Lamarckism

August Weismann cut off the tails of mice for 22 consecutive generations. The offspring of the 23rd generation still developed normal tails, proving that somatic modifications (mutilations/acquired traits) are not inherited.

Weismann's Germplasm Theory states that only changes in the germ cells (germplasm) are transmitted to offspring, while somatic cells (somatoplasm) do not pass genetic info to the next generation.

Lamarck postulated that the continuous disuse of an organ leads to its gradual degeneration, reduction in size, and ultimate disappearance (vestigialization), as seen in the limbs of snakes.

Under Lamarckism, the continuous disuse of eyes in a dark cave environment leads to developmental decay, which is then inherited by subsequent generations.

Epigenetics involves study of heritable changes in gene function (like DNA methylation or histone modification) caused by environmental factors without altering the underlying DNA sequence, conceptually echoing Lamarck's environmental influence.

Lamarck's "Philosophie Zoologique" was published in 1809, which coincidentally was the year Charles Darwin was born.

"Besoin" refers to the inner need or urge felt by an organism when faced with environmental change, prompting it to alter its behavior and use certain organs more than others.

The colorful plumage of male peacocks is a product of sexual selection (Darwinian concept). Lamarck focused on physical adaptations gained through use (webbed feet, long wading legs) or disuse (limbless snakes).

Modern genetics shows that phenotype changes in somatic tissues (like muscle hypertrophy from working out) do not alter the DNA sequences of germ cells, making inheritance impossible.

Lamarck explained webbed feet as an acquired physical modification resulting from the continuous effort of spreading the toes to push water while swimming.

While Lamarck recognized adaptation to the environment, he did not propose natural selection (survival of the fittest based on pre-existing genetic variations) as the mechanism.

Lamarck believed in "phyletic transformation" rather than absolute extinction; he argued that species do not die out but continuously evolve into newer, more complex forms.