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  • Why do we have one of some things, and two of other things? The logistics alone are enough

  • to cripple even a pro like me!

  • Happy Monday DNews lovers, thanks for watching! Y'all really are the best. Every Monday we

  • answer one of YOUR questions from the comments and this week, someone named "Dern Sure" wants

  • to know why we have two of certain organs, like, Kidneys, lungs, testes, but not multiple

  • hearts, livers or brains? Scientists debate the answer to this, but it really comes down

  • to how we were locked into our evolutionary path.

  • 550 million years ago, the acoel was the first bilateral organism. Bilateralism

  • is the tendency of some lifeforms to be symmetrical. Today, many organisms -- especially vertebrates

  • -- have inherited bilateral symmetry. If you drew a line down the middle of most primates,

  • birds, fish, crustaceans, amphibians, and MANY othersyou'd see a mirror image (or

  • close to it). Though we don't know EXACTLY why, there are definitely some hypotheses.

  • Like, scientists speculate a bilateral body can move more easily because the appendages

  • are mirrored, or perhaps it's easier to support a central nervous system with a central spinal

  • cord. It's just one of those things we don't know. But, I mean, we've held onto the concept

  • for more than 500 million years, so there must be a good reason for its evolution.

  • 300 million years ago, some animals moved from the sea to the land, toting their evolutionary

  • advantages with them. Which might explain why most land animals are bilaterally symmetrical.

  • But let's not get specist. Undersea animals might have continued to evolve, eschewing

  • bilateralism. Starfish and many undersea animals developed radial symmetry, and others, like

  • sponges, aren't symmetrical at all! So, it's not entirely universal!

  • I know that's not the answer YET, but we're getting there. Evolutionary anthropologists

  • guess that we have two limbs, two lungs and two kidneys because we needed them for some

  • reason! They're NOT spare parts, but instead, the dual organs gave ancestral organisms an

  • advantage in some way. For example, you can SEE with one eye and sure enough, one eye

  • evolved first, but two eyes are required for depth perception. Organisms who developed

  • bilateral eyes were better able to focus on prey; or to see the predators coming. But

  • what about kidneys? A study in Nephrology, Dialysis, Transplantation looked at how people

  • did after getting a kidney removed, and surprisingly found they did better for around 16 years,

  • but like, 24, years later, had declines in renal function. They're not spares, but we

  • still live if they're damaged. We just won’t be at 100%, and the brain does too as well

  • as a number of our other organs.

  • So, why one heart and two of a lot of other stuff? Well, humans start as an egg, and begin

  • to divide. At some point in our embryonic stage, we're literally a blob with a tube

  • down the middle that becomes the digestive system. Along that center line the vital organs

  • (liver, lungs, heart, pancreas) begin as tiny buds. The liver and brain each form from single

  • buds; the lungs, however, come from two, just like the kidneys, which develop buds on complete

  • opposite sides of the centerline. Interestingly, the heart is right in the middleand according

  • to the book, "Heart Development, Volume 342," amphibian bilateral hearts form as two bilaterally

  • symmetrical buds next to each other which eventually merge into one heart! But, if they're

  • artificially interrupted, they'll form two independent hearts! It would be unethical

  • to do this with humans, of course, time lords on the other hand………

  • Okay, soif we take into account symmetry and evolutionary advantage. It would seem

  • to me, having two brains would be more trouble than it's worth, considering how resource

  • heavy they are, right? We have two of some things because we've been symmetrical for

  • over 500 million years, and though we COULD have two hearts, we simply, don't.

  • I hope we enlightened you, Dern Sure. Like I said, we answer viewer questions all the

  • time and we mightve answered yours in the past. Questions like, Am I crazy if I talk

  • to myself?

Why do we have one of some things, and two of other things? The logistics alone are enough

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なぜいくつかの臓器はペアになるのか? (Why Do Some Organs Come In Pairs?)

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    Jeng-Lan Lee に公開 2021 年 01 月 14 日
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