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Do creationists effect the study of evolution?

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Do creationists effect the study of evolution?

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This article really helped me know that creationists don't believe in evolution.

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The theory of evolution by natural selection, first formulated in Darwin's book "On the Origin of Species" in 1859, is the process by which organisms change over time as a result of changes in heritable physical or behavioral traits. Changes that allow an organism to better adapt to its environment will help it survive and have more offspring.

Evolution by natural selection is one of the best substantiated theories in the history of science, supported by evidence from a wide variety of scientific disciplines, including paleontology, geology, genetics and developmental biology.

The theory has two main points, said Brian Richmond, curator of human origins at the American Museum of Natural History in New York City. "All life on Earth is connected and related to each other," and this diversity of life is a product of "modifications of populations by natural selection, where some traits were favored in and environment over others," he said.

More simply put, the theory can be described as "descent with modification," said Briana Pobiner, an anthropologist and educator at the Smithsonian Institution 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 can be misleading, Pobiner said. Here, "fitness" refers not to an organism's strength or athletic ability, but rather the ability to survive and reproduce.

For example, a study on human evolution on 1,900 students, published online in the journal Personality and Individual Differences in October 2017, found that many people may have trouble finding a mate because of rapidly changing social technological advances that are evolving faster than humans. "Nearly 1 in 2 individuals faces considerable difficulties in the domain of mating," said lead study author Menelaos Apostolou, an associate professor of social sciences at the University of Nicosia in Cyprus. "In most cases, these difficulties are not due to something wrong or broken, but due to people living in an environment which is very different from the environment they evolved to function in." [ If You Suck at Dating, It's Not You - It's Evolution]

In the first edition of "On the Origin of Species" in 1859, Charles 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, which were known to catch insects by swimming in the water with their mouths open:

"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. 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 instead been looking at cows and hippopotamuses.

The story of the origin of whales is one of evolution's most fascinating tales and one of the best examples scientists have of natural selection.

The last shore-dwelling ancestor of modern whales was Sinonyx, top left, a hyena-like animal. Over 60 million years, several transitional forms evolved: from top to bottom, Indohyus, Ambulocetus, Rodhocetus, Basilosaurus, Dorudon, and finally, the modern humpback whale.

Credit: NOAA

To understand the origin of whales, it's necessary to have a basic understanding of how natural selection works. Natural selection can change a species in small ways, causing a population to change color or size over the course of several generations. This is called "microevolution."

But natural selection is also capable of much more. Given enough time and enough accumulated changes, natural selection can create entirely new species, known as "macroevolution." It can turn dinosaurs into birds, amphibious mammals into whales and the ancestors of apes into humans.

Take the example of whales - using evolution as their guide and knowing how natural selection works, biologists knew 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 happened in the following way:

Random genetic changes resulted in at least one whale having its nostrils placed farther back on its head. Those animals with this adaptation would have been better suited to a marine lifestyle, since they would not have had to completely surface to breathe. Such animals would have been 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.

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. The colorful plumage of peacocks and the antlers of male deer are both examples of traits that evolved under this type of selection.

But Darwin wasn't the first or only scientist to develop a theory of evolution. The French biologist Jean-Baptiste Lamarck came up with the idea that an organism could pass on traits to its offspring, though he was wrong about some of the details. Around the same time as Darwin, British biologist Alfred Russel Wallace independently came up with the theory of evolution by natural selection.

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

The physical and behavioral changes that make natural selection possible happen at the level of DNA and genes. Such changes are called mutations. "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 chemical or radiation damage. Most times, 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.

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.

Even though scientists could predict what early whales should look like, they lacked the fossil evidence to back up their claim. Creationists took this absence as proof that evolution didn't occur. They mocked the idea that there could have ever been such a thing as a walking whale. But since the early 1990s, that's exactly what scientists have been finding.

The critical piece of evidence came in 1994, when paleontologists found the fossilized remains of Ambulocetus natans, an animal whose name literally means "swimming-walking whale." Its forelimbs had fingers and small hooves but its hind feet were enormous given its size. It 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 otter, 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 Ambulocetus 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, Richmond said.

Fossil "links" have also been found to support human evolution. In early 2018, a fossilized jaw and teeth found that are estimated to be up to 194,000 years old, making them at least 50,000 years older than modern human fossils previously found outside Africa. This finding provides another clue to how humans have evolved.

Despite the wealth of evidence from the fossil record, genetics and other fields of science, some people still question its validity. Some politicians and religious leaders denounce the theory of evolution, 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. "If someone could really demonstrate a better explanation than evolution and natural selection, [that person] would be the new Darwin," Richmond said.

Additional reporting by Contributor Alina Bradford and Staff Writer Tanya Lewis, Follow Tanya on Twitter. Follow us @livescience, Facebook & Google+.

Additional resources

The National Oceanic and Atmospheric Administration has a presentation on whale evolution.

To read the theory in its original form, see Darwin's book, "On the Origin of Species."

For an overview of natural selection, check out this article.

To understand the difference between a theory and fact, see this National Academy of Sciences website.

Related:

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The theory of evolution by natural selection, first formulated in Darwin's book "On the Origin of Species" in 1859, is the process by which organisms change over time as a result of changes in heritable physical or behavioral traits. Changes that allow an organism to better adapt to its environment will help it survive and have more offspring.

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What discoveries have been made to improve the study of evolution?

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What discoveries have been made to improve the study of evolution?

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This video helped me be able to explain natural selection.

# data[].attributes.headline
What discoveries have been made to improve the study of evolution?

# data[].attributes.subject
What discoveries have been made to improve the study of evolution?

# data[].attributes.body
This article helped me learn about how genetics are used in the study of evolution.

# data[].attributes.attachment_link.readable_text
An unusual species of fish that can walk and breathe air shows that these animals may be more capable of adapting to life on land than previously thought, researchers say.

The new findings may help explain how the ancient fish ancestors of humans colonized the land, the researchers said.

The evolution of the ancient fish that switched from living in water to living on land about 400 million years ago is one of the most pivotal moments in the history of the animal kingdom. These first four-limbed animals, the so-called stem tetrapods, ultimately gave rise to amphibians, reptiles, birds and mammals, including the largest animals to ever live on the planet.

When fish started moving onto land, "the fossil record suggests there was a great deal of diversity among fish, and thus a lot of competition between the fish," said lead study author Emily Standen, an evolutionary and comparative biomechanist at the University of Ottawa in Canada. "One can imagine there was a pretty good drive for those fish that could to get out of that environment and make use of opportunities on land." [Video: Unusual Fish that Can Walk & Breathe Hold Clues to Animal Evolution]

But just how ancient fish made this shift to terrestrial life still remains largely a mystery. To learn more about what happened when the now-extinct fish tried living on land, scientists investigated the bichir ( Polypterus senegalus), a modern African fish that has lungs for breathing air, and stubby fins it can use to pull itself along on land. The bichir possesses many traits similar to ones seen in fossils of stem tetrapods, the researchers said.

The scientists raised groups of juvenile bichir on land for eight months to see whether these fish differed in their anatomy and how they moved on land compared with bichir raised in the water. Researchers wanted to test how life on land might trigger changes in such fish.

Raising the fish on land posed some challenges.

"The number one difficulty we faced was how the heck to keep fish alive on land for months at a time," Standen told Live Science. "I designed and built an aquarium setup that had kept a few millimeters of water on its floor, enough to keep the fish moist. In addition, I used misters, like you see in the lettuce aisle at grocery stores to freshen the vegetables, to keep the fish moist and in a very humid environment that helped them survive."

The researchers discovered the bichir raised on land were dramatically different than those raised in water. The land-raised fish lifted their heads higher, held their fins closer to their bodies, took faster steps and undulated their tails less frequently and had fins that slipped less often than bichir raised in water. These land-based fish also underwent changes in their skeletons and musculature that likely paved the way for their changes in behavior. All in all, these alterations helped bichir move more effectively on land.

"I'm very surprised the fish survived so well on land," said Standen, who conducted this research while she was a postdoctoral researcher at McGill University in Montreal. "That was an initial gamble with this experiment - could the fish even be raised on land?"

These findings reveal the bichir is more plastic - that is, malleable - during its development than previously thought. This plasticity is what made this fish capable of growing up very differently depending on its environment.

Given the anatomical similarities found between the bichir and stem tetrapods, the researchers suggest the animals' common ancestor could have possessed the kind of plasticity seen in the bichir today. If so, "this raises the possibility that plasticity may have also existed in stem tetrapods to facilitate their transition to land," Standen said.

"Fish that had the plasticity to allow them to move out onto land benefited by removing themselves from a very competitive environment into a new habitat of plants and insects supplying shelter and food resources, free of major predation or competition," Standen added. Over time, traits permitted by such plasticity may have proven advantageous enough to evolve into permanent fixtures in these ancient animals, she said.

Uncovering evidence of whether or not stem tetrapods really displayed such plasticity is very challenging. "The best way to find such evidence is to unearth fossils of a single population of these stem tetrapod fishes and look for natural variation in it," study co-author Hans Larsson, a vertebrate paleontologist at McGill University, told Live Science. "If we can, we might be able to find fossils that showed this population demonstrated some degree of plasticity."

Future research can seek to uncover the genetic and developmental mechanisms underlying the plasticity of the bichir, Larsson said. The researchers also want to raise multiple generations of bichir on land "to see how far this plasticity goes, how consistent developmental changes are in the long run," Standen said.

Standen, Larsson and their colleague Trina Du detailed their findings in the Aug. 28 issue of the journal Nature.

Follow Live Science @livescience, Facebook & Google+. Originally published on Live Science.

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Unusual Fish that 'Walks' Holds Clues to Animal Evolution

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Unusual fish that walk and breathe air turn out quite differently when raised on land, rather than in water. Their development holds clues to a pivotal moment in animal evolution, when the first creatures moved out of the water and onto land.

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How does natural selection affect the study of evolution?

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How does natural selection affect the study of evolution?

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This article was really helpful to me because it explained that even the same species that live in different places adjust differently.

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" Nothing in biology makes sense except in light of evolution" - Theodosius Dobzhansky (1973)

INTRODUCTION
Understanding natural selection is crucial to understanding wildlife ecology and practically any other topic in biology. This chapter gives you the basic concepts of natural selection so that you will be able to apply this important principle throughout this course, as well as in your day-to-day life.

WHAT IS NATURAL SELECTION?
Natural selection is the process by which the organisms in a population that are best adapted to the environment increase in frequency relative to less well-adapted forms, over a number of generations. The consequence of natural selection is that through time species (generally) develop characteristics that make them increasingly well-adapted to their environments, ultimately resulting in a world filled with a fascinating diversity of life forms. Natural selection is a simple but immensely powerful concept, and is a pillar of our understanding of biology at all organizational scales. This process commonly is summed up as "the survival of the fittest" in popular culture, although this simplification leaves out some of the important subtleties of natural selection, as described below.

WHAT ARE THE CONDITIONS NECESSARY FOR NATURAL SELECTION TO OCCUR?
Four general conditions necessary for natural selection to occur are:

A. More organisms are born than can survive.
B. Organisms vary in their characteristics, even within a species.
C. Variation is inherited.
D. Differences in reproduction and survival are due to variation among organisms.

If all four of these conditions occur, which they commonly do in both natural and human-influenced ecological systems, then natural selection will occur. If any of these is not true, then natural selection cannot occur. Let's consider each of these in a bit more detail.

A. MORE ORGANISMS ARE BORN THAN CAN SURVIVE
If every individual organism born were to survive and reproduce to its maximum ability, we would expect explosive exponential growth in populations to occur regularly. The fact that this rarely happens (and never continues for long) indicates that there are many individuals born into the world with low probabilities of survival and reproduction. Let's illustrate this concept with rabbits and assume they have an average litter size of 10 offspring (5 males, 5 females) and a generation time of approximately 4 months. Starting with a single female rabbit, and keeping track of just female organisms for the sake of simplicity, we will have 5 new female rabbits in 4 months. In four more months those new female rabbits will be reproducing, and we will have approximately 5×5=25 new female offspring. Those 25 rabbits will in turn produce 25×5=625 offspring in 4 months, and the process will continue so that after 10 generations, a mere 40 months, the number of new female rabbits born would be 50 billion! There is of course not enough space or food for this many rabbits in the real world and in a natural ecosystem forces such as competition, disease, predators, and harsh abiotic (physical) conditions prevent such exponential growth from occurring for long. Competition, disease, predation, and abiotic conditions are among the most important limiting factors in ecological systems, and they quite often shape the path of natural selection.

B. ORGANISMS VARY, EVEN WITHIN A SPECIES
Variation among individual organisms of the same species has been well documented, and you can illustrate this to yourself by thinking of the range of differences in physical appearance and aptitudes that exists among people you know. Of course, variation among individuals occurs in other species as well and this variation fuels the process of natural selection because it gives natural selection something to "act on." That is, if a faster gazelle were better able to elude the claws of a cheetah, then this gazelle would be more likely to survive. If all of the organisms within a population were completely identical, it would not be possible for natural selection to occur; if all gazelles ran the same speed, then there would be no "faster" individuals to avoid the clutches of predators. There are biomechanical limits, of course, to just how fast a gazelle can run and eventually all healthy adult gazelles will be able to run at the same maximum speed. However, natural selection also acts on other factors, such as the ability to dodge back and forth or to detect the predator from further away. Meanwhile, natural selection also favors cheetahs that can overcome the speed and agility of gazelles. When you start to realize that each species varies in hundreds of different ways and has to constantly adapt to changing conditions (including behavior of its predators or of its prey), you begin to understand how the complex and often bizarre life on this planet has developed through time.

C. VARIATION IS INHERITED
In general the causes behind variation in organisms can be divided into two categories, environmental and heritable. Environmental variation is that which has no genetic basis, but is the result of the conditions under which an individual lives. For example, our generation tends to have a diet higher in protein than that of our grandparents and in general we grow taller than our grandparents did. This is due to the food we consume, not to any underlying genetic superiority. If you prefer a more "natural" example, imagine predators existing in sites rich vs. poor in prey species. If a predator is raised in a site rich in prey, it likely will eat more and grow larger. On the other hand, if raised in a place where prey are limiting, they would be more likely to remain smaller when fully mature, simply because they could not acquire sufficient food. Only when variation among organisms is inherited from the previous generation, i.e. it has a genetic basis, will natural selection be able to occur. Natural selection cannot act on variation that is due purely to environmental conditions. In reality, variation among organisms often is the result of a combination of environmental and heritable causes, as illustrated by the variation in height among humans. People may be short because they have short parents who possess genes for short stature that they have passed down to their offspring. However, people may also be short if they did not receive proper nutrition when they were in their growing years, even if they do possess genes for a tall stature. The first cause for shortness is heritable, whereas the second is environmental, but natural selection would only be able to act on height to the degree that it is in fact heritable.

D. DIFFERENCES IN REPRODUCTION AND SURVIVAL ARE DUE TO VARIATION AMONG ORGANISMS
It is widely observed that the probability of survival and reproduction often varies tremendously among organisms. Furthermore, differences in the traits of organisms will often be the cause of their differences in survival and reproduction. It is readily apparent that the organisms with the highest rates of survival and reproduction will be those that have their genes best represented in the next generation, and hence natural selection occurs whenever variation in survival and reproduction is at least partially caused by a heritable trait that varies among organisms.

Let's look at the example of tule perch to demonstrate this. Tule perch are small (4-6 inch long) fish that occur only in the fresh waters of Central California. Each female tule perch gives birth to 15-40 young, which are essentially miniature adults (which swim away after being born). It turns out that the number and size of young produced by a female is an inherited trait and is an adaptation to the environment in which the perch live. Thus female tule perch that live in the Russian River produce 25-35 small young and typically become pregnant in their first year of life. In contrast, tule perch in Clear Lake typically produce 15-20 large young and wait until their second year to become pregnant. The reason for the striking difference in life histories of the two populations is the nature of the environments. The Russian River is a large, isolated coastal stream that fluctuates enormously in flow from year to year; in this harsh system each adult female has a relatively low probability of survival from year to year so natural selection has favored females that produce a lot of young quickly. Clear Lake, in contrast, is a relatively benign environment where each adult female has a fairly high probability of survival from year to year, provided they are large enough to escape predators. Thus natural selection favors females that produce large young and that devote all their energy in the first year to becoming even larger. If both forms were brought into laboratory aquaria and raised under identical conditions, the Russian River fish would still produce lots of small young and Clear Lake fish would still produce comparatively small numbers of large young.

Table of Contents

1. Roots of the modern environmental dilemma: A brief history of the relationship between humans and wildlife
2. A history of wildlife in North America
3. Climatic determinants of global patterns of biodiversity
4. Biodiversity
5. Natural selection
6. Principles of ecology
7. Niche and habitat
8. Conservation biology
9. Conservation in the USA: legislative milestones
10. Alien invaders
11. Wildlife and Pollution
12. What you can do to save wildlife

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" Nothing in biology makes sense except in light of evolution" - Theodosius Dobzhansky (1973) INTRODUCTION Understanding natural selection is crucial to understanding wildlife ecology and practically any other topic in biology. This chapter gives you the basic concepts of natural selection so that you will be able to apply this important principle throughout this course, as well as in your day-to-day life.

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How does natural selection affect the study of evolution?

# data[].attributes.subject
How does natural selection affect the study of evolution?

# data[].attributes.body
This article helped me understand how natural selection works.

# data[].attributes.attachment_link.readable_text
The theory of evolution by natural selection, first formulated in Darwin's book "On the Origin of Species" in 1859, is the process by which organisms change over time as a result of changes in heritable physical or behavioral traits. Changes that allow an organism to better adapt to its environment will help it survive and have more offspring.

Evolution by natural selection is one of the best substantiated theories in the history of science, supported by evidence from a wide variety of scientific disciplines, including paleontology, geology, genetics and developmental biology.

The theory has two main points, said Brian Richmond, curator of human origins at the American Museum of Natural History in New York City. "All life on Earth is connected and related to each other," and this diversity of life is a product of "modifications of populations by natural selection, where some traits were favored in and environment over others," he said.

More simply put, the theory can be described as "descent with modification," said Briana Pobiner, an anthropologist and educator at the Smithsonian Institution 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 can be misleading, Pobiner said. Here, "fitness" refers not to an organism's strength or athletic ability, but rather the ability to survive and reproduce.

For example, a study on human evolution on 1,900 students, published online in the journal Personality and Individual Differences in October 2017, found that many people may have trouble finding a mate because of rapidly changing social technological advances that are evolving faster than humans. "Nearly 1 in 2 individuals faces considerable difficulties in the domain of mating," said lead study author Menelaos Apostolou, an associate professor of social sciences at the University of Nicosia in Cyprus. "In most cases, these difficulties are not due to something wrong or broken, but due to people living in an environment which is very different from the environment they evolved to function in." [ If You Suck at Dating, It's Not You - It's Evolution]

In the first edition of "On the Origin of Species" in 1859, Charles 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, which were known to catch insects by swimming in the water with their mouths open:

"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. 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 instead been looking at cows and hippopotamuses.

The story of the origin of whales is one of evolution's most fascinating tales and one of the best examples scientists have of natural selection.

The last shore-dwelling ancestor of modern whales was Sinonyx, top left, a hyena-like animal. Over 60 million years, several transitional forms evolved: from top to bottom, Indohyus, Ambulocetus, Rodhocetus, Basilosaurus, Dorudon, and finally, the modern humpback whale.

Credit: NOAA

To understand the origin of whales, it's necessary to have a basic understanding of how natural selection works. Natural selection can change a species in small ways, causing a population to change color or size over the course of several generations. This is called "microevolution."

But natural selection is also capable of much more. Given enough time and enough accumulated changes, natural selection can create entirely new species, known as "macroevolution." It can turn dinosaurs into birds, amphibious mammals into whales and the ancestors of apes into humans.

Take the example of whales - using evolution as their guide and knowing how natural selection works, biologists knew 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 happened in the following way:

Random genetic changes resulted in at least one whale having its nostrils placed farther back on its head. Those animals with this adaptation would have been better suited to a marine lifestyle, since they would not have had to completely surface to breathe. Such animals would have been 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.

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. The colorful plumage of peacocks and the antlers of male deer are both examples of traits that evolved under this type of selection.

But Darwin wasn't the first or only scientist to develop a theory of evolution. The French biologist Jean-Baptiste Lamarck came up with the idea that an organism could pass on traits to its offspring, though he was wrong about some of the details. Around the same time as Darwin, British biologist Alfred Russel Wallace independently came up with the theory of evolution by natural selection.

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

The physical and behavioral changes that make natural selection possible happen at the level of DNA and genes. Such changes are called mutations. "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 chemical or radiation damage. Most times, 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.

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.

Even though scientists could predict what early whales should look like, they lacked the fossil evidence to back up their claim. Creationists took this absence as proof that evolution didn't occur. They mocked the idea that there could have ever been such a thing as a walking whale. But since the early 1990s, that's exactly what scientists have been finding.

The critical piece of evidence came in 1994, when paleontologists found the fossilized remains of Ambulocetus natans, an animal whose name literally means "swimming-walking whale." Its forelimbs had fingers and small hooves but its hind feet were enormous given its size. It 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 otter, 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 Ambulocetus 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, Richmond said.

Fossil "links" have also been found to support human evolution. In early 2018, a fossilized jaw and teeth found that are estimated to be up to 194,000 years old, making them at least 50,000 years older than modern human fossils previously found outside Africa. This finding provides another clue to how humans have evolved.

Despite the wealth of evidence from the fossil record, genetics and other fields of science, some people still question its validity. Some politicians and religious leaders denounce the theory of evolution, 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. "If someone could really demonstrate a better explanation than evolution and natural selection, [that person] would be the new Darwin," Richmond said.

Additional reporting by Contributor Alina Bradford and Staff Writer Tanya Lewis, Follow Tanya on Twitter. Follow us @livescience, Facebook & Google+.

Additional resources

The National Oceanic and Atmospheric Administration has a presentation on whale evolution.

To read the theory in its original form, see Darwin's book, "On the Origin of Species."

For an overview of natural selection, check out this article.

To understand the difference between a theory and fact, see this National Academy of Sciences website.

Related:

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The theory of evolution by natural selection, first formulated in Darwin's book "On the Origin of Species" in 1859, is the process by which organisms change over time as a result of changes in heritable physical or behavioral traits. Changes that allow an organism to better adapt to its environment will help it survive and have more offspring.

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How do genetic mutations affect the study of evolution?

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How do genetic mutations affect the study of evolution?

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This video helps me know what DNA is and how it works.