Lamarckism

Lamarck believed that all living organisms possess an innate, vital force that drives them to become more complex, organized, and structurally perfect over time.

Lamarck's first postulate suggested that living organisms possess an inherent internal vital force that drives them toward greater organizational complexity.

Under the use and disuse principle, frequent running strengthens and elongates the limbs, and under the inheritance of acquired characters, this trait is passed down.

Both Darwin and Lamarck recognized that organisms adapt to their environments over time, though they proposed different mechanisms for how these adaptations occur.

Lamarck proposed that the giraffe's ancestors had short necks but stretched them to reach leaves on high branches, leading to a longer neck through "use" which was then inherited.

Lamarckism is rejected because somatic changes (acquired characters) cannot alter germ-line DNA, meaning they cannot be inherited under modern genetic principles.

Genetic engineering alters the genome directly. Lamarckism refers to somatic phenotypic changes (like organ use/disuse) being converted into heritable genetic info, which does not happen here.

Under Lamarckism, the disuse of wings because of terrestrial lifestyle and abundant ground-level resources led to the degeneration of wings over generations.

Lamarck argued that variations are purposefully acquired during life in response to environment, whereas Darwin proposed that variations exist naturally in a population before natural selection acts.

Under Lamarckism, the mental training/acquired skill of navigating the maze would be passed to the offspring, making subsequent generations progressively better at it without training.

Lamarckism explains vestigial organs (like the human appendix, coccyx, or wisdom teeth) as structures that lost their function and gradually degenerated due to continuous disuse over generations.

This is Lamarck's second postulate (environmental changes produce new needs, which lead to the development of new organs through effort or behavior).

Mutilating the tail alters somatic tissue (somatoplasm) but leaves the germplasm (reproductive cells) untouched, demonstrating that somatic changes are not inherited.

Orthogenesis (straight-line evolution) is conceptually linked to Lamarck's internal vital force, suggesting organisms have an innate drive to evolve in a specific, progressive direction.

Lamarckism posits that the plant responds to the environmental dry stress by adapting its physiology (succulence) to meet its new need, then transmitting this acquired trait.

Darwin proposed Pangenesis to explain how physical modifications in body parts might be communicated to reproductive cells, aligning closely with Lamarckian inheritance.

Lamarck's theory posits that environmental changes create new needs ("besoin") in an organism, which drives changes in habits, leading to the use or disuse of specific organs.

Lamarck's fourth postulate states that somatic modifications acquired during an organism's lifetime due to use/disuse are directly transmitted to the next generation.

The elongation of the giraffe's neck via stretching (use of organ) and subsequent inheritance of this stretched neck is the classic textbook example of Lamarckism (Inheritance of Acquired Characters).