The length of life on earth is unclear. However, scientists have made great progress in discovering aspects that help explain our existence today. Charles Darwin, for example, brought about profound changes in human thinking when he published The Origin of Species in 1859. Through research, experimentation, and dedication, he successfully laid the foundation for the theory of evolution (Quammen, 2006). According to Darwin, the theory of evolution involves the belief that populations, through natural selection, change from one generation to the next. By increasing diversity, natural selection allows the survival of species that are better adapted to their environment (Darwin, 1859). Species are usually classified based on their ability to interbreed and produce fertile offspring (Templeton, 1989). When two divergent genomes are combined into a common nucleus, the offspring is known as a hybrid (Salmon et al., 2005). Hybrids can result from crossing two animals or plants of different subspecies (intraspecific), species (interspecific), genera (intergeneric) or very rare interfamilials. Take Hercules, the liger, for example, its parents belong to the same genus but are different species (Mott, 2005; Shankaranarayanan et al., 1997). Although not much is known about the evolutionary importance of hybridization in animals, several cases have been observed among plants. Hybridization not only serves as a source of new variations but also as the initiation of new species in plants (Mooney and Cleland, 2001). Polyploidy is the condition in which an individual has three or more sets of chromosomes. Although the effects are comparable, the composition and causes of polyploidy differ. When an offspring's chromosomes are born ... middle of paper ... ploidy change can modify epigenetic silencing. Proceedings of the National Academy of Sciences, 93(14), 7114-7119. Schierenbeck, K. A., & Ellstrand, N. C. (2009). Hybridization and evolution of invasiveness in plants and other organisms. Biological Invasions, 11(5), 1093-1105. Shankaranarayanan, P., Banerjee, M., Kacker, R. K., Aggarwal, R. K., & Singh, L. (1997). Genetic variation in Asiatic lions and Indian tigers. Electrophoresis, 18(9), 1693-1700.Stebbins, G.L. (1959). The role of hybridization in evolution. Proceedings of the American Philosophical Society, 103(2), 231-251. Templeton, A. R. (1989). The meaning of species and speciation: a genetic perspective. The Units of Evolution (Cambridge: MIT, 1992), 159-83. Weiss, H. & Maluszynska, J. Chromosome rearrangement in autotetraploid Arabidopsis thaliana plants. Hereditas 133, 255

Topic > The length of life on earth is unclear. However, scientists have made great progress in discovering aspects that help explain our existence today. Charles Darwin, for example, brought about profound changes in human thinking when he published The Origin of Species in 1859. Through research, experimentation, and dedication, he successfully laid the foundation for the theory of evolution (Quammen, 2006). According to Darwin, the theory of evolution involves the belief that populations, through natural selection, change from one generation to the next. By increasing diversity, natural selection allows the survival of species that are better adapted to their environment (Darwin, 1859). Species are usually classified based on their ability to interbreed and produce fertile offspring (Templeton, 1989). When two divergent genomes are combined into a common nucleus, the offspring is known as a hybrid (Salmon et al., 2005). Hybrids can result from crossing two animals or plants of different subspecies (intraspecific), species (interspecific), genera (intergeneric) or very rare interfamilials. Take Hercules, the liger, for example, its parents belong to the same genus but are different species (Mott, 2005; Shankaranarayanan et al., 1997). Although not much is known about the evolutionary importance of hybridization in animals, several cases have been observed among plants. Hybridization not only serves as a source of new variations but also as the initiation of new species in plants (Mooney and Cleland, 2001). Polyploidy is the condition in which an individual has three or more sets of chromosomes. Although the effects are comparable, the composition and causes of polyploidy differ. When an offspring's chromosomes are born ... middle of paper ... ploidy change can modify epigenetic silencing. Proceedings of the National Academy of Sciences, 93(14), 7114-7119. Schierenbeck, K. A., & Ellstrand, N. C. (2009). Hybridization and evolution of invasiveness in plants and other organisms. Biological Invasions, 11(5), 1093-1105. Shankaranarayanan, P., Banerjee, M., Kacker, R. K., Aggarwal, R. K., & Singh, L. (1997). Genetic variation in Asiatic lions and Indian tigers. Electrophoresis, 18(9), 1693-1700.Stebbins, G.L. (1959). The role of hybridization in evolution. Proceedings of the American Philosophical Society, 103(2), 231-251. Templeton, A. R. (1989). The meaning of species and speciation: a genetic perspective. The Units of Evolution (Cambridge: MIT, 1992), 159-83. Weiss, H. & Maluszynska, J. Chromosome rearrangement in autotetraploid Arabidopsis thaliana plants. Hereditas 133, 255–261 (2000).