Januari 13, 2017
your body is a temple, but it’s also a museumof natural history. look closely and you’ll see parts that aren’tthere 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 bynatural selection. with your arm on a flat surface, push yourthumb against your pinky and tip your hand slightly up.if you see a raised band in the middle of the wrist, you’ve got a vestigial musclein your forearm. that tendon you see connects to the palmarislongus,
a muscle that around 10-15% of people are missingon 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 thatsurgeons 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 thosethat use their forelimbs to move around. in primates, that means the muscle is longerin lemurs and monkeys and shorter in chimps, gorillas, and other apes that don’t do alot of scrambling through trees. it’s not the only leftover muscle that we've got. lookat the three that are attached to our outer ear.we can’t get much movement out of these
muscles, especially compared to some of ourmammal 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 responseto 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 froma 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 vestigialbody parts when you get goosebumps.
when we’re cold, tiny muscles attached toour body hairs contract, pulling the hair upright which causes the surrounding skinto form a bump. for our furry mammal relatives, the raisedhair increases the amount of space for insulation, helping them stay warm.birds can do this too. you’ve 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 they’re 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 - somepeople 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 ourancestors’ tails. every one of us actually had a tail at onepoint. when the basic body plan is being laid out at around 4 weeks of gestation, humansembryos 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 weeksafter they appear.
vary rarely though, a mutation allows theancestral 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 untilthey’re about 6 months old have this incredible grasp on whatever you put in their hand. there’sa similar reflex for their feet. i wanted to show you this great piece of footage fromthe 1930s where they demonstrated this behavior. these babies are only 1 month old and youcan see that their inner monkey can support their entire weight.
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