Anal evolution may have promoted the body plan for all advanced animals, including humans
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The anus is a very successful innovation, how did it evolve? Genetic analysis suggests that it probably started as an opening used to release sperm that was later fused with the intestine. This is an example of evolutionary reuse structures.
“Once you have a hole, you can use it for other things.” Andreas Hezinol At the University of Bergen, Norway.
It is believed that early animals evolved their mouths and intestines before the anus, as some simple creatures, such as jellyfish, still have plans for this body. They must banish the last meal of their mouths and banish them before eating again, Henor says.
One idea of how early animals evolved the anus is that the mouth is split into two parts. However, in 2008, Hejnol shows that the key genes controlling the development of the oral region are completely different from those in the hindgut, suggesting the independent origin of the anus. And now he thinks he’s tracked it down.
Hezinol and his colleagues xenoturbella bocki, It is a worm-like organism located on the seabed with its mouth and intestines, but it does not have anal. This could be a living representative of an ancient group that was intermediate between the jellyfish ancestors and the first animal with anals.
Now they discovered it X. Bocki There is another opening for releasing sperm called male gonopores. Instead, the eggs are released from the mouth, so there is no female opening. The team also found that some of the key genes that control the development of the hindgut in animals with anus also control the development of gonads in animals, such as animals. X. Bockipropose evolutionary links.
“What happened is that there is a likely hole [gonopore] It was there and the digestive system was nearby,” he says. They connected with each other and created a common opening. ”
“The data is beautiful and very persuasive.” Max Telford University College London. “I worked on it Xenoturbella For a long time, and the fact that we didn’t realize it had a gonopore is extraordinary. ”
Tracking the origins of the anal is more than just a lazy curiosity. This is because the animal is thought to have an intestine that runs from the mouth to the anus, reducing the body plan that is still used today. “The presence of almost every animal we see around us may have something to do with the invention of intestinal thru,” Telford says.
But he doesn’t think X. Bocki is It points us in the right direction. He believes that the group of animals that once belonged to had a connected gonopore and anal, and that it lost the anal. In other words, according to Telford, the group only appeared after anal evolution, rather than representing the stage just before it. Hejnol believes his own interpretation is more likely, but for now there is no way to end the discussion.
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