The theory of evolutionism suggests that all life stems from the same root and that we are related, more or less distant, to every living thing on Earth. Our closest ancestors, as Charles Darwin has assumed, are found among great apes. But beyond this, confusion over the branching pattern of the tree of life means that things become less clear.
We know that life evolved from a common universal ancestor that gave rise to bacteria, archaea (other types of single-celled microorganisms), and eukaryotes (including multicellular organisms such as plants and animals). But what did the animals look like before? Have seen one in the last ten years Particularly hot debate On this question. Now our new study, Published in Science Advances, Has come up with an answer.
Sponge vs Comb Jelly
About ten years before the 19th century, there was a general consensus that our farthest relatives are Sponge. Sponges are so different from most animals that they were originally classified as members of the algae. However, genes and other features of modern sponges, such as the fact that they produce sperm cells, indicate that they are definitely animals. His uniqueness and simplicity certainly fit with the idea that sponges came first.
But in the last decade, this model Has been challenged By several studies comparing DNA from different animals. There are alternative candidates for our farthest animal relatives Comb jelly: Beautiful, transparent, globe-shaped animals were named after flickering comb-rows of cilia, which they killed to spread themselves through water.
Comb jelly is superficially similar to jellyfish and, like them, is found floating in the ocean. Comb jelly is undoubtedly far from humans, but, unlike sponges, they share with us advanced features such as nerve cells, muscles, and a gut. If comb jellies are indeed our farthest relatives, it means that all animal ancestors also had these common characteristics. More extravagantly, if the first animals had these important characters then we would have to assume that SpongeBob once possessed them but eventually lost them.
Evolutionary tree detection
To understand how the species evolved, scientists often use Astrological tree, In which the tips of the branches represent the species. The points where the branches divide represent a common ancestor. The image below shows an example of a phylogenetic tree in which the sponge closes first, and a comb jelly stops first.
Both sponge-first and comb jelly-first evolutionary trees have been supported by separate studies of the gene, and the controversy has resulted in a transatlantic stalemate, with most European traditional sponge-first and North Americans generally preferring the novel . Comb jelly-first.
This argument boils down to the question of how best to analyze the abundant genetic data we now have available. One possibility has been put forward by sponge-first supporters that the animal tree that first combed jelly Is the result of an error. The problem occurs when one of the groups being studied has developed much faster than the others. Rapidly developing groups often see that they have been around for a long time. Comb jelly is one such group. Might Rapid development of comb jelly We are being misled into thinking that they actually originated from an earlier division?
Are we being fooled by jelly?
We have approached this problem in a new way – directly investigating the possibility that fast-growing comb jellies are fooling us. We wanted to ask if we could give an incorrect answer to the uneven rate of growth in these animals.
Our new way of working was how DNA evolution takes place using computers. We started with a random synthetic DNA sequence representing the ancestral animal. In computers, we allow this sequence to evolve, by accumulating mutations under two different conditions – either according to the sponge-first model or the comb jelly-first model. The sequence develops according to the pattern of the branches of each tree.
We ended up with a set of species with DNA sequences that are related to each other that denote the trees they were developed. We then used each of these synthetic data sets to reconstruct the evolutionary tree.
We found that when we constructed trees using the data according to the comb jelly-first model, we could always correctly assimilate the tree. This is because the prejudice that comes from their rapid rate of change has actually reinforced the information from the tree – in this case also showing that they are the oldest branch. The fact that both the tree information and the bias point in the same direction will yield the correct result. In short, if the comb jelly was indeed the first branch, there would be no doubt about it.
When we simulated the data with the sponge as the first branch, however, we very often regrouped the wrong tree, with the comb jelly ending up as the first branch. This is clearly a more difficult tree to obtain correctly and the reason is that tree information – in this case showing that the sponge is the oldest branch – biases coming from the rapidly developing comb jelly Is contrasted with (which supports comb jelly- first).
The long branch known for comb jellies can actually cause them to look older than they really are and the difficulty of realigning the tree is exactly what we face with real data.
So, who came first? The possibility is that genetic analyzes suggesting that comb jellies came first do not actually suffer from accounting for the bias that these animals look older than they actually are. Finally, our work suggests that sponges are in fact our most distant animal relatives.
By this article Max telford, Professor of Zoology, UCL And Paschalia Kapali, Research Fellow in Genetics, Evolution and Environment, UCL Republished from chit chat Under a Creative Commons license. read the Original article.