Short Answer
Lamarck’s theory was rejected because it stated that acquired characteristics developed during an organism’s lifetime could be inherited by offspring. Later scientific studies proved that such acquired traits are not passed from parents to children.
Advances in genetics showed that only changes in genes can be inherited. Experiments failed to support Lamarck’s ideas, so his theory was replaced by more accurate explanations of evolution, especially Darwin’s theory of natural selection.
Detailed Explanation :
Rejection of Lamarck’s Theory of Acquired Characteristics
Lamarck’s theory of acquired characteristics was an early attempt to explain evolution. Jean-Baptiste Lamarck proposed that organisms change during their lifetime due to use and disuse of body parts and that these changes are passed on to the next generation. Although this idea was important in the early history of biology, it was later rejected because it lacked scientific proof and did not match experimental evidence.
As biology developed, scientists began to test Lamarck’s ideas using experiments and observations. Over time, it became clear that Lamarck’s explanation of inheritance and evolution was incorrect.
No Scientific Evidence for Inheritance of Acquired Traits
One major reason Lamarck’s theory was rejected is that there was no scientific evidence to support the inheritance of acquired characteristics. Lamarck believed that changes developed during an organism’s lifetime could be passed to offspring.
For example, he claimed that giraffes developed long necks because they stretched to reach tall trees, and this longer neck was inherited by their young. However, later studies showed that stretching the neck does not change genes and cannot be passed to the next generation.
Many experiments were conducted to test this idea. One famous experiment involved cutting the tails of mice for many generations. Even after many generations, the mice were always born with tails. This clearly showed that acquired traits are not inherited.
Development of Genetics
The discovery of genetics played a major role in rejecting Lamarck’s theory. Scientists learned that traits are controlled by genes present in reproductive cells. Only changes in these genes can be passed from parents to offspring.
Changes that occur in body cells during an organism’s lifetime do not affect genes. For example, muscle growth due to exercise or loss of limbs due to injury does not change genetic material. Therefore, such traits cannot be inherited.
Gregor Mendel’s work on inheritance further proved that traits follow fixed genetic rules. This genetic understanding directly contradicted Lamarck’s idea of inheritance of acquired characteristics.
Incorrect Explanation of Evolution
Lamarck believed that organisms actively change themselves to meet environmental needs. According to him, organisms make efforts to adapt, and these efforts cause changes in body structures.
Modern biology shows that organisms do not change because of need or effort. Instead, variations already exist in populations. Nature selects individuals with useful variations through natural selection. This means evolution happens naturally, not by conscious effort.
Because Lamarck’s explanation of how evolution occurs was incorrect, his theory was rejected.
Contradiction with Darwin’s Theory
Charles Darwin later proposed the theory of natural selection, which provided a better explanation of evolution. Darwin showed that organisms with useful inherited traits survive and reproduce more.
Darwin’s theory was supported by strong evidence from fossils, comparative anatomy, and later genetics. Unlike Lamarck’s theory, Darwin’s ideas explained evolution without relying on inheritance of acquired traits.
As Darwin’s theory gained acceptance, Lamarck’s theory lost support among scientists.
Lack of Experimental Support
Lamarck’s theory was based mainly on observation and imagination rather than controlled experiments. He did not provide experimental proof to show that acquired characteristics are inherited.
Modern science relies on experiments, testing, and evidence. When Lamarck’s ideas were tested experimentally, they failed. This lack of experimental support was a strong reason for rejecting his theory.
Modern Understanding of Evolution
Today, evolution is explained using genetics, mutation, variation, and natural selection. These processes clearly show how traits are inherited and how populations change over time.
Lamarck’s theory does not fit with modern biological knowledge. While he correctly believed that organisms evolve, his explanation of how evolution occurs was wrong.
Historical Importance Despite Rejection
Although Lamarck’s theory was rejected, his contribution to biology is still important. He was one of the first scientists to propose that evolution occurs and that organisms are not fixed.
His ideas encouraged further research and discussion, which eventually led to better theories of evolution. Lamarck is remembered as a pioneer, even though his theory is no longer accepted.
Conclusion
Lamarck’s theory was rejected because it lacked scientific evidence and was proven incorrect by experiments and genetic studies. Acquired characteristics cannot be inherited, and organisms do not evolve by effort or need. Modern genetics and Darwin’s theory of natural selection provided accurate explanations of evolution, replacing Lamarck’s ideas. However, Lamarck’s early contribution helped shape the development of evolutionary biology.