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The Two Reasons Why Humans Have Such Bad Backs

2023-03-24 · explainer · Hank · 3:59 · watch on YouTube

Topic: Science & nature (also: Personal life, Health) · mode: Explainer

Responding to John's bad back, Hank explains how intervertebral discs herniate and why humans, unlike other great apes, get them: not mainly lifestyle, since ruptured discs appear throughout the fossil record, but spines not yet well suited to bipedalism, as studies linking chimpanzee-like vertebra shape to herniation suggest.

What is said

The parts of the video and what is said in each (★ — how much it matters to the video).

00:00:00 — Hank is sorry about John's back, previews that bad backs may go back to bipedalism, starts on vertebrae

  • ★★ Hank is sorry to hear about John's back, hopes he feels better, and did a lot of research on herniated discs, since that's kind of his thing. — 00:00:00 · John Green
  • ★★★ Hank says the reason humans so often have bad backs may stretch all the way back to the advent of bipedalism. (hedged) — 00:00:00
  • ★★ Hank explains that vertebrates' bone-protected spinal column stays flexible through many vertebrae separated by intervertebral discs: a firm but squishy ring containing a gel. (playful) — 00:00:15 · TikTok

00:00:29 — Intervertebral discs and what wears them out (age, injury, misaligned load, sitting, genetics); herniation; Hank is scared too

  • ★★ Hank says discs can wear out from getting older, from injury, and from load placed on them out of alignment. — 00:00:43
  • ★★ Hank says standing puts weight roughly where it should be, but sitting, especially slouching with the butt forward, adds pressure on the lower-back discs. — 00:00:58
  • ★★ Hank says genetics matter too, such as the kinds of collagen proteins you make and the shape of your spine and vertebrae. — 00:01:08
  • ★★ Hank explains that if the disc breaks down enough, the gel leaks out: that is a herniated disc, and it is painful. — 00:01:15

00:01:27 — Why apes don't herniate discs: lifestyle hypothesis vs human backs not suited to bipedalism; chimpanzee-shaped vertebrae studies; spondylolysis

  • ★ Hank says he and John have very similar genetics and lifestyles, so he is now scared and will watch for the warning signs. (playful) — 00:01:27 · John Green
  • ★★ Hank says chimpanzees, gorillas and orangutans, our three closest relatives, don't get herniated discs, which raises the question of why. — 00:01:35
  • ★★ Hank says the first hypothesis is that apes' bodies evolved for their lifestyle; it looked good at first because people with hunter-gatherer lifestyles reported less back pain. — 00:01:45
  • ★★ Hank says on closer study it was the reporting of back pain, not the pain, that was rare: people were just living through their pain. (hedged) — 00:01:56
  • ★★★ Hank says there is now lots of evidence of ruptured discs in the human fossil record, so they seem to have been a thing the whole time. — 00:02:05
  • ★★ Hank says this does not mean lifestyle doesn't affect whether you get a ruptured disc; it absolutely does. — 00:02:12
  • ★★ Hank says the other hypothesis is that something is not great about human backs: we are seven million years into the shift to bipedalism, a relatively large shift. — 00:02:18
  • ★★ Hank says having all your body weight stacked on the vertebral column is totally different from it hanging off the column, as for a dog or, to some extent, a chimpanzee. — 00:02:26
  • ★★★ Hank says scientists comparing human vertebrae found those with damaged discs much more likely to resemble chimpanzee vertebrae, as if those spines were more ancestral. — 00:02:35
  • ★★ Hank cautions that it was a pretty small study that only looked at Europeans, so you can't take much from it. — 00:02:58
  • ★★★ Hank says a follow-up study using three-dimensional scans led one author to say humans with disc herniations tend to have vertebra shapes statistically indistinguishable from chimpanzees'. — 00:03:03
  • ★★ Hank says some of those researchers found that spines can swing too far toward bipedal optimization, causing spondylolysis, which causes stress fractures in the spine. — 00:03:24
  • ★★★ Hank concludes that maybe humans are not optimized for bipedalism, or bipedalism is just very hard to optimize for in our body type. (hedged) — 00:03:36
  • ★ Hank notes kangaroos seem to have bipedalism figured out, and all birds are bipedal and seem to be doing fantastic. (playful) — 00:03:43
  • ★★ Hank tells John he is sure this didn't help his pain at all, but it is pretty much all he knows how to do in a situation like this. — 00:03:50 · John Green

00:03:53 — This won't help John's pain, but it's all Hank knows how to do; sign-off

Threads in this video

Where the stories that moved here went next

Mentioned

Central: back pain · bipedalism · spinal disc herniation

Also: Organizations: TikTok

Concepts: ancestral shape hypothesis · bird · chimpanzee · Fossil · gorilla · Hunter-gatherer · intervertebral disc · orangutan · spondylolysis

Also centred on back pain: Pain

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