Why do giraffes have long necks? A new study by biologists at Penn State University explores this classic question, offering fresh perspectives.
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Contrary to the prevailing theory that long necks are due to male competition, researchers observed that female giraffes have proportionally longer necks. This finding suggests that the high nutritional needs of females may be a key factor in the evolution of the giraffe's long neck.
Classical evolution theories by Lamarck and Darwin suggest that giraffes' long necks evolved to reach the high leaves of trees. However, the recent "necks-for-sex" hypothesis posits that this evolution is due to male competition. Males with longer necks would perform better in dominance battles known as necking fights.
The study, recently published in the journal
Mammalian Biology, examined the body proportions of wild and captive giraffes. The results indicate that neck length might be a result of females striving to reach hard-to-access leaves. By analyzing hundreds of photos of Masai giraffes, researchers found that body proportions change from a young age.
Through photos of both captive and wild giraffes, researchers were able to measure relative body proportions. They observed that females have longer necks and trunks, while males have longer forelimbs and thicker necks. These differences are apparent in adults, indicating that females use their long necks to reach leaves inaccessible to other herbivores.
Although males and females have similar body proportions at birth, they differ significantly by sexual maturity. Females have proportionally longer necks and bodies, which might aid in foraging and child-rearing, while males have thicker necks and longer forelimbs, which might help in fights and reproduction.
Credit: Penn State Researchers suggest that sexual selection has likely contributed to size differences between males and females, as is the case for many polygynous ungulate mammals. The team is also using genetics to better understand the reproductive relationships among wild giraffes to guide conservation efforts for this threatened species.
Conserving giraffe habitats is crucial for their survival. The population of Masai giraffes has significantly declined over the past 30 years, partly due to habitat loss and poaching.