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  • For a long time the measurement of a healthy baby was having 10 fingers and 10 toes. Wait,

  • why didn't anybody care about the eyes, nose, or anything else?

  • Hey digitals, Lissette here for Dnews. I am the proud owner of 10 fingers and 10 toes,

  • I can prove half of this just right now. Youll just have to trust me on the 10 toes thing. But,

  • have you ever wondered why that is? Why don’t we have 12 fingers and 14 toes? Or 6 fingers

  • and 1 toe? Well, this may not come as a shocker to you DNews fans out there, but no one really

  • knows. It might all come down to math.

  • Mark Changizi, a theoretical neurobiologist, developed a hypothesis called the Limb Law,

  • first published in the Journal of Theoretical Biology in 2001. It’s a mathematical equation

  • that tries to figure out the correct number of limbs an animal needs in order to connect

  • to the world around it based on the length of its limbs relative to it’s body size.

  • Okay, wow. The equation looks like this. Confusing, I know. But he used this equation with 190

  • different animal species from seven different animal Phyla, and the math seems to check

  • out. Mark thinks this same equation could be used to figure out why humans have five

  • fingers on each hand.

  • The calculation treats our palms as the animal and our fingers as limbs. Also it takes into

  • account that the whole reason behind having fingers is that theyre able to fold over

  • our entire palm, in order to grasp things. So, first, fingers have to be at least as

  • long as our palms, also known as length need to connect to the outside world. When you crunch the

  • numbers, you'll get 9.42 digits per hand. But, he argues, since our hand is not a free

  • roaming creature, but is attached to our arm, it doesn't need limbs protruding from all

  • sides. Hands only need half the total number of limbs. That gets us to 4.71 fingers per

  • hand. Just based on math. Pretty amazing.

  • But other explanations are simpler than that. Evolutionary biologists say that we have 10

  • fingers and 10 toes because that’s the best combination for us. If 8 fingers and 8 toes

  • would have given us an evolutionary advantage, humans would have 4 fingers on each hand.

  • Cliff Tabin, a Harvard Medical school geneticist focusing on limb development in vertebrates,

  • pointed out that our motor skills come down to our thumb and index finger, and that another

  • small, 6th finger wouldn’t really change anything. And if we ever did grow a 6th finger,

  • Tabin argues, it would probably grow out of our wrists, like panda’s . It gives

  • them extra support when gripping bamboo, which gives them an evolutionarily advantage. So,

  • basically, we'd have six if people with six fingers got an advantage.

  • Then, there is this more complicated science answer to why we have the number of digits

  • we do. James Sharpe from the Centre for Genomic Regulation in Barcelona discovered

  • it all comes down to three molecules in our body. Bmp, Wnt and Sox9. Theyre responsible

  • for marking out in an embryo where fingers will go and how far apart theyll grow.

  • And for the most part it marks out space for five fingers on each hand and five toes on

  • each foot. But of course sometimes things can go wrong, resulting in the gaps between

  • fingers being bigger and only having room for four fingers. Or, sometimes it screws

  • up and you have room for an extra finger. Oh and fun fact, the basis for this discovery

  • was a theory first proposed by Alan Turing back in 1952 about how animals get their spots and

  • stripes. Love you, Alan.

  • So why 10 fingers and 10 toes? Again, were still not entirely sure. But it all seems

  • to come down to because that’s exactly the number of fingers and toes we need. Sometimes

  • it’s best to just trust evolution and be thankful we don’t have hoofs. Amirite?

  • So that’s hands. But what about feet?

  • When did they evolve and why do they look

  • different from hands? Julia walked a mile in those shoes, here.

  • Toes likely evolved from the same bones that became fins, wings and hoofs in other species.

  • The dominating scientific theories are that fingers and toes are exclusive features of tetrapods.

  • Or vertebrates with limbs.

  • But according to one study toes may evolve even before our fishy ancestors left the ocean.

  • Why do you think we have 10 fingers and toes? Would you rather have more or less?

  • Let us know on the comments and remember to subscribe to DNews for more episodes everyday.

  • Thanks for watching, guys.

For a long time the measurement of a healthy baby was having 10 fingers and 10 toes. Wait,

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B1 中級

なぜ指と足の指が10本もあるのか? (Why Do We Have 10 Fingers and 10 Toes?)

  • 8039 473
    Angela Hsu に公開 2021 年 01 月 14 日
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