This paper presents a colloquium titled "Tempo and Mode in Evolution," organized by Walter M. Fitch and Francisco J. Ayala, held in Irvine, CA, in 1994. The colloquium celebrated the 50th anniversary of George Gaylord Simpson's book "Tempo and Mode in Evolution," which explored evolutionary tempo (rates of change) and mode (patterns of evolution). Simpson's work was influenced by Theodosius Dobzhansky's "Genetics and the Origin of Species," which integrated Darwinism with Mendelian genetics. Simpson argued that evolutionary rates depend on factors like variability, mutation rates, generation length, population size, and natural selection. He also emphasized that natural selection is not merely a negative process but can drive evolutionary creativity. Simpson's book introduced concepts like "bradytelic" and "tachytelic" rates, and he recognized "so-called living fossils" and "major transitions" in evolution. The colloquium featured 16 papers in five categories: Early Life, Macroevolution, Human Evolution, Rates, and Patterns. Topics included the origins of life, the Cambrian explosion, species extinction, human evolution, and molecular biology's role in understanding evolutionary rates. Papers discussed the genetic diversity of the human histocompatibility complex, the evolution of chloroplasts, and the use of molecular clocks to determine evolutionary timelines. The colloquium highlighted the integration of paleontology, genetics, and molecular biology in understanding evolutionary processes. It also addressed the role of chance in adaptive evolution and the complexity of evolutionary patterns. The papers emphasized the importance of molecular biology in elucidating the history of life, particularly in the early three billion years of Earth's history. The colloquium underscored the ongoing relevance of Simpson's work in the context of modern evolutionary biology.This paper presents a colloquium titled "Tempo and Mode in Evolution," organized by Walter M. Fitch and Francisco J. Ayala, held in Irvine, CA, in 1994. The colloquium celebrated the 50th anniversary of George Gaylord Simpson's book "Tempo and Mode in Evolution," which explored evolutionary tempo (rates of change) and mode (patterns of evolution). Simpson's work was influenced by Theodosius Dobzhansky's "Genetics and the Origin of Species," which integrated Darwinism with Mendelian genetics. Simpson argued that evolutionary rates depend on factors like variability, mutation rates, generation length, population size, and natural selection. He also emphasized that natural selection is not merely a negative process but can drive evolutionary creativity. Simpson's book introduced concepts like "bradytelic" and "tachytelic" rates, and he recognized "so-called living fossils" and "major transitions" in evolution. The colloquium featured 16 papers in five categories: Early Life, Macroevolution, Human Evolution, Rates, and Patterns. Topics included the origins of life, the Cambrian explosion, species extinction, human evolution, and molecular biology's role in understanding evolutionary rates. Papers discussed the genetic diversity of the human histocompatibility complex, the evolution of chloroplasts, and the use of molecular clocks to determine evolutionary timelines. The colloquium highlighted the integration of paleontology, genetics, and molecular biology in understanding evolutionary processes. It also addressed the role of chance in adaptive evolution and the complexity of evolutionary patterns. The papers emphasized the importance of molecular biology in elucidating the history of life, particularly in the early three billion years of Earth's history. The colloquium underscored the ongoing relevance of Simpson's work in the context of modern evolutionary biology.