All animals on earth have a common ancestor. Trace the history of any creature, from human to snail, and eventually you can trace all the branches of the animal tree of life down to its trunk. But once that trunk had to branch out, otherwise we wouldn’t have all the modern animals. And this first split was a little difficult for scientists because it happened about 600 million years ago.

However, we do know a few things. That is, we know that the first split led to the birth of two creatures – the ancestor of almost all animals and the “sister” of these ancestors. This sister is the ancestor of only one group of modern animals. For decades, scientists have debated which group of animals literally descended from the “sister” of all other animals. For a long time they had two rivals – sea sponges and clam jelly. And now, thanks to new techniques that allow researchers to analyze the chromosomes of these creatures, scientists believe they have finally found the answer.

The key to this technique was to study not only what genes each animal had, but also where these genes were located on the chromosomes of living things. As a living thing develops, chromosomes will change over time and genes will move. However, as soon as they move, it is almost impossible for them to return to their former positions.

Thus, essentially, any animal that showed the least gene entanglement in chromosomes would have to have evolved first. As we know, we only have two options for the first compartment – sponges or comb gel – whichever is less messy, it’s sister. The first to develop is equal to the first division. To find out, the team compared the placement of specific gene groups in sponges and scallops with the placement of the same groups in their closest single-celled, non-animal relatives. These single-celled relatives would be closely related to the “root” organism and retain evidence of what the original genome would have looked like. The closer an organism is to this genome, the less it has changed and the more likely it is to be a sibling.

The researchers found 14 sets of genes located on separate chromosomes in both non-animal creatures and comb jellyfish. In sponges, however, the researchers found that these 14 groups were rearranged into 7 groups, suggesting that they later separated from the original genome from the clam jelly. And that means we have a winner! Sister of all other animals, the first to branch and the most genetically isolated animal… drumming please… clam jelly!

In addition to answering a long-paining biological question, scientists are excited to discover what this new knowledge can tell us about the history of animal evolution and the mechanisms driving it. The search for answers continues, but at least we have one more in our pocket. Source