Dr. Jeffrey Laitman joins WIRED to break down every ‘useless’, vestigial organ and structure in our evolved human bodies. From the “wisdom” teeth and our simian tailbones down to muscles made less important by our double-arched feet, Dr. Laitman highlights where it came from—and how it ended up still inside of us.
Category
🤖
TechTranscript
00:00 Everything in the body has some meaning.
00:02 We're gonna take a look, starting at the head
00:04 and going all the way down to the toes
00:06 at some of the most interesting body parts
00:09 that have often been categorized as maybe useless.
00:12 Auricular muscles.
00:15 Some people have muscles where they can
00:18 wiggle their ears a little bit.
00:20 These are rare.
00:21 We have three on the outside.
00:22 So these are remnant auricular muscles
00:25 that originally had great functions,
00:28 particularly with sound, the way your dog or your cat do.
00:32 Even in many of the monkeys, our ancestors' ears
00:37 are able to move a bit with sound,
00:40 but now they've largely lost that function
00:43 and they are usually considered vestigial.
00:46 The term vestigial comes from the Latin meaning footprints.
00:50 So there are structures that were thought
00:52 to be sort of footprints in time,
00:54 giving us little clues to what came before.
00:57 So we, when we hear a sound,
00:59 do not necessarily move our ears in that direction.
01:04 We tend to move our entire head towards the sound.
01:07 What's interesting to show that it's still hooked up,
01:10 studies have shown that when we hear a sound,
01:13 the brain areas that deal with these muscles
01:17 have some activity.
01:19 Flicca semilunaris.
01:21 When you look at the medial side of the eye area,
01:24 you're going to see a vertical line.
01:26 Here is the location.
01:28 Next time you look at a dog or a cat or a reptile,
01:32 you'll notice that they don't have two,
01:34 but they have three eyelids.
01:36 We have an up, we have a down.
01:37 They have one that goes side to side.
01:39 That's the nictitating membrane.
01:41 And this little fold is the remnant.
01:44 We know we don't have it in our closest relative,
01:47 the chimp, and we don't have it in ourselves.
01:49 It's a moistener.
01:50 And apparently we have sufficient moistening
01:53 without needing that.
01:56 Wisdom teeth, technically known as our third molars.
01:59 You can see here they're largely problematic
02:02 in which they bend or twist,
02:04 and you have to go to the oral surgeon
02:07 to have them removed.
02:08 Over the eons of our evolutionary changes,
02:13 our diet became very varied.
02:15 The molars are grinding teeth
02:18 for eating leaves and vegetable type things.
02:21 We became more omnivorous.
02:23 This is a gorilla.
02:24 And you can see how the face is very forward in a gorilla.
02:29 In the course of human evolution,
02:32 our face became very flattened in.
02:36 Our molar teeth became shoved all the way back.
02:40 The molars became squished in.
02:43 We developed a very, very pronounced chin
02:48 found only in Homo sapiens.
02:50 It's a distinguishing feature of our species.
02:54 And we're not exactly clear what made it come about.
02:58 It's a byproduct.
02:59 It's called a spandrel.
03:01 Sometimes things occur in our body
03:05 that had no discrete meaning or function.
03:08 Male nipples.
03:12 Nipples are extremely important structures.
03:14 They're important for breastfeeding.
03:17 But why do I have a nipple?
03:18 The male nipple is not useless.
03:21 It's highly stimulatable.
03:22 It is an erogenous zone.
03:24 And these are not unimportant things.
03:26 By the way, for example, dogs and cats,
03:29 they have multiple nipples.
03:31 There's a developmental ridge where nipples appear.
03:34 That's called the nipple line.
03:37 Nipples can appear all along a series of lines.
03:42 And you may find, for example,
03:44 that somebody has a nipple all the way down in the pelvis
03:47 or frequently in the armpit.
03:50 It's a bit of a throwback.
03:51 We sometimes call it an atavism.
03:54 And that term is usually used for something
03:56 that has missed a few generations
03:58 or something that pops up
04:00 due to an interesting recombination of genes.
04:04 Body hair.
04:07 We have hair, but our hair is not densely packed all over
04:12 like our closest relatives.
04:14 Hair's prime function is for thermoregulation.
04:18 And it played a very vital part
04:20 when our ancestors came from forest-like environments,
04:25 helping to keep heat in.
04:27 When it got too hot, it kept heat away.
04:30 We lost our hair.
04:31 The weather was changing.
04:33 Things were shifting on the plains of Africa.
04:36 And our ancestors started to go to savannas.
04:39 We were starting to be bipedal.
04:41 We were starting to be hunters.
04:43 We were starting to learn to run.
04:46 And the loss of hair helped us
04:49 in our active lifestyles with sweating.
04:53 The glands involved in sweatings are much greater in us.
04:57 And it allows us to maintain our temperatures better.
05:02 Hair in our furry relatives had a purpose
05:05 with little babies being able to hang onto it.
05:08 We think we still maintain
05:09 the little grasp reflex of newborns.
05:11 And that has been related back to it.
05:13 Certain areas in primates, particularly apes,
05:17 became hairless early on, the face.
05:19 We do a lot of signaling with our face.
05:23 So do chimps.
05:24 So do gorillas.
05:25 We do retain some hair on the top of our head,
05:29 in our anogenital area, and in our armpit area.
05:33 The brain has to be kept somewhat cool.
05:36 Hair up there aids in cooling the area and protecting it.
05:41 And that's why they seem to be retained.
05:44 Erector pili muscles produce the effect of goosebumps.
05:49 Here's a hair.
05:50 Here's an erector pili.
05:51 What they do when they're stimulated is they contract.
05:55 They force the hair to stand erect.
05:58 It'll aid in the skin responding to some type of threat.
06:02 You'll get the hair stand up in the back of your neck.
06:05 When this occurs in our ancestors, or your cat,
06:09 the hair will become puffed up.
06:11 What does that puffiness do?
06:13 It increases the appearance of your size,
06:17 so it's a display feature as well.
06:19 Appendix.
06:21 This is called the cecum,
06:24 and this worm-like structure coming off of it
06:27 is known as the appendix.
06:29 It's not useless, it's very useful,
06:34 because it was removable.
06:36 The appendix was thought to be vestigial,
06:38 and worse, bad, because it can swell.
06:42 What we've learned over the last few years
06:45 is that the appendix has healthful bacteria
06:48 and assists the gut when there are
06:51 different problems and diseases.
06:53 Coccyx.
06:55 The coccyx was our primitive tail.
07:00 Here we can look and see the vertebral column.
07:04 The last three to five vertebrae
07:07 that comprise the little funky thing
07:10 that looks like a cuckoo's beak
07:12 that's known as the coccyx.
07:14 This is a vestigial structure.
07:16 A distinguishing difference between great apes
07:19 and monkeys is that none of the apes have tails.
07:23 Our ape ancestors do not locomote
07:27 the same way a monkey does.
07:28 Swinging through a tree, they locomote differently.
07:31 The more these animals started to walk on all fours,
07:35 and then with us, to walk bipedally,
07:38 the tails were not useful any longer.
07:41 And so, it was pushed to the side.
07:44 It became a vestige.
07:45 Every once in a while, pretty rare,
07:48 due to an interesting recombination of genes,
07:51 somebody's born with a tail.
07:53 Pyramidalis muscle.
07:57 If you look in the mirror, you will notice your six pack.
08:00 I don't have a six pack anymore.
08:02 I never had a six pack.
08:03 This forms what's called the rectus sheath.
08:06 We have a muscle called the pyramidalis
08:09 because of its shape.
08:10 At one time, it was thought to give support to the abdomen.
08:13 Various monkeys are shown to have it.
08:16 In us, it's become very small,
08:18 and we're not really certain what it does.
08:20 We might have lost it because of our unique mode
08:23 of bipedal locomotion.
08:25 Every time we've modified our locomotor behavior,
08:29 certain muscles enlarge, certain muscles become less.
08:33 We have a number of muscles in the body
08:37 that have become largely vestigial.
08:40 They've shrunk.
08:41 Their function has shifted.
08:43 Plantaris muscle.
08:46 We have a muscle in the leg
08:49 which has become largely vestigial.
08:51 It's become just a tendon.
08:54 The plantaris comes from the area of the knee,
08:57 comes from the femur,
08:58 and goes all the way down to have a separate tendon.
09:01 They are larger in the apes.
09:03 We have a number of muscles in the body
09:06 that have become largely vestigial.
09:09 They've shrunk.
09:10 Their function has shifted.
09:13 Flat feet.
09:14 The human foot has been modified
09:19 solely for the purposes of ambulation for running.
09:23 In order to do that, we have a double arch system.
09:27 One arch goes from front to back.
09:30 We call this a longitudinal arch.
09:32 And another goes side to side to reduce muscle usage.
09:37 This is one reason why a chimp or a gorilla
09:40 cannot ambulate or run the way we can.
09:44 They don't have double arches.
09:46 Their feet tend to be flatter.
09:49 And every once in a while,
09:51 we'll have somebody who genetically born with flat feet.
09:55 Here's an individual who is showing
09:58 what we call pes planus, or flat feet.
10:01 The arches sink.
10:03 When the arches sink,
10:04 the muscles that go underneath it must fire.
10:08 So anybody with flat feet has to use muscles
10:12 to try to pull those arches up,
10:15 and that's very expensive.
10:18 I'll also tell you how you can damage your arches.
10:22 Nobody ever anticipated something like high-heeled shoes.
10:27 They're dangerous, they're hurtful,
10:29 and they work to destroy
10:31 what nature has taken millions of years to create.
10:36 There have been body parts
10:38 that have diminished greatly in function.
10:41 We have things that we thought may have been useless
10:43 that we've discovered are very useful.
10:46 So our body is the culmination of our history.
10:51 (upbeat music)
10:53 (upbeat music)
10:56 [BLANK_AUDIO]