Latest research suggests that female giraffes have driven the evolution of long giraffe necks to feed on probably the most nutrient-rich leaves

Biology is ultimately about food and sex. To survive as a person, you would like food. To survive as a species, you would like sex.

Not surprisingly, the age-old query of why giraffes have long necks revolves around food and sex. After 150 years of debating the query, biologists still cannot agree on which of those two aspects was most significant for the evolution of the giraffe neck. Over the past three years, my colleagues and I even have attempt to unravel this query.

Necks for sex

In the nineteenth century, biologists Charles Darwin and Jean Baptiste Lamarck speculated that the long necks of giraffes helped them reach acacia leaves high up within the treesalthough they probably didn’t observe the actual behavior of giraffes once they recommend this theory. Several a long time later, when scientists began observing giraffes in Africa, a bunch of biologists developed a alternative theory based on gender and reproduction.

These pioneering giraffe biologists noticed how male giraffes standing side by side used their long necks To swing their heads and hit one anotherThe researchers called this behavior “neck fighting” and suspected that it helped the giraffes prove their dominance over one another and court mates. The males with the longest necks won these contests and in return increase their reproductive successThese favorable circumstances, scientists predicted, led to the evolution of long necks.

Since its founding, the Hypothesis of sexual selection by necks for sex has overshadowed Darwin and Lamarck’s “throat as food” hypothesis.

The hypothesis that necks represent gender equality predicts that males must have longer necks than females, since only males use them for fighting, and so they do. But adult male giraffes are also about 30 to 50 percent larger than female giraffes. All of their Body parts are larger. Therefore, my team wanted to seek out out whether males have a proportionally longer neck relative to their overall size (head, neck and forelimbs).

Necks should not for sex?

However, it will not be easy to measure the body proportions of giraffes. Firstly, their necks grow in the primary six to eight years of their livesAnd within the wild, it’s inconceivable to say exactly how old a person animal is. To avoid these problems, measured body proportions on captive Masai giraffes in North American zoos. Here we knew the precise age of the giraffes and will then compare this data with the body proportions of untamed giraffes that we knew obviously were older than 8 years.

To our surprise, we found that adult female giraffes have proportionally longer necks than males, contradicting the hypothesis that necks determine sex. We also found that adult female giraffes have proportionally longer trunks, while adult males have proportionally longer forelimbs and thicker necks.

A diagram showing a male giraffe, which is taller and has a shorter trunk, and a female giraffe, which has shorter legs and a longer trunk.
Gender differences between female and male giraffes.
Douglas Cavener

Baby giraffes don’t exhibit any of those gender differences in body proportions. They only appear when giraffes reach maturity.

The finding that female giraffes have each proportionally longer necks and longer bodies led us to propose that the evolution of the giraffe's long neck was driven by females slightly than males, and never for sexual reasons, but for foraging and reproduction. Our theory agrees with Darwin and Lamarck that food was the first driver of the evolution of the giraffe's neck, but with the emphasis on the reproductive success of females.

A type of dying

Giraffes are notoriously picky eaters and can eat fresh leaves, flowers and seed pods. Female giraffes specifically must eat enough as they spend most of their adult lives either pregnant or give milk to their calves.

Females are inclined to use their long necks to penetrate deep into bushes and trees to seek out probably the most nutritious foods. In contrast, males are inclined to feed high up in trees by extending their necks vertically. Females require proportionally longer trunks to lift calves, which might be well over six feet tall at birth.

For the males, I’d suspect that their proportionally longer front legs are an adaptation that permits them to more easily mount females during intercourse. While we’ve got found that their necks should not as long proportionally because the necks of the females, they’re thicker. This is probably going an adaptation that helps them win neck fights.

A male giraffe eats from a tree.
The body of a male giraffe with long front legs supporting the torso and neck – a shocking shape.
Douglas Cavener

But giraffe necks should not their only long feature. They have relatively long legs, which contribute to their height almost as much as their neck. However, their long legs come at a price – especially for male giraffes. A disproportionately large a part of their body mass rests on their thin front legs, which might result in injuries and mobility problems in the long run.

Graham Mitchell, a widely known giraffe biologist, has described the giraffe body as “a form of dying.” In captivity, where staff can determine the reason behind death, well over half of male giraffes die from problems with their front legs, which shortens their life expectancy by 25% in comparison with females. Very few female giraffes die from health problems related to their legs.

Because of their size, giraffes are also not good at climbing steep slopes. Investigations have shown that this restriction probably prevented them from climbing the steep slopes of the Great Rift Valley in East AfricaBut the mating advantage they gain from their size must outweigh these costs to health and mobility.

This research doesn’t completely rule out the idea that necks are sex. The long neck probably plays a vital role in male neck fights and in attracting a mate. However, our research suggests that male neck fights were probably a side effect of giving females higher access to food.

In the long run, my team will study the genetic aspects that led to the giraffe's extraordinary stature and construct, and hope to trace and reconstruct the evolutionary path it took to succeed in the skies.

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