Jean-Baptiste Lamarck (1744-1829) and Charles Darwin (1809-1882) were both scientists and each had opinions about how evolution got to where it is today. Both men had some similar and some very different ideas. Lamarck's idea of evolution was based on how organisms change during their life time, and then pass them onto their offspring. Whereas, Darwin's theory, also referred to as natural selection was the belief that the organisms gained variation in their species, some now being more likely to survive and reproduce then the others of the same kind. And it is from this idea we get the phrase 'survival of the fittest'.
Darwin's theory of natural selection is the most scientifically supported form of evolution. This is supported by a variety of evidence
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It has also been proposed that this change happened quickly, likely because the extreme conditions forced them to adapt and change many aspects of them, including their physical appearance and their diet that would eventually affect other mammals surviving on the same species. "It's a schoolbook example of evolution," says Eske Willerslev, an evolutionary geneticist at the University of Copenhagen who assisted as lead in the research. Brown bears and polar bears still to this day are genetically closely related, they are even able to interbreed. Recent research has begun using genetic information to gain more knowledge on the species relationship and evolution from one another. Overtime, the polar bear has evolved from the brown bear by changing its fur colour from a common brown to a white, this is ideal as it allows the bear to camouflage and prey. Some researchers believe that the brown bear migrated north in the warmer period and when the cold period arose that group of bears might of became isolated and therefor forced to adapt to the new climate. This idea of evolution may stem back to either Lamarck's or Darwin's theory of