Skepticism

Is the “Natural Human Lifespan” Only 37?? The Daily Mail vs Science

This post contains a video, which you can also view here. To support more videos like this, head to patreon.com/rebecca!

Transcript:

In my live science trivia show Quiz-o-Tron I used to always end with a round called “Science According to the Daily Mail” and after several rounds of answering questions about real science it was fun to ask questions like, “According to the Daily Mail, what’s the moon made of” because the answer could literally be anything from “cheese” to “Muslims.” Muslims were pretty much always the answer for the Daily Mail back then.

But over time, the Daily Fail has actually chilled out considerably. I finally had to swap the theme to “Science According to Infowars” because the Daily Mail’s science section was more consistently publishing actual science news, albeit with really dumb, randomly capitalized titles and mixed in with things that weren’t actually science, like “The ultimate billionaire’s retreat: James Bond-style luxury super yacht that could transform into a SUBMARINE allowing occupants to hold meetings ‘in complete secrecy’ is revealed” and jesus why does that headline even have to be that long?

Still though, sometimes they report on real science but get it really wrong, which is why today I’m talking about this article titled “Humans have a natural lifespan of only 38 years – but our life expectancy has more than DOUBLED over the centuries thanks to lifestyle changes and advances in medicine.” My first thought was wow, what a stupid and wrong headline. “Humans have a maximum natural lifespan of only 38 years, according to researchers, who have discovered a way to estimate how long a species lives based on its DNA.” Like, what the fuck is a maximum “natural” lifespan? Have I, at the age of 39, entered into my unnatural life? I wondered what actual science this article was based on. So I did that thing I do and I read the actual paper, and tried to figure out who was wrong: the scientists who did the study, the Daily Mail, me, or all of us.

The real science was done by the Commonwealth Scientific and Industrial Research Organisation, which is Australia’s national science agency in charge of, obviously, scientific research. Dr. Benjamin Mayne is a molecular biologist there, and he led a team that looked at the genes of vertebrates to determine which ones are related to a species’ total lifespan. They compared those to the maximum lifespan for various known species using AnAge, a resource that collects verified accounts of the oldest known specimen for hundreds of species. They then used the patterns they found to create a “predictive lifespan clock” that would allow them to figure out the max age of a species just by looking at their genes. The idea is that no matter what happens in an animal’s life, if it avoids every predator, mortal illness, or accident it still can’t live past a certain time because at some point its DNA will break down, causing all kinds of problems that will eventually lead to death. That’s just life, and it’s to be expected if we consider that the purpose of a species is to reproduce and then stop taking up resources that will help the next generation reproduce. So once you’re past the age at which you can reproduce, we can expect (in an overly simplified world) that you will die. We don’t live in an overly simplified world which is why there are species that live long past their reproduction age, like humans, but we will get back to that. Anyway, that genetic breakdown is what determines your “maximum lifespan”. Being able to study some DNA and figure out the species’ max lifespan would be very helpful for studying little known or extinct species. So the researchers applied their new tool to animals like the wooly mammoth, which they found had a max lifespan of 60 years. Okay, cool.

Then they applied their tool to ancient homo sapiens, and found that it said they had a max lifespan of, sure enough, 38 years. But the paper doesn’t make it clear whether they looked at ancient humans or modern humans, which is strange considering research that shows humans are likely evolving to be genetically more long-lived. I assume they looked at ancient DNA, since it’s pretty obvious humans do not currently have a max lifespan of 38 years, but more on that in a minute. The scientists write, “In the past 200 years, the average life expectancy of humans has more than doubled because of modern medicine and changes in lifestyle. Early humans have been reported to have a maximum life expectancy of 40 years.”

And there you have it — that’s where the Daily Mail got their headline. So I can’t exactly blame them for this. Here’s the problem: the authors back up that last sentence by linking to two articles, both of which are summaries of the literature and neither of which say anything about early humans’ “maximum life expectancy.” They only guess at average human lifespan, and there’s a big difference between those two terms. If you have two subjects and one who dies at 1 year of age and the other at 40, the average lifespan is about 20 but we have no idea what the max life expectancy is because we need way more information. We know it’s at least 40 but it could also be 200. We can’t observe a large population of this species in the Panglossian Best of All Possible Worlds. We can only observe some individuals in this world to see what happens.

One of the paper’s references, “Broken Limits to Life Expectancy” published in Science in 2002, is even explicitly about this: “experts have repeatedly asserted that life expectancy (for humans) is approaching a ceiling: these experts have repeatedly been proven wrong.” Awkward when you cite an article that kind of pokes a hole in one of your points.

How the Australian study handles humans can give us some insight into how they got the idea that humans (ancient or modern) have a maximum lifespan of 38 years. As I mentioned, they used data from AnAge to figure out the oldest known individual of each species, but they discarded humans. Why? They write, “We removed humans (Homo sapiens) from the data set as they were listed with a maximum lifespan of 120 years, which does not reflect the variability and the true global average lifespan (60.9–86.3 years).”

This is the point where my brain exploded, because this implies that the researchers themselves are confusing maximum possible lifespan with average lifespan. Like, I literally started writing this video to be about how The Daily Mail made that mistake but the research was sound, but it appears that nope, it’s the researchers. 

Which brings us back to the idea that ancient humans had a maximum lifespan of about 40 years. I’ll be honest, I was skeptical of that at first thanks to the common misconception that everyone was dying by 40 before the 20th century, when in fact the problem was everyone dying as children. If you lived to adulthood you were likely to live at least until your hair went gray. But then I learned that the human genome really has done a lot of evolving in terms of longevity in the past 100,000 years, so I thought, okay, maybe the researchers are correct and early homo sapiens really were succumbing to their broken DNA by the age of 40. 

But now I’m not so sure, when they conflate average lifespan with max lifespan, base their research on human specific promoters but then delete human data from the max lifespan, and report that the average life expectancy of humans has doubled in the past two centuries without offering context on that regarding people dying as children. 

For the record, the references the paper points to are more educational on that point, discussing issues like human life expectancy once you hit 50. I actually learned a lot while going down this rabbit hole.

My biggest takeaway was this: we don’t know what the maximum human lifespan is, and every time a scientist takes a stab at it, we beat it a few years later. Or, in one hilarious case, we beat it before the paper is even published. In 1928, a scientist named Louis Dublin published a study based on US mortality figures claiming the 64.75 years was as long as a person could hope to live. At that very moment, non-Maori women in New Zealand were regularly living to 65.93 years of age. Oops.

So, to get back to the Daily Mail, no, the “natural human lifespan” is not 38. If there is a natural human lifespan, and if we do invent ways to surpass it, then it will no longer be our “natural human lifespan.” Humans are natural. We do natural things. We are starting to change our own genes, and then that will be natural. If it comes down to it, the only way we will outlive our final genetic death sentence is by uploading our consciousnesses into the cloud, which of course by then will be sponsored by Facebook and it’s really going to suck, so honestly if you die before then you’ll probably be better off.

Rebecca Watson

Rebecca is a writer, speaker, YouTube personality, and unrepentant science nerd. In addition to founding and continuing to run Skepchick, she hosts Quiz-o-Tron, a monthly science-themed quiz show and podcast that pits comedians against nerds. There is an asteroid named in her honor.

Related Articles

2 Comments

  1. It’s bizarre they confused “max” for “avg”. And really, by now if you do a study like that, you’d expect – from many years of anecdotes at least – to expect an answer somewhere around 120 years. It wouldn’t mean that 120 or very nearby is the definitive answer, but it’d be a red flag needing much more evidence if it fell far from there.

    But again, “max” as “avg”. How is it even possible to do that, since all you need to know to know that the avg isn’t the max is to know or have heard of a single person over that average age. It doesn’t even need study or much data; you turn on any show with Betty White or Bob Newhart on it, think for a moment, and you’re on the corrected path. How did they manage to avoid making those obvious connections?

  2. The data on humans that the researchers discarded seems to be pretty close. The oldest documented human was Jeanne Calment, who died at 122 years, 164 days. That’s pretty close to the 120 years that their study estimated was the max natural lifespan.

Leave a Reply

Back to top button
%d bloggers like this: