Scientists Identify Ancestor of Sister Group to All Animals, Settling Evolutionary Debate

The debate over the ancestors of sea sponges (left) and comb jellies (right) has been going on for decades.

Scientists have made a groundbreaking discovery in the field of evolutionary biology, successfully identifying the most recent common ancestor of the sister group to all animals. 

After decades of debate and speculation, this finding has settled a central question regarding the evolutionary history of the entire animal kingdom. The study, published in the journal Nature on May 17, introduces a novel analytical technique involving chromosomal analysis.

All animal life can be traced back to a multicellular organism that likely existed over 600 million years ago. This ancestral organism had two offspring, one of which led to the evolution of all animals we know today, while the other became known as the sister group to all animals. 

Determining which living organisms are most closely related to this sister group has been a persistent challenge, with two main contenders: sea sponges and comb jellies (ctenophores). However, concrete evidence supporting either candidate has been lacking until now.

The breakthrough came when Darrin T Schultz, the lead author and a postdoctoral researcher at the University of Vienna, and a team of scientists from various institutions embarked on sequencing the genomes of comb jellies and their close relatives. 

Their aim was to gain a deeper understanding of the evolution of these organisms. Instead of comparing individual genes, the researchers focused on the positions of genes on chromosomes across different species.

While DNA changes over time, genes typically remain on the same chromosome. Occasionally, through fusion and mixing, genes can transfer from one chromosome to another in an irreversible process. Schultz likened this phenomenon to shuffling a deck of cards: once shuffled, the cards cannot be returned to their original order. 

By examining the large-scale movement of gene groups across different animal groups, the research team uncovered valuable insights into the animal family tree.

The study revealed that 14 groups of genes appeared on separate chromosomes in comb jellies and their single-celled, non-animal relatives. Strikingly, sponges and all other animals displayed these genes rearranged into seven groups. 

The fact that comb jellies retained the original gene group positions suggests that they are descendants of the sister group that diverged from the animal family tree before the rearrangements occurred.

Moreover, the shared gene location rearrangements observed in both sponges and other animals indicate a common ancestor from which these rearrangements were inherited. Consequently, this groundbreaking research has resolved the long-standing debate surrounding the lineage of the entire animal tree of life.

While we cannot precisely determine the appearance of the first animals based on the evolution of comb jellies and sponges since their ancestral split, studying these modern animals in light of their newly identified lineage holds great significance. 

Understanding the relationships among all animal groups aids in unraveling the evolutionary processes that have shaped the defining characteristics of animals throughout history.

 As Darrin T Schultz affirms, "If we understand how all animals are related to one another, it helps us understand how animals evolved the things that make them animals."