The scientific theory according to which populations change gradually through a process of natural selection.
Did crocodiles share a common ancestor with birds?
Asked in Miscellaneous, Africa, Evolution
How did Hominids evolve in Africa?
The frequently-heard answer is that we moved, or were driven, from the jungle to the grasslands, losing our ape-hair in response to the heat. However, baboons, who did this, have not lost their hair, nor have any of the other grassland animals. However, a recent hypothesis suggets we had an aquatic period (other animals who have streamlined, minimised, or total loss of, body hair had or have an aquatic period - otters, seals, hippos, etc). The suggestion is that our ancestors evolved the primary human characteristics (vertical posture, etc.) as a response to living in, or habitually frequenting, water - and the target place for this origin is the Danakil Horst, at the mouth of the Red Sea. Another perspective: In general terms Hominids split from living apes somewhere between 5 - 10 million years ago. They evolved from being small brained, part-time bipedal/part-time quadrupedal with fingers and hands optimized for tree climbing and lacking fully developed language processing structures in the brain (e.g.: Australopithecus Afareneis); to large brained, full-time bipedal, with hands suited to manipulating object and fully developed language processing brains structures (e.g.: Homo Erectus -> Homo Sapien). It is thought that rapid changes in climate and survival conditions provided selective pressure that gave an advantage to Hominids that were able to quickly adapt to a variety of conditions. This drove changes that favored intelligence, tool making and language. Regarding body hair, later bipedal hominids were hunters that ran down their prey by outlasting them. Hominids could/can run much longer distances than other animals (although not typically as fast) because bipedal running, at a jogging pace, is more energy efficient than quadrupedal running and hominids could/can cool themselves by sweating. Most "Hairy" or fur-bearing animals don't have sweat glands and those that do (Horses etc) cannot cool themselves as effectively as hairless hominids can. Loss of body hair was an adaptation to promote cooling the body temperature.
Asked in Biology, Charles Darwin, Evolution
How old is the theory of evolution?
Aristotle came up with the first theory about life on Earth and he believed that species were fixed creations arranged by their complexity, and those ideas alone lasted for 2000 years. Lamarck later discover that change occurs over a long period of time and he discovered that in the early 1800s. Finally, in 1859, Darwin published his book about his theory of evolution (On the Origin of Species by Natural Selection.) This encompassed his findings from his voyage on the HMS Beagle in 1831-36 on divergent evolution of finches on Galapagos Island and also his research in Australia.
What are the two broad processes that make evolution possible?
Answer 1 Two broad processes that make evolution possible are 1 : directional forces including mutation , migration and selection and 2: nondirectional forces that include random genetic drift , bottleneck effect , founders effect ,and chance variations . Answer 2 Evolution is most commonly described as a combination of reproductive variation and differential reproductive success. Reproductive variation in itself is a "non-directional" phenomenon, that produces mostly random variations. Differential reproductive success (or: natural selection) is a "directional" phenomenon, that basically acts as a mechanism limiting the set of "directions" produced by random variation.
Where do you expect genetic differences between cells to arise from mitosis or from meiosis?
Asked in History of Science, Evolution
Is evolution reversible?
Answer 1 Evolution is not a process that can be reversed. The core principle behind evolution is that traits with a positive impact on survivability or reproduction tend to passed on to subsequent generations. Evolution itself is merely the slight alteration of a species gene pool over many generations. Perhaps you can see that the question "Is evolution reversible is something of a misnomer. Is the process by which you change something reversible In certain processes the thing that is changed can be returned to its original state, but this process also requires change. If you intended to reverse an evolutionary process the only way you could do so would be through evolution. This type of process has no non-reflexive logical inverse. Perhaps what the question intended to ask was whether a species could "revert" back to a "less evolved" state. An example to explain this would be the reversion of humans to a more apelike genetic structure. This is certainly possible. If traits that were more apelike positively impacted the survival rate or the reproduction rate of the humans that had them than humans would begin to evolve to become more and more like our simian ancestors. Answer 2 : There are certain examples of reversal in evolution .Most familiar trend can be seen in evolution of Dinosaurs which were of small size in Triassic period , evolved to maximum size in Jurassic period ,and again decreased in size in Cretaceous period . Answer 3: The process of Evolution doesn't have a "direction", it doesn't favor one type of organism or trait as being "higher" than another. So in a broad sense evolution simply goes where environmental conditions dictate, there's no backward (reverse) or forward. Could traits that were once non-adaptive reappear in a population if environmental conditions changed to make them adaptive again? Yes Can an individual organism reacquire older traits that were not part of it's original genetic makeup? No Do some older traits occasionally reappear in vestigial form in some individual organisms. Yes (there are instances of humans being born with a short tail etc.) Answer 4 Evolution is basically a stochastic phenomenon. In order for evolution to "back-track", every single change in the genome that had occurred would have to be reversed in the exact reversal of the order that they occurred in. This is so extremely unlikely to ever occur that, were it observed, we would have to conclude aliens were pulling our legs. But although evolution is not reversible, it is possible for traits to evolve a similarity with an earlier form. Consider for instance the fish-like shapes of whales: they evolved from land-dwelling mammals, which in turn can trace their ancestry back to early fish. Same shape, completely different genetics. Answer 5 If you cloned an extinct animal, it might count as evolution going backwards. Not sure about that though, cause it's a pretty philosophical question.
Asked in Evolution, The Bible
How do naturalistic evolution and special creation differ in regard to this change?
Asked in Trees, Paleontology, Evolution
How many years have trees existed?
About 360 million years. (After the Cambrian period 550 million years ago, or "Cambrian explosion", as it is known, when most animal life began on this planet, plant life began to appear. The first plants, in the ocean, appeared 460 million years ago, and the first trees about 100 million years after that.) Answer 2 : Trees must not be confused with plant ! Word trees is reserved for tree ferns , gymnosperms and angiosperms , which appeared in late Paleozoic Era nearly 400 million years ago .
Asked in Farm Animals, Evolution
What is the related change in two or more species?
Why was the urey-miller experiment important?
Answer 1 It suggested that complex organic molecules, the constituents of life, might have been created on the early Earth from existing inorganic chemicals. This left open a possible source for abiogenesis, rather than life being brought here from elsewhere in the universe. Answer 2 The Miller-Urey experiment demonstrated that it is possible for complex organic elements to spontaneously form under abiotic circumstances, one of the key requirements for any potential explanation for the emergence of life on Earth. It was later shown that Miller's assumptions about the atmosphere of pre-biotic Earth were off, however, similar experiments have been done for various types of atmosphere, with similar results: a broth of diverse complex organic molecules, up to and including polypeptides and amino-acids.
Asked in Charles Darwin, Evolution
How does coevolution differ from evolution?
It doesn't. Co-evolution is simply a special case of evolution in which two or more species affect the direction of one another's evolution. The classic example is predator/prey interaction. All rabbits are variants and all fast rabbits vary among themselves also, with the faster ones surviving to reproduce ever faster rabbits. ( within physical limits and incrementally; think of how humans have shaved time off the mile run in the last 50 years ) This drives the evolution of faster, within limits, predators to chase these rabbits. Thus you get a arms race of coevolution in two interacting organisms.
Asked in Evolution
What are an Alligator's adaptations?
An alligator's adaptations include: A long and powerful tail for swimming and defense. Nostrils on the top of the snout so the alligator can stay mostly submerged in water while approaching prey. Rows of conical teeth that make it easier to capture and hold prey. A tough waterproof hide which is also a good defense. A four chambered heart that is metabolically efficient. Webbed and clawed feet that help them with swimming and digging. Massive jaw muscles for feeding. Camouflage in swamp waters so they can catch their food
How does adaptation helps the mustang survive?
Truthfully, the American Mustang has very few natural predators. There isn't much to stop them from surviving in the wild except maybe the elements and human interference. Technically, they are an invasive species as they are not native to the Americas. The current Mustang isn't even related to the horses brought over by the Spaniards as wild Mustang populations have been culled many times over the years. There were even times when complete eradication was attempted. However, to the point, Mustangs naturally have thicker hooves than many other breeds of horses. This has to do with the terrain they live on. It only takes a few generations of horses living on rocky ground to result in thicker than average hoof growth. They also have a thicker and hardier structure than many other breeds. What they lack in speed and agility they make up for in ruggedness and endurance. Their bone density is also very high, making them less prone to injury.
Asked in Evolution, Human Anatomy and Physiology
Can the fight or flight instinct be traced to a physical location in human biology?
What are the character states shared by the ancestor or outgroup of a clade called?
Why does thermodynamics not preclude the evolution of life on earth?
A common creationist misconception is that the Second Law of Thermodynamics prohibits things getting more complex. The law is usually misrepresented as demanding that "everything runs down." But if this were true, not just evolution would be impossible, but also the growth of an adult human from a fertilized egg cell. The simplest counter to the creationist argument that "thermodynamics precludes evolution" is to observe that the second law does *not* prohibit a temporary, localized reversal of entropy. In the case of life on Earth, the laws of gravity and chemistry, combined with the energy provided by the sun, provide the engine that drives a localized, temporary (on cosmic scales) reversal of entropy.
Asked in Evolution, Biochemistry
How do scientists use biochemistry to determine relationships?
The biochemical pathways that exist between organisms that also have close physiological homology strongly suggest common ancestry. Even organisms that look nothing like each other have very similar biochemical pathways. The amoeba and you, both being eukaryote, have mitochondria that use the biochemical pathway of oxidative phosphorilation. Traditionally, biologists looked at visible characteristics to try to work out the relationships between organisms. This isn't always very reliable, because often two species will develop similar adaptations for the same reason. For example, dolphins/whales have most of the same adaptations as fish for living in water, even though their ancestors lost the ability to live in water. Koalas are often called koala bears, even though they're not bears. And so on. But I think that this isn't much of a problem if you look at DNA/protein. For example, the genes for fins in whales would be different from the fin genes in fish (unless those genes have been present but inactive in the land-dwelling ancestors of whales, which is possible).
Asked in Evolution
What is inorganic evolution?
Why is it difficult for the systematist to classify asexually reproducing organisms as a species?
Asexually reproducing organisms do not interbreed. In sexually reproducing organisms, speciation is defined in terms of the hybridisation rate between populations. In other words, how often males and females from separate (sub)populations mate with one another. In asexually reproducing organisms, hybridisation does not occur in this manner, so a different definition for speciation is required. In single celled organisms strains are usually considered separate species when their genomes differ from one another by a given percentage.