Shadowing Practice: تطور العين - Learn English Speaking with Video

Elige un modo de práctica

Cada modo abre una sala de práctica a pantalla completa.

477 oraciones

Si las oraciones son demasiado cortas o largas, haz clic en Editar para ajustarlas.

Nature's battleground.

Animals fight for their survival.

Out of this conflict, an extraordinary weapon has evolved.

One that forever changed the rules of engagement between predators and prey.

It is one of evolution's greatest achievements.

The eye.

The animal kingdom encompasses millions of species, and more than 95 % of them share a common trait.

The power of sight.

Eyes are everywhere, but look closer.

No two species see the world in quite the same way.

Animals have a tremendous variety of eyes.

We see different appearances of eyes, we see different sizes of eyes, we see different configurations of eyes, and this is because animals have different lifestyles.

Among the sharpest eyes in the animal kingdom are those belonging to birds of prey.

searching high in the sky for tiny prey demands remarkable vision

and birds of prey have evolved eyes

that are second to none this eagle spies its prey from more than a mile away even

while diving at speeds of 200 miles per hour it tracks its target with deadly precision The secret to the eagle's success?

The anatomy of its eye.

In most cases, the larger the animal's eyes, the sharper its vision.

And the eyes of the eagle are huge.

Eagles are a hundred pounds lighter than we are.

But their eye weighs the same as ours.

Size is just for starters.

The back of our eye has 200 ,000 light capturing cells per square millimeter.

The eagles has one million, providing five times the image resolution.

Its lens is flatter and placed farther away from the retina than ours.

The result?

A gaze as sharp as a telescope, magnifying its helpless prey to three times what our own eyes can see.

What force drives the development of such a remarkable innovation?

Evolution.

The sparks of evolution are tiny, random genetic changes.

Every once in a while there's a little mistake made when the DNA is passed on from generation to generation.

And those mistakes are called mutations.

And sometimes the mistakes cause problems, other times they create new opportunities.

Mutations that boost survival and reproduction are favored by natural selection.

Species that can't adapt disappear.

99 % of all species have gone extinct over time.

The survivors are equipped with mutations that have given rise to uniquely powerful traits.

The eagle has evolved one of the most powerful eyes in nature, but it is just one of the many different types of eyes that have evolved over time.

Animal eyes are an excellent example of convergent evolution.

All the eyes on different animals across the planet today did not evolve from the same ancestral eye.

In fact, eyes have evolved numerous times in different lineages.

Remarkably, evolution has used the same basic genes to build the eyes of creatures as profoundly different as flies,

squid, and humans.

Research points to an origin for these building blocks of all vision, 600 million years ago.

The Earth's oceans are calm.

There are no monstrous predators to contend with.

No creatures armed and ready for combat.

Sea life is simple.

Animals come in two sizes.

Small and extra small.

They're soft with little protection.

And they have one speed, slow.

But it is here that one group of creatures took a dramatic step toward vision.

These pioneers are long extinct,

but one of the oldest living lineages of animals still swimming in today's oceans provide a peek into the past.

Jellyfish.

Biologists Alex Goodell and Chad Widmer of the Monterey Bay Aquarium are on the hunt for a test subject.

Go get him!

One that can give them insight into the roots of vision.

Oh yeah, that's a nice looking one right there.

This is Polyorkis, more commonly known as the bell jelly.

The anatomy of this delicate creature is about as simple as animals get.

It has no skeleton, no heart and no brain, just a loose network of nerves.

But it has a crucial innovation that its survival depends on.

A ring of small dark spots line its base.

Light sensitive organs called eye spots.

We can only imagine what these most basic of eyes can see.

Vision for them is very different than for us because we are able to form images quite well and they aren't.

So it's kind of more of a blurry world for them than for us.

Scientists don't know why the distant ancestors of modern jellies evolved light -sensing cells when they did.

But Goodell can show how they have helped jellyfish survive for 600 million years.

She has designed a simple experiment showing how bell jellies use light detection to their advantage.

I'm interested in seeing if different animals

that don't form images can see different colors if they respond to different wavelengths of light.

Goodell subjects the jelly to light waves that it would find in its natural environment.

First, she hits the jellyfish with a dose of green light.

On cue, its body goes limp and drifts to the bottom of the tank.

See, the tentacles are getting longer.

Oh yeah, yeah.

So you can definitely see when they're relaxing.

Tentacles extend, they pulse less frequently.

The green light usually makes them appear to relax.

They usually will drop down to the bottom and their tentacles will extend and their bell pulse rates will decrease.

Why does green light put the jelly so at ease?

It's the wavelength of its home turf, the ocean floor.

They usually spend most of their time on the bottom, where they would naturally be getting a lot of green light.

They find most of their food on the bottom, so they're used to being in this type of light.

Goodell then switches things up.

Purple light fills the tank.

Suddenly, the jelly pulses wildly.

When I click on the purple light, the jelly seems to go into this escape response.

Their tentacles shorten up and their bell pulse rate increases.

It's a reaction akin to us fleeing from a fire.

To the jelly, purple light means one thing.

Injury or even death might be imminent.

The reason is simple.

Short wavelength light like purple or ultraviolet, blue lights, it's actually higher energy and it can be very damaging for organisms that are transparent.

So a lot of transparent animals rise up in the water column in the evening

100

and hang out on top at night and then in the morning as the sun's coming up they migrate back down.

101

Light triggering action.

102

A simple vision system to be sure.

103

But it's helped jellyfish survive over half a billion years as they find food and evade predators.

104

But the eyes evolution would not stop there.

105

More than 500 million years ago, the calm waters are to be overrun with a new breed of creatures.

106

Eyes are about to get a powerful upgrade and unleash an evolutionary arms race that will forever change life on Earth.

107

The dawn of the Cambrian period, 544 million years ago.

108

The animal kingdom is undergoing a time of transition.

109

Early animals were simple passive creatures, drifting through the current or anchored to the sea floor.

110

But over the course of 50 million years, a lot is going to change.

111

Life undergoes an explosive transformation.

112

Thousands of new species burst into being, including the oceanic ancestors of dinosaurs, elephants, and humans.

113

This is evolution's Big Bang, the Cambrian Explosion.

114

Before that time, there was little, if any, animals present on planet Earth.

115

Within about a 20 to 30 million year period, basically all of the major animal groups appear in the fossil record and start diversifying.

116

So it's a time of major evolutionary change.

117

Scientists like Bruce Lieberman are discovering ancient clues about why the explosion happened.

118

This really is one of evolution's big unanswered questions.

119

Darwin talks about the Cambrian explosion in The Origin of Species back in 1859, and he was puzzled by how quickly organisms appeared.

120

We'd like to know what were the triggers that caused this real explosion of life.

121

The creatures that emerged from the Cambrian were larger and more mobile than any of their predecessors.

122

And what's more, they evolved weapons for battle.

123

An important aspect of the Cambrian explosion is that it is an evolutionary arms race.

124

For the first time, creatures evolved the natural weapons they still use on today's battlefields.

125

Jaws, claws, body armor, and most critical of all, eyes appear.

126

They're obvious, they're there, and there's no evidence for complex eyes before this Cambrian explosion.

127

These eyes are the first type to appear in the fossil record.

128

Compound eyes.

129

The invention of a group of arthropods called trilobites.

130

Arthropods are joint -limbed animals that today include things like crustaceans, insects, spiders and so on.

131

The compound eye is a type of eye that's possessed by these arthropods.

132

On closer look, it's clear that these eyes are nothing like our own.

133

So you can see these two round structures on the head,

134

and when you look at them in detail you can see small circular bodies in a series of rows.

135

Each row has several of these circles, and when you look at them you can recognize that these are eyes with many lenses.

136

Trilobite eyes are one of the earliest results of the animal kingdom's most feverish arms race coincidence

137

or was the evolution of more powerful eyes the spark that triggered the Cambrian explosion?

138

My sight is part and parcel with predation and things avoiding predators.

139

So if there were not the development of eyes, you might have had some of the sparks of the Cambrian explosion, but I don't think you would have had the full bang.

140

Just how did the trilobite manufacture an eye of such complexity?

141

They took advantage of the materials at hand.

142

Their eyes are made of rock.

143

This rock is calcite and in fact it's the same rock or mineral that makes up the trilobite eye.

144

Trilobites secreted this mineral from their skin to form both their rigid shells and equally rigid eyes.

145

That's what their skeleton was made of.

146

They had to evolve an eye out of this substance.

147

So it means we've got a beautiful record of what their eyes looked like.

148

Without calcite, trilobites would be not only naked, but blind.

149

These crystal eyes represented a major advance from the simpler light -sensing cells that came before,

150

and likely gave trilobites a supreme survival advantage.

151

The eyes present before the Cambrian explosion would have been nowhere near as complex as the type of eye

152

that you'd see in the trilobite.

153

The compound eye would have allowed them to better track down prey or find dead carcasses of things to eat.

154

True visionaries,

155

trilobites diversify and endure for nearly 300 million years before a mass extinction event wipes out the last of their species.

156

But other arthropods survive, and one group takes the compound eye to new heights.

157

insects.

158

Insects.

159

If we look at the most abundant animal life form on land, it's the insects.

160

There are literally more than a million species of insects that are present.

161

They all have a complex compound eye.

162

The first insects evolved around 400 million years ago.

163

While they share a common ancestor with trilobites, they are not their direct descendants.

164

Studies show they evolved their comp - compound eyes independently, but from the same genetic blueprint.

165

An array of microscopic lenses that work together to form an image.

166

The greater the number, the finer the detail.

167

Fruit flies have hundreds of lenses per eye.

168

Bees boast an astonishing 7 ,000 lenses.

169

But evolution drove one insect to develop the compound eye of staggering complexity, the dragonfly.

170

Each eye has a mind -boggling 29 ,000 lenses, making for the ultimate motion detector.

171

In pursuit of fast -moving prey, dragonflies give chase at a staggering 38 miles per hour.

172

Their eyes focusing power is poor, but their processing speed is spectacular,

173

resolving images five times faster than our own.

174

The result?

175

Lightning reflexes.

176

Ideal for timing strikes and avoiding high -speed collisions.

177

The success of insects has made the compound eye the most prevalent in all of nature.

178

But it would not be the only vision system to emerge from the Cambrian explosion.

179

Another group of animals evolved.

180

One that would launch the prototype for an advanced eye of their own.

181

The vertebrates.

182

The eyes of insects and the eyes of vertebrates represent different instances of the origin of eyes.

183

They've evolved from different ancestors to achieve the same end.

184

The vertebrate eye gets its start as a simple light detector.

185

Over time, it will evolve and become the targeting system for history's largest predators.

186

When we look at Earth's creatures, we find that many of them look back with an eye akin to our own.

187

In fact, one type of eye powers the vision of all vertebrates, animals with a backbone.

188

A single lensed camera made of soft tissue, known as the vertebrate eye.

189

The vertebrate line includes reptiles, mammals, and birds.

190

And they all have a common ancestor.

191

A primitive worm -like animal that lived during the time of the Cambrian explosion.

192

How this creature's crude eyes developed into the intricate organs we see with today has fascinated scientists since Darwin.

193

The vertebrate eye is really an icon of evolution.

194

Early detractors of Darwin used it as an example of a feature that is so unbelievably complicated,

195

and it's so obviously a machine, and there's so obviously the mark of an intelligent designer there.

196

Darwin's famous response was to go through a series of intermediate evolutionary steps

197

and show how you could start with a cluster of photosensitive cells on the surface of the skin.

198

From there you could create a pit eye, which essentially putting those photosensitive cells at the bottom of a pit creates the first directional sensitivity.

199

And from there you could evolve other sorts of focusing

200

or accommodating parts of the eye and essentially show

201

that it was plausible that you could have a whole series of steps that lead up to a complex camera eye.

202

This new eye would sweep through the ocean, providing an advanced weapon in the escalating battle between predators and their prey.

203

The genes for building the eye were passed down to all the branches of the vertebrate tree, from the first fish, to sharks,

204

and on to shallow water swimmers who would boldly set their sights on an unexploited world.

205

Land.

206

A new arena that one group of predators would come to dominate.

207

These creatures, carnivorous dinosaurs, first evolved 230 million years ago.

208

For the next 160 million years, they would rule the animal kingdom, littering the fossil record with the bones of their vanquished prey.

209

What was it that made carnivorous dinosaurs such successful predators?

210

Was it their size?

211

Their speed?

212

Their array of vicious weapons?

213

Such traits are the stuff of any mega predator.

214

But they're useless without another key skill.

215

The ability to target prey.

216

Carnivorous dinosaurs surely possess some of the largest eyes in history.

217

But how might their vision have helped them become such extraordinary predators?

218

Paleontologist Kent Stevens made it his mission to find out.

219

Very interesting to know what it was like to be a dinosaur.

220

What kind of vision did it have?

221

How did it use its eyes?

222

Stevens faced a major obstacle.

223

Unlike their bones, the eyes of dinosaurs have not stood the test of time.

224

It's essential to fill in the missing pieces because the soft tissue, the eyeball, of course, never is preserved.

225

What you mostly have is just the bone.

226

Stevens used the bones to make scale models of dinosaur heads.

227

These models would serve as a window into dinosaur vision.

228

What I came up with is a way to estimate how

229

well the dinosaur could look out into the world by my looking at the animal.

230

Stevens devised a novel way to make his dinosaurs see.

231

Lasers.

232

The beam lit up the eye, allowing Stevens to plot its line of sight.

233

When the illuminated eye became obscured by the creature's brow or snout, Stevens had reached the limit of what that eye could see.

234

I've decided I will trace those lines of sight on an intervening glass between me and the animal, where if I couldn't see it, it couldn't see me.

235

By mapping the lines of sight of both eyes, Stevens could calculate their degree of overlap.

236

When I have these dots now, if I connect them, this actually represents the region which both eyes could see.

237

The area where Stevens' markings overlap is known as the binocular field of vision.

238

What advantage does binocular vision provide?

239

Binocular vision, seeing something with two eyes, is very good for making fine depth judgments.

240

If you have two eyes and you can simultaneously focus on an object in space in front of you,

241

your brain can do a little bit of trig and decide exactly how far away that object is.

242

How would this aid a predator?

243

Imagine a large dinosaur whose two eyes face to the side, resulting in two fields of view that don't overlap.

244

This makes it difficult for the creature to see an object as distinct from its background

245

and to gauge the distance to it.

246

But if its eyes face more forward, their fields overlap, providing a degree of binocular vision.

247

Suddenly it's a 3D world.

248

Engaging distance to a target is no longer a problem.

249

Stevens knew if he could work out the binocular vision of carnivorous dinosaurs he could determine how they hunted their prey.

250

He trained his sights on the most iconic member of their group Tyrannosaurus Rex.

251

With 13 -inch canines, this six -ton beast was certainly armed to the teeth.

252

But did T -Rex have the targeting system to back up its bite?

253

T -Rex had 55 degrees, which is very substantial binocular overlap, as much as hawks.

254

Stevens concluded that this vision system allowed T -Rex to target its prey at a distance and pursue it on the run.

255

That certainly would have selective advantage toward being a better predator.

256

You can just stay locked onto your target

257

and the amount of overlap could allow you to see how the world is moving as you're moving forward.

258

3D vision was a vital part of T -Rex's arsenal.

259

And looking at skulls from different points in the animal's history, Stevens found it evolved even better 3D vision over time.

260

Its snout narrowed and its cheeks hollowed out to allow for increasingly forward -facing eyes.

261

These animals reshaped their heads evolutionarily for a purpose.

262

You see the steady progression toward more and more binocular vision.

263

So it must have been of advantage to the animal.

264

With forward -facing, four -inch diameter eyes, T -Rex's vision likely ranked among the most detailed in the animal kingdom.

265

But as Stevens discovered, not all carnivorous dinosaurs could hope to follow T -Rex's lead.

266

This is Allosaurus.

267

He was the top predator in the late Jurassic.

268

This animal has very lateral facing eyes.

269

And not only that, but there's a whole structure here along the top of the snout of this animal,

270

which completely obliterates the view from the left eye to the animal's right and vice versa.

271

This animal has essentially blinders on it that keep it from being able to have a very wide field of view.

272

Allosaurus turns out to have about 20 degrees of binocular overlap.

273

How could a dinosaur saddled with blinders be a top dog of the Jurassic.

274

It turns out less binocular vision led Allosaurus to assume a craftier mode of predation.

275

Modern predators that have so little overlap between the two eyes, you tend to find that they are ambush predators, like a modern crocodile.

276

One of the important aspects of an ambush predator is to be able to have surveillance

277

and awareness of what's going on around it.

278

So the idea of lateral facing eyes is completely consistent with an ambush predator.

279

They basically wait until the meal comes to them.

280

They have a task of judging whether the time is right to lunge and try to take out the prey.

281

Dinosaurs show how the same winning strategy evolves again and again in predator vision.

282

The opposite strategy holds true for prey animals.

283

Their vision has evolved to help them escape their killers.

284

As predators evolved eyes closer and closer together for targeting, the eyes of their prey moved further and further apart.

285

Today, rabbits take this strategy to the extreme.

286

360 degree vision.

287

Rabbit eyes evolved to sit high and to the sides of its skull.

288

While its vision is not three -dimensional, it allows the rabbit to see any threat at any angle.

289

Rabbits, like humans, are mammals.

290

And back when dinosaurs still ruled the Earth, our mammal ancestors had to do much more than keep an eye out.

291

To survive, they had to find a new niche in vision.

292

One that would allow them to co -exist with creatures threatening their existence.

293

One hundred million years ago, dinosaurs rule the Earth.

294

The odds are stacked against any animal competing with these mega predators,

295

especially for the evolutionary newcomers, the world's first mammals.

296

Pint -sized animals not much larger than mice.

297

When the dinosaurs were running around, there were also mammals.

298

But the only mammals that were around were very small, they'd fit in the palm of your hand, and they were just trying to keep out of the way of the dinosaurs.

299

For mammals, the era's underdogs, it was either scurry or be squashed.

300

These tiny creatures adapted to an unexploited niche,

301

the nighttime, and evolved a vision system that could thrive in the dark.

302

Night vision, a triumph of eye evolution and a trait essential for survival in many mammal species today.

303

Many varieties of modern mammals also see well in the dark and many of them are also nocturnal.

304

And in some cases at least, this is probably left over from their evolutionary heritage as small mammals hiding in the shadows of dinosaurs,

305

emerging at night and feeding.

306

What changes did evolution make to the eyes of nocturnal animals?

307

That's a question Chris Kirk is trying to answer.

308

I tell my friends it's one of those things

309

that you would have expected that somebody back in the 18th century went around collecting eyeballs.

310

But to my surprise, when I started looking for data on just the gross anatomy of the eye, there was very little that had been published.

311

And so I spent, you know, about a year and a half collecting eyes.

312

Kirk uses his extensive collection of eyeballs to study the mechanics of night vision.

313

By putting his subjects eyeball to eyeball, he's able to compare them and see how their anatomy has evolved to deal with the dark.

314

What's the difference between the eye of a day active monkey called a marmoset and a night active fat tailed dwarf lemur?

315

It's the size of their corneas.

316

The cornea is the window to your eye.

317

It sets the ultimate limit on how much light your eye.. can gather.

318

The cornea is a clear curved shell that provides focusing power and ushers light into the pupil.

319

The light hits the retina, where it is converted into electrical impulses that are funneled through the optic nerve to the brain.

320

A complex process in the blink of an eye.

321

The diurnal monkey has got a very small cornea

322

because it doesn't need to let in as much light

323

which you can see here as the nocturnal lemur

324

which has a very large cornea that takes up nearly the entire anterior surface of the eyeball.

325

For night hunters a bigger cornea is key to catching fast -moving critters in the dark

326

and one night hunter has pushed this anatomy me to the max.

327

Tarsiers are something completely unique.

328

There's nothing else like this in the world of vertebrate eyes.

329

The diameter of the tarsier cornea is almost equal to the diameter of the eyeball.

330

There are 5 ,400 species of mammals.

331

Relative to size, none have eyes as large as the tarsier.

332

At six inches tall, it's one of the world's smallest predators but its surveillance system outsizes the competitions.

333

So, tarsiers need both highly sensitive vision and acute vision.

334

One of the only ways you can get this is to build a bigger and bigger eye, and that's exactly what tarsiers have done.

335

How big?

336

Try bigger than its own brain.

337

So this is the eye of a Philippine tarsier, and you can see that its cornea is actually a little bit larger than my own cornea's.

338

But what's really amazing about this is the fact that a tarsier's head is only this big.

339

The tarsier's eyes are so large, they need extra support to keep from tumbling out.

340

The eyeball extends past the margins of the orbit, and they have to have strong connective tissue in their eyelid to hold the eyeball in place.

341

With immobile eyes, the creature compensates.

342

with a neck that rotates more than 180 degrees.

343

Tarsier's visual adaptations show the extremes to which evolution will go.

344

Many mammals, such as big cats, evolved another way to boost their nocturnal vision.

345

A staple in fables and fairy tales, glowing eyes have haunted children for centuries.

346

A nightmare to some is evolution's gift to others.

347

And they can see us just fine.

348

They can see us a lot better than we can see them, for sure.

349

If one of them was over there stalking us, we wouldn't even know that they were there.

350

Even, you know, without this kind of light, they know when we're coming and they know who's coming.

351

Eyeshine functions as more than a mere scare tactic.

352

It's an adaptation that has made cats spectacularly successful night hunters.

353

These guys, they're very active at night, and in fact, you can hear them making their noise.

354

particularly the lion when he starts to roar even at this hour hiking.

355

Also the eye shine, not only can they see their prey better, but also I think it makes it more intimidating to any other predators that are out there.

356

The source of the eye shine is buried deep in the anatomy of the cat's eye.

357

Hold on to your hat.

358

Kirk's careful dissection reveals its inner workings.

359

First, the retina.

360

Then, the light -sensitive tissue lining the back of the eye.

361

This area is known as the tapetum lucidum.

362

Tapetum lucidum is Latin for bright carpet.

363

So it's the bright carpet in the back of your eye behind your retina.

364

So how does the tapetum work?

365

In your eye, or my eye, there's a black pigment behind the retina that absorbs the light so that it's not scattered.

366

But in species of tapeta, any light that's not absorbed by the retina bounces off the tapetum, the mirror behind the retina, and it essentially has a second chance to be absorbed.

367

So you've got twice the chance to absorb every incoming photon of light that your eye captures.

368

On the rebound, some of the light shoots back out of the eye, resulting in a glowing effect.

369

For cats, this mechanism yields extraordinary benefits.

370

They require only one -sixth of the light that humans need to be active in the dark.

371

I think of the tipitum as just this marvelous adaptation.

372

You know, it's such an elegant solution to a pretty straightforward biological problem, and putting a mirror behind your retina to increase sensitivity,

373

what could be simpler?

374

Cats were far from the only mammal group to evolve such an ingenious solution to night vision.

375

Other species would reach the same result entirely on their own.

376

But I think really the most interesting thing about the evolution.. of the tapetum lucidum is

377

that it's such a good solution to this problem of enhancing sensitivity

378

that many many different groups of mammals have arrived at this same solution independently.

379

What about us?

380

Even though we are mammals, we struggle to see clearly at night.

381

That's because 30 million years ago, our ancestors shifted from the night to the day.

382

When these monkey -like creatures moved to a new niche, they would evolve eyes that could see the world like never before.

383

The human eye, able to decipher 2 .3 million colors with speed and precision that makes a computer look slow.

384

Our color vision is superior to that of many other mammals, who must get by with far less.

385

To a dog, the world is virtually devoid of color.

386

Only a small number of species, including our primate relatives, can see a full range of yellows,

387

blues, greens, and most significantly, reds.

388

But such adept color vision does not exist in the earliest primates.

389

Its evolution has its roots in the aftermath of a mass extinction.

390

About 66 million years ago, a gigantic asteroid caused the extinction of all non -avian dinosaurs and paved the way for the rise of mammals.

391

After the dinosaurs disappear, mammals radiate.

392

All of a sudden they start diversifying and one group of mammals is the primates and they go straight for the trees.

393

Once primates settle into the forest canopy, they evolve into new species.

394

One of those lineages becomes day active.

395

The ancestors of today's monkeys, apes and humans.

396

They evolve a new adaptation in their eyes not seen in earlier species.

397

An expansion of their color vision.

398

A standard range of colors consisting of blues and greens now include red.

399

Why would primates need to see red in their new world?

400

For clues, biologists look to primates today.

401

Howling monkeys are this wonderful, unique animal that may give us some insights into our own evolutionary past.

402

Biologist Nate Dominey has spent his career researching primates as a means of understanding our own evolution.

403

They are almost like a time machine for looking at what the ancestral monkey in Africa and Asia might have been like.

404

You might get clues to what its diet was like, its social behavior, its anatomy.

405

And that ancestral animal was the one that gave rise to all subsequent monkeys and apes and ultimately humans.

406

Domini wanted to know why natural selection favored improved color vision in our ancestors.

407

What did they gain by evolving to see the color red?

408

Domini went on a year -long journey to study primates in their natural habitats.

409

Part of my PhD research was to go to Africa to study monkeys with different diets

410

and to study chimpanzees and to see if there was some sort of common

411

or unifying food item that they might have all turned to

412

that might explain why these monkeys all routinely share a very similar type of color vision.

413

Domini scanned the rainforest canopy for test subjects, hoping to capture leaf samples from where the monkeys had stopped to eat.

414

But he had a problem.

415

What a monkey eats was high above his reach.

416

It's challenging in the rainforest in particular.

417

When an animal is at the top of that tree eating something and you want the sample, there's not many ways to get it.

418

Left with no other choice, he had to take up arms.

419

We use this very stout handmade slingshot from Panama that fires small pebbles up into the canopy and leaves will come down.

420

And it's a great way for sampling the types of foods that primates might eat.

421

After collecting and packing up the key samples, Domini's real work began.

422

Using an instrument called a spectrometer, he recorded the color of each leaf he had gathered in the field.

423

You see that peak in this green spectrum?

424

So that's telling you that this is a green leaf.

425

Now you see how compared to that last one, this is peaking much more here in this orange region into the red region.

426

discovery.

427

Not only were the monkeys eating red leaves, red leaves compose the majority of their diet.

428

It turns out the red of the leaf, the younger and more nutritious it is.

429

Old, mature leaves, the green leaves, they are tough, they're full of toxins, they're generally leaves you want to avoid.

430

So primates in general tend to go for the youngest leaves possible.

431

And if those young leaves also have a color cue that distinguishes them from mature leaves, then it may be advantageous to evolve a mechanism for detecting those young leaves.

432

To primates, red wasn't simply another color.

433

It was a beacon, a homing device, allowing them to target their key food source from a distance.

434

If it sees red leaves in the canopy, then it knows automatically that those particular leaves are young.

435

And so it can save energy, it can save time, it can travel directly to those young red leaves rather than randomly searching throughout its environment.

436

Increased color vision, a strategic evolutionary leap that scientists discovered was one of many.

437

Primates would soon reap the rewards of another crucial adaptation, binocular vision.

438

It's a trait that predators have repeatedly evolved, but for primates it served a new function.

439

Primates have eyes at the front of their head, but they're not predators, so why would they do that?

440

Great thing about having two eyes pointing the same direction is you get depth perception.

441

If you're going to jump from one tree and try to land on another tree, depth perception is a really good trick to have.

442

Over time, primates evolved a binocular field of vision of 60 degrees, on par with birds of prey.

443

It's an evolutionary step that allows primates to capitalize on their hand -eye coordination.

444

But this increased binocular vision comes at a price.

445

Unlike the rabbit, primates now had a limited field of view.

446

Most animals have eyes that are laterally placed on their heads, which is to say the eyes are on the side of the head.

447

And this provides these animals with a panoramic view.

448

And that's really, really useful for detecting predators that may be coming from behind you.

449

So there's a significant cost to putting your eyes in the front of your head.

450

But the advantages are that you have better depth perception, you have better acuity.

451

Once primates abandoned a vision system built for protection, birds of prey were ready to benefit.

452

Swooping in from the sky and plucking primates from the treetops, these aerial terrors were threats to be reckoned with.

453

Based upon the evidence that we have from the fossils, birds of prey have been exerting some type of selective pressure

454

on primates for as long as there have been primates and raptors.

455

Primates were easy targets for these winged predators.

456

Under siege, primates evolved a new kind of behavior.

457

They had to depend on each other.

458

You can imagine then that once these animals evolved eyes on the front of their heads, they needed to live with other animals so that they could improve the probability of detecting a potential predator.

459

Group living was the primates answer to predation.

460

It allowed them to maintain their high degree of binocular field of vision without sacrificing safety.

461

Their keeping watch with the communal eye resulted in an evolutionary side effect.

462

Larger, more powerful brains.

463

So you can see the evolution of group living.

464

And once group living evolves you have a strong selective pressure

465

or you might say the evolution favored larger brains because that's more individuals that you have to remember.

466

Fossils show how the visual system of primates improved over time.

467

Both the eye sockets and the optic nerve canal grew larger as brain size increased.

468

Primates put huge demands on their sight.

469

From color vision to increased binocular vision,

470

they became extremely sensitive to the slightest change of expression on the faces of other primates.

471

This increased need for visual processing fueled the development of intelligence.

472

And you can see how this sort of runaway process for group living,

473

larger brains, avoiding predation, could give you the suite of characteristics that define the primate order to which we belong.

474

A complex and mysterious organ, One that has fueled evolution for more than 500 million years.

475

Driving an eternal arms race between predator and prey.

476

And becoming an indispensable tool for millions of species.

477

The Eye, an engine of evolution and one of its ultimate masterpieces.

Descargar app

Todo lo que necesitas para hablar con fluidez

Pronunciación con IAEvalúa cada oración

Práctica de IPADomina cada sonido

VocabularioConstruye tu banco de palabras

Juego de vocabularioAprende mientras juegas

Escanea el QR

Download on theApp Store Get it onGoogle Play

FOR YOU

Recomendar Video

81 oraciones

Vocabulario y notas de pronunciación para esta lección

Las palabras que más se repiten: eye, vision, animal, primate, predator. Este vídeo tiene 477 frases y 6028 palabras para practicar shadowing. La parte hablada dura 44:48. El hablante mantiene un ritmo constante de unas 135 palabras por minuto, cómodo para el shadowing. Solo el 77 % de las palabras está entre las 3.000 más comunes del inglés, por lo que el vocabulario es exigente.

Vocabulario clave de este vídeo

Las 15 palabras más avanzadas del vídeo, con su pronunciación y significado:

Palabra	Pronunciación	Significado
evolve verbo	/ɪˈvɑlv/	desarrollar
primate sustantivo	/ˈpɹaɪmeɪt/	primate
predator sustantivo	/ˈpɹɛd.ə.tɚ/	predador, depredador
dinosaur sustantivo	/ˈdaɪnəsoɹ/	dinosaurio
prey sustantivo	/pɹeɪ/	presa
mammal sustantivo	/ˈmæməl/	mamífero
monkey sustantivo	/ˈmʌŋki/	mono, chango
trilobite sustantivo	/ˈtɹaɪ.ləˌbaɪt/	trilobite
evolutionary adjetivo	/ˌiː.vəˈluː.ʃən.ɛɹ.i/	evolutivo, evolucionista
ancestor sustantivo	/ˈæn.sɛs.tɚ/	ancestro, antepasado
eyeball sustantivo	/ˈaɪ.bɔl/	globo ocular
vertebrate sustantivo	/ˈvɛɹ.tɪ.bɹeɪt/	vertebrado
retina sustantivo	/ˈɹɛt.ə.nə/	retina
overlap verbo	/ˌəʊvəˈlæp/	solapar, traslapar
insect sustantivo	/ˈɪn.sɛkt/	insecto

Phrasal verbs que vas a escuchar

Palabra	Significado
turn out verbo	resultar
back down verbo	recular, echarse atrás
back up verbo	retroceder, ciar
come up verbo	salir a relucir
come up with verbo	ingeniar, ingeniarse
find out verbo	averiguar, anoticiarse
go around verbo	cundir
go through verbo	atravesar

Gramática en este vídeo

Las estructuras que más usa el hablante, con las palabras exactas del vídeo:

Estructura	En el vídeo
Present perfect have/has + participio pasado — una acción pasada que sigue importando ahora	has evolved · have evolved · have gone
Voz pasiva be + participio pasado — importa lo que ocurre, no quién lo hace	is passed · are called · are favored
Oraciones de relativo who / which + oración — información extra sobre una persona o cosa	One that can · One that would · degrees, which is

Pronunciación a tener en cuenta

El hablante usa 32 contracciones y formas reducidas, como they're, don't, couldn't. Dilas en su forma corta, tal como las oyes.

Los sonidos de “th”: arthropod /ˈɑːθɹəpɒd/, wavelength /ˈweɪvˌlɛŋ(k)θ/
Los sonidos de “sh” y “zh”: evolutionary /ˌiː.vəˈluː.ʃən.ɛɹ.i/, jellyfish /ˈd͡ʒɛliˌfɪʃ/, adaptation /ˌæd.æpˈteɪ.ʃən/, ambush /ˈæm.bʊʃ/, mutation /mjuˈteɪʃən/
Palabras largas — cuida el acento: binocular /(ˌ)baɪˈnɑ.kjə.lɚ/, evolutionary /ˌiː.vəˈluː.ʃən.ɛɹ.i/, anatomy /əˈnætəmi/, carnivorous /kɑːˈnɪv.ə.ɹəs/, adaptation /ˌæd.æpˈteɪ.ʃən/

Sonidos difíciles para hispanohablantes:

s + consonante al inicio — sin añadir una “e” delante: stagger /ˈstæɡɚ/, skeleton /ˈskɛlətən/, spark /ˈspɑɹk/
/v/ — no es /b/: los dientes tocan el labio inferior: evolve /ɪˈvɑlv/, evolutionary /ˌiː.vəˈluː.ʃən.ɛɹ.i/, vertebrate /ˈvɛɹ.tɪ.bɹeɪt/, overlap /ˌəʊvəˈlæp/, carnivorous /kɑːˈnɪv.ə.ɹəs/
/z/ — sonora, no /s/: lens /lɛnz/, organism /ˈɔɹ.ɡəˌnɪz.əm/

Cómo practicar con este vídeo

Escucha el vídeo entero una vez sin hablar y anota las palabras que no conoces.
Haz shadowing frase por frase a velocidad normal, repitiendo cada una hasta que tu ritmo coincida con el del hablante.
Grábate y compara con el original, prestando atención a palabras como evolve, primate, predator.

¿Qué es la Técnica de Shadowing?

Shadowing es una técnica de aprendizaje de idiomas respaldada por la ciencia, desarrollada originalmente para la formación de intérpretes profesionales y popularizada por el políglota Dr. Alexander Arguelles. El método es simple pero poderoso: escuchas audio en inglés nativo y lo repites en voz alta de inmediato, como una sombra que sigue al hablante con solo 1-2 segundos de retraso. A diferencia de la escucha pasiva o los ejercicios de gramática, el shadowing obliga a tu cerebro y músculos de la boca a procesar y reproducir simultáneamente patrones de habla reales. Las investigaciones muestran que mejora significativamente la precisión de la pronunciación, la entonación, el ritmo, el habla conectada, la comprensión auditiva y la fluidez al hablar, convirtiéndola en una de las metodologías más efectivas para la preparación del IELTS Speaking y la comunicación en inglés en el mundo real.

Técnica de shadowing: lee la guía completa paso a paso →

Shadowing Practice: تطور العين - Learn English Speaking with Video

Elige un modo de práctica

Descargar app

Land of the Lions | Making Nature: How we see animals

The Hidden Danger Of Bionic Vision 😨

SEtalk: Why Deep Reading Still Matters

Biggest Breakthroughs in Biology and Neuroscience: 2025

Why do Humans Have Different Skin Colors?

Human Anatomy Eye

Great White Shark (Carcharodon carcharias)

Why Ancient Humans Were The Most TERRIFYING Animal Alive

LITERATURE - Charles Darwin

What Actual Aliens Might Look Like

Technology Made Us Human

Biodiversity | Consider This #4