1. Lack of Evidence: Lamarck's theory proposed that organisms could pass on to their offspring traits or characteristics that they acquired during their lifetime due to environmental factors. However, scientific evidence did not support this claim. There was no concrete evidence to show that acquired traits could be inherited.
2. Mendelian Genetics: The rediscovery of Gregor Mendel's work on heredity in the early 20th century challenged Lamarck's ideas. Mendel's laws of inheritance provided a more accurate understanding of how traits are passed from one generation to the next, demonstrating that offspring inherit genetic variations from both parents through discrete units called genes.
3. August Weismann's Experiments: August Weismann conducted experiments that further disproved Lamarck's theory. Weismann performed tail amputations on several generations of mice, but no offspring were born without tails, indicating that acquired characteristics could not be directly passed on.
4. Molecular Biology: Advances in molecular biology revealed the molecular mechanisms of heredity, including DNA replication, gene expression, and protein synthesis. These discoveries provided a deeper understanding of the underlying processes of heredity and showed that Lamarck's proposed mechanism was not supported by molecular evidence.
5. Modern Evolutionary Theory: The modern theory of evolution, also known as the theory of natural selection proposed by Charles Darwin and Alfred Russel Wallace, presented a more comprehensive and well-supported explanation for the diversity of life on Earth. Darwin's theory focused on the role of genetic variation, natural selection, and the inheritance of advantageous traits over successive generations.
In summary, Lamarck's theory was disproved due to the lack of evidence supporting the inheritance of acquired characteristics, the emergence of Mendelian genetics, Weismann's experiments, advances in molecular biology, and the acceptance of the modern evolutionary theory based on natural selection.