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Evolution
The scientific theory according to which populations change gradually through a process of natural selection.
5,264 Questions
How did Charles Darwin provide evidence that evolution occurs?
Natural selection needs variation to act. Victorian scientists however thought that individuals of a species were not variable to any extent where it might be important. One of Darwin's major achievements was to change this view and make biologists think about individuals rather than about populations or species as a whole. His work on variation was typical of the man; he collected lots of facts, and performed lots of experiments. One of his key study organisms was the fancy pigeon, which Darwin found to be a fountain of variation and also a 'great treat'.
The Need To Study VariationFor evolution by natural selection to occur individuals of a species must be variable. Slight differences in size, colour, behaviour, physiology and all the other components of living things must exist. Furthermore these variations must be evolutionarily meaningful; that means two things:- they have to have some effect on survival and reproductive success
- these differences must be heritable; they have to be passed on from parent to offspring
The existence of variation may not seem like a major problem now; scientists have become very used to thinking about species in a way known as 'population thinking'. Population thinking emphasizes the uniqueness of each individual within a population. For example when you see lions on a TV documentary it's clear some are bigger than others, or better hunters, or better parents, some are more aggressive to other lions and some sleep more than others.
This may seem like an obvious way to view species, but Darwin was the first scientist to really see this; it was one of his greatest observations. Darwin's peers, from the great Victorian naturalists to the beetle collectors and village parsons who dabbled in science, all agreed: species were species. They ascribed to a school of thought (to varying degrees) known as 'essentialism'. The same logic that led Pythagoras to state that a triangle is always a triangle led Victorian scientists to consider a species as a fixed type or 'natural kind'.
The predominance of essentialism posed a serious problem for Darwin. If essentialism was correct, if species are fixed, if a lion is and has always been a lion in its present state there can obviously be no evolution; a new species could only come to be if it was created in its modern form.
Not only did Darwin's theory argue that species were not fixed and that they did evolve, but his mechanism for evolution, natural selection, was based on small differences between individuals of the same species. This posed three further problems: first of all, what differences? If species varied to an extent that they could change, why had no one noticed before? Secondly, natural selection depends on individuals of the same species competing and out doing each other. But to Victorian eyes the natural world was harmonious; they saw no struggle for existence. Finally, an animal or plant works as a unit; if you change one bit, won't it affect all the others?
It would be no good for Darwin to present the bones of his theory and hope, in time, people would come to accept it, because they probably wouldn't have. The vast majority of scientists just weren't looking at the living world in the right way. Darwin himself would have to change this, he would have to provide the evidence and the argument to persuade the world that:
- individuals of a species vary (a lot)
- this variation affects the individual's survival and the number of offspring it has (even just a little)
- this variation is heritable and can be additive
- selection can act on particular traits independently from the rest of the organism
Luckily, there was ample proof available, and it was already familiar to most people. Darwin's proof of concept lay in wheat, rice, cows, sheep, chickens and pigeons: the products of domestication of wild animals and plants by artificial selection.
Darwin's StrategyDarwin's strategy to persuade his readers of the scope for natural selection to act had from quite early on been by analogy with artificial selection. For thousands of years man had selected crops to improve yields and selected animals to provide food, clothing, company and to behave in a way that makes them easy to farm. Darwin would use the domestic animals and plants to show that variation does exist and it has the right characteristics to allow natural selection to act. If variation exists for artificial selection to work, there is no reason why natural selection can't.His strategy had two parts. First he would document evidence that variation exists in domestic animals and plants. To do this he utilised his old network of contacts from his barnacle research, sending out for carcasses of ducks, sheep and all sorts, to be sent to his house where he would take detailed measurements of their skeletons. He called on experts, sending out letters of requests for information in farming and country journals and wrote directly to hundreds of peoples quizzing them on their animals and plants.
The second phase of his strategy was to discuss the power of artificial selection to modify domestic species in almost any way: 'the key is man's power of accumulative selection: nature gives successive variations, man adds them up in certain directions useful to him'. He would show that variation is there, but that it is not controlled by the breeder. The breeder merely selects favoured traits from variation that is produced naturally. The key point here is that variation allows selection; it occurs naturally and ubiquitously and has the right characteristics that allow the selection of traits in a quasi-independent way from other traits.
One of the key organisms in Darwin's study of variation was the domesticated pigeon. It was at the pigeon that Darwin directed his most scrutinising gaze, and with dividends. His studies of different pigeon breeds provided him with the evidence for meaningful variation that he needed, evidence enough to take up almost two full chapters of The Origin with enough spare to be a major focus of The Variation.
Darwin & The Pigeons'Believing that it is always best to study some special group, I have, after deliberation, taken up domestic pigeons'. So begins Darwin's most complete example of his analogy between natural and artificial selection, such a thorough treatment that Darwin's editor, after reading the first chapter, thought that the book's main subject was the pigeon.Darwin's foray into pigeons started in March 1855, strictly as a means of collecting facts: there was to be 'no amusement'. To begin with he used his contacts from the barnacle years and some new ones acquired through friends and friends of friends to rekindle his postal-network. He sent letters to breeders and other experts asking for facts and where possible skins and skeletons for him to measure.
Soon though, as with most of Darwin's studies, he became engrossed and set up an elaborate pigeon house at Down House, buying pigeons of many different breeds to perform his own crosses and experiments. The 'no amusement' plan quickly went out of the window; in November 1855 he wrote to his friend Charles Lyell, who was planning a visit, 'I will show you my pigeons! Which are the greatest treat, in my opinion, which can be offered to a human being'. All the family, especially the children, delighted in Charles' latest quarry.
His enthusiasm led him to join at least two societies of pigeon fanciers and he frequently visited others. At this time, Columbarian societies, as they are known, were dominated by class; there were clubs for gentlemen, and clubs for working men. Darwin went to both, socialising with and mining information from all types of men, all the 'odd specimens of the Human species, who fancy pigeons'. When he received or asked for help from those who were less well off he always refunded them any costs they encountered. By seeking help from all quarters Darwin ensured his knowledge of pigeons was as complete as it could possibly be. With an army of fact gatherers, and skins and skeletons of pigeons and other domestic animals arriving daily by post he quickly amassed a mountain of facts he needed to discuss variation.
Why Pigeons?Darwin answers this in The Origin: 'the diversity of the breeds is something astonishing'. There are many, many breeds of domestic pigeons all with different appearances and behaviours. Almost any anatomical feature is different between the breeds; beak size and shape, feather coloration, feather orientation, some have feather feet, some scaly feet, some webbed feet, some are very thin and tall, others fatter and larger, some have enlarged nasal skin appendages, some can expand their throats into a puff almost the size of their bodies, some have tail feathers which fan out like a peacock, almost all bones vary in dimension. Even behaviours change: some have odd coos, others have an odd flight pattern where they 'tumble' out of the sky. They even grow at different rates, and hatch at differing stages of development.Yet despite this mass of variation, all pigeon breeds are descended from one wild pigeon species; Columba livia, the rock pigeon, which lacks all these fancy characters. In the 1850s there was a debate over whether or not all pigeon breeds descended from one stock. Most naturalists believed they were, but most pigeon fanciers believed they were descended from probably 7 or 8 species, and felt the naturalists too quickly dismissed domestic animals and made sweeping generalisations. When Darwin first started his pigeon work, he claims to have 'felt fully as much difficulty in believing that they could have descended from a common parent, as any naturalist could in coming to a similar conclusion in regard to many species of finches'. But in the opening chapter of The Origin he laid out an argument showing that they were in fact one species.
This argument was based on a number of observations. For example he noticed the reversion of feral pigeons to appearances similar to that of the rock pigeon. He also concluded that all breeds can mate and produce fertile young. In addition he thought domesticating one species was difficult enough let alone seven or eight, and found no evidence for ancestry with any other birds than the rock-pigeon.
By uniting the breeds under one species, Darwin could then use the pigeons to show various points. First, he drew an analogy between the breeders' disbelief in all breeds being from one common ancestor, and that of naturalists and their similar disbelief about species of wild animals and plants: 'may not those naturalists… learn a lesson of caution when they deride the idea of species in a state of nature being lineal descendents of other species?'. As an aside, Darwin produced a tree showing the relationship between the pigeon breeds; the first evolutionary tree for any real group of animals.
Second, he showed that amongst breeds of pigeons, breeders have been able of select for a vast number of traits, in almost any body part, and in behaviour. The discrete differences among breeds are linked by smaller, continuous differences among sub-breeds. Within breeds and sub-breeds, the traits which differ most between the breeds are often the most variable. This proved that naturally-produced variation has the properties needed to allow selection to occur, and for change to occur gradually, over many generations. If humans have been able to bring about such change in a few thousand years, why then couldn't the natural processes of competition and death, acting over much longer times, not bring about the same change?
What Did Darwin Learn? How Did It Help His Theory?The demonstration that variation occurs naturally and has the right properties to allow selection to occur is a key point. Having established this fact, Darwin could move on to wild animals where he showed that just as much variation occurs within species as it does within breeds of pigeons, sheep, cows, wheat or geranium. This variation was the key to evolution, but had been overlooked by scientists until Darwin shed light on its importance. In The Origin, Darwin would combine the presence of variation, with the over-production of young and the struggle for survival to show that evolution by natural selection is an inevitable fact.His work on variation was started when Darwin planned to write a massive tome, a book so large and full of evidence for evolution that it would be accepted by all. The emergence of Alfred Russell Wallace, and the realisation that another scientist had come to the same conclusions as he had rushed Darwin to produce an 'abstract' of this great book; this becameOn the Origin of Species. Only a fraction of Darwin's study on variation made it into this book. Much of the rest appeared inThe Variation of Animals and Plants Under Domestication (1868). Here Darwin presented all his views and facts on variation and the laws governing it and proposed a theory of inheritance - the missing link in his theory of evolution - which he called Pangenesis.
Written by Stephen Montgomery
References & Further ReadingThe Autobiography of Charles Darwinby Charles Darwin (Edited by Francis Darwin), The Thinker's Library: 1929
Darwin
by John van Wyhe, Andre Deutsch: 2009
Darwin
by Adrian Desmond & James Moore,Penguin: 1991
Darwin's Islands: The Galapagos in the Garden of England
by Steve Jones, Little, Brown: 2009
Journal of Researches
by Charles Darwin, 1839 (any edition)
On the Origin of Species
by Charles Darwin, 1859 (any reprint - 2nd edition preferable)
The Variation of Animals and Plants Under Domestication (Vol I & II)
by Charles Darwin, 1868 (any edition)
Environmental changes almost demand variation in organisms so that the best fitted to the changing environment survive and reproduce in a greater number. Asexual reproduction produces clones with little to no genetic variation. Good enough for a static environment, but in a challenging environment with no variation that could be more beneficial than cloning the asexual species could find itself selected against.
The scientific method uses observation and which other process to answer?
Hypothesis construction and experimental testing of such hypothesis.
if I were to inherit traits based on Lamarcks explanation of evolution were correct we wouldn't be the people we are now. Lamarcks´ explanation was that acquired characteristics were genetically passed to the offspring so if that were so, the human brains would be much more developed, more knowledge, and bigger parts of the body. This question is also tricky since a human would turn out to be a giant by the time they got to the 100th offspring
They are internally consistent, supported by many lines of converging evidence, tested and passed tests innumerable time over many years, make testable prediction and are very good explanations for a broad class of phenomenon.
As scientific theories they have been around a long time and have been modified as new information was gather, but basically, they have stood the test of time very well.
What is a common cause of stablilizing selection?
The type of selection that removes the fringe from both ends of phenotype distribution and establishing a means or average. Genetic diversity decreases and there is a stabilization on a particular trait.
Lists and describe the indirect evidence to support theory of evolution?
Direct evidences of evolution include studying fruit flies. These insects breed quickly and have very short lifespans, so you can study genetic differences that occur relatively quickly over a short period of time. Indirect evidences of evolution include fossils left from prehistoric animals, as well as DNA samples.
That is incorrect. Evolution IS important. It is a theory that states that a gradual, slow change happens within a species over a long period of time. Without evolution we might still be apes or something else. So Evolution is very far from being unimportant.
How do females pick the males in sexual selection?
it doesnt matter if you are a female and you want a female mate you can have a girlfriend when your a girl. if you want a male and you are a female then you can choose a male it doesnt matter if you are a female and you want a female mate you can have a girlfriend when your a girl. if you want a male and you are a female then you can choose a male
How do studies of body structure and embryos support evolution?
It does. It is NOT true that "ontogeny recapitulates phylogeny." But there are numerous facets of embryological development that make no sense except in the light of common ancestry.
What we see in developing embryos is a similar pattern of development; one thing developed first, then another thing, then another couple of things, then a bunch of other bits, all in roughly the same order even when compared between different species, we also see features appear that do not exist in the adult form but the embryos have, like limb buds in Dolphins and human tail buds.
While it does not prove evolution outright (and the historical method of using it as proof were shown by scientists to be wrong), evolution does explain this well enough that it is not evidence against: These species share a common ancestor, so their developmental processes occur in a similar way, regardless of what other changes have taken place since their divergence.
Does speciation form new species?
The term 'speciation' does indeed refer to the 'formation' of new species. 'Formation' is probably better replaced with 'divergence' as in 'the divergence of two species from one'. A common ancestor of two species may have two of its populations isolated, so the two populations cannot interbreed. Genetic differences (via mutation) should build up in the two populations over time or indeed, simply the mixing of genes via meiosis within the two populations could follow different routes. The non-mixing of the two populations would ensure the non-homogenisation of the gene pool, ensuring a homogenisation of the morphology of the species back to the morphology of the common ancestor. Eventually, so much genetic difference should build up between the two populations that, be they removed from isolation or not, the two populations would no longer be able to interbreed and produce fertile offspring. Remove the ability of interbreeding and, within the Biological Species Concept, the two populations would have diverged into two separated species. Speciation would have occurred.
How did cyanobacteria affect evolution process?
Cyanobacteria photosynthesised, which meant that they released oxygen. This was the key to the evolution of eukaryote cells that aerobically respired. From their evolution, the O2 levels in the atmosphere was able to increase; this is why we eventually evolved.
Why would breeding dogs support Darwin's theory of evolution by natural selection?
Selective breeding supports Darwins theory because, we adapt to our environments and believe whoever is compatible with breeding will pass on the trait, even if that means outside their own species.
The most direct evidence that evolution has occurred comes from what?
Bacteria because they reproduce every 20 minuites which is fast enough so scientist can see them evolve over time.
or
Viruses, they evolve, that's why we have to constantly change are vacines.
Which type of natural selection favors the average individual in a population?
That would be the Stabilizing Selection where there will me not a lot of genetic variation. The curve of the population allele frequency would be quite thin with the extreme being in the middle.
How did the Victorian Age view Charles Darwin's theory?
The Victorian Age pretty much Didn't view Charles Darwin's Theory of Evolution. He kept it a secret most of his life, because he Knew what effect it would have. Darwin, like most people of his time, believed in the standard religious statement that God created the Universe and made each species of animal separate and independent. Man was the pinacle of Creation, created in God's image. When he first began to realize what he was seeing, Darwin was shocked and confused. As the full implication of his discoveries dawned on him, Darwin realized that this information completely contradicted Church dogma. God could Not have personally created each separate species of animal, if the species was the result of choices and adaptations made by its forerunners. The contradiction was especially impossible with Man. If, instead of being personally created by God, in His image, he/she was Actually the product of millions of years of a process that not only produced him/her, but Also produced all the Other Great Apes, that meant that Man was Not special; Not unique, but simply another species in a long chain, on the way to something Else. Social change, however, and the work of other scientists made it safer for Darwin to make his Theory public as the Victorian Age went on. The book "On The Origin Of Species" was finally published in 1859, when he was 51 years old. Although some religious leaders condemned the work, some others championed it. Liberal churches welcomed the Theory as the explanation of God's mechanism in the creation of the Universe. The respect which such scientific luminaries as Thomas Huxley and Joseph Hooker commanded in their advocacy for the Theory managed to make it more a matter of Scientific debate than Religious dogma.
What are 3 factors leading to evolution?
Evolution is driven by a change in environment. A large interbreeding population in a static (unchanging) environment faces little need for the acquisition of new adaptations.
Competition for resources (whether from other members of one's own species or other) can drive evolutionary change.
The availability of new forms (random mutations) also plays a factor. Mutagens may come in the form of radiation or chemicals, and sometimes simple exposure such as viral infections. Natural selection can only operate when there is something to select. If the environment changes more rapidly than mutations can keep pace with, extinction results. Most of the species that ever existed have subsequently disappeared.
Your question sounds like it came from a book, and you would do well to read the chapter and determine what three factors the author had in mind. Otherwise, how would some person decide there were 3 factors, and not 2 or 7?
Which traits are the result of natural selection?
They are selected of course!
Traits that lead to greater survivability and reproductive success in individuals, on average and against the immediate environment, out reproduce their conspecifics leaving more progeny having these traits and changing the allele frequency over time in the populations gene pool.
Simple put and subject to the vagaries of existence in the real world.
What can cause genetic variation?
genes are kept in chromosomes, there is this thing called meiosis which is when the chromosomes/genes get split in half, one from both parents that way it equals the normal amount of genes later. the genes have tons of ways to mix and match around while getting split apart and then ending up in the same place.
How evolution occurs via natural selection?
Evolution occurs via natural selection when certain traits become more favorable in a population over time. This is typically due to the environment or natural selection pressures in the population. Natural selection works by favoring individuals with traits that are better suited to the environment while those with less favorable traits may die off or be less likely to reproduce. Over time these favored traits become more common while unfavorable traits become less common. This process eventually leads to evolution as the population changes to adapt to its environment.
The three main components of natural selection are:
- Variation: Individuals within a population have different traits
- Inheritance: Traits are passed from generation to generation
- Differential Reproduction: Traits that are more favorable are more likely to be passed on
Natural selection is an ongoing process as the environment is constantly changing and influencing the traits of the population. It is important to note that natural selection is not a directed process and does not necessarily lead to a specific outcome. The result of natural selection is determined by the environment and the traits that are favored in the population.
