Lamarckism — Core Principles

Core Principles

Lamarckism, proposed by Jean-Baptiste Lamarck in the early 19th century, was one of the first theories to explain biological evolution. It is built on two main principles: the 'Principle of Use and Disuse' and the 'Inheritance of Acquired Characters'.

The first principle suggests that organs used more frequently develop and strengthen, while unused ones degenerate. The second, and most distinctive, principle states that these changes acquired during an organism's lifetime are passed on to its offspring.

For example, Lamarck explained the giraffe's long neck by proposing that ancestral giraffes stretched their necks to reach food, and this acquired length was inherited by subsequent generations. While revolutionary for its time in suggesting species change, Lamarckism was largely disproven by August Weismann's experiments and modern genetics, which showed that acquired somatic changes are not heritable.

Despite its rejection, it remains historically significant as a precursor to Darwinism and for introducing the concept of adaptation and evolutionary change.

Important Differences

vs Darwinism (Natural Selection)

Aspect	This Topic	Darwinism (Natural Selection)
Mechanism of Evolution	Lamarckism: Inheritance of acquired characters (use/disuse leads to changes, which are then inherited).	Darwinism: Natural selection acting on pre-existing heritable variations.
Role of Environment	Lamarckism: Environment directly causes changes in organisms, which are then inherited.	Darwinism: Environment selects individuals with advantageous variations; it does not cause the variation.
Source of Variation	Lamarckism: Variations arise from an organism's response to its environment and differential use of organs during its lifetime.	Darwinism: Variations are random, inherent, and pre-existing within a population, arising from mutation and recombination.
Direction of Change	Lamarckism: Directed towards perfection or adaptation, often implying an internal 'will to progress'.	Darwinism: Non-directional; survival and reproduction are based on fitness in a given environment, not a predetermined goal.
Fate of Individual Changes	Lamarckism: Changes acquired by an individual during its lifetime are passed to offspring.	Darwinism: Changes acquired by an individual during its lifetime are generally not passed to offspring; only heritable traits are passed.
Example (Giraffe's Neck)	Lamarckism: Giraffes stretched their necks to reach leaves, and this acquired length was inherited.	Darwinism: Giraffes with naturally longer necks had a survival advantage, reproduced more, passing on their longer neck genes.

Lamarckism and Darwinism offer fundamentally different explanations for how evolution occurs. Lamarck believed that organisms acquire traits during their lifetime through use and disuse, and these acquired traits are then passed to offspring. In contrast, Darwin proposed that evolution occurs through natural selection, where individuals with pre-existing, heritable variations that are advantageous in a given environment are more likely to survive and reproduce, thus passing on those beneficial traits. Lamarck's theory implies a direct, purposeful change and inheritance of somatic modifications, while Darwin's theory emphasizes random variation and differential survival based on environmental pressures acting on germline traits. Modern biology overwhelmingly supports Darwinian natural selection.