimates. Human growth is fairly reliable for a while, and it’s easy enough to tell a kid apart from a really short adult, but things get tough once people stop growing and become adults. In fact, anthropologists have typically had trouble accurately determining the precise age of death for older adult remains. They’ll even tell you this. They can’t rely on the same methods and must turn to others.
One method is to measure bone mineral density, especially of the femur. It’s a general rule that bone density decreases with age. It’s a pretty accurate method for determining the age of death in modern people, but I’m skeptical of its utility when dealing with the bones of our ancestors. Even its proponents admit that while general age and sex-related trends can be observed for bone loss, there have been cases of “young adult” bone density patterns in skeletons of aged individuals. That is, bone density degradation is not linear, and it’s not set in stone. Instead, it depends on “numerous genetic, environmental, and cultural factors.” Old guys can have young guy bones, but it’s rare. Most modern old guys have old guy bones.
What kind of environmental factors can influence bone density – can give old guys young bones? Remember, environmental factors include anything that the organism interacts with, and as far as bone health, diet, activity level, and micronutrient intake are some of the big ones.
Vitamin D status is a strong predictor of osteoporosis risk. Folks deficient in vitamin D tend to have lower bone mineral densities and are at a higher risk for breaks and fractures. If you slather on sunscreen, avoid the sun, avoid pastured animal organs and fatty fish, and do not supplement with vitamin D3, like most modern humans, you are most likely deficient and at risk for low bone density. Paleolithic humans, on the other hand, did not sit in offices all day shielded by windows that blocked UVB rays, nor did they wear sunscreen. They didn’t know about vitamin D, either, but they didn’t have to. They either spent most of their lives in sunny, tropical climates with plenty of UVB exposure, or, in the case of Europeans, had lighter skin selected for to ensure sufficient vitamin D synthesis from fewer UVB rays. They also ate plenty of animal foods, and they didn’t shy away from organ meat or fatty cuts. We don’t know exactly what our ancestors’ vitamin D statuses were, but we can surmise that, given their lifestyle, their exposure to the elements, and their diet, they probably had sufficient levels to avoid bone density deficiencies.
Although calcium gets all the press, magnesium is also vitally important for the building and maintenance of strong bones. In fact, serum magnesium levels are a strong predictor of bone mineral density. In “The Paleo Diet,” Dr. Loren Cordain estimates that the magnesium intake of Paleolithic humans ranged between 800 and 1,500 mg per day. Contrast that with the recommended daily intake of 400 mg and consider that very few people even reach that recommended amount – according to Cordain, 65% of the American population. If the average 55 year old American eats an inadequate amount of magnesium and sports a low serum level, while the average 55 year old Paleo (real Paleo, not one of you guys) ate plenty of magnesium and most likely had a high serum level, whose bones are going to be denser? Whose bones might an observer assume to be those of a younger man?
Strength training builds muscles, but it also builds bones. Like muscles, bones are reactive things that respond to stress. When you lift heavy things, heavy enough to “threaten” your body, you are sending the message that the affected lean tissue must adapt. Muscles adapt by adding fibers; bones adapt by ossifying. Today’s sedentary populations are plagued with osteoporosis, partly because of nutritional deficiencies, but also because they are sedentary. Their bones, by and large, aren’t getting the stimulus required to maintain density. They don’t have to hunt, kill, and carry their food, nor do they have to build their domiciles. Heck, it isn’t even necessary to leave the house. Our hunter-gatherer ancestors, on the other hand, worked for their livelihoods. They were active by necessity; they lifted heavy things because their lives depended on it. Whose bones do you think would receive the stimulus necessary for maintaining density – the sedentary sitters or the active hunters?
The idea of strength training strengthening and fortifying bone is well supported in the literature. It’s true that some results have been mixed, but most reviews of the literature argue that the studies showing little effect employ insufficient intensity or improper training methods.
If anthropologists have included fossil bone density as a factor in their determination of age of death, I think the matter of vitamin D, magnesium, and resistance “training” (obviously, they weren’t lifting barbells in the Paleolithic, but they were certainly lifting heavy things, arguably at a greater intensity than many modern lifters) throws the popular notion of hunter gatherer’s lives being short and brutal into question. Were they shorter than ours? Yeah, on average. I’m not tossing everything out entirely. I’m just questioning whether modern bone density data are accurate reference points for analyzing the age of death of Paleolithic remains. It might be more accurate to simply say, “We don’t exactly know,” instead of tossing out the “cavemen died at 30!” knee-jerk response.
What if the dense bones of what appear to have been a robust 30-year old hunter were actually bones of an incredibly capable 60-year old?
Next time, I’ll discuss a paper that takes an in-depth look at hunter-gatherer ages. The results might pleasantly surprise you.