Comparison of Evolutionary Theories (Darwin vs. Lamarck)
📌 Darwin's theory posits evolution occurs via natural selection, where only individuals suited to the environment survive and reproduce.
🦒 In the giraffe example, long-necked giraffes survive because they can reach high leaves, reproduce, and pass on the trait, while short-necked ones perish.
🔄 This inheritance of favorable traits leads to a reduction in less-suited individuals, such as the short-necked giraffes eventually disappearing.

Lamarck's Theory of Inheritance of Acquired Characteristics
💪 Lamarck proposed evolution results from the continuous use of body parts, leading to changes known as the "use and disuse" law.
🦒 Lamarck suggested long giraffe necks resulted from stretching over years to reach high leaves, and this acquired trait was inherited by offspring.
❌ Conversely, unused body parts degenerate over generations, a core concept contrasting with later genetic understanding.

Comparison of Darwin and Weismann's Theories
🧬 Weismann, a supporter of Darwin, argued that changes in body cells due to environmental influence are not inherited by offspring; evolution depends on germline genes.
🔬 Weismann demonstrated this using mice: repeatedly cutting the tails of successive generations resulted in offspring that still possessed tails, disproving the inheritance of acquired physical traits.
🦒 In genetic terms, Weismann suggested the long neck in giraffes is controlled by dominant genes, while the short neck is recessive, aligning with Mendelian genetics.

Contrasting Lamarck and Weismann
🐀 Lamarck believed acquired traits (like horns growing on stags due to fighting) are passed down, which Weismann fundamentally rejected.
🧪 Weismann's mouse experiment across 21 generations consistently showed that surgically acquired traits (missing tails) were not passed on, supporting the idea that environmental impacts on somatic cells are irrelevant to inheritance.

Key Points & Insights
➡️ Darwinian selection focuses on pre-existing variation being selected by the environment.
➡️ Lamarckian inheritance relies on traits acquired during an organism's lifetime being passed to its progeny.
➡️ Weismann's contribution established that heredity is strictly through sex cells (genes), invalidating the inheritance of environmentally induced physical changes.

📸 Video summarized with SummaryTube.com on Jan 13, 2026, 11:54 UTC