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Research on a small, headless sea creature is casting light on the cloudy origins of humans, an article in the science journal Nature says.

The research, described in a Nature editorial as groundbreaking, was into the fishlike Amphioxus, the closest invertebrate relative of the vertebrates.Scientists studying the creature, which lives half-buried in inland waters straining algae through a built-in filter, said they were able to match its cluster of so-called hox genes with the four hox clusters found in mammals, including humans.

The hox genes, which encode the proteins that control other key genes, have long intrigued researchers.

Lined up in a fixed order, the arrangement in the cluster from top to bottom coincides with the body parts they affect.

The match is so close that some fruitfly hox genes can be substituted by their opposite numbers in mice. But researchers have long been puzzled why mammals and humans have four hox clusters that largely duplicate each other.

Another problem is how those things that make vertebrates different - skull, skeleton and developed brain - evolved.

The Amphioxus has a hollow spinal cord. It has no eyes, teeth, skeleton, skull or developed brain.

But in Thursday's article the scientists say the similarity of the creature's hox cluster with the genes in the four that mammals have suggest that the evolution of things like the spine and the head were paralleled by a duplication of these clusters.

The discovery could open new possibilities in studying how the hox genes work, they wrote.