What is the Evidence for Evolution?

Summary

This video explores the evidence supporting the theory of evolution, specifically the claim that all living things on Earth are related and share a common ancestor. Focusing on cetaceans, the video presents evidence from comparative anatomy, embryology, and the fossil record, revealing that whales evolved from four-legged land mammals. The script also touches on DNA evidence, showing the genetic link between whales and hippos, and concludes by emphasizing the interconnectedness of all life forms, supported by various scientific disciplines.

Takeaways

• 🌿 The theory of Biological Evolution posits that all living things on Earth are related and have evolved from a common ancestor.
• 🐳 The focus is on Cetaceans, a group including whales, dolphins, and porpoises, which are believed to have evolved from a four-legged land mammal.
• 🦴 Comparative anatomy provides evidence with whales having mammalian traits like placentas, live birth, milk production, warm-bloodedness, and lungs instead of gills.
• 🐋鲸鱼和海豚的胚胎学研究显示，它们在发育早期具有四肢的芽状结构，这支持了它们是从四足陆地动物演化而来的观点。
• 🦶 Fossil evidence, such as the basilosaurid whales and Maiacetus, shows transitional forms with features of both land mammals and modern whales.
• 🧬 DNA analysis reveals that whales are most closely related to hippos, suggesting a common ancestor around 54 million years ago.
• 🦇 The script also touches on other evolutionary histories, like birds evolving from dinosaur-like ancestors and bats from five-fingered hands.
• 🧬 DNA evidence is a powerful tool that can confirm evolutionary relationships without the need for physical fossils.
• 🌐 The script emphasizes that evidence from multiple, independent fields of study converges to support the idea that all life on Earth is interconnected.
• 🔬 The video is a production of Stated Clearly, which aims to communicate complex scientific concepts in an accessible manner.

Q & A

What are the two bold claims made by the theory of Biological Evolution?

The theory of Biological Evolution claims that all living things on Earth are related and evolved from a common ancestor, and that the evolution of living things is powered by natural processes that can be studied and understood.

Why do biologists believe that cetaceans, such as whales, dolphins, and porpoises, are closely related?

Biologists believe cetaceans are closely related because they share many anatomical and embryological features with land mammals, suggesting a common ancestry.

How do the anatomical features of whales differ from those of fish, indicating a mammalian heritage?

Whales, unlike fish, have placentas, give live birth, feed milk to their young, are warm-blooded, and breathe air with lungs instead of using gills. They also have blowholes that may be modified mammal noses, and possess hair, arm, wrist, hand, and finger bones inside their flippers.

What evidence from comparative anatomy suggests that whales might have evolved from land mammals?

The presence of hair, the structure of the blowhole and nasal passages, and the presence of bones in the flippers that resemble arm, wrist, hand, and finger bones found in other mammals are evidence suggesting whales evolved from land mammals.

What role does embryology play in supporting the idea that whales evolved from four-legged land creatures?

Embryology shows that both dolphin and human embryos initially develop arm and leg buds, with the dolphin's eventually regressing. This shared developmental pattern supports the idea of a common ancestor with four limbs.

How do the fossil records of extinct basilosaurid whales support the evolutionary theory?

Fossils of basilosaurid whales show intermediate features between land mammals and modern whales, such as a midline nostril placement and small but fully developed hind limbs, suggesting an evolutionary transition.

What is the significance of the Maiacetus fossils in understanding whale evolution?

Maiacetus fossils are significant because they show features of both land mammals and early whales, such as sturdy hip bones for walking and aquatic adaptations like webbed hands and feet, indicating a transitional form in whale evolution.

How does DNA evidence contribute to the understanding of whale evolution?

DNA evidence shows that whales share the closest genetic match with hippos, suggesting a common ancestor around 54 million years ago, which supports the idea that whales evolved from land mammals.

What other evolutionary histories have been worked out using evidence from fossils, DNA, and embryology?

Evolutionary histories worked out using various evidences include birds evolving from dinosaur-like ancestors, bats evolving from five-fingered hands, and humans sharing a recent common ancestor with chimpanzees, with a lineage tracing back to fish-like creatures and beyond.

What is the overall message conveyed by the evidence from independent fields of study on evolution?

The overall message is that all living things on Earth are related, as evidenced by thousands of observable facts from independent fields of study, including comparative anatomy, embryology, fossil records, and DNA analysis.

Outlines

00:00

🐳 Evidence for Evolution: Cetaceans

The paragraph introduces the theory of biological evolution, which posits that all living things on Earth are related and have evolved from a common ancestor. It focuses on cetaceans, including whales, dolphins, and porpoises, to explore this claim. The evidence from comparative anatomy reveals that cetaceans share many characteristics with land mammals, such as having placentas, giving live birth, feeding milk to their young, being warm-blooded, and possessing lungs for breathing air. The presence of hair, limb bones, and vestigial hip bones in cetaceans suggests a terrestrial ancestry. The paragraph also hints at the possibility that the blowhole may be a modified mammalian nose. The discussion invites further exploration of embryology and the fossil record to confirm these suspicions.

05:03

🦴 Fossil Evidence of Whale Evolution

This paragraph delves into the fossil record to provide evidence for whale evolution. It discusses extinct basilosaurid whales, which lived 34 to 40 million years ago, and had intermediate features between modern whales and their land mammal ancestors. The basilosaurids had a nasal opening in a midline position and small, developed hind limbs, suggesting a transitional form. The paragraph also introduces Maiacetus, an ancient whale with sturdy hip bones and a mix of aquatic and terrestrial features, indicating it was a 'walking whale.' The fossil evidence supports the idea that whales evolved from land mammals, with DNA evidence further suggesting a close relationship between whales and hippos, sharing a common ancestor around 54 million years ago. The paragraph concludes by emphasizing the consistency of evidence from multiple lines of study, reinforcing the theory of evolution.

10:07

🌿 The Broader Picture of Evolution

The final paragraph summarizes the evidence presented and extends the discussion to other evolutionary histories. It mentions that similar comparative anatomy, embryology, and DNA evidence support the evolution of bird wings from dinosaur-like ancestors and bat wings from five-fingered hands. The paragraph also touches on the evolutionary lineage of humans, chimpanzees, mammals, reptiles, amphibians, fish, and segmented worms. The narrator, Jon Perry, wraps up by emphasizing the convergence of evidence from various scientific fields, all pointing to the interconnectedness of all life on Earth. The paragraph concludes with a call to action for viewers to share the video and a note of appreciation for contributors and advisors who helped create the animation.

Keywords

💡Evolution

Evolution refers to the process by which different kinds of living organisms arise and change over time. In the context of the video, it is the central theme that explains how all living things on Earth are related and have evolved from common ancestors. The script provides evidence from various fields to support this concept, such as the evolution of whales from land mammals.

💡Common Ancestor

A common ancestor is a species from which multiple species have descended. The video script discusses how all living things on Earth are related through a common ancestor, highlighting the interconnectedness of the tree of life. This concept is exemplified by the claim that cetaceans, including whales, evolved from a four-legged land mammal.

💡Comparative Anatomy

Comparative anatomy is the study of the anatomical similarities and differences among various organisms. The video uses comparative anatomy to provide evidence for evolution, such as the presence of mammalian traits like placentas, live birth, and lungs in whales, which are not found in fish.

💡Embryology

Embryology is the study of the development of embryos. The script mentions embryology as evidence for evolution, noting that both dolphins and humans have similar embryonic stages, such as leg buds, which later develop differently in each species, suggesting a shared ancestry.

💡Fossil Record

The fossil record is the preserved evidence of life found in the Earth's crust. The video script uses the fossil record to trace the evolutionary history of whales, showing transitional fossils like basilosaurids that had both aquatic and terrestrial features, supporting the idea of evolution from land to water.

💡DNA

DNA, or deoxyribonucleic acid, is the molecule that carries genetic instructions for the development, functioning, and reproduction of all known living organisms. The video discusses how DNA evidence supports the evolutionary relationship between whales and hippos, indicating a shared common ancestor.

💡Cetaceans

Cetaceans is an order of mammals that includes whales, dolphins, and porpoises. The video focuses on cetaceans to illustrate the concept of evolution, showing how these marine mammals evolved from land-dwelling ancestors, as evidenced by their anatomical and genetic traits.

💡Basilosaurid

Basilosaurids are an extinct group of whales that provide crucial evidence for whale evolution. The script describes basilosaurids as having both aquatic and terrestrial features, such as small hind legs, indicating an intermediate stage in the transition from land to water.

💡Maiacetus

Maiacetus is an extinct genus of early whales that is considered a 'walking whale' due to its combination of terrestrial and aquatic features. The video script uses Maiacetus as an example to show the evolutionary progression from land mammals to fully aquatic whales.

💡Hippopotamus

The hippopotamus is a large, mostly herbivorous, semi-aquatic mammal. The video script mentions that whales and hippos share a close genetic relationship, suggesting they evolved from a common ancestor. This relationship is surprising due to the different diets and habitats of the two species.

💡Ancient Whale-like Mammals

Ancient whale-like mammals are extinct species that are part of the evolutionary lineage leading to modern whales. The video script discusses various fossils of these creatures, which show a gradual transition from land-dwelling to fully aquatic forms, reinforcing the evidence for evolution.

Highlights

The theory of Biological Evolution makes two bold claims: all living things on Earth are related, and their evolution is powered by natural processes.

Evolution’s first claim is that all living things on Earth are related, supported by evidence from various fields of study.

Cetaceans, which include whales, dolphins, and porpoises, evolved from an ancient four-legged land mammal, supported by comparative anatomy.

Whales, unlike fish, have placentas, give live birth, feed milk to their young, are warm-blooded, and breathe air through lungs, indicating mammalian traits.

Whales’ blowholes are highly modified mammal noses, further supporting the link between whales and land mammals.

Whales possess arm, wrist, hand, and finger bones inside their front flippers, similar to the front appendages of bats, hippos, and humans.

Modern whales lack back legs but have tiny, vestigial bones resembling hips and legs, suggesting evolutionary remnants.

Embryology shows that both dolphin and human embryos develop arm and leg buds, supporting the theory that whales evolved from four-legged land creatures.

The fossil record provides evidence of basilosaurid whales, which have intermediate features between land mammals and modern whales.

Maiacetus fossils, found among sea creatures, suggest a species that could walk on land and swim in water, referred to as 'walking whales.'

DNA evidence reveals that whales are closely related to hippos, sharing a common ancestor that lived roughly 54 million years ago.

Unique features shared between hippos and whales, such as multi-chambered stomachs and internal testicles, support their evolutionary connection.

Bird wings evolved from modified arms and claws, and bat wings evolved from five-fingered hands, showing evolutionary links between species.

Human evolution shares a fairly recent common ancestor with chimpanzees, highlighting the connection between different species.

Thousands of facts from independent fields like fossils, DNA, and embryology, all tell the same story: all living things on Earth are related through evolution.

Transcripts

Stated Clearly Presents:

What is the evidence for evolution?

The theory of Biological Evolution makes two very bold claims about living creatures:

First: All living things on earth are related. They evolved from a common ancestor.

Second: The evolution of living things is powered by natural processes. Things which

can be studied and understood.

But is there really any evidence that these two claims are true?

Yes. There are so many observable facts from so many different fields of study that the

only way we can even begin to talk about them is to group them into categories or lines

of evidence.

To keep things simple, here we’ll focus on Evolution’s first claim that: All living

things on Earth are related.

We cannot tackle the entire tree of life at once (after all there’s an estimated 8.7

Million species alive today), so instead we’ll focus most of our attention on one fairly

small but fascinating branch of the evolutionary tree: Cetaceans. This branch includes whales,

dolphins and porpoises.

Biologist claim that all these creatures are closely related, and that the entire group

evolved from an ancient 4 legged land mammal.

Instead of taking their word for it, let’s look at the facts. We’ll start with a few

from field of comparative anatomy: the study of differences and similarities between living

things.

Whales live in water and from a distance, they sort of look like giant fish. A close

inspection of their anatomy however, tells us a very different story.

Whales, just like land mammals but unlike fish:

have placentas and give live birth

They feed milk to their young

They are warm blooded (which is extremely rare for a fish)

and whales do not have gills, instead, just like us, they breath air with 2, fully developed

lungs.

Whales don’t seem to have noses like mammals do. Instead they breathe through blowholes

coming out the tops of their heads. Some whales have two blowholes that almost look like nostrils,

but dolphins and porpoises only have one. Surprisingly, if you look at their skulls,

you find that the blowhole splits into 2 nasal passages inside the head. Could it be that

the blowhole is actually a highly modified mammal nose? It looks that way but we’ll

need more evidence to be sure.

Many whales have hair, just like land mammals. In this photograph, you can actually see the

whiskers of this baby gray whale as he rests his chin on mama's back.

Strangely, whales have arm, wrist, hand, and finger bones inside their front flippers.

Here’s a photo of these bones, the same bones that bats, hippos and people have in

their front appendages: One bone, two bones, wrist bones and finger bones.

Modern whales do not have back legs but they do have a pair of strange tiny bones where

the hips and hind legs should be. Here’s a picture of these bones from a bowhead whale.

They almost look like shriveled hip, thigh, and shin bones. This one even has what looks

like a deformed ball and socket joint between the hip and thigh bone, just like the ball

and socket joint in your own hip. Is this resemblance a mere coincidence or are these

real leg bones? Perhaps leftovers from the whales evolutionary history?

Before we draw any bold conclusions, let’s see if a completely separate line of evidence

will confirm our suspicions.

Embryology is the study of how creatures develop before being born or hatching from an egg.

Here we see a dolphin and a human embryo, side by side, at similar stages of development.

Notice that they both have what look like arm buds, and leg buds. In humans, the leg

buds grow to become legs. In whales, they grow for a while, but then stop, effectively

fading away as the rest of the whale continues to grow.

These are all photographs of a common dolphin at different stages of development. Notice

that early on, we see two nostril grooves on the front of the face, just like you’d

expect in a puppy or a human.

As the dolphin continues to grow, the nostril groves migrate to the top of the head and

fuse together becoming the dolphin’s blowhole.

So far we have multiple facts from two independent lines of evidence, comparative anatomy, and

embryology, both telling us the exact same story: The ancestors of whales were once 4

legged land creatures! Will the fossil record act as a third witness confirming this idea?

These are two species of extinct basilosaurid whales!

These creatures are known from multiple well preserved skeletons. They appear to have lived

side by side roughly 34 to 40 million years ago.

In this photo we are looking down at the top of a basilosaurid skull. This is not a model

or a cast, these are the actual bones which were pulled from the ground. Notice that the

nasal opening is not on the top of the head like those of modern whales, and not at the

end of the snout like those of most land mammals. Instead their nostrils sit right in the middle,

this is an intermediate species, exactly what the theory of evolution tells us we should

find!

At the back-end of a basilosaurid’s body, there are small, yet fully developed hips,

legs, ankle, feet and we suspect they had at least 3 toes though we’ve only found

the bones for one.

These legs are far too small for walking on land, but may have been useful for mating

or scratching away parasites and itchy skin.

Evolutionary theory tells us that the further we go back in time, the harder it will be

to distinguish whales from regular land mammals.

Meet Maiacetus. Scientists have found multiple well preserved skeletons of this species,

one of which appears to be a pregnant mother.

The hip bones of Maiacetus do seem sturdy enough to walk on land, but this animal is

considered to be a whale for many reasons: Their skeletons have all been found among

fossils of sea-creatures

Their short legs combined with long flat fingers and toes, suggest they were strong swimmers

with webbed hands and feet.

Here we see the bottom side of a maiacetus jaw and skull as it looked at the dig site.

Her teeth match those of the basilosaurid whales we saw earlier.

And unique structures of her middle ear bones, the bulbs behind her jaw, match those of basilosaurid

whales and modern whales.

Maiacetus appears to be, a walking whale!

The fossils of many ancient whale-like mammals have been found, and people continue to find

more. Together, these fossils blur the line between 4 legged land mammals and fully aquatic

whales, solidifying the idea that whales indeed, evolved from land creatures.

Now lets look at a 4th line of evidence: DNA?

DNA molecules contain chemical codes which act like recipes for living things.

Without ever looking at bones, embryos, or anatomy, researchers can compare the DNA code

of different living creatures to find out who is most closely related to who.

Whale DNA has been compared to all kinds of other animals: fish, sea lions, you name it,

and so far, the closest genetic match, is to the pudgy, water-loving hippopotamus.

This does not mean that whales evolved from hippos, but if this genetic finding is correct,

whales and hippos both evolved from a common ancestor which lived roughly 54 million years

ago.

At first the link between whales and hippos surprised researchers. Whales are mainly carnivores

- they eat things like fish and small crustaceans, while hippos are mostly vegetarian.

A closer look however, reveals that hippos and whales, actually share many strange features,

some of which may have come from their common ancestor.

Ancient walking whales have specially shaped ankle bones, found only in hippos and the

close relatives of hippos, hippos, just like whales, often give birth and even nurse their

young underwater, they both have multi chambered stomachs (which is common for herbivores but

unheard of in fish-eating mammals), they are both missing a coat of fur, and here’s a

fun fact - whales and hippos are some of the only mammals on earth that have internal testicles.

So there you have it, dozens of facts from 4 independent lines of evidence, all tell

us the exact same story, whales evolved from 4 legged land mammals, but the history of

whales isn’t the only evolutionary history that we’ve been able to work out.

We know from fossils, DNA, embryology and many other lines of evidence that bird wings

are actually modified arms and claws! Birds evolved from dinosaur-like ancestors.

We can also clearly see that bat wings evolved from 5 fingered hands, similar to those of

monkeys and shrews.

We’ve found that humans share a fairly recent common ancestor with chimpanzees, that mammals

evolved from reptile-like creatures, those reptile-like creatures evolved from amphibian-like

creatures, those amphibian-like creatures evolved from fish-like creatures, and fish

if you go back far enough, share a common ancestor with segmented worms.

So to sum things up, thousands of observable facts from completely independent fields of

study, are coming together to tell us the exact same story.

All living things on earth are related.

I’m Jon Perry and that’s a basic overview of the evidence for evolution, Stated Clearly.

Thanks for watching our show, if you enjoyed it, be sure to share it with your friends

on facebook and twitter.

If you want to learn more about whale fossils, and who doesn't, we have links in the description

of this video which take you to articles on our website.

Special thanks to Tyler Proctor, Zaid Ghasib, Anthony Danzl, Leon Z Newman, Rosemary Mosco,

and Jordan Collver. All of these folks volunteered their time and talents to make this animation

happen.

Special thanks to Dr. Philip D. Gingerich and Dr. Hans Thewissen. They both volunteered

hours of their time advising us, and preparing images of fossils and embryos.

I'm proud to announce that for the first time in Stated Clearly's history, this animation

was completely paid for with contributions from our viewers. If you are able to help

support our please visit us at statedclearly.com and click "contribute"

So long for now, stay curious.