Revisited human-worm relationships shed light on brain evolution

Feb 09, 2011

"Man is but a worm" was the title of a famous caricature of Darwin's ideas in Victorian England. Now, 120 years later, a molecular analysis of mysterious marine creatures unexpectedly reveals our cousins as worms, indeed.

An international team of researchers, including a neuroscientist from the University of Florida, has produced more evidence that people have a close evolutionary connection with tiny, flatworm-like organisms scientifically known as "Acoelomorphs."

The research in the Thursday (Feb. 10) issue of Nature offers insights into and human diseases, possibly shedding light on animal models used to study development of and complex such as Alzheimer's and Parkinson's.

"It was like looking under a rock and finding something unexpected," said Leonid L. Moroz, a professor in the department of neuroscience with the UF College of Medicine. "We've known there were very unusual twists in the evolution of the complex brains, but this suggests the independent evolution of complex brains in our lineage versus invertebrates, for example, in lineages leading to the octopus or the honeybee."

The latest research indicates that of the five animal phyla, the highest classification in our evolutionary neighborhood, four contain worms.

But none are anatomically simpler than "acoels," which have no brains or centralized nervous systems. Less than a few millimeters in size, acoels are little more than tiny bags of cells that breathe through their skin and digest food by surrounding it.

Comparing extensive genome-wide data, mitochondrial genes and tiny signaling called microRNAs, the researchers hailing from six countries determined a strong possibility that acoels and their kin are "sisters" to another peculiar type of from northern seas, called Xenoturbella.

From there, like playing "Six Degrees of Kevin Bacon," the branches continue to humans.

"If you looked at one of these creatures you would say, 'what is all of this excitement about a worm?'" said Richard G. Northcutt, a professor of neurosciences at Scripps Institution of Oceanography, who was not involved in the study. "These are tiny animals that have almost no anatomy, which presents very little for scientists to compare them with. But through genetics, if the analysis is correct — and time will tell if it is — the study has taken a very bothersome group that scientists are not sure what to do with and says it is related to vertebrates, ourselves and echinoderms (such as starfish).

"The significance of the research is it gives us a better understanding of how animals are related and, by inference, a better understanding of the history of the animals leading to humans," Northcutt said.

Scientists used high-throughput computational tools to reconstruct deep evolutionary relationships, apparently confirming suspicions that three lineages of marine worms and vertebrates are part of a common evolutionary line called "deuterostomes," which share a common ancestor.

"The early evolution of lineages leading to vertebrates, sea stars and acorn worms is much more complex than most people expect because it involves not just gene gain, but enormous gene loss," said Moroz, who is affiliated with the Whitney Laboratory for Marine Bioscience and UF's McKnight Brain Institute. "An alternative, yet unlikely, scenario would be that our common ancestor had a central , and then just lost it, still remaining a free living organism.

Understanding the complex cellular rearrangements and the origin of animal innovations, such as the brain, is critically important for understanding human development and disease, Moroz said.

"We need to be able to interpret molecular events in the medical field," he said. "Is what's happening in different lineages of neuronal and stem cells, for example, completely new, or is it reflecting something that is in the arrays of ancestral tool kits preserved over more than 550 million years of our evolutionary history? Working with models of human disease, you really need to be sure."

Explore further: Lost memories might be able to be restored, new study indicates

Related Stories

Simple marine worms distantly related to humans

Feb 09, 2011

Two groups of lowly marine worms are related to complex species including vertebrates (such as humans) and starfish, according to new research. Previously thought to be an evolutionary link between simple animals such as ...

MicroRNA: A glimpse into the past

Feb 01, 2010

The last ancestor we shared with worms, which roamed the seas around 600 million years ago, may already have had a sophisticated brain that released hormones into the blood and was connected to various sensory organs. The ...

The bizarre lives of bone-eating worms

Nov 09, 2009

The females of the recently discovered Osedax marine worms feast on submerged bones via a complex relationship with symbiotic bacteria, and they are turning out to be far more diverse and widespread than scientists expected. ...

Brainy worms: Evolution of the cerebral cortex

Sep 02, 2010

(PhysOrg.com) -- Our cerebral cortex, or pallium, is a big part of what makes us human: art, literature and science would not exist had this most fascinating part of our brain not emerged in some less intelligent ...

Early family ties: No sponge in the human family tree

Apr 02, 2009

Since the days of Charles Darwin, researchers are interested in reconstructing the "Tree of Life", and in understanding the development of animal and plant species during their evolutionary history. In the case of vertebrates, ...

Recommended for you

Researchers unlock mystery of skin's sensory abilities

Dec 19, 2014

Humans' ability to detect the direction of movement of stimuli in their sensory world is critical to survival. Much of this stimuli detection comes from sight and sound, but little is known about how the ...

Tackling neurotransmission precision

Dec 18, 2014

Behind all motor, sensory and memory functions, calcium ions are in the brain, making those functions possible. Yet neuroscientists do not entirely understand how fast calcium ions reach their targets inside ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

panorama
5 / 5 (1) Feb 09, 2011
HAVE YOU THE BRAIN WORMS!?!

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.