Lamarckism: Theory of Inheritance of Acquired Characters

Lamarckism is the early theory of evolution proposed by Jean-Baptiste Lamarck in 1809. It states that organisms change during their lifetime by using or not using body parts, and that these acquired changes are passed to their offspring. Although later science rejected its main mechanism, Lamarck was the first to propose a systematic theory of evolution.

Studying Lamarckism matters because it shows how scientific ideas are tested and improved.

Key Concepts

• Use and disuse: organs used more become larger and stronger; unused organs shrink over generations.
• Inheritance of acquired characters: traits gained during life, like muscles from exercise, are inherited by offspring.
• Internal vital force and environmental need: Lamarck proposed that new needs created by the environment drive organisms to develop new organs, and that life tends towards greater complexity.
• Acquired character: a trait arising from habit, environment or injury, not present in the genes at birth.

How It Works

In Lamarcks explanation, the classic example is the giraffe. Ancestral giraffes with short necks stretched to reach leaves on tall trees during food shortage. This constant stretching slightly lengthened the neck and front legs in each individual. The lengthened neck was then inherited by calves, which stretched still further in their own lives. Over many generations, this produced the modern long-necked giraffe. Similarly, he argued that aquatic birds developed webbed feet by stretching the skin between toes while swimming, and that snakes lost their legs through disuse while elongating their bodies. The theory rested on two laws: first, use develops and disuse weakens an organ; second, such acquired changes are transmitted to the next generation. August Weismann later tested this by cutting off the tails of mice for many generations; every generation was still born with full tails, showing that body changes that do not alter the germ cells are not inherited. Modern genetics explains why: only changes in DNA of reproductive cells pass to offspring.

Worked Example

Work through Weismanns test numerically. Suppose tails are cut in 20 successive generations of mice, with each generation having, say, 50 pups measured. If Lamarckism were correct, the average tail length should steadily fall and pups should eventually be born tailless. Generation 1 pups are born with normal tails, about 10 centimetres on average for the strain, despite their parents tails being cut. After 20 generations, 20 times 50 equals 1,000 pups examined, the newborn tail length remains about 10 centimetres, with no downward trend. The arithmetic is simple but decisive: 1,000 observations, zero inherited shortening. Compare this with a real hereditary change: if a mutation shortened tails in the germ line, it would appear in pups immediately. This experiment, backed by genetics, refuted the inheritance of acquired mutilations while leaving room for genuine evolution by other mechanisms.

Common Misconceptions

• Lamarck was not foolish; he correctly recognised that species change and that environment matters, but proposed the wrong mechanism before genes were known.
• A bodybuilders children are not born muscular; training changes the parents body cells, not the DNA in sperm or eggs.
• Modern epigenetic effects, where some chemical marks on DNA can persist briefly, are not a return of Lamarckism; they do not rewrite genes from habits in the way Lamarck proposed.

Real-World Applications

Understanding why Lamarckism fails is practical: it prevents false expectations in medicine, farming and animal breeding, where improvement requires selecting heritable variation, not training parents.

Lamarck first argued that life evolves, driven by use, disuse and inheritance of acquired traits. Experiments and genetics disproved that mechanism, but his challenge opened the road to modern evolutionary theory.