Evolution
Evolution is the change of a species over time. Evolution has caused old species to change and become new species. It is important to note that evolution is not an organism adapting to a new environment; that's entirely different than evolution. Evolution takes place over long periods of time and very slowly, slowly enough that it would be impossible to perceive this change over the lifetime of a single person. As a matter of fact, most changes brought about by evolution take hundreds of thousands if not millions of years to occur.
The first work with evolution was done by Charles Darwin. His work with evolution began after his exploration of the Galapagos Islands with a ship. He was very interested with the different bird species that lived on the various islands in the area. He noticed that all the birds were very similar except that they had different kinds of beaks. Some of the beaks were long and elongated while others had a shorter, stouter shape. He realized that they were all suited for a particular kind of food that that species of bird ate. Eventually, he reasoned that all of those birds must have come from the same original species. He thought that even if just one female bird from the mainland had been blown into the islands, it would be very easy for a new species to form. This formed the basis for Darwin's Theory of Evolution that is commonly accepted today as the process by which species change and new species are created.
Another scientist who did work with evolution was Jean Baptiste Lamarck. He had similar ideas to Darwin but also believed in a concept called inheritance of inquired characteristics. This accounted for evolution by assuming that traits acquired by an organism during its lifetime are passed on to its offspring. This was proven false later and let me explain why: For example, say you teach a dog to sit and lay down when you command it to do so. If that dog were to have puppies, those puppies would not know how to perform those tricks. It Lamarck's hypothesis were true, they would remember these facts.
The first work with evolution was done by Charles Darwin. His work with evolution began after his exploration of the Galapagos Islands with a ship. He was very interested with the different bird species that lived on the various islands in the area. He noticed that all the birds were very similar except that they had different kinds of beaks. Some of the beaks were long and elongated while others had a shorter, stouter shape. He realized that they were all suited for a particular kind of food that that species of bird ate. Eventually, he reasoned that all of those birds must have come from the same original species. He thought that even if just one female bird from the mainland had been blown into the islands, it would be very easy for a new species to form. This formed the basis for Darwin's Theory of Evolution that is commonly accepted today as the process by which species change and new species are created.
Another scientist who did work with evolution was Jean Baptiste Lamarck. He had similar ideas to Darwin but also believed in a concept called inheritance of inquired characteristics. This accounted for evolution by assuming that traits acquired by an organism during its lifetime are passed on to its offspring. This was proven false later and let me explain why: For example, say you teach a dog to sit and lay down when you command it to do so. If that dog were to have puppies, those puppies would not know how to perform those tricks. It Lamarck's hypothesis were true, they would remember these facts.
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Anyway, Darwin eventually came up with a theory to explain evolution called descent with modification. This theory states that all species, living or dead, have come from another previous species. Through time, they inherited different characteristics that caused them to become more and more different from the ancestor species until they eventually become the same species entirely. The process of a new species forming out or an existing one is called speciation.
A populations of organisms breaking off from a species and forming a new species is generally caused by one of several types of isolation. With isolation, two separate populations are formed because they become, well, isolated from each other.
- Geographical Isolation: Populations are isolated by physical inabilities to converge, for example a mountain range or large river.
- Reproductive Isolation: Members or a species are unable to reproduce successfully with each other. This has two subtypes - prezygotic isloation and postzygotic isolation.
- Prezygotic Isolation: Two organisms are unable to produce offspring successfully.
- Postzygotic isolation: Species produce offspring but the offspring either don't survive or can not reproduce successfully themselves.
- Mutation: The vast majority of all mutations have to little to no effect on an organism but occasionally a mutation alters the phenotype of an organism.
- Recombination: During meiosis, the chromosomes found in each gamete are randomly chosen from the chromosomes contained within the original diploid cell. Because of this randomness, offspring are different form parents.
- Randomness of Gamete Pairing: As each gamete is different because of recombination, two gametes containing the same genes will almost definitely not pair again, ensuring variation in the genotypes of offspring.
Natural Selection, commonly referred to as survival of the fittest, is the idea that organisms with the best traits for surviving in their environment will be the most likely to succeed and reproduce successfully. There are several types of selection as shown to the left:
Rates of Evolution: Evolution runs in different rates in different situations. When it occurs gradually and slowly through time, it is called gradualism. When it occurs rapidly in spurts, it is called Punctuated Equilibrium.
- Disruptive Selection: Organisms with the most extreme versions of a trait are most likely to survive.
- Stabilizing Selection: Organisms with the average version of a trait have the most chance of success.
- Directional Selection: Organisms with one of the most extreme versions of a trait have the most success.
Rates of Evolution: Evolution runs in different rates in different situations. When it occurs gradually and slowly through time, it is called gradualism. When it occurs rapidly in spurts, it is called Punctuated Equilibrium.