BYOD 9th Grade lesson. Darwin vs Lamarck

Hey everyone. Let's go deeper and try to understand different ideas on organism's changing over time.

Lamarck

Lamarck was affected by the similarities of many of the animals he studied, and was impressed too by the growing fossil record. It led him to argue that life was not fixed.

When surrounding conditions changed, organisms had to change their behavior to survive. If they began to use an organ more than they had in the past, it would increase in its lifetime. If a giraffe stretched its neck for leaves, for example, a "nervous fluid" would flow into its neck and make it longer. Its children would inherit the longer neck, and continued stretching would make it longer still over many generations. Meanwhile organs that organisms stopped using would become smaller.

This sort of evolution, for which Lamarck is most famous today, was only one of two ways he suggested. As organisms changed to fit their surroundings, nature also drove them unstoppably upward from simple forms to increasingly complex ones. Lamarck believed that life had begun through spontaneous generation. But he claimed that new primitive life forms suddenly changed throughout the history of life.

Darwin

Darwin depended on much the same evidence for evolution that Lamarck did, but made completely different arguments from Lamarck. Darwin argued that complexity changed simply as a result of life adapting to its local conditions from one generation to the next, much as modern biologists see this process. Darwin tried on and eventually rejected different ideas about heredity and never came to any conclusion about how qualities were passed from parent to offspring.

Lamarckian inheritance is an idea that today is known mainly from textbooks, where it is used to as a historical contrast for our modern understanding of genetic inheritance. Despite all he got wrong, Lamarck can be credited with envisioning evolutionary change for the first time.

And NOW do this! Enjoy!