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  • Your body is a temple, but it’s also a museum of natural history.

  • Look closely and youll see parts that aren’t there because you need them

  • but because your animal ancestors did. No longer serving their previous function

  • but not costly enough to have disappeared, these remnants of our deep history only make

  • sense within the framework of evolution by natural selection.

  • With your arm on a flat surface, push your thumb against your pinky and tip your hand slightly up.

  • If you see a raised band in the middle of the wrist, youve got a vestigial muscle in your forearm.

  • That tendon you see connects to the palmaris longus,

  • a muscle that around 10-15% of people are missing on one or both of their arms.

  • It doesn’t make them any weaker though. There’s no difference in grip strength.

  • In fact, it’s one of the first tendons that surgeons will take out so they can use it

  • in reconstructive and cosmetic surgeries. You can find the palmaris longus across mammal species,

  • but it’s most developed among those that use their forelimbs to move around.

  • In primates, that means the muscle is longer in lemurs and monkeys and shorter in chimps,

  • gorillas, and other apes that don’t do a lot of scrambling through trees.

  • It’s not the only leftover muscle that we've got. Look at the three that are attached to our outer ear.

  • We can’t get much movement out of these muscles,

  • especially compared to some of our mammal relatives who use them to locate the sources of sounds.

  • Presumably this would have been quite helpful for early nocturnal mammals.

  • In humans, you can still detect the remnants of this adaptation with electrodes.

  • In one study researchers recorded a spike of activity in the ear muscle cells

  • in response to a sudden sound. Not enough to move the ear,

  • but detectable. And you can probably guess the location of

  • the sound based on the results - it came from a speaker to the left of the study subjects.

  • So this is their left ear subconsciously trying and failing to pivot toward the sound.

  • You can see another futile effort by our vestigial body parts when you get goosebumps.

  • When were cold, tiny muscles attached to our body hairs contract, pulling the hair

  • upright which causes the surrounding skin to form a bump.

  • For our furry mammal relatives, the raised hair increases the amount of space for insulation,

  • helping them stay warm. Birds can do this too. youve probably seen

  • a puffy pigeon on a cold day. Adrenaline is one of the hormones involved

  • in the body’s response to cold temperatures, and it’s also part of the fight or flight response.

  • So it helps some animals appear larger when theyre threatened.

  • And it may be why surprising and emotional

  • turns in music can give some people goosebumps. And then there’s our tail. At the end of

  • our spine are a set of fused vertebrae - some people have 3, some have 5. We call it the tailbone.

  • It now serves as an anchor for some pelvic muscles

  • but it’s also what’s left of our ancestorstails.

  • Every one of us actually had a tail at one point. When the basic body plan is being laid

  • out at around 4 weeks of gestation, humans embryos closely resemble embryos of other vertebrates.

  • And that includes a tail with 10-12 developing vertebrae.

  • In many other animals it continues to develop

  • into a proper tail. But in humans and other apes, the cells in

  • the tail are programmed to die a few weeks after they appear.

  • Vary rarely though, a mutation allows the ancestral blueprint to prevail and a human

  • baby will be born with a true vestigial tail.

  • The most adorable vestigial behavior is the palmar grasp reflex,

  • where infants up until theyre about 6 months old have this incredible

  • grasp on whatever you put in their hand. There’s a similar reflex for their feet. I wanted

  • to show you this great piece of footage from the 1930s where they demonstrated this behavior.

  • These babies are only 1 month old and you can see that their inner monkey can support their entire weight.

Your body is a temple, but it’s also a museum of natural history.

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B2 US Vox vestigial tail muscle mammal body

Proof of evolution that you can find on your body

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    Shirley Huang posted on 2016/06/24
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