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The species of animals and plants living today weren’t around in the past, but are descended from those that lived earlier.
Not completely true for some living beings.
the coelacanth “living fossil,”
When natural selection is strong, as when an animal or plant colonizes a new environment, evolutionary change can be fast. Once a species becomes well adapted to a stable habitat, evolution often slows down.
Yet we have many: well over ten million species inhabit our planet today, and we know of a further quarter million as fossils. Life is diverse.
Speciation doesn’t happen very often.
Darwin didn’t really explain how new species arose, for, lacking any knowledge of genetics, he never really understood that explaining species means explaining barriers to gene exchange. Real understanding of how speciation occurs began only in the 1930s.
the nested arrangement of life was recognized long before Darwin. Starting with the Swedish botanist Carl Linnaeus in 1635, biologists began classifying animals and plants, discovering that they consistently fell into what was called a “natural” classification.
By sequencing the DNA of various species and measuring how similar these sequences are, we can reconstruct their evolutionary relationships.
Fosil bile bulmdan türlerin evrimi nasil kanitlanir
natural selection can, over eons, sculpt an animal or plant into something that looks designed.
for all cases of extinction, which represent well over 99 percent of species that ever lived. (This, by the way, poses an enormous problem for theories of intelligent design (ID). It doesn’t seem so intelligent to design millions of species that are destined to go extinct, and then replace them with other, similar species, most of which will also vanish. ID supporters have never addressed this difficulty.)
natural selection does not yield perfection—only improvements over what came before.
a scientific theory is “a statement of what are held to be the general laws, principles, or causes of something known or observed.”
Bilimsel teori ile gunluk yasamdaki teori kelimesini karistimayin birbirine.
For a theory to be considered scientific, it must be testable and make verifiable predictions. That is, we must be able to make observations about the real world that either support it or disprove it.
When Darwin wrote The Origin, most Western scientists, and nearly everyone else, were creationists.
We can say, then, that evolution was a theory (albeit a strongly supported one) when first proposed by Darwin, and since 1859 has graduated to “facthood” as more and more supporting evidence has piled up.
most of the fossils we have are of marine organisms,
we have discovered around 250,000 different fossil species,
Ironically, the fossil record was originally put in order not by evolutionists but by geologists who were also creationists,
It is radiometric dating of meteorites that tells us that the earth and solar system are 4.6 billion years old.
Each day—one revolution of the earth-is a tiny bit longer than the last one.
we can cross check the “tidal” age against the “radiometric” age.
For example, nineteenth-century anatomists predicted that, from their bodily similarities, mammals evolved from ancient reptiles. So we should be able to find fossils of reptiles that were becoming more mammal-like.
But Darwin still had some fossil evidence for evolution. This included the observation that ancient animals and plants were very different from living species, resembling modern species more and more as one moved up to more recently formed rocks.
the fossils in the most recently deposited rocks tended to resemble the modern species living in that area, rather than the species living in other parts of the world.
The fossil record showing first appearance of various forms of life that arose since the earth formed 4,600 million years ago (MYA). Note that multicellular life originated and diversified only in the last 15 percent of life’s history.
Although over the entire period of sampling every species showed a net increase in segment number, the changes among different species were not only uncorrelated, but sometimes went in opposite directions during the same period.
It is always easier to document evolution in the fossil record than to understand what caused it, for although fossils are preserved, their environments are not. What we can say is that there was evolution, it was gradual, and it varied in both pace and direction.
the formation of a new species usually begins when populations are geographically isolated from one another.
the fossil record gives no evidence for the creationist prediction that all species appear suddenly and then remain unchanged. Instead, forms of life appear in the record in evolutionary sequence, and then evolve and split.
This divergence may have been the result of natural selection acting to reduce competition for food between the two species.
like the early amphibians, Tiktaalik has a neck. Fish don’t have necks—their skull joins directly to their shoulders.
we now have the fossils that clearly show how flying birds evolved.
The problem is that feathers are preserved only in special sediments—the fine-grained silt of quiet environments like lake beds or lagoons.
While we may speculate about the details, the existence of transitional fossils—and the evolution of birds from reptiles—is fact.
Scientists predicted that birds evolved from theropod dinosaurs, and, sure enough, we find theropod dinosaurs with feathers.
Hippos are obviously well adapted to their environment, and it’s not hard to see that if they could find enough food in the water, they might eventually evolve into totally aquatic, whalelike creatures.
Whales happen to have an excellent fossil record, courtesy of their aquatic habits and robust, easily fossilized bones.
They are warm-blooded, produce live young whom they feed with milk, and have hair around their blowholes. And evidence from whale DNA, as well as vestigial traits like their rudimentary pelvis and hind legs, show that their ancestors lived on land.
Biologists now believe that the closest living relative of whales is—you guessed it-the hippopotamus, so maybe the hippo-to-whale scenario is not so far-fetched after all.
The evolution of whales from land animals was remarkably fast: most of the action took place within only 10 million years.
From anatomical similarities, entomologists had long supposed that ants evolved from nonsocial wasps. In 1967, E. O. Wilson and his colleagues found a “transitional” ant, preserved in amber, bearing almost exactly the combination of antlike and wasplike features that entomologists had predicted
Sphecomyrma freyd,
Haikouella lanceolata,
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.
Within the bodies of animals and plants lie clues to their ancestry, clues that are testimony to evolution.
Sometimes we find “atavisms”—throwback traits produced by the occasional reawakening of ancestral genes that have long been silenced.
organs and other features appear, and then change dramatically or even disappear completely before birth.
All flightless birds have wings. In some, like the kiwi, the wings are so small-only a few inches long and buried beneath their feathers—that they don’t seem to have any function. They’re just remnants. In others, as we saw with the ostrich, the wings have new uses.
It is vestigial not because it’s functionless, but because it no longer performs the function for which it evolved.
