Why do some animals sacrifice themselves in the course of evolution | National Geographic

Male musk ox can weigh about 400 kg and reach speeds of about 50 kilometers per hour while attacking. In mating season, these furry behemoths from the Arctic Circle dart headfirst into each other and attempt to pummel their opponents with their large, sharp horns.

Over the course of their ten to twelve-year life, musk oxen experience up to 2,100 such seals.

You wonder how these animals survive this without having their brains smashed into pulp.

“People have long assumed that animals that blow their heads off, like musk oxen and bighorn sheep, somehow can’t sustain a head injury,” says neuroscientist Nicole Ackermans of the Icahn School of Medicine at Mount Sinai in New York. “Like they have magic horns or something.”

But when Ackerman sifted through the scientific literature, she found that no one had studied whether these North American herbivores suffered brain damage from tampons. So she and her colleagues decided to dig into the brains of musk oxen and bighorn sheep, which they had obtained through expeditions, gifts from professional hunters, and herds kept in captivity for research.

“We discovered a specific pattern in all of our laboratory animals that is very similar to the onset of brain trauma in humans,” says Ackermans, lead author of an article about the research findings recently published in the journal. Acta Neuropatholica.

The new research can add to our understanding of brain injury in humans, Ackermann says, because cows (animals like oxen and sheep) have wrinkled, contorted brains that are more similar to human brains than, say, mice, which have smooth brains. .

It’s also evidence that species can engage in surprisingly self-destructive behavior over the course of evolution. And in this regard, musk oxen are certainly not alone.

“As long as it doesn’t kill you.”

In their research, Ackermans and her colleagues applied the biomarkers to the brains of three musk oxen and four bighorn sheep. These chemical compounds reveal patterns of traumatic brain injury often associated with conditions such as Alzheimer’s disease or CTE (chronic traumatic encephalopathy) in humans. In this case, the scientists were looking specifically for what is also known as the tau protein.

“When your neurons are damaged, for example due to age, genetic problems, or mechanical collisions, they rupture, the protein is damaged, and clumps form,” Ackermans explains. “When you find a pattern, you can tell if the brain is normal or aged, or if there is Alzheimer’s disease or maybe trauma.”

Unfortunately, the biomarker method did not work well in sheep brains, although there were signs of tau protein accumulating there. But the musk oxen’s brains looked like a Christmas tree with all that glowing brilliance.

At first glance, it seems strange that a natural behavior such as decapitation could cause so much harm. You have to see it in the long term, Ackermans says.

“Musk oxen give and get a lot of heads each year, but if they only manage to reproduce once, that’s really enough,” she says. “As long as it doesn’t kill you, that’s all that matters from an evolutionary standpoint.”

She believes that male musk oxen are likely to live less than 15 years, while females can live from 15 to 23 years. Although the amount of tau protein builds up throughout a male’s life, it will likely never reach a level where it can lead to conditions such as Alzheimer’s disease or other forms of dementia.

“Their lives are not that complicated,” Ackermans says. “So it is possible that they can last long enough to do what they need to do.”

And even if they did get terms, who would notice? There is no measure for the behavior of musk oxen. So maybe they forget a little bit,” she says.

Ackermann now also wants to study different species of woodpeckers, to see if they show brain damage from the knocking of their heads. The only other study in bird brains found some evidence of tau protein, but “it wasn’t actually in any specific pattern,” she said.

a couple until you drop

Musk oxen are somewhat similar to a certain type of marsupial, says mammalian ecologist Diana Fisher of the University of Queensland’s College of Biological Sciences.

The broad-footed opossum is a small carnivore found in remote areas of Australia and Tasmania. They’ve been in the news in recent years because males have near-symmetry: They only reproduce once in their lives, then die. Female broad-footed possums can live for two to three years, sometimes longer. Males rarely live beyond eleven months.

“Their mating season is very intense,” Fisher said. Mating can last 12 to 14 hours, and the males attempt to mate with as many females as they can—ultimately proving their downfall.

“The collagen in their skin breaks down, their intestinal tract becomes damaged, and they start to bleed internally,” says Fisher. They have become highly susceptible to parasites and diseases and their immune system no longer works. After a few weeks they died.

“This is very unusual for a mammal,” says Fisher. They usually live long enough to experience several mating seasons.

Suicidal reproduction is more common in insects, fish, plants, and spiders. For example, another male from Australia, the red spider, happens to be in the mouth of the female during mating.

“It prevents her from mating with another male because she is too busy eating,” says Fisher.

Self-destruct insects

Similar mechanisms occur in colonies of large social insects.

If a European honey bee stings an attacker with soft skin, like a bear’s, the insect dies because its stingers remain in the victim’s skin. A falling ant can tear its abdomen in half while it is defending a nest from attackers. And in some termite species, older worker termites can transform themselves into suicide bombers.

But what is the evolutionary point of killing yourself?

Cornell University biologist Thomas Seeley, author of “Simple,” writes: bee life, in an email. “Workers achieve their genetic (evolutionary) success not by reproducing themselves, but by enabling their mother, the queen of the colony, to do so.”

“One of the ways they can help is by defending the colony,” he explains.

“Some scientists call this a ‘superorganism,’” entomologist Alice Lasseny, who studies blaster ants at the Naturhistorisches Museum in Vienna, says in an e-mail. In addition, an ant colony or bee colony is a type of large animal, and the queen is the reproductive organ. There are countless subordinate workers who need very little food, so they are like body cells.

As with the musk ox, the behavior we consider aggressive and self-destructive to worker ants seems worth it if it eventually leads to reproduction.

“In this system, defending the queen and her sisters, by sacrificing herself if necessary, is how a worker ant can protect and pass on her genes,” said Laciny.

The highest sacrifice of a mother

Another form of sacrifice in the animal kingdom is what some mothers make to help their young begin in life.

Certain species of legless amphibians, the amphipods, literally eat the top layer of their mother’s skin as their first meal after birth. Certain species of African social spiders take this a step further. They have matrophagy, the young that kill and eat their mother.

Giant Carnage is perhaps the ultimate self-sacrificing mother. Females sometimes watch their eggs for up to four years without feeding in that time.

“The females irreversibly deplete their reserves, causing them to die while monitoring their eggs,” Fisher said.

“It’s very sad for them, but in many species this is the most successful way for their offspring into the next generation.”

This article was originally published in English on nationalgeographic.com

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