The Origin of Species · Chapter
Organs of Little Apparent Importance, as Affected by Natural Selection explained
Darwin explores how natural selection can act on seemingly trivial organs, arguing that ignorance of an organism's full economy prevents dismissing any part as unimportant.
What happens
Darwin explores how natural selection can act on seemingly trivial organs, arguing that ignorance of an organism's full economy prevents dismissing any part as unimportant. He uses examples like the giraffe's tail, the hooks of a trailing palm, and the sutures in young mammal skulls to show that organs may have had past importance, arise from correlated growth, or be co-opted for new functions. He also cautions against over-attributing every character to natural selection, noting roles of sexual selection, conditions of life, and laws of growth.
Themes in this chapter
Adaptation and the Utilitarian Doctrine
Darwin examines whether organs of little apparent importance can be explained by natural selection, defending the utilitarian view while acknowledging that some features may arise from other causes.
Variation and Inheritance
Discussion of slight variations, correlation of growth, and the transmission of characters from aquatic ancestors to land animals, as in the case of the tail.
Characters to notice
- Charles Darwin
Author and narrator, reflecting on the difficulty of understanding the origin of organs of little apparent importance and cautioning against over-attributing characters to natural selection.
- H. von Nathusius
Mentioned for his excellent Treatise showing that lessened exercise and abundant food are chief causes of modification in swine breeds.
Key passages
“The tail of the giraffe looks like an artificially constructed fly-flapper; and it seems at first incredible that this could have been adapted for its present purpose by successive slight modifications, each better and better fitted, for so trifling an object as to drive away flies; yet we should pause before being too positive even in this case, for we know that the distribution and existence of cattle and other animals in South America absolutely depend on their power of resisting the attacks of insects.”
The giraffe's tail appears to be a fly-swatter, and it seems unlikely that such a trivial function could drive its evolution through gradual improvements, but we must be cautious because in South America, cattle survival hinges on insect resistance.
Darwin uses the giraffe's tail to illustrate that even seemingly minor adaptations can be crucial for survival.
“A trailing palm in the Malay Archipelago climbs the loftiest trees by the aid of exquisitely constructed hooks clustered around the ends of the branches, and this contrivance, no doubt, is of the highest service to the plant; but as we see nearly similar hooks on many trees which are not climbers, and which, as there is reason to believe from the distribution of the thorn-bearing species in Africa and South America, serve as a defence against browsing quadrupeds, so the spikes on the palm may at first have been developed for this object, and subsequently have been improved and taken advantage of by the plant, as it underwent further modification and became a climber.”
A climbing palm uses hooks on its branches to ascend tall trees, but similar hooks on non-climbing trees serve as defense against herbivores, suggesting the palm's hooks originally evolved for protection and were later co-opted for climbing.
Darwin shows how a structure can change function over evolutionary time, a key concept in adaptation.
“The sutures in the skulls of young mammals have been advanced as a beautiful adaptation for aiding parturition, and no doubt they facilitate, or may be indispensable for this act; but as sutures occur in the skulls of young birds and reptiles, which have only to escape from a broken egg, we may infer that this structure has arisen from the laws of growth, and has been taken advantage of in the parturition of the higher animals.”
Skull sutures in young mammals are often said to help with birth, but since birds and reptiles also have them when hatching from eggs, the sutures likely originate from growth patterns and were later used to assist mammalian birth.
Darwin argues that a structure may arise from developmental constraints and later be co-opted for a different function.