How is evolution proven

In this way, natural selection guides the evolutionary process, preserving and adding up the beneficial mutations and rejecting the bad ones.

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 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.

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.

Even though scientists could predict what early whales should look like, 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.

But since the early s, 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. The critical piece of evidence was discovered in , when paleontologists found the fossilized remains of Ambulocetus natans , which means "swimming-walking whale," according to a 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 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 A. 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 , a geologist discovered the fossil of an extinct aquatic mammal, called Indohyus , 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. 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 , 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 , researchers thought pigs were more closely related to whales, but this study overturned that idea, as the Associated Press reported. In , 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.

And they always have, which is what Darwin suspected when he was defining what a species actually was. On the Origin of Species by Means of Natural Selection, was first published in after Darwin returned home from a five-year voyage of discovery.

In the seminal book, Darwin argued that organisms gradually evolved through a process called 'natural selection' -- often known as survival of the fittest.

His pioneering work was considered highly controversial because it contradicted the Bible's account of creation. Subspecies form, diversify and increase in number in a different way in non-terrestrial and terrestrial habitats, and this in turn affects how subspecies may eventually become species. For example, if a natural barrier like a mountain range gets in the way, it can separate animal groups and send them off on their own evolutionary journeys. Flying and marine mammals -- such as bats and dolphins -- have fewer physical barriers in their environment.

The research explored whether subspecies could be considered an early stage of speciation -- the formation of a new species. But evolution isn't determined by the same factors in all groups and for the first time we know why because we've looked at the strength of the relationship between species richness and subspecies richness. The research acts as another scientific warning that the human impact on the habitat of animals will not only affect them now, but will affect their evolution in the future.

This information could be used by conservationists to help them determine where to focus their efforts. The impact on animals will vary depending on how their ability to roam, or range, is affected.

Animal subspecies tend to be ignored, but they play a pivotal role in longer term future evolution dynamics. Notes to editors: What Darwin said on page 55 in 'On the Origin of Species': "From looking at species as only strongly-marked and well-defined varieties, I was led to anticipate that the species of the larger genera in each country would oftener present varieties, than the species of the smaller genera; for wherever many closely related species i.

Among those hundreds of thousands of scientific reports, he found none. Krauss, now at Arizona State University, were similarly fruitless. Creationists retort that a closed-minded scientific community rejects their evidence. Yet according to the editors of Nature , Science and other leading journals, few antievolution manuscripts are even submitted.

Some antievolution authors have published papers in serious journals. Those papers, however, rarely attack evolution directly or advance creationist arguments; at best, they identify certain evolutionary problems as unsolved and difficult which no one disputes. In short, creationists are not giving the scientific world good reason to take them seriously.

The disagreements among even evolutionary biologists show how little solid science supports evolution. Evolutionary biologists passionately debate diverse topics: how speciation happens, the rates of evolutionary change, the ancestral relationships of birds and dinosaurs, whether Neandertals were a species apart from modern humans, and much more.

These disputes are like those found in all other branches of science. Acceptance of evolution as a factual occurrence and a guiding principle is nonetheless universal in biology. Unfortunately, dishonest creationists have shown a willingness to take scientists' comments out of context to exaggerate and distort the disagreements.

Anyone acquainted with the works of paleontologist Stephen Jay Gould of Harvard University knows that in addition to co-authoring the punctuated-equilibrium model, Gould was one of the most eloquent defenders and articulators of evolution. Punctuated equilibrium explains patterns in the fossil record by suggesting that most evolutionary changes occur within geologically brief intervals—which may nonetheless amount to hundreds of generations.

Yet creationists delight in dissecting out phrases from Gould's voluminous prose to make him sound as though he had doubted evolution, and they present punctuated equilibrium as though it allows new species to materialize overnight or birds to be born from reptile eggs.

Fossil record shows a succession of hominins, with features becoming progressively less apelike and more modern. When confronted with a quotation from a scientific authority that seems to question evolution, insist on seeing the statement in context. Almost invariably, the attack on evolution will prove illusory.

This surprisingly common argument reflects several levels of ignorance about evolution. The first mistake is that evolution does not teach that humans descended from monkeys; it states that both have a common ancestor.

The parent species may survive indefinitely thereafter, or it may become extinct. The origin of life remains very much a mystery, but biochemists have learned about how primitive nucleic acids, amino acids and other building blocks of life could have formed and organized themselves into self-replicating, self-sustaining units, laying the foundation for cellular biochemistry.

Astrochemical analyses hint that quantities of these compounds might have originated in space and fallen to Earth in comets, a scenario that may solve the problem of how those constituents arose under the conditions that prevailed when our planet was young.

Creationists sometimes try to invalidate all of evolution by pointing to science's current inability to explain the origin of life. But even if life on Earth turned out to have a nonevolutionary origin for instance, if aliens introduced the first cells billions of years ago , evolution since then would be robustly confirmed by countless microevolutionary and macroevolutionary studies.

Mathematically, it is inconceivable that anything as complex as a protein, let alone a living cell or a human, could spring up by chance. Chance plays a part in evolution for example, in the random mutations that can give rise to new traits , but evolution does not depend on chance to create organisms, proteins or other entities. As long as the forces of selection stay constant, natural selection can push evolution in one direction and produce sophisticated structures in surprisingly short times.

But in the s Richard Hardison, then at Glendale College, wrote a computer program that generated phrases randomly while preserving the positions of individual letters that happened to be correctly placed in effect, selecting for phrases more like Hamlet's. On average, the program re-created the phrase in just iterations, less than 90 seconds. Even more amazing, it could reconstruct Shakespeare's entire play in just four and a half days. The Second Law of Thermodynamics says that systems must become more disordered over time.

Living cells therefore could not have evolved from inanimate chemicals, and multicellular life could not have evolved from protozoa. This argument derives from a misunderstanding of the Second Law. If it were valid, mineral crystals and snowflakes would also be impossible, because they, too, are complex structures that form spontaneously from disordered parts. The Second Law actually states that the total entropy of a closed system one that no energy or matter leaves or enters cannot decrease.

Entropy is a physical concept often casually described as disorder, but it differs significantly from the conversational use of the word. More important, however, the Second Law permits parts of a system to decrease in entropy as long as other parts experience an offsetting increase. Thus, our planet as a whole can grow more complex because the sun pours heat and light onto it, and the greater entropy associated with the sun's nuclear fusion more than rebalances the scales.

Simple organisms can fuel their rise toward complexity by consuming other forms of life and nonliving materials. Mutations are essential to evolution theory, but mutations can only eliminate traits. They cannot produce new features. On the contrary, biology has catalogued many traits produced by point mutations changes at precise positions in an organism's DNA —bacterial resistance to antibiotics, for example. Mutations that arise in the homeobox Hox family of development-regulating genes in animals can also have complex effects.

Hox genes direct where legs, wings, antennae and body segments should grow. In fruit flies, for instance, the mutation called Antennapedia causes legs to sprout where antennae should grow. These abnormal limbs are not functional, but their existence demonstrates that genetic mistakes can produce complex structures, which natural selection can then test for possible uses.

Moreover, molecular biology has discovered mechanisms for genetic change that go beyond point mutations, and these expand the ways in which new traits can appear.

Functional modules within genes can be spliced together in novel ways. Whole genes can be accidentally duplicated in an organism's DNA, and the duplicates are free to mutate into genes for new, complex features. Comparisons of the DNA from a wide variety of organisms indicate that this is how the globin family of blood proteins evolved over millions of years.

Natural selection might explain microevolution, but it cannot explain the origin of new species and higher orders of life. Evolutionary biologists have written extensively about how natural selection could produce new species.

For instance, in the model called allopatry, developed by Ernst Mayr of Harvard University, if a population of organisms were isolated from the rest of its species by geographical boundaries, it might be subjected to different selective pressures.

Changes would accumulate in the isolated population. If those changes became so significant that the splinter group could not or routinely would not breed with the original stock, then the splinter group would be reproductively isolated and on its way toward becoming a new species. Nautilus shell has become a symbol of evolution and biological change. As the creature that occupies the shell outgrows one chamber, it builds another, larger chamber next to it, creating a growing spiral pattern.

Natural selection is the best studied of the evolutionary mechanisms, but biologists are open to other possibilities as well. Biologists are constantly assessing the potential of unusual genetic mechanisms for causing speciation or for producing complex features in organisms.

Lynn Margulis of the University of Massachusetts Amherst and others have persuasively argued that some cellular organelles, such as the energy-generating mitochondria, evolved through the symbiotic merger of ancient organisms.

Thus, science welcomes the possibility of evolution resulting from forces beyond natural selection. Yet those forces must be natural; they cannot be attributed to the actions of mysterious creative intelligences whose existence, in scientific terms, is unproved. Speciation is probably fairly rare and in many cases might take centuries. Furthermore, recognizing a new species during a formative stage can be difficult because biologists sometimes disagree about how best to define a species.

The most widely used definition, Mayr's Biological Species Concept, recognizes a species as a distinct community of reproductively isolated populations—sets of organisms that normally do not or cannot breed outside their community. In practice, this standard can be difficult to apply to organisms isolated by distance or terrain or to plants and, of course, fossils do not breed. Biologists therefore usually use organisms' physical and behavioral traits as clues to their species membership.

Nevertheless, the scientific literature does contain reports of apparent speciation events in plants, insects and worms. In most of these experiments, researchers subjected organisms to various types of selection—for anatomical differences, mating behaviors, habitat preferences and other traits—and found that they had created populations of organisms that did not breed with outsiders.

For example, William R. Salt of the University of California, Davis, demonstrated that if they sorted a group of fruit flies by their preference for certain environments and bred those flies separately over 35 generations, the resulting flies would refuse to breed with those from a very different environment.

Evolutionists cannot point to any transitional fossils—creatures that are half reptile and half bird, for instance. Actually, paleontologists know of many detailed examples of fossils intermediate in form between various taxonomic groups. One of the most famous fossils of all time is Archaeopteryx , which combines feathers and skeletal structures peculiar to birds with features of dinosaurs. A flock's worth of other feathered fossil species, some more avian and some less, has also been found.

A sequence of fossils spans the evolution of modern horses from the tiny Eohippus. An amazing fossil creature from million years ago named Tiktaalik embodies the predicted and long-sought transition of certain fishes to life on land. Whales had four-legged ancestors that walked on land, and creatures known as Ambulocetus and Rodhocetus helped to make that transition.

Fossil seashells trace the evolution of various mollusks through millions of years. Perhaps 20 or more hominins not all of them our ancestors fill the gap between Lucy the australopithecine and modern humans. Creationists, though, dismiss these fossil studies. They argue that Archaeopteryx is not a missing link between reptiles and birds—it is just an extinct bird with reptilian features. They want evolutionists to produce a weird, chimeric monster that cannot be classified as belonging to any known group.