Since I am currently out of the country, I regrettably was not able to attend Dr. Though I missed seeing him in person, by the way, his usual lecture can be viewed on YouTube. The book covers his arguments in much more detail. This stands in contrast to many treatments of evolution, which have a tendency to confuse readers by conflating different meanings of the word e. No one disputes that allele frequencies in populations change over time or that different organisms have lived on the planet at different times.
Furthermore, no one disagrees that natural selection as well as nonselective mechanisms such as genetic drift plays a role in this process. At 17, Owen feels like his life is finally on track. As he struggled to socialize and form Cataclysmic floods.
Unprecedented heat waves and protracted droughts. Devastating wildfires breaking The little-known Amur River, the 10th longest in the world, acts as the natural border of Russia and Book Club Discussion. A deliciously strange and daringly original novel from Pulitzer Prize finalist Margaret Verble. About Discuss. Reader Reviews. Who Said Common sense is genius dressed in its working clothes. Annual Reports. Media Center. Our Partners. Need a Speaker? Our Impact. Our Research. View All Forbes.
Financial Times. Washington Post. We support teachers How it Works. Online Resources. We investigate science education. Donate Our Work We support teachers. We block threats to science education. In the Press. DIYSci Activities. Reports of the National Center for Science Education. Why Evolution is True. New York: Viking Press, The vast majority of species — more than 99 percent of them — go extinct without leaving any descendants.
It simply means that we can always look back in time, using either DNA sequences or fossils, and find descendants joining at their ancestors. By sequencing the DNA of various species and measuring how similar these sequences are, we can reconstruct their evolutionary relationships. The fifth part of evolutionary theory is what Darwin clearly saw as his greatest intellectual achievement: the idea of natural selection. Over time, the population will gradually become more and more suited to its environment as helpful mutations arise and spread through the population, while deleterious ones are weeded out.
Natural selection is not a master engineer, but a tinkerer. Evolution is like an architect who cannot design a building from scratch, but must build every new structure by adapting a preexisting building, keeping the structure habitable all the while.
So natural selection does not yield perfection — only improvements over what came before. It produces fitter , not the fittest. According to the Oxford English Dictionary , a scientific theory is. There are two points I want to emphasize here. First, in science, a theory is much more than just a speculation about how things are: it is a well-thought-out group of propositions meant to explain facts about the real world.
All scientific truth is provisional, subject to modification in light of new evidence. In the process of becoming truths, or facts, scientific theories are usually tested against alternative theories. So how do we test evolutionary theory against the still popular alternative view that life was created and remained unchanged thereafter?
There are actually two kinds of evidence. The first comes form using the six tenets of Darwinism to make testable predictions. Rather, it predicts what we should find in living or ancient species when we study them. The crust of the earth is a vast museum; but the natural collections have been made only at intervals of time immensely remote.
Fossils have been known since ancient times: Aristotle discussed them, and fossils of the beaked dinosaur Protoceratops may have given rise to the mythological griffin of the ancient Greeks. The formation of fossils is straightforward, but requires a very specific set of circumstances. How incomplete? The total number of species that ever lived on earth has been estimated to range between 17 million probably a drastic underestimate given that at least 10 million species are alive today and 4 billion.
Since we have discovered around , different fossil species, we can estimate that we have fossil evidence of only 0. Figure 3. The fossil record showing first appearance of various forms of life that arose since the earth formed 4, million years ago MYA. Groups appear on the scene in an orderly evolutionary fashion, with many arising after known fossil transitions from ancestors.
Instead, forms of life appear in the record in evolutionary sequence, and then evolve and split. What really excites people — biologists and paleontologists among them — are transitional forms : those fossils that span the gap between two very different kinds of living organisms. Showing common ancestry of two groups, then, does not require that we produce fossils of the precise single species that was their common ancestor, or even species on the direct line of descent from an ancestor to descendant.
Rather, we need only produce fossils having the types of traits that link two groups together, and, importantly, we must also have the dating evidence showing that those fossils occur at the right time in the geological record. One of the greatest fulfilled predictions of evolutionary biology is the discovery, in , of a transitional form between fish and amphibians. This is the fossils species Tiktaalik roseae , which tells us a lot about how vertebrates came to live on the land. Tiktaalik shows that our ancestors were flat-headed predatory fish who lurked in the shallow waters of streams.
It is a fossil that marvelously connects fish with amphibians. And equally marvelous is that its discovery was not only anticipated, but predicted to occur in rocks of a certain age and in a certain place. The first link between birds and reptiles was actually known to Darwin, who, curiously, mentioned it only briefly in later editions of The Origin , and then only as an oddity.
It is perhaps the most famous of all transitional forms: the crow-sized Archaeopteryx lithographica , discovered in a limestone quarry in Germany in As these fossils get younger, we see the reptilian tail shrinking, the teeth disappearing, the claws fusing together, and the appearance of a large breastbone to anchor the flight muscles.
While we may speculate about the details, the existence of transitional fossils — and the evolution of birds from reptiles — is fact.
Fossils like Archaeopteryx and its later relatives show a mixture of birdlike and early reptilian traits, and they occur at the right time in the fossil record. Scientists predicated that birds evolved from theropod dinosaurs, and, sure enough, we find theropod dinosaurs with feathers.
We see a progression in time from early theropods having thin, filamentous body coverings to later ones with distinct feathers, probably adept gliders. What we see in bird evolution is the refashioning of old features forelimbs with fingers and thin filaments on the skin into new ones fingerless wings and feathers — just as evolutionary theory predicts.
Can we find any mammals that live on both land and water, the kind of creature that supposedly could not have evolved? A good candidate is the hippopotamus , which, although closely related to terrestrial mammals, is about as aquatic as a land mammal can get. Similarly, snakes have long been supposed to have evolved from lizard-like reptiles that lost their legs, since reptiles with legs appear int he fossil record well before snakes.
The fossil record teaches us three things. First, it speaks loudly and eloquently of evolution. The record in the rocks confirms several predictions of evolutionary theory: gradual change within lineages, splitting of lineages, and the existence of transitional forms between very different kinds of organisms.
There is no reason why a celestial designer, fashioning organisms from scratch like an architect designs buildings, should make new species by remodeling the features of existing ones. Each species could be constructed from the ground up. But natural selection can act only by changing what already exists. Darwinism predicts, then, that new species will be modified versions of older ones. The fossil record amply confirms this prediction.
Nothing in biology makes sense except in the light of evolution. In medieval Europe, before there was paper, manuscripts were made by writing on parchment and vellum, thin sheets of dried animal skins. Because these were hard to produce, many medieval writers simply reused earlier texts by scraping off the old words and writing on the newly cleaned pages. Like these ancient texts, organisms are palimpsests of history — evolutionary history.
The long and short of it is this: flight is metabolically expensive, using up a lot of energy that could otherwise be diverted to reproduction. In other words, our appendix is simply the remnant of an organ that was critically important to our leaf-eating ancestors, but of no real value to us. Occasionally an individual crops up with an anomaly that looks like the reappearance of an ancestral trait. A horse can be born with extra toes, a human baby with a tail.
Dead Genes. In other words, there should be vestigial genes. As one group evolves from another, it often adds its development program on top of the old one. But this notion is true in only a limited sense. Embryos still show a form of recapitulation: features that arose earlier in evolution often appear earlier in development.
And this makes sense only if species have an evolutionary history. Bad Design. Although organisms appear designed to fit their natural environments, the idea of perfect design is an illusion. Perfect design would truly be the sign of a skilled and intelligent designer. Courtesy of evolution, human reproduction is also full of jerry-rigged features. Males are further disadvantaged because o the poor design of the urethra, which happens to run right through the middle of the prostate gland that produces some of our seminal fluid.
They give birth through the pelvis, a painful and inefficient process that, before modern medicine, killed appreciable numbers of mothers and babies.
Yes, a designer may have motives that are unfathomable. But the particular bad designs that we see make sense only if they evolved from features of earlier ancestors. If a designer did have discernible motives when creating species, one of them must surely have been to fool biologists by making organisms look as though they evolved.
When on board H. These facts seemed to me to throw some light on the origin of species — that mystery of mysteries, as it has been called by one of our greatest philosophers. The biogeographic evidence for evolution is now so powerful that I have never seen a creationist book, article, or lecture that has tried to refute it.
We now have many of the answers that once eluded Darwin, thanks to two developments that he could not have imagined: continental drift and molecular taxonomy. All they can do is invoke the inscrutable whims of the creator. But evolution does explain the pattern by invoking a well-known process called convergent evolution. Species that live in similar habitats will experience similar selection pressures form their environment, so they may evolve similar adaptations, or converge , coming to look and behave very much alike even though they are unrelated.
Convergent evolution demonstrates three parts of evolutionary theory working together: common ancestry, speciation, and natural selection. If evolution happened, species living in one area should be the descendants of earlier species that lived int he same place.
So if we dig into shallow layers of rocks in a given area, we should find fossils that resemble the organisms treading that ground today. And this is also the case. Creationism is hard-pressed to explain these patterns: to do so, it would have to propose that there were an endless number of successive extinctions and creations all over the world, and that each set of newly created species were made to resemble older ones that lived in the same place.
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