Charles Darwin famously used his “survival of the fittest” theory in the 19th century to explain why giraffes have long necks.
Millions of years ago, giraffes with longer necks could reach more leaves on trees and survive competition, before passing the long-neck trait on to their genes, the legendary English naturalist said.
Now, scientists in the United States elaborate on Darwin’s findings with a new theory, and believe that it was women who drove the evolutionary trait.
They found that female giraffes have proportionally longer necks than males, and the cause was likely the high nutritional needs of females during pregnancy and lactation.
Interestingly, female giraffes have a more sloping body shape, while males are more upright, which may help develop their love interest.
Although males and females have the same body proportions at birth, they are significantly different when they reach sexual maturity. Males have wider necks and longer front legs, which could help in winning fights against other males and in mating.
For the study, researchers gathered thousands of photographs of captive and wild Masai giraffes (Giraffa tippelskirchi, pictured), a species native to East Africa.
The study, which builds on Darwin’s theory rather than disproving it, was led by Douglas Cavener, a professor of biology at Pennsylvania State University.
“Giraffes are picky eaters,” Professor Cavener said.
“They only eat the leaves of a few species of trees, and their longer necks allow them to penetrate deeper into the trees to obtain leaves that no one else can get.
‘Once females reach four or five years of age, they are almost always pregnant and nursing.
“Therefore, we believe that increased nutritional demands on females drove the evolution of giraffes’ long necks.”
Due to their higher nutritional demand, females need a long neck to reach deep into the trees and obtain the best leaves, Professor Cavener and his colleagues say.
For the study, researchers gathered thousands of photographs of captive and wild Masai giraffes (Giraffa tippelskirchi), a species native to East Africa.
In their theories of evolution, naturalists Charles Darwin (pictured) and Frenchman Jean Baptiste Lamarck said long necks evolved to help giraffes reach leaves high in trees, avoiding competition with other herbivores. .
The team says that females have proportionally longer necks than males (relative to the overall height of the animal).
They found that in both captive and wild adult giraffes, females have proportionally longer necks than males, relative to the overall height of the animal.
Females also have proportionally longer “trunks” (the main section of their body that does not include the legs or neck or head).
Adult males, on the other hand, have longer front legs (effective for mounting the female during mating) and wider necks (which can take hits from rival males during fights).
According to experts, males generally grow fastest during the first year and body proportions do not differ significantly until they begin to reach sexual maturity around three years of age.
A more recent hypothesis called “necks by sex” suggests that the evolution of long necks was driven by competition between males, who swing their necks at each other to assert dominance, called neck combat.
‘Necks by sex’ suggests that males with longer, thicker necks have been more successful in competition, leading them to reproduce and pass their genes on to offspring.
“The sex-neck hypothesis predicted that males would have longer necks than females,” Professor Cavener said.
“And technically they have longer necks, but in males everything is longer: they are 30 to 40 percent larger than females.”
The team doesn’t reject the sex-collar hypothesis, but if it had any effect, it probably came later.
They write in their study: “The initial evolution of the giraffe’s long neck and legs was driven by interspecific competition and the maternal nutritional demands of gestation and lactation through natural selection to gain a competitive advantage.
“Later, neck mass increased further as a consequence of male-to-male competition and sexual selection.”
The new study has been published in the journal mammal biology.
EXPERTS CONFIRM THAT THERE ARE FOUR DIFFERENT SPECIES OF GIRAFFE
Efforts to map the giraffe genome have confirmed that there are four distinct species, and that they are as different from each other as brown bears are from polar bears.
Efforts to map the giraffe genome have confirmed that there are four distinct species, and that they are as different from each other as brown bears and polar bears.
Visually they are barely distinguishable, according to scientists at the LOEWE Center for Biodiversity Translational Genomics in Frankfurt, Germany, who carried out the genetic analyses.
Despite looking the same, genetically there are four different species of giraffe and seven subspecies, explained lead author Dr. Axel Janke.
According to their exhaustive genome analyses, the four giraffe lineages have evolved separately for thousands of years.
Distributed from northern to southern Africa, the four different species of giraffe are: the northern giraffe, the reticulated giraffe, the Masai giraffe and the southern giraffe.
Southern giraffe (Giraffa giraffa)
Found in: Angola, Namibia, Zimbabwe, South Africa, Zambia
Subspecies: Angolan giraffe, South African giraffe
Masai giraffe (G. tippelskirchi)
Found in: Kenya, Tanzania, Zambia
Reticulated giraffe (G. reticulata)
Found in: Kenya, Somalia, Ethiopia
Northern giraffe (G. camelopardalis)
Found in: Chad, Central African Republic, Cameroon, Democratic Republic of the Congo, South Sudan
Subspecies: Kordofan giraffe, Nubian giraffe, West African giraffe
Read more: FOUR different species of giraffe, not one, identified by scientists