Lamarckism | Biology for JAMB PDF Download

Introduction

Lamarckism, also known as Lamarckian evolution or the theory of inheritance of acquired characteristics, is a theory of evolution proposed by the French biologist Jean-Baptiste Lamarck in the early 19th century. Lamarckism suggests that organisms can change during their lifetime in response to their environment, and these acquired characteristics can be passed on to their offspring. This theory was an influential precursor to Charles Darwin's theory of evolution by natural selection. This note will explore the key principles and criticisms of Lamarckism.

Key Principles of Lamarckism

• Law of Use and Disuse: Lamarck proposed that organs or traits of an organism that are used frequently become stronger and more developed, while those that are not used tend to deteriorate and eventually disappear. He believed that the environment directly influences an organism's physical characteristics.
• Law of Inheritance of Acquired Characteristics: According to Lamarck, the changes acquired by an organism during its lifetime are inherited by the next generation. He suggested that traits acquired through the individual's efforts or experiences would be passed on to offspring, leading to gradual evolutionary changes over time.
• Law of Complexity: Lamarck argued that organisms have an innate drive to become more complex and better adapted to their environment. He believed that simple organisms can transform into more complex ones through a continuous process of change and adaptation.
• Progression and Linearity: Lamarckism implies a linear progression of species, suggesting that organisms move from simpler forms to more complex forms over time. Lamarck proposed a ladder-like hierarchy of species, with humans representing the most complex form.

Criticism of Lamarckism

• Lack of Experimental Evidence: Lamarck's theory lacks substantial experimental evidence to support the inheritance of acquired characteristics. Many experiments conducted after his time have failed to demonstrate the direct transmission of acquired traits to subsequent generations.
• Genetic Inheritance: The discovery of genetics and the understanding of DNA have provided strong evidence that traits are primarily inherited through the transmission of genes. Lamarckism does not adequately explain the mechanism of genetic inheritance.
• Evolutionary Mechanism: Lamarckism fails to explain the process of variation and natural selection, which are fundamental to Darwin's theory of evolution. It does not account for the role of random genetic mutations and differential reproductive success in driving evolutionary change.
• Fossil Record: The fossil record does not show a gradual and linear progression of species as proposed by Lamarckism. Instead, it reveals a complex pattern of extinction, diversification, and transitional forms that align more with the principles of Darwinian evolution.

Conclusion

Lamarckism, although influential in shaping early evolutionary thought, has been largely discredited in light of subsequent scientific discoveries. While Lamarck's emphasis on the role of the environment and the concept of adaptation were valuable contributions, his theory's lack of a mechanism for inheritance and its inability to explain the complexity of evolutionary processes ultimately limited its acceptance. Darwin's theory of evolution by natural selection, with its emphasis on genetic inheritance and gradual changes over time, has become the prevailing explanation for the diversity of life on Earth.