How did different environments produce lateral branches in Lamarck’s classification system?

In Jean-Baptiste Lamarck’s classification system, the primary structure was a single, linear scale of increasing complexity, ranging from the simplest microscopic organisms to mammals. However, Lamarck recognized that species did not fit perfectly into this simple series.1

To account for this, he described species as forming "lateral ramifications" or branches relative to the general "masses" of organization. These lateral branches were produced when organisms underwent transformations in response to the diverse, particular environments to which they were exposed.1

According to Lamarck, these environmental influences acted as a modifying force that disrupted the regularity of the primary scale of increasing complexity. As animals encountered different environments, they developed new needs (besoins) and adopted new habits. These habits led to the increased use or disuse of specific organs, resulting in physical modifications that were then inherited by subsequent generations. Over vast periods, these accumulated changes caused species to diverge from the main line of progression, creating the lateral branches in his classification.123