# Summary explained — The Origin of Species > Chapter companion for The Origin of Species by Charles Darwin. ## What happens Varieties cannot be distinguished from species except by intermediate linking forms and an indefinite amount of difference. In large genera, species show a strong analogy with varieties, and dominant species yield the most varieties, which tend to become new species. Thus, larger genera grow larger and dominant forms become more dominant, while also breaking into smaller groups. ## Themes in this chapter ### Variation and Inheritance The chapter discusses how varieties cannot be distinguished from species and how varieties tend to become new species, emphasizing the role of variation. ### Extinction and the Succession of Forms The text describes how dominant species yield varieties that become new species, leading to the succession and dominance of forms. ## Key lines > varieties cannot be distinguished from species⁠—except, first, by the discovery of intermediate linking forms; and, secondly, by a certain indefinite amount of difference between them Varieties and species are only distinguishable by finding intermediate forms or by an undefined degree of difference. _Highlights the difficulty in distinguishing varieties from species._ > the species of large genera present a strong analogy with varieties Species in large genera closely resemble varieties in their characteristics. _Emphasizes the analogy between species and varieties in large genera._ > it is the most flourishing or dominant species of the larger genera within each class which on an average yield the greatest number of varieties The most successful and dominant species in large genera produce the most varieties. _Links dominance to the production of varieties._ ## Links - HTML: https://www.betterreads.online/discover/the_origin_of_species_se/chapters/summary - Book: https://www.betterreads.online/discover/the_origin_of_species_se - All chapters: https://www.betterreads.online/discover/the_origin_of_species_se/chapters