By analyzing the chromosomes, the research team answers the question of what they looked like. first animals, which led to the diversity of animals in the modern world. These first animals were animal carrier and no spongesthey say.

For more than a century, biologists have wondered what the first animals were like when they first appeared on Earth. ancient oceans half a billion years ago.

Searching among modern primitive animals, scientists gradually narrowed the range of possible options to two groups: sponges, which spend their entire adult lives in one place, filtering food from sea water, and comb jellies, voracious eaters, predators that move around the world’s oceans in search of food.

In a new study published in the journalNature”, the researchers use a new approach based on the organization of genes on chromosomes to answer: cetaceans were the first lineage from which branches on the animal tree descended.

Sponges followed, and then the diversification of all other animals, including the lineage leading to man.

“The most recent common ancestor of all animals probably lived 600 or 700 million years ago. It is difficult to say what they looked like because they were soft-bodied animals and did not leave direct trace fossils. But we can use comparisons between animals that exist today to learn about our common ancestors,” he says. Daniel Roxarprofessor of molecular and cellular biology at the University of California at Berkeley and one of the authors of the paper.

“It’s exciting. “We’re looking back into time where we have no hope of finding fossils, but by comparing genomes, we’re learning something about these very early ancestors,” he adds.

Most of the known animals called bilateria, including worms, flies, mollusks, vertebrates, and even humans, have a head with a central brain, an intestine that extends from the mouth to the anus, muscles, and other common features that they have already developed since then. the time of the famous “Cambrian explosion”, when the animal world was created.

However, other animals such as jellyfish, sea anemones, sponges, and cetaceans have simpler body designs. They lack a definite brain and may not even have a nervous system or muscles, but they still have the characteristics of animals, primarily the development of multicellular bodies from a fertilized egg.

OUR the evolutionary relationship between these different creatures has been controversial. With the development of DNA sequencing, biologists have been able to compare the sequences of genes shared by animals and build a family tree showing how animals and their genes have evolved over time. However, the question remained whether sponges or cetaceans were the first branch of animals.

Understanding the relationships between animal lineages will also help scientists study how key features of animal biology, such as the nervous system, muscles and digestive system, have evolved over time, the researchers report.

MONKEY BEE