
According to scientists, the origin of the human anus can be found 550 million years ago and what is even more intriguing, its path of evolution which is mind-blowing.
A group of researchers has concluded that the anus was a reproductive opening with a gut that later fused with the sexual organ.
The same team, headed by Andreas Hejnol from the University of Bergen, found out that the worm Xenoturbella bocki, which had been considered a primitive species, could have been the origin of the anus of higher animals. This was their conclusion from the study of the worm. Their research shows that a simple creature like this could answer the anus’s evolutionary roots.
These male gonopore worms do not have the anus but possess a tiny hole for sperm release, which seem to be a source of evolutionary hints. So, it seems that despite the absence of an anus a sperm-releasing pore in the worm contains the same genes as those in higher animals thus the two organs are linked through evolution.
It turned out from the study made on the worm aforesaid that the worm originally shaped its anus from the genetic blueprint which in like manner constructed the sperm release pore in the animals higher up in the phylogenetic hierarchy. In other words, according to the study, it is the similar set of genes.
These genes are almost everywhere in the animal kingdom, that is, from insects to mollusks to humans, and they reveal that these genes have the ancient most roots of evolution. In the case brought forward by the authors, the existence of such a gene in all animals indicates they shared this feature at some point in the origin of life.
The research alludes to the probability that our first ancestor with an anus might have shared features with the contemporaneous species of X. bocki i.e. they were both worms having only a mouth, a gut, and a sperm-release pore. The body plan was very simple, and that was the beginning of the two-opening digestive system used till now by most animals.
After thousands of years of evolution, the separate parts of the gut and gonopore began merging. Then, after they were fully merged, the combination became the first enterocoelic (entero= within + koilia= cavity) which linked the mouth with the anus in a continuous system via a digestive tube. Thursday, the hole through which sperm was released also became the site where an entirely new organ system was discharged.
The human anus is the design that people have obtained through evolution from 550 million years ago.
It is the fact that almost all animals have two entrances and two ways out of the digestive system accordingly, mouth, and anus.
Mouth and stomach were the first to appear in the process of evolution, and the anus began to exist only later. In this staggered manner of formation, we can see how the digestive system got more and more complicated with every step taken by early animals.
Some of the animals still do have only partly developed body plans, such as X. bocki, a worm-like creature that is still to be found at the bottom of the ocean.
These worms get their nourishment and removal of unwanted substances done through one pore—thus, they are able to convert their mouth into the anus. Such a crude structure tells about the deep divergence of the digestive-trajectory.
Covering that ground, Hejnol puts forward the hypothesis that these worms might show an intermediate between the primitive jellyfish and the first creatures that had evolved an anus. Therefore, their body may be the link between the stages of the development of the digestive system.
‘You can use the holes for all kinds of other things once they are there,’ he said to The New York Times.
Being in the process of peer review, the research is a preprint at bioRxiv, thus being available to the scientific community before the formal publication. This allows the scientific community to get the first impressions of the findings before they are published in the scientific literature.
Formerly, scientists were under the impression that the anus was formed as a result of the mouth splitting and thus becoming two different holes.

