BYU-Idaho Online Learning
Video Transcript
[The “hhmi Biointeractive” logo appears on screen.]
[Camera cuts to black and fades into an icy scene of the tundra. Loud, dramatic music plays in the background as the camera shows a bird’s-eye view of the icy mountains and plains. It appears to have been filmed from a helicopter.]
Male Narrator: For tens of thousands of years, much of North America lay buried under ice up to a mile thick.
[Camera cuts to a sunrise shot of the tundra. The music slows down and fades out.]
Then the massive ice sheets receded.
[Camera cuts quickly between different shots of icicles and glaciers in different portions of Alaska. The final view shown is of the large river systems of Alaska, with snow near the edges of the rivers. There are large rivers that branch off into smaller streams.]
In what is now Alaska, ocean bound streams and rivers emerged, opening up new possibilities for countless species.
[Two white cranes are shown walking through a deep stream. A bear is shown walking away from the river towards the healthy foliage. Camera cuts to a different stream, where green and yellow trees are growing and brown gravel is seen dividing the stream.]
One of the animals that came calling was the three spine stickleback.
[A close up shot of a silver fish is shown, where only the eyes and mouth are visible. A wider shot of the fish swimming is shown. It is silver, small, and has spines protruding from its back. It’s assumed to be the three spine stickleback fish.]
Common to the Northern Ocean, this little fish spawns in freshwater.
[Multiple three spine stickleback fish are shown swimming together. They appear to be in the same enclosure.]
There were now lots of new spawning grounds to explore.
[Green rolling hills are seen.]
But as the ice-free land began to rise, streams and the fish in them were cut off from the sea.
[The camera pans over and shows a pond that was blocked previously by the large hill. The music changes to a dark and intense mood. A three spine stickleback fish is shown, its head appearing from the tank foliage.]
Isolated populations of sticklebacks faced a survival challenge. Could they adapt to full-time life in a freshwater lake?
Ten thousand years later, they're still there, but they have been transformed.
[Additional footage of the three spine stickleback is seen. Camera zooms out to show Steve Carroll looking at the tank of fish. He turns to talk to the camera.]
Carroll: Stickleback bodies changed in many ways as they adapted to life in post-glacial lakes. They got smaller, their coloring changed, and most strikingly, even their skeletons changed.
[The screen shows a typical three spine stickleback and then transitions to showing the fish’s underlying skeletal structure against a black screen.]
Narrator: As we begin to learn exactly how stickleback bones evolved, we're learning about a lot more than just fish.
[The fish skeletal structure remains centered on screen. The text “The Making of the Fittest” is shown centered in the top third of the screen. Underneath overlaying the skeleton the text “Evolving Switches Evolving Bodies” is shown in a larger font.]
We're learning about how all animal bodies evolved.
[Screen shows an Alaskan sunrise, with snowy mountains in the background of a lake. Ominous music plays in the background. Leaves rustle and branches snap as two men, a young man and an older man, walk towards the camera. They are holding buckets.]
Bell: Well, I hope we caught some fish.
[The ominous music continues. The men are shown near the edge of a lake, standing in green and lush foliage. The older man is shown throwing a fishing basket into the lake. The basket is attached to a string which the man holds.]
Narrator: This is Bearpaw Lake, one of many lakes created in Alaska by the glaciers' retreat eight to ten thousand years ago.
[Screen shows a geological map of the area. Many lakes of a variety of sizes are shown. No rivers or additional bodies of water connect them together. Camera cuts to an underwater shot of the basket. It appears to be made out of metal, with lines intersecting together. There are small holes in the basket. The water is murky, but small fish can be seen inside the basket.]
The sticklebacks one can catch here are especially intriguing to biologists interested in evolution, such as Mike Bell.
[Mike Bell, the older gentleman, is shown pulling a basket out of the lake. He is holding both baskets out of the water on the shoreline. He gently pours out the basket of fish into a white, plastic bucket with water.]
Like all freshwater sticklebacks, their ancestors lived in the sea.
[A shot of the three spined stickleback is shown floating in a tank. The camera cuts to a close up shot of Mike Bell in an interview setting. He is sitting in a lab where there are many light brown tables and cabinets. The words “Michael A Bell” appear on the bottom left corner of the screen. The words “Suny, Stony Brook” appear underneath his name.]
Bell: In the ocean, there are lots of large predatory fish and there's no place to hide.
[Another shot of the silver fish are shown, swimming in the tank.]
Narrator: So, sticklebacks evolved body armor, bony plates on their side, and long sharp spines coming off their pelvis and back.
[The camera shows a stickleback fish in the tank. The fish’s three spines are raised. Two of the spines are aligned on the back of the fish. One spine is on the underside of the fish. The pelvic spine has bright red tissue connected to the spine. The fish's spines are retracted back towards the body. Camera cuts back to the interview with Mike Bell in the lab setting.]
Bell: They're generally easy for predatory fish to catch, but they're not easy to swallow.
[Camera cuts back to the lake. The focus is on the young man near the shoreline. He is throwing a metal fishing basket into the lake.]
Narrator: In Bearpaw Lake, however, spines are a liability.
There are no large- mouth predators here, but there are hungry dragonfly larvae that grab sticklebacks by their spines.
[The camera cuts to a shot of a tan dragonfly larva. Then, the sticklebacks are shown in a natural environment. The dragonfly larva peeks from behind an underwater plant and tries to grab one of the fish. The fish is startled and swims away quickly.]
So, pelvic spines actually reduce fitness and lessen a fish's chances of surviving and reproducing.
[The camera cuts back to the shore, where the young man is pouring another basket of fish into the white bucket. The camera cuts to a shot of the fish inside the white bucket. The water is clear and many fish are seen swimming in a circular pattern at the bottom.]
In this lake, natural selection has been at work.
[Mike Bell is shown on the shore. He reaches down to grab something, then stands up. The camera zooms in on his hand. A silver fish lies in the middle of his palm. In his other hand, he has a pen. He uses the pen to point at the fish’s pelvis.]
Bell: If you look at the pelvis of this fish, there's practically nothing there.
Narrator: In just a few thousand years, these fish underwent a dramatic skeletal change, completely losing their pelvic spines.
[A shot of the fish in the bucket is shown again. In the foreground, there is a red 2D skeletal structure of the original three spined stickleback shown. Then, the skeletal structure is changed. The three spines are taken away and the skeletal structure is smaller. The screen changes to black with the original 3D model of the stickleback skeleton shown in the foreground with red highlighting the pelvic spine and the connecting bone structure. There is a horse skeletal structure in the background.]
As pelvic spines are homologous to the hind limbs of four-legged vertebrates, the change we see in sticklebacks is the equivalent of losing legs.
[The horse’s hind legs are now red in color. The 3D fish skeletal model is shown spinning slowly in a circle.]
How does such a dramatic change in form occur?
[Camera cuts to a scene at an urban park on a college campus. A man wearing a white bike helmet is shown biking towards the camera.]
For Stanford molecular geneticist David Kingsley, the transformation of the stickleback pelvis opened a door on an evolutionary puzzle.
[The man parks his bike at a crowded bike rack. Camera cuts to a close up on David Kingsley in an interview setting. It appears to be in a personal office with a window overlooking the connecting building. The text, “David Kingsley” appears at the bottom right corner of the screen. Additional text, “Stanford University” is seen underneath.]
Kingsley: What happened at the genetic level at these early stages, where the body plan is first being laid out that makes the difference that we now see?
[Camera cuts to a close up shot of a petri dish. Inside the petri dish, there are little cream colored circles. Within each of these circles, there are two dark dots near the upper edge of the sphere. They appear to be eyes on small organisms.]
Narrator: The physical forms of all animals are products of development, that process in which a fertilized egg grows and is shaped into an adult.
[A time lapse of an egg becoming a small fish is shown.]
Changes in form, therefore, arise from changes in development, and since genes control development, changes in form are ultimately due to changes in genes.
[On screen is a depiction of two three spined sticklebacks. On the left side is a stickleback with the three spines. Underneath the fish is a box. Within the box is a series of lines. There are two lines that are red and spiral shaped. Between these two spirals, there are lines connecting them together. In the center of the spiral shape is a bright red rectangle. On the right side of the screen, another three spined stickleback is shown. However, this fish is smaller and has no pelvic spine. Underneath the fish on the right side is another box with a series of lines inside. It copies the shape found in the box on the left hand side. There is one main difference between the shapes. There is a black rectangle in the center of the spiral shape on the right hand side.]
[Camera cuts to a conversation between Mike Bell and David Kingsley. It appears to take place in David Kinglsey’s office. Skeletons and books are seen in the background. The window on the right hand side is now closed by blinds. Mike Bell is sitting on the right side of the table, while David Kingsley is on the left side. Kingsley has a laptop in front of him on the table.]
Carroll: David, these two fish look different, but they have thousands of genes.
[Camera cuts to a close up of Carroll’s face.]
How do you pinpoint which genes make the difference?
[Camera cuts to a close up on Kingsley.]
Kingsley: We started like any geneticist starts. You've got to have two things that are different, you've got to cross them.
[Camera cuts to a woman working in a lab setting. She has a beaker in front of her. Inside the beaker is a bag. The beaker also has clear liquid inside. The person reaches in with a gloved hand and removes the bag and moves to another portion of the lab. Many different scientific tools are seen, including a microscope and several petri dishes.]
Narrator: Geneticists use crosses to map the location of genes that make the difference. Ocean and freshwater varieties of stickleback can be crossed by collecting sperm-filled testes from males and eggs from females and mixing them together.
[Gloved hands add stickleback eggs and sperm into a petri dish using a pipette.]
In a matter of days, the beating hearts of stickleback embryos are visible through a microscope.
[A shot of a stickleback embryo is shown through a microscope. The embryo has large black eyes. The brain is visible through the opaque tissues of the head and body. A large sack is shown attached to the fish’s underside. In the space where the sack is connected to the underside of the fish, a small pink sphere is shown expanding and contracting quickly. The whole fish is translucent with small silver dots speckled across it.]
When mature, this first generation is bred again.
[Screen shows a green, murky water background with two drawn stickleback fish on it. On the right side of the screen is a stickleback fish with spines. On the left side of the screen is a smaller stickleback with no pelvic spine.]
Each cross reshuffles the genetic material and traits that are passed on from one generation to the next.
[A black X appears in between the two fish. A red circle is drawn over the pelvic spine on the fish on the right side of the screen. A black circle is drawn over the space where the pelvic spine would be found on the fish on the left side of the screen. Five additional fish are shown underneath the original two to represent the offspring of the two fish. All of the additional fish have pelvic spines. The text “F1” is shown on the bottom right hand side of the screen.]
Traveling with the genes are stretches of DNA geneticists use as markers.
[Two of the offspring are zoomed in on and made the focus on-screen. A black X is placed between the two fish. An additional eight smaller fish are shown underneath, representing the offspring of this generation. The camera shifts down to the eight offspring. Two of the eight do not have pelvic spines. The text “F2” is shown on the bottom right side of the screen.]
[Camera cuts back to the interview between Bell and Kingsley in Kingsley’s office. Kingsley is seen on the right side of the screen, talking to Bell off-screen.]
Kingsley: And that gives you the chance, then, to try to figure out which of the pieces at the genetic level go together with the traits that you see visually at the whole organism level.
[The camera cuts back to two fish on the murky, green water background. The fish on the right side of the screen has a spine protruding from the pelvis. The fish on the left side does not have a spine protruding from the pelvic.]
Narrator: That's done using the DNA markers to link the trait, in this case, the presence or absence of a pelvic spine, to general locations on specific chromosomes.
[Two boxes appear underneath the fish. In each box, there are lines of differing lengths. Each line has a number located on top of the line. Each box has 21 lines with corresponding numbers. The lines represent genetic markers in the fish’s DNA. On the fish, there are now circles. On the fish on the left side of the screen, there is a red circle over the pelvic spine. On the fish on the right side of the screen, there is a black circle over the spot where a pelvic spine should be. In each box, the line marked number seven is colored. In the box on the left, the line marked number seven is red. In the box on the right, the line marked number seven is black.]
This hunt eventually pointed a finger at a well-known and powerful developmental control gene called Pitx1.
[The boxes merge together into one box. The seventh line remains black. The camera zooms in on the seventh marker. All of the other lines are removed. A small white rectangle covers the line near the bottom corner. The text “Pitx1” is shown on the right side of the line.]
So, naturally, they compared the Pitx1 protein coding sequence in fish with and without pelvises.
[The screen changes to show two drawn fish on a murky, green water background. They are on the right side of the screen. One is on the upper part of the screen and the other is on the bottom portion of the screen. Behind each of the fish text is shown. It is a random arrangement of the letters “C”, “G”, “T”, and “A” in different colors scrolling from behind to the right and eventually off screen. Each fish has its own line of letters. The letter combinations in both lines match.]
Carroll: And what did you find?
[Camera cuts to show Kingsley in his office. He is talking to Carroll, but Kingsley’s face is the main focus of the frame.]
Kingsley: Well, we actually didn't find anything at all at the, at the coding region of the Pitx1 gene, the actual part that makes the protein, there isn't any difference between marine and freshwater fish.
Carroll: Well, that's fairly puzzling.
[Screen shows a blue background. In the foreground, a red DNA helix is shown. A section in the middle of the helix is covered in a blue highlight. A yellow protein-like blob labeled as "mRNA" moves along the DNA strand. As it moves, a strand of blue comes out of it, similar in appearance to the DNA strand. The blue line with the connected yellow blob is transformed into a blue organic shape. Light blue text on the left side of the organic shape reads “Protein”.]
I mean, we for years were used to the idea that if there is an evolutionary change, that would be a change in the protein made by a gene.
[Another organic yellow shape appears on the left side of the screen. It moves along the red helix until it hits the blue highlighted box. The highlighted box changes from a solid blue to having a stripe of green highlighted in the center. The yellow blob stops at the right edge of the highlighted box. A blue line emerges from the blob. This line matches the other blue line, but has a yellow section in the center. The line and yellow blob vanish and a neon green blob is left on screen. It sits on the right side of the blue organic shape from earlier.]
[Camera cuts to show Carroll sitting in Kingsley’s office.]
So you see no differences in the sequence of the Pitx protein between the two fish. I mean, isn't that a paradox? Isn't that a surprise?
Kingsley: Well, it's still possible that there's something about the expression or the regulation of the gene that's changed.
[Camera shifts to Kingsley and makes him the focal point on screen.]
So the structure is fine, but maybe the timing or the place that's normally expressed is different.
[Camera cuts to show a young man in a lab setting. He is wearing gloves and pouring a vial into another container. A microscope can be seen sitting on the table on the right side of the screen. Many cords are shown in the foreground.]
Narrator: To find out, Kingsley's team soaked embryos with a chemical dye that turns blue any tissue where the Pitx1 messenger RNA is produced.
[The camera cuts to a shot behind the young man. He uses a pipette to take a liquid out of a vial. A close up shot is shown of the pipette sucking up a clear liquid. Within the tip of the pipette, a dark circular blob can be seen. The camera cuts to show the pipette pushing out the liquid and unidentified shape into a petri dish. The pipette is removed and the shape is now identifiable as a fish that is dyed a dark violet color. It cuts to a close-up shot of the fish, likely under a microscope.]
Kingsley: Well, if you look at a marine embryo, you see the Pitx1 gene is expressed in multiple places that turns on in the head region and the lips, inside it would be on in the pituitary, but it also turns on along the side of the body, this very strong blue patch here.
[Camera cuts to show Kingsley and Carroll in his office. They are continuing to converse. Kingsley points to something off screen. The camera cuts to show a large photo of a fish. The fish is a tan color with brown dots all over its body. The eye is large and takes up most of the head. There is one dark blue spot shown on the bottom of the pelvis of the fish.]
Narrator: In that tissue, it's telling cells to start growing a full pelvis and spines.
[Camera cuts back to the professors talking. Kingsley is the focus on screen.]
Carroll: And what about in fish that aren't going to make a pelvis?
[Camera cuts to a close up of Carroll’s face as he is talking. Kingsley leans forward and appears to be using a computer that is out of sight.]
Kingsley: A key moment in the lab was the same experiment in the lake fish, the head region you still see blue on the lips. You still see blue inside the head. You don't see that little key blue spot along the side or on the ventral surface of the fish.
[A picture of the same type of fish is shown. The main difference is that the blue spot on the pelvis is no longer present. The camera shifts to show another image of the fish. It is a close up of the pelvis. The pelvis is tan with burnt sienna spots dotting the skin of the fish. Two white fins can be seen near the left edge of the photo. White text reading “Mark Shapiro” is seen on the bottom ride side of the image. Camera cuts to a close up of Carroll’s face.]
Carroll: So the structure of the protein is the same between the two populations. And the expression of the gene is the same between the two populations, except for just in the pelvis.
[The screen shows a blue background with a red DNA helix in the middle of the screen. The center section of the helix is now highlighted in a dark blue box. A yellow organic shape is seen floating in from the top left corner of the screen. The yellow blob floats along the DNA helix until it reaches the right edge of the highlighted box. A navy blue line emerges out of the yellow organic shape. The line has little lines sticking out of the left side of the line. Then, the line and yellow shape vanish. They are replaced by a royal blue blob that floats to the left.]
Narrator: How can the expression of a gene change in one part of the body but not another?
[The blue blob vanishes. The screen zooms out to show a large arching DNA helix. The helix starts at the top right side of the screen, and creates a curved line that looks like an arch. Near the upper portion of the arch are three different highlighted sections. The one on the right is a neon green box. The one in the middle is a bright red box. The one on the left is a neon light blue box.]
This is possible because the coding regions of most genes that control development are surrounded by a number of regulatory switches, each of which controls gene expression in a different tissue.
[The screen splits. In the background is the close up shot of the fish in the petri dish. The image of the DNA helix just shown is now split into three boxes. One box is found on the upper right corner of the screen. The second box is found on the bottom left corner of the screen. The third box is found on the bottom right corner of the screen. In the first box, the red highlighted box is illuminated and the dark blue box is illuminated. Light blue text at the bottom of the box reads “Jaw Switch”. In the second box, the neon blue highlighted box and the dark blue highlighted box are illuminated. Light blue text at the bottom of the box reads “Pituitary Switch”. In the third box, the neon green highlight and the navy blue highlight are illuminated. Light blue text at the bottom of the box reads “Pelvic Switch”. All three boxes have a yellow organic blob in the center. This blob floats to the edge of the dark navy highlight and stops. A dark blue line emerges out of the blob. The blob and line vanish and are replaced with a blue organic blob.]
Like all DNA, the sequences of switches can acquire mutations.
[The screen becomes blurry. In the foreground, the letters “A”, “T”, “C”, and “G” are shown. “A”s are green. “G”’s are black. “T”s are red. “C”s are blue. They are in a line and scroll to the left. Some of the letters vanish from the line, leaving blank spaces behind.]
Kingsley had a hunch that the switch regulating Pitx1 expression in the pelvic tissue of freshwater sticklebacks was broken.
[The letters vanish and the background is sharp again. The box on the bottom right corner has a black X that covers the first highlighted box on the DNA helix. The process of the yellow blob becoming a blue blob is shown in the other two boxes. It is not shown in the third.]
[Camera cuts to a darkly lit lab with a wall of fish tanks. Fish can be seen inside the tanks. The camera pans to the right, showing many different tanks and additional equipment.]
But to find out, he had to first find that switch.
[Camera cuts to a close up of a fish. It is dark, almost pitch black. The only source of light is the green spines on the fins and the glowing green eyeballs. The light reflects off the surroundings in the tank.]
Geneticists find switches by tracking the expression of a reporter protein that glows green where a switch is active.
[Screen shows a red DNA helix on a blue background. A central segment of the helix is covered in a dark blue highlighted box.]
After cutting the DNA around the Pitx1 coding sequence into many different fragments, they attach the green reporter gene to each of them.
[The highlighted segment of the red DNA helix trails off screen. The remaining DNA helix is broken into eight equal segments. Each segment has a green helix added to the right end.]
Then, they injected those fragments into stickleback eggs.
[The eight segments of the DNA helix are placed into eight petri dishes. Each dish has one DNA segment. All of the segments vanish once they are put in the petri dish. Each petri dish also has yellow-green dots that represent the stickleback eggs.]
[Camera cuts to a close up of Kingsley’s face.]
Kinglsey: We wait a week or two and then we ask, are our sticklebacks glowing in the pelvis?
[A close up shot of a fish is shown. It is on a green and murky background. The fish appears to be on its side. The eye glows green. The fish appears to have brown dots all over its body. A small green dot can be seen on the pelvis of the fish.]
Narrator: After five years of testing different fragments, they had fish with glowing pelvic tissue.
[A white arrow appears on screen pointing directly to the green spot on the fish’s pelvis. The camera zooms in on the green spot.]
They'd found the stretch of DNA that contained the Pitx1 switch.
[Camera cuts to a fish swimming in a dark lake.]
Sequencing that region revealed a dramatic mutation.
[A block of text appears on screen covering the footage of the fish. The text is white and appears to be a random arrangement of the letters ‘A”, “T”, “G”, and “C”. The block of text covers the majority of the screen.]
Kingsley: Fish that have lost their pelvis have deleted the pelvic switch. It's gone.
[The block of text fades out. The footage of a fish swimming in a dark lake is seen clearly.]
Narrator: But because this mutation only crippled one specific switch, the Pitx1 gene remained fully functional in the rest of the body.
Kingsley: If you do that, you can have a huge effect on the development of that structure.
[Camera cuts back to showing Kingsley and Carroll talking in an office setting. The focus is on Kingsley.]
But the fish is fine.
[Camera cuts to footage of fish swimming in a dark and murky lake.]
Actually, the fish is better than fine. When that deletion occurred, it conferred an advantage on the fish and that mutation spread throughout the entire population.
Carroll: So the obliteration of that switch actually makes these fish better adapted to the new environment they're in.
Kingsley: That's right.
Carroll: And their ancestors.
[A DNA helix is shown on screen. The background is blue while the helix is orange. The DNA helix starts at the top right portion of the screen, curls toward the left portion of the screen until it reaches the edge of it, and then curves back toward the right. Near the top of the DNA helix there are three highlighted boxes. The rightmost box is neon green. The middle box is a bright red. The left box is neon light blue. On the bottom right portion of the DNA helix is a dark navy highlighted box.]
Narrator: With the switch identified, he was ready for a final test.
Kingsley: If you've got the right switch, you ought to be able to put it back and reverse the evolutionary tree.
[The DNA helix curls tightly, making a “S”-like shape. The neon green and dark blue highlighted boxes are illuminated. A yellow organic blob appears near the top left corner of the screen. It floats down to the dark blue highlighted segment. Once it touches the segment, a blue line emerges from the blob. This line has little lines sticking out of the left hand side. Once the blob reaches the right edge of the blue segment, both the line and yellow blob vanish. A blue blob takes its place and floats back towards the upper left section of the screen.]
[Camera cuts to a young man in a laboratory setting. He is wearing blue gloves and is holding paint brushes in both of his hands. He is looking in a microscope occasionally as he brushes the petri dish.]
[The camera cuts to a close up of the brushes and the petri dish. Some kind of clear liquid and a clear orb is being spread on the petri dish by the paint brushes. On the petri dish, there is a metal tool that has ridges in it. The brush pushes the clear orb into one of the ridges. Another tool appears that has a thick, clear handle and a thin and long neck and tip. A close up shot is shown where the needle-like tip of the tool is stabbed into the clear egg. The ridge holds the egg in place.]
Narrator: So, they joined the working switch to the Pitx1 coding region and injected the combination into eggs from a freshwater stickleback that would normally never form pelvic spines.
[Camera cuts back to Carroll and Kingsley talking in Kingsley’s office. The focus remains on Kingsley.]
Carroll: And?
Kingsley: That was a good day in lab.
[A photo is shown on screen. The photo is a close up of a fish. It has a blue overtone. A white arrow points to a spine sticking out of the pelvis of the fish.]
It works. There's a fish now swimming around in the tank.
[The camera cuts to a personal interview with Kingsley. It is in an office environment.]
Hasn't formed a pelvis for, you know, maybe thousands of years.
[A shot of a silver stickleback fish in a clean environment is seen. The water is clear, so the details of the fish’s scales and body features are crisp.]
It does, if you put back in the key sequence.
Narrator: Kingsley's team had found the broken switch that caused fish from one lake to be without spines. But that isn't the only place one can find spineless sticklebacks.
[Camera cuts to a digital rendition of the Earth. The focus is on the northern region. The Earth rotates around until a clear shot of Europe and Northern Africa are seen. A white box appears around the tip of a landmass in Europe. This box has lines sticking out perpendicular to the box sides. A digital beep is heard in the background.]
When he looked at fish from other lakes, he found something remarkable.
[The box moves to point to a variety of locations on the Earth. Some of the locations include Scotland, Iceland, Alaska, and British Columbia.]
Kingsley: If you look at a fish that's lost its pelvis in Scotland, or Iceland, Alaska, or British Columbia, the same switch has been thrown away over and over and over again whenever the fish have evolved the loss of a pelvis.
[A close up show of a fish in a dark lake is shown on-screen. The camera cuts between footage of several similar fish in similar environments.]
Narrator: Given the same selective conditions, evolution can and does repeat itself, right down to the level of the same gene and genetic switch. And amazingly, it appears that the same adaptation has also occurred in the much deeper past.
[Camera cuts to footage panning over a desert landscape. On the right side of the screen, a big rock formation is seen. It looks steep and has ridges. On the left side of the screen is a sandy and fairly hilly landscape. Wild foliage is seen growing in bunches sporadically. Camera pans to the left. A man in hiking gear is seen near the large rock formation.]
Ten million years ago, this Nevada desert was a lake full of sticklebacks.
[An older man in hiking gear uses a pickaxe against a large rock. It can be inferred that the rock is a type of sedimentary rock similar to limestone in color. Different shots are seen of the man chipping away at the rock.]
Their fossil remains have long fascinated Mike Bell.
[The older man chips away rock slabs, examines them closely, and tosses the ones he doesn’t appear to like on the desert ground. The camera cuts to a shot of the older man walking away.]
[The old man fades away. The camera pans over a large, dark, sandy desert scene. As the camera pans, the sky becomes a bigger focal point. There are very few clouds to be seen. The sun is bright. It appears to be around the middle of the afternoon.]
Bell: Every year, many stickleback would die and their bodies would drift to the bottom and be covered with sediment.
[The older man, presumed to be Mike Bell, is seen chipping away at more rock on a rocky ledge. The rock appears to be sandy and crumbles easily. Mike Bell chips away at the rock using a long and thick stick with a flattened edge.]
[Camera cuts to a shot of Mike Bell. It appears to be an interview setting outside in the Nevada Desert. In the background is a large rock formation. The rock formation has a beige-gray appearance to it. The sky is barely seen over the edge of the formation. Mike Bell has thick salt and pepper hair, a beard and mustache, and a pair of large glasses. He is wearing a blue button up. He appears to be sitting and is seen on the left side of the screen.]
The flesh would rot off the bones and very often would leave a beautiful intact skeleton.
[The camera cuts to a close up of him using a yellow glove to pick up a slab of rock. Once the white slab is lifted up and off screen, a dark amber colored fossil is revealed. It is distinct and easy to identify as a small fish.]
[Another shot is shown of Mike Bell working in the stone. This time he is not wearing gloves. He has a tool that appears to be a thin sheet of metal attached to a wooden handle. He uses a pushing motion with the tool to pull up small slabs of rock.]
Narrator: Early on, Bell realized that there were two distinct types of sticklebacks preserved here.
[Camera shows Mike Bell is sitting on the desert floor. He has a large slab of white rock and makes an “Aha” noise.]
[Camera cuts to show Mike Bell in an interview held outside in the Nevada Desert. He appears to be talking directly to the camera.]
Bell: Some of the fish had a really big pelvic bone behind the head.
[Camera cuts to show a close up of a fish skeleton. The fossil is imprinted into the stone and has a amber yellow tone. A pen is used to point to the pelvic bone on the fossil.]
[The camera cuts back to the interview with Mike Bell.]
And other fish didn't have that bone, but a little tiny pelvic bone.
[Camera cuts to a close up of another fish skeleton. The fossil is imprinted into the rock slab. This time, the slab appears to be held by Mike Bell. He uses a pen to point to where the pelvic bone structure should be. There is no pelvic bone structure easily identified.]
[A photo of both skeletons are shown together. The images are rectangular and are organized horizontally. The top image shows an orange fish fossil on a tan stone. A yellow circle is drawn on the pelvic area. A pelvic bone structure can be easily seen and identified. The bottom image also shows an orange fish fossil on a tan stone. A yellow circle is also drawn over the pelvic area. However, no bone structure is seen.]
Narrator: One might expect one or the other to be favored by natural selection. So why were they both here?
[Camera cuts to a shot of the Nevada Desert. Two men, Mike Bell and another man, are seen sitting on a rock formation. The other man appears to be wearing a tank top, shorts, and a black brimmed hat. The rock is a sandy beige and has many indentations and ridges. A shrub is seen near the middle of the screen. Both men appear to be digging and chipping away at the rock.]
This quarry has a thousand sediment layers in every foot of rock, a thousand years of annual deposits.
[Camera pans over the rock formation. Digital editing is done to draw lines on the rock formation. The lines are slanted to the right. On the left side of each line a number appears, one number per line starting at “7,000”. Additional lines with the corresponding numbers are added. The last line is labeled with the number “12,000”.]
A record of change like that is an evolutionary biologist's dream.
[Additional lines and numbers are added onto the rock formation. The numbers “13,000”, “14,000”, “15,000”, “16,000”, “17,000”, and the beginnings of “18,000” are shown with their corresponding lines.]
To move from one end to the other is to move through time.
[Camera cuts to another shot of Mike Bell and the other man chipping away at rocks. This time the men are sitting next to each other in from of a pile of rock. They both are deeply engrossed in work. A small wheelbarrow is seen in the top right corner of the screen.]
By painstakingly checking fossil pelvis size over a 20 thousand year period, Bell made a surprising discovery.
[A graph overlays the footage of Bell and the other man working. The graph is opaque so the desert scene is still visible. The y axis is shown on the left side of the screen. The graph’s y axis is labeled “Relative Frequency”. The label is found on the right side of the axis. On the top of the y axis is the number “1.0”. At the bottom of the graph’s y axis is the number “0.0”. On the right side of the y axis is a blue gradient spreading outward towards the empty space in the graph. Near the upper left corner of the graph, a white line is drawn showing a downward slope. A fish sketch is shown. On the fish sketch is a blue circle around the pelvic area. Text underneath the circle acts as a label, stating “Reduced Pelvis”. At the bottom left corner of the graph a white line appears and is slanted upward. The line has a red glow around it. Above the line is another sketch of a fish. This fish has a red circle around it’s pelvic area. There is text underneath it that says “Full Pelvis”. The x axis of the graph is labeled “Time”. The title of the graph is “Elapsed Years”.]
[By the title is a set of numbers that goes up as time progresses. As the number of years increases, the number of fish with reduced pelvis’ continues to decrease slowly white the number of fish with full pelvis’ continues to increase slowly.]
Bell: He's got a fish, pretty nice fish.
Narrator: Fish with a full pelvis had arrived suddenly, perhaps when some geological event briefly opened the lake to the sea.
[When the number in the title hits around “9,568”, the lines on the graph coincide. The red line continues to have a positive incline while the blue line continues to plummet. This shows that the full pelvis sticklebacks increased drastically in population around this time.]
Yet within a few thousand years, almost all sticklebacks here lacked pelvic spines.
[When the number in the title reaches around “15,000”, the lines coincide. After connecting, the red line continues to plummet while the blue line continues to rise. This shows that the reduced pelvis stickleback population was increasing at a rapid rate at this time while full pelvis stickleback populations were dwindling. The edges of the graph eventually start to match the starts of the graph once “21,000” is shown in the title of the graph.]
[Camera cuts to Mike Bell being interviewed in the Nevada Desert.]
Bell: And in Alaska we're seeing exactly the same phenomenon taking place, but it's ten million years later.
[Mike Bell and another man are seen sitting and working on a rock formation. The rock formation is a beige-gray color. There is a steep slanted cut in the rock that gives it a large flat face. Mike Bell is sitting where the cut begins near the upper left corner of the screen. He appears to be looking at a rock he is holding. The other man is sitting on the top of the ridge. He appears to be working at chipping away at the top of the rock formation. He is placed near the center of the screen.]
[A red fish appears at the center of the screen overlapping the footage of the men working in the desert. It appears to be a picture of a fish skeletal structure with some of the internal structures like the eyes, stomach, and heart being identifiable. It appears to be a spined stickleback with its pelvic spines.]
Narrator: The same animal, at two distant moments in time, undergoing the same transformation, in both cases pretty quickly, and in all likelihood, be the same evolving switch.
[The red fish skeleton vanishes and is replaced by another red fish skeleton. The internal structures are not easily identifiable, but it is clear that more than the skeleton is pictured. The second red fish skeleton is significantly smaller than the original and doesn’t have pelvic spines.]
[The second red fish skeleton vanishes and is replaced by a block of text. The block of text is still overlaying the footage of the men working. The block of text contains a random assortment of the letters “C”, “T”, “A”, and “G”. The middle portion of the text becomes opaque. Only the first two and a half lines and the last half of the last line of text are visible.]
Bell: This is a really exciting time to be a biologist.
[Camera cuts to footage of a set of silver fish swimming. Little rocks and marine foliage can be seen.]
Only ten years ago, we couldn't get at the DNA of stickleback in a detailed way. And now you can combine that kind of information with natural history.
[Camera cuts to an interview with Mike Bell. He is the focal point of the footage and appears to be talking to someone behind the camera. He is wearing many winter layers in this footage. He is being interviewed outside of a large lake. The lake is surrounded by a thick forest landscape. The sky is full of thick, gray clouds.]
We can link up genetics to development, development to phenotypes. Phenotypes to environments. We can look at change through time in the fossil record.
[Camera cuts to close up footage of a silver fish in a dark environment. Only the face of the fish is visible.]
We can put together the whole package.
[Camera cuts between many different clips of wildlife. It starts with a fly on a brown sticky substance. It switches to a cut of a flock of birds flying in a circular motion. Bird chirps and squawks are heard. It then switches to an underwater shot of a manatee swimming in pristine blue water. The footage continues to switch as the narrator talks between different animals and environments.]
Narrator: As biologists do just that, they're finding that the most common mechanism driving the seemingly endless diversity of animal bodies is mutations in the switches that regulate developmental control genes.
[As the narrator speaks, additional footage of animals in different environments is shown. A brown and orange butterfly is seen resting on a small, white flower. The camera cuts to a gray and gold snake slithering on a beige stone. Camera cuts to a fruit bat hanging upside down on a tree. The leaves are a vibrant green. Another shot of a butterfly is shown. This butterfly is a pale green and brown insect resting on a purple, spiky flower. Footage of a herd of zebras is shown. This footage fades out into a deep blue shot of whales swimming in the ocean. Camera cuts to a close up of a Chimpanzee's face on a neutral gray background. Footage fades to black.]
[Outro music begins to play. The background becomes footage of fish swimming in a dimly lit environment. The video credits begin to scroll. The “hhmi Biointeractive” logo is shown.]
[End of video]