Summary
Hypotheses explain why sexual reproduction persists despite its costs, including the Red Queen and mutation clearance.
In depth
Sex has a two-fold cost: only half the offspring produce young. Benefits: new genotypes in changing environments, faster spread of beneficial alleles (Fisher-Muller) and purging of harmful mutations (Muller's ratchet is avoided). Bdelloid rotifers are an ancient asexual group exception.
The paradox is that asexual reproduction doubles reproductive output, yet most eukaryotes reproduce sexually at least sometimes. Hypotheses explaining it include the Red Queen (parasites), Muller's ratchet (asexuals accumulate harmful mutations irreversibly), the Fisher-Muller effect (combining beneficial mutations), and Kondrashov's deterministic mutation hypothesis. DNA repair by recombination may also be a reason.
Evidence comes from bdelloid rotifers (ancient asexuals that survive using horizontal gene transfer and desiccation), whiptail lizards (asexual lineages from hybrids) and species such as Daphnia and aphids that alternate sex and clonal phases, using sex when conditions deteriorate. Anisogamy then evolved from isogamy through disruptive selection on gamete size.
Remember: the cost of males is the two-fold cost; the benefits are long-term and depend on environment.
Frequently asked questions
What is Evolution of Sex?
Hypotheses explain why sexual reproduction persists despite its costs, including the Red Queen and mutation clearance.
Which area of biology covers Evolution of Sex, and how advanced is it?
Evolution of Sex is one of the 53 topics in Evolution. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include Red Queen Hypothesis, Sexual Selection, Antibiotic Resistance Evolution.
Can you give an example of Evolution of Sex?
Lizards and fish have species that reproduce parthenogenetically.
What should I learn before Evolution of Sex?
Work through the Beginner topics in Evolution first, such as Evolution, Natural Selection, Charles Darwin, then return to Evolution of Sex. Advanced topics assume the Intermediate vocabulary.
What topics are related to Evolution of Sex?
The closest topics to Evolution of Sex are Red Queen Hypothesis, Sexual Selection, Antibiotic Resistance Evolution, Evolutionary Trade-offs. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Evolution of Sex?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Evolution of Sex. To practise the whole of Evolution, use the Evolution quiz.
How is Evolution of Sex different from Red Queen Hypothesis?
Evolution of Sex: Hypotheses explain why sexual reproduction persists despite its costs, including the Red Queen and mutation clearance. Red Queen Hypothesis: Species must constantly evolve just to keep pace with coevolving enemies such as parasites. Read both side by side and note what each one explains.
How should I study Evolution of Sex 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 Red Queen Hypothesis and explain the difference aloud. Finally, take the Evolution quiz and come back to this page for any question you miss.