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. Even if a creationist does accept a fossil as transitional between two species, he or she may then insist on seeing other fossils intermediate between it and the first two.
These frustrating requests can proceed ad infinitum and place an unreasonable burden on the always incomplete fossil record. Nevertheless, evolutionists can cite further supportive evidence from molecular biology. All organisms share most of the same genes, but as evolution predicts, the structures of these genes and their products diverge among species, in keeping with their evolutionary relationships.
These molecular data also show how various organisms are transitional within evolution. Living things have fantastically intricate features—at the anatomical, cellular and molecular levels—that could not function if they were any less complex or sophisticated. The only prudent conclusion is that they are the products of intelligent design, not evolution. In theologian William Paley wrote that if one finds a pocket watch in a field, the most reasonable conclusion is that someone dropped it, not that natural forces created it there.
By analogy, Paley argued, the complex structures of living things must be the handiwork of direct, divine invention. Darwin wrote On the Origin of Species as an answer to Paley: he explained how natural forces of selection, acting on inherited features, could gradually shape the evolution of ornate organic structures. Generations of creationists have tried to counter Darwin by citing the example of the eye as a structure that could not have evolved.
The eye's ability to provide vision depends on the perfect arrangement of its parts, these critics say. Natural selection could thus never favor the transitional forms needed during the eye's evolution—what good is half an eye? Biology has vindicated Darwin: researchers have identified primitive eyes and light-sensing organs throughout the animal kingdom and have even tracked the evolutionary history of eyes through comparative genetics.
It now appears that in various families of organisms, eyes have evolved independently. Today's intelligent-design advocates are more sophisticated than their predecessors, but their arguments and goals are not fundamentally different.
They criticize evolution by trying to demonstrate that it could not account for life as we know it and then insist that the only tenable alternative is that life was designed by an unidentified intelligence. Recent discoveries prove that even at the microscopic level, life has a quality of complexity that could not have come about through evolution.
One easy-to-understand example of how humans have evolved over recent centuries is how, on some continents, our bodies have adapted to tolerate the most abundant food sources common to that region. Around 11, years ago , for instance, adult humans were unable to digest lactose — the sugar in milk.
As humans in some regions began to rely on dairy farming as a source of nourishment, our bodies adjusted over time to be more able to digest this food, which, previously, was only tolerated by infants and toddlers. We can see evidence of this evolution today because humans in areas with a long tradition of dairy farming — such as Europe — are much more tolerant of lactose in their diet than people in regions that do not have a heritage of dairy farming — such as Asia.
Around 5 percent of people descended from Northern Europeans are lactose intolerant , compared with more than 90 percent of people of East Asian descent. Another source of evidence for recent human evolution cited by biologists is the Framingham Heart Study — the longest-running multigenerational medical study in the world. The Framingham Heart Study is ongoing, and it has become an important repository for scientific data, not only relating to heart disease but also on changing trends in human health overall.
Scientists say that the Framingham data demonstrate that natural selection influenced the Framingham population — reducing height, increasing weight, lowering cholesterol levels, and lowering systolic blood pressures. Importantly, the data do not show that average weight is increasing in Framingham because the women in the study are eating more. Instead, people with genes that affect these traits tend to have more children, meaning that these traits will become more common with subsequent generations.
But the Dutch were not always the tallest people on Earth. The researchers observe that in the midth century, the average height of Dutch soldiers was centimeters, which was well below the average of soldiers from other European countries and tiny compared with American soldiers, who were 5—8 centimeters taller than the average Dutch soldier. But Dutch men have experienced a relatively sudden growth spurt, adding an extra 20 centimeters to their average height over the past years.
During the same period, American men have only added 6 centimeters to their average height, and men from other European countries have struggled to keep pace with their neighbors from the Netherlands. Splitting one species into two takes millions of years, but we can sometimes catch this happening. A huge new source of evidence for evolution came with the discovery of DNA, which is shared by all life on Earth. DNA changes slowly as mutations accumulate. Read more: Curious Kids: are humans going to evolve again?
Hello, curious kids! Ask an adult to send your question to curiouskids theconversation. Portsmouth Climate Festival — Portsmouth, Portsmouth. In research with a population of guppies, the scientists observed male colour patterns impacting their ability to make babies and survive longer. Working in a river in Trinidad, the researchers determined which male guppies would contribute more offspring to the population as well as which would live longer and which would have a shorter lifespan.
It involved transplanting guppies from a river with a diverse community of predators into a river with no predators - except for one other fish species, an occasional predator - to record how the guppies would evolve and how they might impact their environment. When they returned the guppies to the river and new unmarked guppies showed up, the latter were marked and samples of their scales were taken for study. The research also found that males with more or larger orange and black spots produce more offspring, while males with black spots have a higher risk of mortality.
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