What experiment did Weismann conduct to challenge Lamarckism?

Weismann's experiment involving the cutting off of mice tails was pivotal in challenging Lamarck's theory of inheritance of acquired traits. Lamarck proposed that characteristics acquired during an organism's life could be passed on to its offspring. For instance, according to Lamarck, if an organism alters its body (like a mouse losing its tail), that change could be inherited by the next generation.

In his experiment, Weismann performed a series of tests where he cut the tails off several generations of mice, expecting that their offspring would either show the same tailless condition or exhibit some variation related to it. However, the offspring of these tailless mice were born with tails. This result demonstrated that even though the parent's tails were removed, the genetic information that determined tail presence had not changed, thus supporting the idea that acquired characteristics cannot be inherited.

This experiment laid the groundwork for understanding genetics and inheritance, ultimately supporting the principles of Darwinian evolution rather than Lamarckian theories. Weismann's work helped to clarify the distinction between heritable traits encoded in genes and modifications that occur purely as a result of environmental influences or experiences.