# Multiple, Rudimentary, and Lowly-Organised Structures Are Variable explained — The Origin of Species > Chapter companion for The Origin of Species by Charles Darwin. ## What happens This chapter discusses the tendency for multiple, rudimentary, and lowly-organised structures to be more variable than specialized ones. Darwin notes that repeated parts (like vertebrae or stamens) are often variable in number and structure, while parts occurring in lesser numbers are more constant. He attributes this to low specialization: when a part performs diverse functions, natural selection does not fix its form as precisely as when it serves a single purpose. Rudimentary parts, being useless, are also highly variable because natural selection has no power to check deviations. ## Themes in this chapter ### Variation and Inheritance Explores how multiple and rudimentary structures exhibit high variability due to lack of specialization or utility. ### Adaptation and the Utilitarian Doctrine Discusses how natural selection preserves or rejects deviations based on the advantage to the organism, with rudimentary parts escaping this scrutiny. ## Character check-ins ### Geoffroy Saint-Hilaire Cited for the rule that multiple repeated parts are variable in number and structure. ### Professor Owen Mentioned for the expression 'vegetative repetition' as a sign of low organisation. ## Key lines > It seems to be a rule, as remarked by Is. Geoffroy St. Hilaire, both with varieties and species, that when any part or organ is repeated many times in the same individual (as the vertebrae in snakes, and the stamens in polyandrous flowers) the number is variable; whereas the number of the same part or organ, when it occurs in lesser numbers, is constant. Geoffroy St. Hilaire observed that in both varieties and species, parts that appear many times (like snake vertebrae or stamens in certain flowers) tend to vary in number, while parts that appear fewer times are more constant. _Introduces the rule of variability in multiple structures._ > As 'vegetative repetition,' to use Professor Owen's expression, is a sign of low organisation; the foregoing statements accord with the common opinion of naturalists, that beings which stand low in the scale of nature are more variable than those which are higher. Because 'vegetative repetition' indicates low organisation, this supports the naturalist view that lower organisms are more variable than higher ones. _Links multiple parts to low specialisation and higher variability._ > In the same way that a knife which has to cut all sorts of things may be of almost any shape; whilst a tool for some particular purpose must be of some particular shape. Just as a general-purpose knife can have any shape, but a specialized tool must have a specific shape, so too are unspecialized parts more variable. _Analogy illustrating why unspecialized parts remain variable._ > Rudimentary parts, as is generally admitted, are apt to be highly variable. We shall have to recur to this subject; and I will here only add that their variability seems to result from their uselessness, and consequently from natural selection having had no power to check deviations in their structure. Rudimentary parts are highly variable because they are useless, so natural selection does not act to prevent structural changes. _Explains variability of rudimentary organs due to lack of selective pressure._ ## Links - HTML: https://www.betterreads.online/discover/the_origin_of_species_se/chapters/multiple-rudimentary-and-lowly-organised-structures-are-variable - Book: https://www.betterreads.online/discover/the_origin_of_species_se - All chapters: https://www.betterreads.online/discover/the_origin_of_species_se/chapters