Editing Handicap principle (section)

=== Signals to members of the same species ===

<!--[[File:Babblers, Ardon Creek, Ramon Makhtesh, Negev, Israel (cropped).jpg|thumb|[[Arabian babbler]] are highly social, helping to care for nestlings of unrelated individuals.<ref name=Zahavi1990/>]]
-->
Zahavi studied in particular the [[Arabian babbler]], a highly social bird, with a life-length of 30 years, which appears to behave [[altruism|altruistically]]. Its helping-at-the-nest behavior, where non-parent birds assist in feeding, guarding, and caring for nestlings, often occurs among unrelated individuals. This, therefore, cannot be explained by [[kin selection]], [[natural selection]] acting on genes that close relatives share with the altruistic individual. Zahavi reinterpreted these behaviors according to his signalling theory and its correlative, the handicap principle. The altruistic act is costly to the donor, but may improve its attractiveness to potential mates. The evolution of this condition may be explained by [[competitive altruism]].<ref name=Zahavi1974>{{cite journal |last=Zahavi |first=Amotz |author-link=Amotz Zahavi |year=1974 |title=Communal nesting by the Arabian Babbler: A case of individual selection |journal=Ibis |volume=116 |pages=84–87 |doi=10.1111/j.1474-919X.1974.tb00225.x}}</ref><ref>{{cite journal |last1=Anava |first1=A. |last2=Kam |first2=M. |last3=Shkolnik |first3=A. |last4=Degen |first4=A.A. |year=2001 |jstor=4089815 |title=Does group size affect field metabolic rate of Arabian Babbler (''Turdoides squamiceps'') nestlings? |journal=[[The Auk]] |volume=118 |issue=2 |pages=525–528 |url=http://sora.unm.edu/node/131937 |doi=10.1642/0004-8038(2001)118[0525:DGSAFM]2.0.CO;2 |s2cid=38680548 |doi-access=free }}</ref><ref name=Zahavi1990>{{cite book |last=Zahavi |first=Amotz |author-link=Amotz Zahavi |year=1990 |chapter=Arabian Babblers: The quest for social status in a cooperative Breeder |pages=105–130 |title=Cooperative Breeding in Birds |editor1-first=P. B. |editor1-last=Stacey |editor2-first=W. D. |editor2-last=Koenig |publisher=[[Cambridge University Press]]}}</ref>

French biologist Patrice David showed that in the [[stalk-eyed fly]] species ''[[Cyrtodiopsis dalmanni]]'', genetic variation underlies the response to environmental stress, such as variable food quality, of a male sexual ornament, eye span. He showed that some male [[Genotype|genotypes]] always develop large eye spans, but others reduce eye span in proportion to environmental worsening. David inferred that female mate choice yields genetic benefits for offspring.<ref name="david">{{cite journal |first1=P. |last1=David |author2=T. Bjorksten |author3=K. Fowler |author4=A. Pomiankowski |year=2000 |title=Condition-dependent signalling of genetic variation in stalk-eyed flies |journal=[[Nature (journal)|Nature]] |volume=406 |pages=186–188 |doi=10.1038/35018079 |pmid=10910358 |issue=6792|bibcode=2000Natur.406..186D |s2cid=4425172 }}</ref>