Evolution: Lamarck is back (Introduction)

by David Turell , Tuesday, June 04, 2024, 22:14 (171 days ago) @ David Turell

Giraffe necks due to high grazing:

https://www.sciencedaily.com/releases/2024/06/240603114245.htm

"Why do giraffes have such long necks? A study led by Penn State biologists explores how this trait might have evolved and lends new insight into this iconic question. The reigning hypothesis is that competition among males influenced neck length, but the research team found that female giraffes have proportionally longer necks than males -- suggesting that high nutritional needs of females may have driven the evolution of this trait.

"The study, which explored body proportions of both wild and captive giraffes, is described in a paper that appeared in the journal Mammalian Biology. The findings, the team said, indicate that neck length may be the result of females foraging deeply into trees for otherwise difficult-to-reach leaves.

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"'The necks-for-sex hypothesis predicted that males would have longer necks than females," said Doug Cavener, Dorothy Foehr Huck and J. Lloyd Huck Distinguished Chair in Evolutionary Genetics and professor of biology at Penn State and lead author of the study. "And technically they do have longer necks, but everything about males is longer; they are 30% to 40% bigger than females. In this study, we analyzed photos of hundreds of wild and captive Masai giraffes to investigate the relative body proportions of each species and how they might change as giraffes grow and mature."

'The researchers gathered thousands of photos of captive Masai giraffes from the publicly accessible photo repositories Flickr and SmugMug as well as photos of wild adult animals that they have taken over the past decade. Because absolute measurements like overall height are difficult to determine from a photograph without a point of reference of known length, the researchers instead focused on measurements relative to one another, or body proportions -- for example the length of the neck relative to the entire height of the animal. They restricted their analysis to images that met strict criteria, such as only using images of giraffes perpendicular to the camera, so they could consistently take a variety of measurements.

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"At birth, male and female giraffes have the same body proportions. The researchers found that, although males generally grow faster in the first year, body proportions are not significantly different until they start to research sexual maturity around three years of age. Because body proportions change early in life, the team limited their study of wild animals -- whose ages are largely unknown -- to fully grown adults.

"In adult giraffes, the researchers found that females have proportionally longer necks and trunks -- or the main section of their body, which does not include legs or the neck and head. Adult males, on the other hand, have longer forelegs and wider necks. This pattern was the same in both captive and wild giraffes.

"'Rather than stretching out to eat leaves on the tallest branches, you often see giraffes -- especially females -- reaching deep into the trees," Cavener said. "Giraffes are picky eaters -- they eat the leaves of only a few tree species, and longer necks allow them to reach deeper into the trees to get the leaves no one else can. Once females reach four or five years of age, they are almost always pregnant and lactating, so we think the increased nutritional demands of females drove the evolution of giraffes' long necks."

"The researchers noted that sexual selection -- either competition among males or preference among females for larger mates -- was likely responsible for the overall size difference between males in females, as is the case in many other large, hoofed mammals that are polygynous -- where one male mates with many females. They suggest that, following the evolution of the long neck, sexual selection -- including male body pushing and neck sparring behaviors -- may have contributed to males' wider necks. Additionally, the longer forelegs of males may assist in mating, which the researchers said is a brief and challenging affair that is rarely observed."

Comment: straining to support a just-so story. OR God designed the females to get the best leaves.