Many scholars were involved with the exciting project of trying to develop a better understanding of the relations among living things. The name most often associated with the application of the model of ancestral forms and branchings is of course Charles Darwin, although Darwin did not satisfactorily explain everything involved or all of the implications.
For one thing, he lacked a modern understanding of genetics. For another, he had very little fossil evidence showing what extinct life forms looked like. Biological evolution as it is understood today involves populations of plants or animals with slight genetic variation from one individual to the next. Genetic variation in the population can increase through occasional, non-lethal genetic mutations.
And it naturally decreases with lethal genetic mutations birth defects or when any individual dies. An individual organism or a population that produces offspring is referred to as "successful. That is the ONLY meaning of "success" in this technical application of the word. Biological evolution consists of a heritable change in the genetic make-up of a genetically diverse population.
A population containing little or no genetic diversity has little capacity to evolve. An example is sorghum, discussed in the Neolithic essay of the this web site. Link Two processes are responsible. Over time, a single initial population timber wolves — Canis lupus — for example , subjected to different environmental constraints including deliberate manipulation by humans , can produce a wide range of very different populations varieties of domestic dogs — Canis lupus familiaris.
None of this was particularly new. People had been breeding dogs and cultivating varieties of corn and cabbage and tulips for centuries. What was new was proposing that the process was evolutionary that is, that it eventually produced permanent differences , and that it was an inevitable characteristic of all living forms, including ourselves.
This led to opposition from religious "creationists. Something else was new: In this model, evolution is held to be the origin of new species out of increasingly separate biological varieties, just as linguistic evolution posits the gradual development of new languages out of increasingly separate dialects.
The working definition of a species in biology is that it is a plant or animal form, in which male and female members can mate to produce fertile offspring. Pigs and goats are different species because they cannot be crossed. But Irish setters and German shepherds are two variants of the same species, since they can produce fertile puppies. The model of biological evolution holds that if a population is divided into two non-interacting sub-populations in different environments, then the differences in the genotypes in the two populations will eventually become so great that members of the first population will not be able to mate and produce fertile offspring with members of the second population.
That is, that the two populations will have become two species. Darwin proposed that over the vast reaches of time available, this happened over and over, eventually producing the range of modern and extinct life forms.
The logic of the argument is quite similar to the logic that guided the model of linguistic evolution. The idea of changes in the composition of a population being attributable to changes in its environment has been an extremely useful.
With this perspective, we can coherently account for the distribution of forms in the fossil record, for example. However, great interest also lies in species-formation speciation , which occurs when populations that for some reason cease to interbreed become different enough to lose all ability to interbreed.
In actual life, the boundaries between species are not always absolute —varieties only gradually evolve into species, after all— and it has been found that occasional fertile crosses between closely similar species do occur, if rarely. The rule-of-thumb of fertile offspring as defining species remains the way most biologists think of it, but the possible exceptions have generated complexities in classification and in modeling gene flow.
A population split in half by an uncrossable barrier can over time develop substantial differences between its two parts. The most famous example of this process, called "allopatric" —"different country"— speciation, is the squirrels of the Grand Canyon, who have diverged into different species on the two sides of the Canyon. But when the genotype of a single, inbreeding population changes gradually over time, at what point should we say it has turned into a new species? Our "rule of thumb" about producing fertile offspring can hardly be applied to two different points in the history of the same population.
And yet if the differences between early and late specimens are substantial, can we be confident in calling them the same species? As an intellectual matter, it is difficult to know when one continuously changing population should be regarded as a different species from its remote ancestors. As a practical matter, it is also difficult to know how specimens available for study are actually related to each other anyway. If two fossil snake teeth look similar, but neither looks exactly like any modern snake, were they separate species, or were they merely two slightly different variants of the same species?
And is either of them ancestral to any modern snake? Many specialists in prehistoric life —paleontologists— tend to assume that speciation occurs relatively easily when plant or animal communities are separated, and they argue that the default assumption should be that two specimens should be assumed to be different species until they can be convincingly shown to be the same which is hard to demonstrate with extinct forms.
Others argue that speciation is in fact relatively difficult. Barring intervention with atomic bombardment, we have not succeeded in changing a genotype sufficiently to make it a whole new species just through selective breeding alone. That is why all dogs are still the same species. The best assumption when looking at prehistoric forms should therefore be that two similar specimens should be considered to belong to the same species until shown to have more variation between them than is exhibited in a modern population of similar animals, if there is one.
All of this becomes particularly controversial in the case of proto-humans. Darwin did not explore the evolution of humans — indeed only one clearly pre-human hominid fossil had been discovered when he published The Origin of Species Through Natural Selection in Since humans look a lot like modern Great Apes, it seemed logical that we should have a common ancestor with them, but that was about as much as one could say.
In some respects, the exact ways in which we draw the lines among species may not make much difference. The more we learn about genetics, the more obvious it becomes that what matters most is not the label given to a form, but our understanding of the over-all process of evolutionary transformation that is continually going on.
Geneticists are ever refining more detailed "family trees" of biological forms based on the inheritance of specific gene mutations. In these family trees, it makes no significant difference where one species stops and the next begins. What matters is where mutations occur that are inherited by future generations. Since Darwin's time, many fossil forms have turned up that look more like us than they or we look like modern apes. It is impossible to say that any given bone is ancestral to any modern creature, of course, but there is a clear sequence of forms: Earlier ones tend to look more like the hypothetical common ancestor that we might share with modern apes; more recent ones look more and more like us.
Chancy as biological classification is with the incomplete fragments of extinct animals, virtually all biologists today are satisfied:. Some fossil forms are objects of great controversy. For example, the Neanderthals that roamed Europe in the last ice age and before are clearly Homo , but it was not clear whether they were a separate species or should be classed as Homo sapiens.
If Neanderthals counted as Homo sapiens , then they belonged to the sub-species " Homo sapiens neanderthalensis " and we were of the sub-species " Homo sapiens sapiens. In a logically similar way, the recently discovered Homo floresiensis forms have an unclear relationship to Homo erectus , with which they overlapped in time.
It also supplies explanations for the sometimes wild exceptions we see eg cacti and euphorbs, which look so similar but are clearly only very distantly related to each other.
The explanation is convergent evolution. Comparison of DNA and protein sequences only makes sense in light of evolution. Our understanding of infectious organisms and our tactics to combat them are entirely based upon understanding of evolution. No idea comes from thin air. The historical perspective helps to understand where the concepts behind evolutionary theory came from.
Here are some of the basic historical issues. The typical view of the nature of species at the beginning of the nineteenth century is often described as the Doctrine of Fixed Species. This concept had its primary roots in Greek philosophy: During the eighteenth century, Carolus Linnaeus developed the basis for our nested, hierarchical classification system, or Taxonomy.
The geologic discipline of stratigraphy was developed during the late eighteenth and early nineteenth centuries.
Though this accomplishment was shared by many geologists throughout Europe, the name most commonly associated with developing the concept of stratigraphy is William Smith , who was an engineer engaged in building canals all over England.
George Cuvier eventually Baron George Cuvier was a scientist of the late 18th and early 19th centuries. His specialty was vertebrate anatomy. Because of his expertise in anatomy, Cuvier was the obvious person to ask to examine strange remains found during reconstruction after a major Paris fire.
These remains turned out to belong to extinct organisms, and led to the development of the field of study we call Paleontology. Cuvier was the first to reconstruct dinosaurs. Cuvier is also remembered for coming up with the concept of Catastrophism, as an attempt to reconcile his religious beliefs with the evidence he discovered as a scientist.
Charles Lyell , a British geologist, developed the concept of Uniformitarianism. In other words, the forces acting upon and shaping the Earth today are the same as the forces that acted upon and shaped the Earth in the past.
Uniformitarianism is a central tenet of modern geology. Darwin was born in the first century of the nineteenth century to a wealthy family. His hobby was natural history. He collected beetles, went on geological field trips and became very friendly with the natural history faculty at his universities. During the five-year trip, he collected tons literally of specimens of animals, plants and fossils, which he shipped back to England for later analysis.
Upon returning to England, he officially became a naturalist. Almost all of his specimens were sent to experts for analysis. He kept the barnacles for himself, setting out to become an expert in barnacles.
It was the analyses that were returned to him from his experts that started him thinking along revolutionary pathways. Thus, in order for humans to continue to survive, some have to die. One reason he finally published in and then published Origin of Species in was that he discovered that another man, Alfred Russell Wallace , had independently discovered and was about to publish exactly the same theory Darwin had been working on for 20 years.
Darwin saw a clear pattern of common descent among the species of life. Examining the expert analyses of all of the specimens from the Beagle expedition, it was clear to Darwin that the various forms of life were all descended from one, or many from a very few, common ancestral species.
The mechanism Darwin figured out by which species could change from one thing into something different was natural selection. He saw environmental competition as providing the selective pressure in nature. All living things tend to over-reproduce. There will be competition over resources, and not all members of any generation can survive.
Many aspects of variation are heritable, meaning that they are passed from parents to offspring. Each new generation will tend to be more like the successful parents and less like the unsuccessful parents. Given enough time meaning enough generations , these changes can produce brand new species, especially if the environmental pressure is strong. What is the evidence in support of the theory of evolution?
This question could take weeks to answer. Observations of a wide variety of phenomena demonstrate evolutionary action and consequences.
Here are some examples:. Adaptive radiation, which Darwin saw abundantly demonstrated among the species he observed and collected while on the Beagle.
Adaptive radiation is the phenomenon in which a single species splinters into many daughter species. This phenomenon is very commonly observed among species living on off-shore islands like the Galapagos Islands to the west of South America.
The fossil record abundantly demonstrates evolutionary change.
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The Theory of Evolution Essay Words | 3 Pages Biological evolution is the name for the changes in gene frequency in a population of a species from generation to generation. The Argument- The theory of evolution was developed out of the work of 19th century botanist and explorer, Charles Darwin and his book On the Origin of Species. Essentially, it is a scientific theory that postulates that organisms change over time based on pressures from the environment that cause genetic mutations within the organism.