To see whether the DNA data convincingly supports a close relationship between vertebrates and echinoderms, we looked at the number of changes in DNA that were found in both the vertebrates and the echinoderms but not in other animals. He argued that vertebrates and echinoderms were part of a group called “ deuterostomes” and that the other invertebrates were in a group called the protostomes – including insects, earth worms, molluscs and nematodes. Grobben looked at the earliest events of embryonic development in different groups of species (how the first cells of the embryo divide and how the mouth is first formed) to split the main part of the animal kingdom into two great branches. This was first proposed in 1908 by an Austrian zoologist called Karl Grobben. They are the echinoderms or “spiny skins” – a group including starfishes, sea cucumbers and sea urchins. The general view for over a century has been that, surprisingly, our closest non-vertebrate relatives are a group with no striking similarities to the vertebrates at all. Given these difficulties, the fact that there has long been a consensus over the identity of the closest relatives of the vertebrates is very unusual. Now our new study, published in Science Advances, offers insight. There are inherent difficulties in untangling such ancient relationships, meaning many aspects of them have been bitterly fought over for the past 150 years. Our vertebrate origins lie deep in the history of animal life on Earth, and the earliest fossils with some form of a backbone date to over half a billion years ago. Going deeper in into our history, even Aristotle was aware that mammals, birds, reptiles, amphibians and fishes are united by the shared feature of a backbone in a group we call the vertebrates. It is easy to see that we are members of the great apes, primates and mammals, for example. Many aspects of our family tree are obvious. When piecing together the many steps leading from our first simple animal ancestor to modern Homo sapiens, the first thing we need to know is how we are related to other animal groups. How humans evolved from the very first animals over the last 600 million years is an endlessly fascinating question.
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