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According to Bell et al (2005) Inquiry is an "active learning process" where students are involved in a form of learning that emphasizes questioning, data analysis and critical thinking.

During our lectures and tutorials, we are taught to make students speak up and answer questions. Instead of giving the students the answers straight away (counter-intuitive), we should wait and see how they come up with their own answers and explanations first.

For my lesson plans, I have tried to include as much activities as I could wherein the students could figure out their own expalanation/definition for a topic.
for example:
1. Think-pair-share; students were asked to go in pairs and come up with 3 words or phrases that they think would relate to evolution. After their discussion, they would share what they come up with with the class and the teacher draws up a mind map on the whiteboard. They will use these words to come up with a definition for evolution

2. PhET simulation on Natural selection - Use of prompts such as
- “what would happen if…?”
-  “If I introduced this mutation, how will it affect the population?”
- “If I change the environment from tropical to arctic, how will it affect the population?”
- “which variation would survive and reproduce?”

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Why Horseshoe Crab Blood Is So Expensive | So Expensive

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Charles Darwin's theory of evolution explained | A-Z of ISMs Episode 4 - BBC Ideas

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Horseshoe Crab

Limulus polyphemus

Status: Not Listed

Classification: Invertebrate

Description

Horseshoe crabs have been around for more than 300 million years, making them even older than dinosaurs. They look like prehistoric crabs, but are actually more closely related to scorpions and spiders. The horseshoe crab has a hard exoskeleton and 10 legs, which it uses for walking along the seafloor.

The body of the horseshoe crab is divided into three sections. The first section is the prosoma, or head. The name "horseshoe crab" originates from the rounded shape of the head, because just like the shoe on a horse's foot, the head is round and U-shaped. It's the largest part of the body and contains much of the nervous and biological organs. The head has the brain, heart, mouth, nervous system, and glands-all protected by a large plate. The head also protects the largest set of eyes. Horseshoe crabs have nine eyes scattered throughout the body and several more light receptors near the tail. The two largest eyes are compound and useful for finding mates. The other eyes and light receptors are useful for determining movement and changes in moonlight.

The middle section of the body is the abdomen, or opisthosoma. It looks like a triangle with spines on the sides and a ridge in the center. The spines are movable and help protect the horseshoe crab. On the underside of the abdomen are muscles, used for movement, and gills for breathing.

The third section, the horseshoe crab's tail, is called the telson. It's long and pointed, and although it looks intimidating, it is not dangerous, poisonous, or used to sting. Horseshoe crabs use the telson to flip themselves over if they happen to be pushed on their backs.

Female horseshoe crab are about one-third larger than the males. They can grow to be 18 to 19 inches (46 to 48 centimeters) from head to tail, while the males are approximately 14 to 15 inches (36 to 38 centimeters).

Range

The horseshoe crab species found around the United States (Limulus polyphemus) lives in the Atlantic Ocean along the North American coastline. Horseshoe crabs can also be seen along the East and Gulf coasts of the United States and Mexico. There are three other species of horseshoe crab worldwide, which are located in the Indian Ocean and in the Pacific Ocean along the coast of Asia.

Horseshoe crabs utilize different habitats depending on their stage of development. The eggs are laid on coastal beaches in late spring and summer. After hatching, the juvenile horseshoe crabs can be found offshore on the sandy ocean floor of tidal flats. Adult horseshoe crabs feed deeper in the ocean until they return to the beach to spawn. Many shorebirds, migratory birds, turtles, and fish use horseshoe crab eggs as an important part of their diet. Horseshoe crabs are a keystone species within the Delaware Bay ecosystem.

Diet

Horseshoe crabs like to dine at night on worms and clams, and may also eat algae. A horseshoe crab picks up food with appendages located in front of its mouth. Because it has no mandible or teeth, the horseshoe crab crushes food between its legs before passing it to the mouth.

Life History

During the late spring and early summer, adult horseshoe crabs travel from deep ocean waters to beaches along the East and Gulf coasts to breed. The males arrive first and wait for the females. When the females come to shore, they release natural chemicals called pheromones that attract the males and send a signal that it's time to mate. Horseshoe crabs prefer to breed at night during high tides and new and full moons. The males grasp onto the females and together they head to the shoreline. On the beach, the females dig small nests and deposit eggs, then the males fertilize the eggs. The process can be repeated multiple times with tens of thousands of eggs.

Horseshoe crab eggs are a food source for numerous birds, reptiles, and fish. Most horseshoe crabs will not even make it to the larval stage before being eaten. If the egg survives, the larval horseshoe crab will hatch from the egg after about two weeks or more. The larva looks like a tiny version of an adult horseshoe crab, but without a tail. Larval horseshoe crabs travel into the ocean water and settle on the sandy bottom of tidal flats for a year or more. As they develop, they will move into deeper waters and begin to eat more adult food. Over the next 10 years or so, the juvenile horseshoe crabs will molt and grow. The molting process requires shedding small exoskeletons in exchange for larger shells. Horseshoe crabs go through 16 or 17 molts during their development. At around 10 years of age, horseshoe crabs reach adulthood. They are ready to start breeding and will migrate to coastal beaches in the spring. A horseshoe crab can live for more than 20 years.

Conservation

Threats to horseshoe crabs include habitat loss and overharvesting. Beach developments hinder horseshoe crab breeding. Limulus polyphemus is internationally listed as vulnerable.

Fun Fact

During full moons, new moons, and high tides in May and June, hundreds of thousands of horseshoe crabs converge on the Delaware Bay to breed.

Sources

Florida Fish and Wildlife Conservation Commission

Maryland Department of Natural Resources

National Oceanic and Atmospheric Administration

The Horseshoe Crab, Ecological Research and Development Group

The IUCN Red List of Threatened Species

U.S. Fish & Wildlife Service

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Horseshoe Crab | National Wildlife Federation

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Limulus polyphemus Status: Not Listed Classification: Invertebrate Description Horseshoe crabs have been around for more than 300 million years, making them even older than dinosaurs. They look like prehistoric crabs, but are actually more closely related to scorpions and spiders. The horseshoe crab has a hard exoskeleton and 10 legs, which it uses for walking along the seafloor.

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Evidence of evolution - the "living fossil".

An evidence that natural selection doesn't mean "change" straight away. I thought it would be great to add this in the lessons because it will make the students think about what natural selection really means. It suggests the idea that natural selection can occur without evolution occurring.

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Florida Fish And Wildlife Conservation Commission

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The American horseshoe crab is a common sight on Florida's beaches. Horseshoe crabs are "living fossils" meaning they have existed nearly unchanged for at least 445 million years, well before even dinosaurs existed.

Horseshoe crabs are not actually crabs at all, they are much more closely related to spiders and other arachnids than they are to crabs or lobsters!

There are four species of horseshoe crabs still around today. Only one species, Limulus polyphemus, is found in North America along the Atlantic and Gulf coasts from Maine to Mexico. The other three species are found in Southeast Asia.

Despite existing for hundreds of millions of years, horseshoe crabs are nearly identical to their ancient relatives. This is because their body structure is extremely effective for survival, think, "if it ain't broke, don't fix it!"

Horseshoe crabs have a tank-like structure consisting of a front shell called the prosoma, a back shell called the opisthosoma, and a spike-like tail called a telson. Some people think horseshoe crabs are dangerous animals because they have sharp tails, but they are totally harmless. Really, horseshoe crabs are just clumsy and they use their tail to flip themselves back over if they get overturned by a wave.*

Though the horseshoe crab's shell is hard, it is very sensitive to the world around it. The crabs are especially sensitive to light. They have 10 eyes, a pair of compound eyes on the prosoma, and "photo receptors" in other areas, primarily along the tail.
*Never pick up a horseshoe crab by its tail, as it can harm the animal. Instead, gently pick it up by both sides of the prosoma using both hands.

Horseshoe crabs are known to gather in large nesting aggregations, or groups, on beaches particularly in the mid-Atlantic states such as Delaware, New Jersey and Maryland in the spring and summer, where their populations are largest. Horseshoe crabs can nest year-round in Florida, with peak spawning occurring in the spring and fall.

When mating, the smaller male crab hooks himself to the top of the larger female's shell by using his specialized front claws, and together they crawl to the beach. The male fertilizes the eggs as the female lays them in a nest in the sand.

Some males (called satellite males) do not attach to females but still have success in fertilizing the female's eggs by hanging around the attached pair. Most nesting activity takes place during high tides around the time of a new or full moon.

Horseshoe crab larvae emerge from their nests several weeks after the eggs are laid. Juvenile horseshoe crabs look a lot like adults except that their tails are smaller. The young and adult horseshoe crabs spend most of their time on the sandy bottoms of inter-tidal flats or zones above the low tide mark and feed on various invertebrates.

Why are horseshoe crabs important?
Horseshoe crabs are an important part of the ecology of coastal communities. Their eggs are the major food source for shorebirds migrating north, including the federally-threatened red knot. These shorebirds have evolved to time their migrations to coincide with peak horseshoe crab spawning activity, especially in the Delaware and Chesapeake Bay areas. They use these horseshoe crab beaches as a gas station, to fuel up and continue their journey.

Many fish species as well as birds feed on horseshoe crab eggs in Florida. Adult horseshoes serve as prey for sea turtles, alligators, horse conchs, and sharks.

Horseshoe crabs are also extremely important to the biomedical industry because their unique, copper-based blue blood contains a substance called "Limulus Amebocyte Lysate", or "LAL".

This compound coagulates or clumps up in the presence of small amounts of bacterial toxins and is used to test for sterility of medical equipment and virtually all injectable drugs. That way, when you get a vaccine you know it hasn't been contaminated by any bacteria. Anyone who has had an injection, vaccination, or surgery has benefited from horseshoe crabs! Additionally, research on the amazing and complex compound eyes of horseshoe crabs has led to a better understanding of human vision.

Horseshoe crabs are also used in several fisheries. The marine life fishery collects live horseshoe crabs for resale as pets in aquariums, research subjects, or as educational specimens, and both the American eel and whelk fisheries use horseshoe crabs as bait along many parts of the Atlantic coast.

Threats to horseshoe crabs and research efforts
Horseshoe crab numbers are declining throughout much of their range. In 1998, The Atlantic States Marine Fisheries Commission developed a Horseshoe Crab Fishery Management Plan that requires all Atlantic coastal states to identify horseshoe crab nesting beaches. Currently, with the help of the public, biologists at the Fish and Wildlife Research Institute are documenting nesting sites of horseshoe crabs throughout the state. If you see horseshoe crabs mating and would like to report a sighting, please visit the Report Sightings page for more information.

Frequently Asked Questions About Horseshoe Crabs

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The American horseshoe crab is a common sight on Florida's beaches. Horseshoe crabs are "living fossils" meaning they have existed nearly unchanged for at least 445 million years, well before even dinosaurs existed. Horseshoe crabs are not actually crabs at all, they are much more closely related to spiders and other arachnids than they are to crabs or lobsters!

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Simulation on Natural Selection

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Explore how organisms with different traits survive various selection agents within the environment.

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Ask most folks who came up with the theory of evolution, and they'll tell you it was Charles Darwin.

In fact, Alfred Russel Wallace, another British naturalist, was a co-discoverer of the theory - though Darwin has gotten most of the credit. Wallace died 100 years ago this year.

Wallace developed some of his most important ideas about natural selection during an eight-year expedition to what was then the Dutch East Indies - modern-day Indonesia - to observe wildlife and collect specimens. Few places on earth can rival this vast archipelago's tremendous diversity of plant and animal life.

Wallace collected more than 100,000 insect, bird and animal specimens, which he gave to British museums.

By 1855, Wallace had come to the conclusion that living things evolve. But he didn't figure out how until one night three years later. He was on the island of Halmahera, ill with a fever, when it came to him: Animals evolve by adapting to their environment.

As soon as he could, Wallace wrote his theory down in a closely argued, eight- or nine-page paper, says Tony Whitten, a Wallace expert with British-based Flora & Fauna International.

"He sent that to Darwin, as an older mentor, if you like, to have a peer review before publication," Whitten says.

Darwin had reached the same conclusion years earlier, and Wallace's letter spurred him to act. The two men published a joint paper in 1858, arguing the theory of evolution and natural selection. It shook mankind's assumptions about its origins, which were heavily influenced by religion.

The following year, Darwin published his book On the Origin of Species and rose to fame. Wallace, ultimately, faded into obscurity.
Sulawesi And Survival Of The Fittest
But at the time, Wallace was still refining his ideas about natural selection - and had landed on what is now Indonesia's island of Sulawesi, a place where most of the animals there existed no place else on earth.

Today, Sulawesi's natural abundance has been severely depleted. Many of its unique species are close to extinction in the wild, found only in nature preserves.

The high point for Wallace's explorations on Sulawesi was the search for a bird called the maleo, which exists in nature only on the island.

In Wallace's footsteps, I recently went in search of the bird at the Bogani Nani Wartabone National Park. I walked through a dense, misty highland forest, full of luxuriant fan palms and bubbling hot springs, amid the constant chatter of birds and insects.

At one point, we spotted two male maleos, calling to their mates, with an eerie, trilling sound. The birds are somewhere between a chicken and a turkey in size, with black feathers and a salmon-colored breast.

In his book The Malay Archipelago, Wallace wrote that students of natural history should avoid thinking of animal behavior as "fixed points." He argued that this has "the bad effect of stifling inquiry into the nature and causes of 'instincts and habits.' " Wallace's insatiably curious mind was constantly thinking about how animals' behavior reflected their changing natural surroundings.

For example, Wallace observed that maleos have adapted so perfectly to the environment that they even use Sulawesi's geology to survive. Instead of sitting on their eggs like hens, maleos use geothermal energy to incubate them. They dig into the earth, which is heated by hot springs. They can sense where the temperature is just 86 to 97 degrees, and that's where they lay their eggs.

At the park's hatchery, ranger Max Lela showed us a downy, three-day-old maleo chick. We could see that unlike other species similar to it, the maleo has webbing between three of its claws. Wallace believed that maleos had developed this webbing to help them dig into the earth and bury their eggs.

Lela says that after eight weeks, the buried eggs hatch and the maleo chicks struggle up through the dirt and immediately fly away. That keeps them safe from local predators such as the monitor lizard.

"After reaching the surface, they will stop and then shake their wings and body because they are covered with dirt," Lela says. "But then they can walk and fly right away, without any parental training."

Lela puts the little chick in my hand. It wobbles for a second, and then flies off into a nearby tree - no small feat for a three-day-old bird.
Discovering 'Wallacea'
Perhaps Wallace's greatest contribution to the theory of natural selection was simply to ask: Why do we find this animal in this place?

He realized that just as animals are shaped by where they live, regions can also be defined by the animals that live there.

He noticed, for example, that the maleo is related to species found in Australia, but not in Asia, not even on the island of Borneo just a few miles to the west. Even non-experts may observe that there are no elephants or rhinoceroses in Australia, and no kangaroos or koalas in Asia.

Whitten, Fauna & Flora International's Asia-Pacific regional director, says Wallace concluded that Sulawesi was located on some sort of boundary line that separates different biological regions.

"Clearly this was a transition between the Asian world and the Australian world," Whitten says. "And so came the thought of this line that could be drawn between Borneo and Sulawesi, that would separate the Asian fauna from the Australian fauna."

Wallace didn't know it at the time, but that line is actually the divide between two continental shelves. The line is now called the Wallace Line, and the transitional region around it is called Wallacea.

Wallace believed that Sulawesi is unique because most of the animals that live here are not found anywhere else on earth.

He concluded that these animals had been on this island isolated from other species for a very long time, and slowly evolved into new species.

Sulawesi naturalist John Tasirin says that Wallace found that 64 percent of mammals on Sulawesi are unique to the island. However, if you subtract bats - which are highly migratory mammals - from that figure, it jumps to 86 percent.

Tasirin says that Wallace saw the island's natural history in terms of how species had migrated to new environments on the island, adapted to them, and then evolved.

"You can see the movement of the animals. And when they move, suddenly they become a new species," Tasirin says, adding that it's not exactly "suddenly" but more like 3,000 or 6,000 years.
Foretelling Future Threats
Biodiversity provides the raw material for natural selection to work on. It also allowed Wallace to compare and contrast the differences among many species - differences as subtle as the graceful curve of a butterfly's wing.

Whitten says Wallace marveled at the variety of life on earth, even as he mourned man's effect on it.

"He just wondered how could it possibly be that ... we celebrate creation, in whatever way you want to understand that, and yet destroy it at the same time; [and that] just was so awful that we should all work to try to conserve that biodiversity," Whitten says.

As Wallace's eyes observed life around him, his mind roamed millions of years back in time, to imagine the birth of islands and continents. He also peered into the future. Back in England in 1863, he wrote:

"Future ages will certainly look back on us as a people so immersed in the pursuit of wealth as to be blind to higher considerations."

Wallace foretold today's situation, in which Sulawesi's unique animals face extinction. He wrote that we have it within our power to save these creatures, and not let them, as he put it, "perish irrecoverably from the face of the earth, uncared for and unknown."

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He Helped Discover Evolution, And Then Became Extinct

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Charles Darwin is known as the father of evolution. But another British naturalist, Alfred Russel Wallace, played a major role in developing the theory of natural selection before fading into obscurity. A trip to what's now Sulawesi in Indonesia, and the unique animals he found there, helped form his seminal ideas.

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British naturalist, Alfred Wallace co-developed the theory of natural selection and evolution with Charles Darwin, who is most often credited with the idea.

Photograph courtesy of Biophoto Associates/Science Source

Encyclopedic Entry Vocabulary

Alfred Russel Wallace was born in Wales in 1823. He has been described variously as a naturalist, a geographer, and a social critic. He even weighed in on the debate as to whether or not life could exist on Mars. However, what he is best known for is his work on the theory of natural selection.

Like fellow naturalist and colleague Charles Darwin, Wallace traveled the world, observing and collecting samples of species. He traveled to Brazil and various islands of the Malay Archipelago that make up modern-day Indonesia and the Philippines, where he collected thousands of specimens of insects, birds, and other animals. After four years in Brazil, Wallace fell ill and decided to return home to England. But 26 days into their voyage home, his ship caught fire and sank in the Atlantic. Wallace's team and the ship's crew spent 10 days adrift before being picked up by a passing ship, and all of Wallace's notes and samples were lost at sea.

Despite this setback, Wallace set off on another voyage in 1854 to Southeast Asia to collect more samples. By 1855, his observations led him to the conclusion that living things change over long periods of time-they evolve. However, he could not explain how or why they evolve. Then, in 1858, while still in Southeast Asia, he became ill again. Wracked with a fever, he suffered hallucinations, but when the fever broke, the answer came to him-species evolve by adapting to their environment!

Wallace knew Darwin was working on similar research. In 1858, he sent Darwin a letter outlining his ideas about evolution. The two collaborated on a scientific paper, discussing their evidence for natural selection and evolution.

In 1859, Darwin published his book On the Origin of Species, which presented his theory of natural selection to a broader audience. The theory of evolution by natural selection became known as Darwin's theory. Though Wallace's contributions to the study of evolution were considerable, they are often forgotten.

Wallace spent eight years studying and collecting biological specimens in Southeast Asia. During that time, he gathered over 125,000 specimens. His research on the geographic distribution of animals provided critical support for his evolutionary theories and led him to draw a boundary line through Southeast Asia that divides Asian and Australian animal groups. Wallace's Line, as it was later named, runs from the Indian Ocean to the Philippine Sea. It signifies the unexpected distribution of animals on either side of the line. Several mammal, bird, and fish species are found in abundance on one side of the line and only in small numbers, or not at all, on the other side.

Wallace wrote over 20 books and published more than 700 articles and letters on a wide variety of topics. He died in 1913 at the age of 90.

a group of closely scattered islands in a large body of water.

process by which organisms that are better -adapted to their environments produce more offspring to transmit their genetic characteristics.

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Director

Tyson Brown, National Geographic Society

Author

National Geographic Society

Production Managers

Gina Borgia, National Geographic Society
Jeanna Sullivan, National Geographic Society

Program Specialists

Sarah Appleton, National Geographic Society
Margot Willis, National Geographic Society

Last Updated

Aug. 23, 2019

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Director

Tyson Brown, National Geographic Society

Author

National Geographic Society

Production Managers

Gina Borgia, National Geographic Society
Jeanna Sullivan, National Geographic Society

Program Specialists

Sarah Appleton, National Geographic Society
Margot Willis, National Geographic Society

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When most of us think about natural selection, we attribute that theory to naturalist Charles Darwin. However, what most people do not know is that another scientist, Alfred Wallace, a naturalist, a geographer, and a socialist, also deserves some credit for the theory.

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Many vertebrates have a very similar bone structure despite their limbs looking very different on the outside. This structure is known as the pentadactyl ( five fingered ) limb. This suggests that many vertebrates descended from the same common ancestor.

Although the limbs of crocodiles, birds, whales, horses, bats and humans all look very different they share the same five fingered bone structure. This provides evidence for the theory of .

The pentadactyl limb seen in the horse provides an excellent example of how evolution has happened. As the marshy ground became drier, horses with smaller feet were generally faster. They had an evolutionary advantage because they were able to avoid predators. Over many, many generations horse's feet have evolved to be smaller and the horses themselves taller and stronger.

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The pentadactyl limb - Evolution - Edexcel - GCSE Biology (Single Science) Revision - Edexcel - BBC Bitesize

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Many vertebrates have a very similar bone structure despite their limbs looking very different on the outside. This structure is known as the pentadactyl ( five fingered ) limb. This suggests that many vertebrates descended from the same common ancestor.

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(Image credit: Copyright NHMU/Credit: Mark Johnston)

The Theory of Evolution by natural selection was first formulated in Charles Darwin's book "On the Origin of Species" published in 1859. In his book, Darwin describes how organisms evolve over generations through the inheritance of physical or behavioral traits, as National Geographic explains. The theory starts with the premise that within a population, there is variation in traits, such as beak shape in one of the finches Darwin studied.

According to the theory, individuals with traits that enable them to adapt to their environments will help them survive and have more offspring, which will inherit those traits. Individuals with less adaptive traits will less frequently survive to pass them on. Over time, the traits that enable species to survive and reproduce will become more frequent in the population and the population will change, or evolve, according to BioMed Central. Through natural selection, Darwin suggested, genetically diverse species could arise from a common ancestor.

Darwin did not know the mechanism by which traits were passed on, according to National Geographic. He did not know about , the mechanism by which genes encode for certain traits and those traits are passed from one generation to the next. He also did not know about genetic mutation, which is the source of natural variation. But future research by geneticists provided the mechanism and additional evidence for evolution by natural selection

What is natural selection?

Darwin chose the term "natural selection" to be in contrast with "artificial selection," in which animal breeders select for particular traits that they deem desirable. In natural selection, it's the natural environment, rather than a human being, that does the selecting.

Put simply, the theory of evolution by means of natural selection can be described as "descent with modification," said Briana Pobiner, an anthropologist and educator at the Smithsonian National Museum of Natural History in Washington, D.C., who specializes in the study of human origins. The theory is sometimes described as "survival of the fittest," but that characterization can be misleading, Pobiner said. Here, "fitness" refers not to an organism's strength or athleticism but rather its ability to survive and reproduce.

Natural selection can alter a species in small ways, causing a population to change color or size over the course of several generations, according to The Natural History Museum. When this process happens over a relatively short period of time and in a species or small group of organisms, scientists call it " microevolution."

(Image credit: Leonello Calvetti/Getty Images)

But when given enough time and accumulated changes, natural selection can create entirely new species, a process known as "macroevolution," according to Derek Turner and Joyce C. havstad in "The Philosophy of Macroevolution." This long-term process is what turned into , amphibious mammals (such as an animal called Indohyus) into whales and a common ancestor of apes and humans into the people, chimps and gorillas we know today.

Darwin also described a form of natural selection that depends on an organism's success at attracting a mate - a process known as sexual selection, according to Nature Education. The colorful plumage of and the antlers of male deer are both examples of traits that evolved under this type of selection.

How did whales evolve?

One of the best examples scientists have of natural selection, is the evolution of whales. By using Darwin's theory as a guide, and understanding how natural selection works, biologists determined that the transition of early whales from land to water occurred in a series of predictable steps.

The evolution of the blowhole, for example, might have started with random genetic changes that resulted in at least one whale having its nostrils farther back on its head, according to Phys.org.

The whales with this adaptation would have been better suited to a marine lifestyle, since they would not have had to completely surface to breathe. Such individuals were more successful and had more offspring. In later generations, more genetic changes occurred, moving the nose farther back on the head.

Other body parts of early whales also changed. Front legs became flippers. Back legs disappeared. Their bodies became more streamlined, and they developed tail flukes to better propel themselves through water, according to the Natural History Museum.

Even though scientists could predict what early whales should look like, for a long time they lacked the fossil evidence to back up their claim. Creationists viewed this absence, not just with regard to whale evolution but more generally, as proof that evolution didn't occur, as pointed out in a Scientific American article.

(Image credit: Illustration by Robert W. Boessenecker)

However, since the early 1990s, scientists have found evidence from paleontology, developmental biology and genetics to support the idea that whales evolved from land mammals. These same lines of evidence support the theory of evolution as a whole.

In the first edition of "On the Origin of Species," Darwin speculated about how natural selection could cause a land mammal to turn into a whale. As a hypothetical example, Darwin used North American black bears ( Ursus americanus), which were known to catch insects by swimming in the water with their mouths open, according to the Darwin Correspondence Project.

"I can see no difficulty in a race of bears being rendered, by natural selection, more aquatic in their structure and habits, with larger and larger mouths, till a creature was produced as monstrous as a whale," he speculated.

The idea didn't go over very well with the public or with other scientists. Darwin was so embarrassed by the ridicule he received that the swimming-bear passage was removed from later editions of the book. Scientists now know that Darwin had the right idea but the wrong animal. Instead of looking at bears, he should have been looking at cows and hippopotamuses.

Other theories of evolution

Darwin wasn't the first or only scientist to develop a theory of evolution. Around the same time as Darwin, British biologist Alfred Russel Wallace independently came up with the theory of evolution by natural selection, according to the Natural History Museum. However this had little impact.

"The concept of evolution as a historical event was a hot topic among biologists and geologists prior to Darwin's book because there was so much evidence accumulating, but I suspect biological evolution hadn't really impinged on people outside of the academic bunker," Dr. P John D. Lambshead, a retired science research leader in marine biodiversity, ecology, and evolution at The Natural History Museum, London, told All About History Magazine. "As long as science knew of no mechanism to explain how evolution happened it could be safely dismissed as a crank idea."

Meanwhile, French biologist Jean-Baptiste Lamarck proposed that an organism could pass on traits to its offspring, though he was wrong about some of the details, according to the University of California's Museum of Paleontology.

Like Darwin, Lamarck believed that organisms adapted to their environments and passed on those adaptations. He thought organisms did this by changing their behavior and, therefore, their bodies - like an athlete working out and getting buff - and that those changes were passed on to offspring.

(Image credit: Anup Shah/Getty Images)

For example, Lamarck thought that giraffes originally had shorter necks but that, as trees around them grew taller, they stretched their necks to reach the tasty leaves and their offspring gradually evolved longer and longer necks. Lamarck also believed that life was somehow driven to evolve through the generations from simple to more complex forms, according to Understanding Evolution, an educational resource from the University of California Museum of Paleontology.

Though Darwin wasn't sure of the mechanism by which traits were passed on, he did not believe that evolution necessarily moved toward greater complexity, according to Understanding Evolution - rather, he believed that complexity arose through natural selection.

A Darwinian view of giraffe evolution, according to Quanta Magazine, would be that giraffes had natural variation in their neck lengths, and that those with longer necks were better able to survive and reproduce in environments full of tall trees, so that subsequent generations had more and more long-necked giraffes.

The main difference between the Lamarckian and Darwinian ideas of giraffe evolution is that there's nothing in the Darwinian explanation about giraffes stretching their necks and passing on an acquired characteristic.

What is modern evolutionary synthesis?

According to Pobiner, Darwin did not know anything about genetics. "He observed the pattern of evolution, but he didn't really know about the mechanism," she said. That came later, with the discovery of how genes encode different biological or behavioral traits, and how are passed down from parents to offspring. The incorporation of genetics into Darwin's theory is known as "modern evolutionary synthesis."

The physical and behavioral changes that make natural selection possible happen at the level of and genes within the gametes, the sperm or egg cells through which parents pass on genetic material to their offspring. Such changes are called . "Mutations are basically the raw material on which evolution acts," Pobiner said.

Mutations can be caused by random errors in DNA replication or repair, or by or radiation damage, according to Nature Education. Usually, mutations are either harmful or neutral, but in rare instances, a mutation might prove beneficial to the organism. If so, it will become more prevalent in the next generation and spread throughout the population.

In this way, natural selection guides the evolutionary process, preserving and adding up the beneficial mutations and rejecting the bad ones. "Mutations are random, but selection for them is not random," Pobiner said.

(Image credit: Shutterstock)

But natural selection isn't the only mechanism by which organisms evolve, she said. For example, genes can be transferred from one population to another when organisms migrate or immigrate - a process known as gene flow. And the frequency of certain genes can also change at random, which is called genetic drift.

The reason Lamarck's theory of evolution is generally wrong is that acquired characteristics don't affect the DNA of sperm and eggs. A giraffe's gametes, for example, aren't affected by whether it stretches its neck; they simply reflect the genes the giraffe inherited from its parents. But as Quanta reported, some aspects of evolution are Lamarckian.

For example, a Swedish study published in 2002 in the European Journal of Human Genetics found that the grandchildren of men who starved as children during a famine passed on better cardiovascular health to their grandchildren. Researchers hypothesize that although experiences such as food deprivation don't change the DNA sequences in the gametes, they may result in external modifications to DNA that turn genes "on" or "off."

Such changes, called epigenetic changes, do not modify the actual DNA sequence itself. For instance, a chemical modification called methylation can affect which genes are turned on or off. Such epigenetic changes can be passed down to offspring. In this way, a person's experiences could affect the DNA he or she passes down, analogous to the way Lamarck thought a giraffe craning its neck would affect the neck length of its offspring.

What is the evidence for evolution?

The Theory of Evolution is one of the best-substantiated theories in the history of science. It is supported by evidence from a wide variety of scientific disciplines, including genetics, which shows that different species have similarities in their DNA.

There is also evidence supporting the Theory of Evolution in paleontology and geology. This is through the fossil record, which shows how that species that existed in the past are different from those present today, according to Bruce S. Lieberman and Roger L. Kaesler in " Prehistoric Life: Evolution and the Fossil Record" (Wiley, 2010).

There is also evidence for Darwin's theory found in developmental biology. It has been discovered that species that seem very different as adults pass through similar stages of embryological development, suggesting a shared evolutionary past, according to the open-access textbook " Concepts of Biology."

Evidence for whale evolution from paleontology

(Image credit: Nobumichi Tamura/Stocktrek Images via Getty Images)

The critical piece of evidence was discovered in 1994, when paleontologists found the fossilized remains of Ambulocetus natans, which means "swimming-walking whale," according to a 2009 review published in the journal Evolution: Education and Outreach. Its forelimbs had fingers and small hooves, but its hind feet were enormous relative to its size. The animal was clearly adapted for swimming, but it was also capable of moving clumsily on land, much like a seal.

When it swam, the ancient creature moved like an , pushing back with its hind feet and undulating its spine and tail.

Modern whales propel themselves through the water with powerful beats of their horizontal tail flukes, but A. natans still had a whip-like tail and had to use its legs to provide most of the propulsive force needed to move through water.

In recent years, more and more of these transitional species, or "missing links," have been discovered, lending further support to Darwin's theory. For example, in 2007, a geologist discovered the fossil of an extinct aquatic mammal, , that was about the size of a cat and had hooves and a long tail.

Scientists think the animal belonged to a group related to cetaceans such as Ambulocetus natans. This creature is considered a "missing link" between artiodactyls - a group of hoofed mammals (even-toed ungulates) that includes hippos, pigs, and cows - and whales, according to the National Science Foundation.

Researchers knew that whales were related to artiodactyls, but until the discovery of this fossil, there were no known artiodactyls that shared physical characteristics with whales. After all, hippos, thought to be cetaceans' closest living relatives, are very different from whales. Indohyus, on the other hand, was an artiodactyl, indicated by the structure of its hooves and ankles, and it also had some similarities to whales, in the structure of its ears, for example.

Evidence for whale evolution from genetics & developmental biology

(Image credit: NOAA)

Genetic evidence also supports the idea that whales evolved from land mammals and provides information about the exact branching of the evolutionary tree. For instance, in 1999, researchers reported in the journal Proceedings of the National Academy of Sciences that according to genetic analysis of "jumping gene" sequences, which copy and paste themselves into genomes, hippos were whales' closest living relatives. Before 1985, researchers thought pigs were more closely related to whales, but this 1999 study overturned that idea, as the Associated Press reported.

In 2019, researchers reported in the journal Science Advances about which genes within the whale genome were inactivated during the process of the creature's evolution from land mammals, as Science Friday reported. The researchers could tell that certain genes, including one involved in making saliva, had been inactivated because there are remnants of them, which the researchers call genomic fossils, in whale genomes. This indicates that whales evolved from a salivating creature.

There's also evidence of cetacean evolution from developmental biology. Developmental biology illustrates the fact that animals that are very different as adults share similarities as embryos because they are evolutionarily related. For example, as embryos, cetaceans started to develop hind limbs, which disappear later in development, while the forelimbs remain and develop into flippers, according to the journal Evolution: Education and Outreach. This suggests that cetaceans evolved from a four-legged ancestor.

Is the theory of evolution controversial?

Despite the wealth of evidence from the fossil record, genetics and other fields of science, some people still question the theory of evolution's validity. Some politicians and religious leaders denounce the theory, invoking a higher being as a designer to explain the complex world of living things, especially humans.

School boards debate whether the theory of evolution should be taught alongside other ideas, such as intelligent design or creationism.

Mainstream scientists see no controversy. "A lot of people have deep religious beliefs and also accept evolution," Pobiner said, adding, "there can be real reconciliation."

Evolution is well supported by many examples of changes in various species leading to the diversity of life seen today. "Natural selection, or to put it another way - variation, heredity, and differential fitness - is the core theory of modern biology," John Lambshead explains. "It is to biology what, say quantum mechanics and special relativity are to physics or the atomic model is to chemistry."
Additional reporting by contributors Alina Bradford, Ashley P. Taylor and Callum McKelvie
Additional resources

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Charles Darwin's theory of evolution and natural selection isn't an idea with holes. It's one of the most solid theories in science. But what exactly is it?

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BC: Being Creative

BL: Being Literate

BN: Being Numerate

C: Communicating

MI&T: Managing Information and Thinking

MM: Managing Myself

SW: Staying Well

WWO: Working with others

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Managing information and thinking - Students would be able to tie in the connection between genetics (the topic they covered before evolution) and the diversity of living organisms and the way they evolve over time. Students will be doing a PhET simulation on the effects of natural selection and will use their own knowledge to predict the consequences to different scenarios

Being Literate - Students would be able to come up with their own definition of evolution through their own understanding. They would be able to explain in their own words the mechanism of natural selection.

Communicating and working well with others - Students would be working in pairs and come up with their own ideas through think-pair-share activities. They would be doing activities in groups/pairs in activities like the Human Hand Activity and the Research Poster presentation.

Being creative - Students would make up their own poster on the different evidence of evolution and present it in their own way. They would also do mind maps with the teacher and suggest phrases/words with regards to a topic.

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For class 2A and 2C

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Students would be able to expand their knowledge on the topic on evolution through research. They will be able to tie in their understanding of evolution how adaptation and variation in species has changed the way organisms survive.

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Students would be able to appreciate and recognise the important work of Charles Darwin and Alfred Wallace on the "Theory of Evolution"

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NoS1
NoS9

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Students will be able to define evolution and understand how natural selection works