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The Evolutionary Significance of Mountain Sheep Horns

Valerius Geist
Evolution
Vol. 20, No. 4 (Dec., 1966), pp. 558-566
DOI: 10.2307/2406590
Stable URL: http://www.jstor.org/stable/2406590
Page Count: 9
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
The Evolutionary Significance of Mountain Sheep Horns
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Abstract

The hypothesis was tested, that horns of male mountain sheep evolved as display organs. Seven predictions were made from this hypothesis, of which six were investigated and verified. These are: Rams have a distinct horn display behavior; rams can distinguish horn sizes; large horned individuals dominated smaller horned rams irrespective of the latter's age; horn size conveyed a priori dominance to its bearer; large horned rams enjoyed a reproductive advantage. The prediction, that loss of much horn leads to a loss in dominance was not investigated. The above hypothesis in conjunction with the observation that breeding rams show higher mortality than nonbreeding rams, predicted that rams with good horn growth die younger than rams with poor horn growth. The prediction was verified. The horns of rams are not only important as weapons and shields in combat, but also as the major dominance-rank determinance, and as visual dominance-rank symbols.

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