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Sponge , comb jelly, who is the furthest relative of mankind? In previous studies, phylogenetic evidence showed that the most distant relative of humans is comb jelly. This triggered a protracted and fierce debate.
Now, Ireland scientists believe that they have found the furthest animal relatives on the tree of life. Their research recently published in " Nature-Communication " gives strong evidence that sponges are the most distant relative of humans, not the more complex comb jelly.
Compared with comb jelly, the structure of sponge is much simpler and does not have complex structural features such as nervous system, muscles and intestines. Logically speaking, these complex structural features evolved after the differentiation between humans and sponges, and were then retained in newly evolved organisms.
If comb jelly is the furthest relative of humans, the complex features they evolved may later disappear in animals such as sponges. Or in the history of evolution, the complex features of comb jelly have evolved twice.
"This complex trait seems unlikely to evolve twice independently, but evolution does not always follow a single simple path. For example, birds and bats are distant relatives, but they each independently evolved wings for flight. Anthony Redmond, a postdoctoral researcher at the School of Genetics and Microbiology at Trinity University Dublin and the first author of the paper, said that their further analysis showed that sponges, not comb jelly, are the furthest animal relatives of humans. This returns to the simpler traditional animal evolution hypothesis.
This means that the structure of animal ancestors is very simple, and the evolution of complex structures such as muscles, nerves and digestive systems all have a single origin.
The genetic relationship between species can be assessed by comparative genomic methods. This sounds easy, but the actual operation is difficult. Because there are many ways to do this, but different methods draw different conclusions,Therefore, there are disagreements about who is the furthest relative of mankind, sponge and comb jelly.
In order to resolve this controversy, the research team developed a new method to analyze the amino acid sequence that makes up animal proteins. This method reduces the errors that may occur in the most important comparisons.
Natural selection keeps the protein in its shape and function, which means that any given amino acid in the protein will usually only be changed to other amino acids with similar biochemical properties. If this is not considered, it may lead to errors in the reconstruction of phylogenetic relationships. Researchers believe that in some previous studies, it was this error that caused the comb jelly to become the furthest animal relative of humans.
"Our research method corrected the above problems and provided strong evidence that sponges are the furthest relatives of mankind. This means that the last common ancestor of mankind is simple in form." Trinity University Said Aoife McLysaght, professor of genetics and corresponding author of the paper .
He said that the new methods used in the research help scientists study how certain animals are related to each other. This information is essential for people to understand evolution and may have important impacts on other related fields, such as biodiversity and conservation science. (Xu Rui)
Source: "Chinese Journal of Science"
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