Summary
Consistent differences in size or appearance between the sexes, shaped by sexual selection.
In depth
Differences in size, colour and ornaments between sexes. Often male-biased through sexual selection, but in raptors and spiders females are larger. Extreme in elephant seals where males are 3 to 10 times heavier.
Dimorphism includes size, colour and weapons. It relates to mating systems. It may disappear when selection changes.
Example: male lions have manes.
Dimorphism includes size (male elephant seals are up to 10 times heavier than females), ornaments (peacock tails, lion manes), weapons (stag antlers, beetle horns) and behaviour. Sexual selection favours male traits that help in competition or attract mates, with costs for survival. Reversed dimorphism occurs in birds of prey, owls and spiders such as orb weavers, where females are larger, maybe due to fecundity selection or hunting.
Differences may involve hormones and sex-specific gene expression, and can be plastic (breeding plumage). Dimorphism correlates with mating system: polygynous species show more. In the anglerfish, tiny males fuse to females. Dimorphic species may be at greater risk from environmental change.
Example: in mallards, males have bright plumage in the breeding season, while females are camouflaged for nesting.
Frequently asked questions
What is Sexual Dimorphism?
Consistent differences in size or appearance between the sexes, shaped by sexual selection.
Which area of biology covers Sexual Dimorphism, and how advanced is it?
Sexual Dimorphism is one of the 53 topics in Zoology & Animal Diversity. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include Parental Care Evolution, Domestication Genetics, Life History Strategies.
Can you give an example of Sexual Dimorphism?
Peacock trains versus peahens' camouflage.
What should I learn before Sexual Dimorphism?
Work through the Beginner topics in Zoology & Animal Diversity first, such as Animal Kingdom, Vertebrates and Invertebrates, Sponges, then return to Sexual Dimorphism. Advanced topics assume the Intermediate vocabulary.
What topics are related to Sexual Dimorphism?
The closest topics to Sexual Dimorphism are Parental Care Evolution, Domestication Genetics, Life History Strategies, Island Gigantism and Dwarfism. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Sexual Dimorphism?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Sexual Dimorphism. To practise the whole of Zoology & Animal Diversity, use the Zoology & Animal Diversity quiz.
How is Sexual Dimorphism different from Parental Care Evolution?
Sexual Dimorphism: Consistent differences in size or appearance between the sexes, shaped by sexual selection. Parental Care Evolution: Care by one or both parents evolves when benefits to offspring outweigh costs to parents. Read both side by side and note what each one explains.
How should I study Sexual Dimorphism step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Parental Care Evolution and explain the difference aloud. Finally, take the Zoology & Animal Diversity quiz and come back to this page for any question you miss.