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Comb jellyfish - Ctenophore (Beroe cucumis)

The comb jelly might have been the ancestor of all animals on Earth, according to new research.

Photograph by Franco Banfi, Solent News/Rex Features via AP  

Jane J. Lee

National Geographic

Published December 12, 2013

In a prehistoric version of "the chicken or the egg" question, researchers have long debated which animal group came first. A traditional view pegs sponges—marine creatures that look more like rocks or corals—as our ancient ancestors.

But a new genetic study is stirring the waters, suggesting comb jellies, gelatinous marine animals that look similar to jellyfish, are actually the first animals to have evolved over 600 million years ago.

While an argument over ancient ancestry may seem academic, it's an important question to answer because it influences how researchers think about the nature of animal evolution, said study co-author Andy Baxevanis, a geneticist at the National Human Genome Research Institute in Bethesda, Maryland.

Sponges are simple creatures, lacking muscles or a nervous system, he said, while comb jellies have both. (See a video on how comb jellies hunt.)

"There's been this long-standing tenet in evolutionary biology," Baxevanis explained, that once evolution led to "some kind of complex cell type—like musculature or an eye—you wouldn't lose it."

That's because keeping muscles or a nervous system would be a survival advantage.

But if comb jellies did in fact come before the simpler sponges, that view would be turned upside down, suggesting instead that animals started off with genes for complex biology and some groups then lost them over time.

A Complete Sequence

Baxevanis and colleagues came to this conclusion after producing the first complete genome sequence of a comb jelly using a species called the sea walnut (Mnemiopsis leidyi).

Of the four ancient animal groups in contention for the title of first animal ancestor—sponges, comb jellies, jellyfish, and a group called the placozoa—only the comb jellies lacked a complete genome sequence from one of its members. (See jellyfish pictures.)

Complete genome sequences are important when trying to compare relationships between groups of organisms.

When Baxevanis and colleagues started their project, they were mainly interested in producing that comb jelly genome sequence and filling the gap in the data.

But when they plugged their genome into a computer program that helps researchers determine the evolutionary relationships between organisms—a field of study called phylogenetics—they were in for a shock.

Although their model came up with several possible scenarios for how comb jellies were related to all the other animal groups, some of the most likely scenarios put the gelatinous animals at the base of the animal family tree. (See video of the blood belly comb jelly.)

"The deepest evolutionary split [about 600 million years ago] involved the comb jellies splitting off from the rest of the animals," said Baxevanis. He and his colleagues reported their findings today in the journal Science.

Stirring the Pot

The new study has caused quite a stir among experts in the field.

A study in 2008 first suggested comb jellies were the ancestral group to all other animals, said Mansi Srivastava, an evolutionary developmental biologist at the Massachusetts Institute of Technology in Cambridge.

"That was pretty shocking to the community," said Srivastava, who was not involved in either study. "A lot of people didn't believe the results."

The problem was that fast-evolving genomes like the ones in comb jellies could sometimes trip up the computer programs used to help determine evolutionary relationships, she explained.

That would result in some groups getting lumped together with other organisms they weren't necessarily related to.

"Some people thought the 2008 paper was the result of this," Srivastava said, "and with more analysis, we could answer this question."

That's where the current Science study comes in: The authors provided more data by sequencing a complete comb jelly genome, enabling researchers to take another run at the "who first" question.

But Srivastava and others are still hesitant about the study's claims that comb jellies are indeed the ancestors to animals.

Troublemakers

One of the issues has to do with timing, said Hervé Philippe, a researcher with the National Center for Scientific Research in Moulis, France.

"You have to look over the history of organisms that occurred more than 600 million years ago," said Philippe, who was not involved in the current study.

A lot of mutations can happen over hundreds of millions of years, he explained. Separating out the earlier mutations in an ancestral group that gave rise to all the other animals from more recent genetic changes gets tricky.

Some of the methods Baxevanis and colleagues used in their analysis couldn't resolve more recent relationships between modern-day animal groups, said Philippe. "If you can't recognize recent events, it's unlikely that you'll recognize ancient events."

The study authors acknowledge that some of the evolutionary family trees they came up with leave the door open for more debate. Some still place the sponges as the ancestral group to animals.

But Baxevanis seems excited about the coming debate.

"We're being the troublemakers here," he said. When the study authors set out on this project, they didn't expect to get the results they did.

"I think it's a great example of not knowing where science is going to take you when you start," Baxevanis said.

Follow Jane J. Lee on Twitter.

24 comments
Noel Bernard
Noel Bernard

The  problem with humanity is that for one Darwin , for one Einstein , for one Newton , for  one Galillé , for one Aristote .....there  is a million Gordon Gekko.....

Gordon Gekko
Gordon Gekko

Bunch of BS... all science can do is hypothesize and predict through formula, based on empirical data.

Amusing to watch idiot after idiot try to explain something that has NO proof, NO cause and NO reason.  Evolution is pure nonsense which tries to explain the HOW but can never explain the WHY.  Existence itself requires a cause in order to follow the logic argument science must follow. The Big Bang HYPOTHESIS claimed by science to have followed existence also needs a cause.

For something to exist in the first place (even if infinite) you're going to need an existence argument (keeping with logic)... And as evolution sticks to both, existence AND logic, there’s a clear dead end where evolution can’t go any further and clearly becomes a belief in itself.

What caused existence?That question alone is proof enough that there is a God, or IT, beyond human comprehension... because in order for science to explain what caused the Big-Bang, science first has to explain what caused existence without a God.

Simply put... proving evolution is in itself science... but the IDEA of evolution is not.  It is simply a GUESS!

Science will never be able to explain existence because if they could explain in absolutes, not empirical formula and theory... then they can reproduce it.

In short... the WHAT that caused existence will always be the Achilles heel of science theory without invoking God.



Asok Smith
Asok Smith

Uh, how can the first animals to supposedly have evolved be comb jellys, which are predators of OTHER small animals? Perhaps the first ones were vegan and then EVOLVED to be carnivores. Or not.

Riccardo Moretti
Riccardo Moretti

maybe there is a simple solution to these doubts. Comb jellies may have evolved from the ancestor of all animals as like as the sponges but not encountering the evolutionary changes that consented the sponges to become what they are, that could be an advantage if environment is rich of organic resources (in fact, in the story of life many other groups of more complex organisms developed sessile species). Probably, we just do not have yet found evidence of the possible ancestor of comb jellies, sponges and all animals...

Miklos Legrady
Miklos Legrady

Creationism is starting to make sense.  How else could giraffes have come about, if God hadn't come down and pulled on their necks?

Mireia Estrany
Mireia Estrany

But, is there evolution if there is no time? How will evolutionary biology meet new physical paradigms about time, space and so on? Will new conceptual changes deny evolution? Or on the contrary, will it become a more extraordinary process, full of astonishing implications? Will human being nature become different as science progresses? Can knowledge change human beings nature, can it change yours? Along these lines, a serious-funny b-book recommendation, a preview in goo.gl/rfVqw6 Just another leisure suggestion, far away from dogmas or axioms.

Yu Xiang
Yu Xiang

What we learned from the books may not be totally truth, which leave the space for us to argue or to overthrow.

Xiu Ma
Xiu Ma

Whatever the answer, it should not evoke too much surprise, because we MUST have evolved from some ancient species, if it was not the sponge, then it might be the comb jelly, or something else. 

Vamsi Konjeti
Vamsi Konjeti

Very interesting, if the fact that comb jellies are actually the ancestors of us, then that could revolutionize many things.

Amairani Arce
Amairani Arce

@Gordon Gekko  

you claim that there's no explanation to existence without God in it, yet what makes you so sure that "God" exists. A bible don't mean crap. i could write a book too and say the holy spirit told me to write, could you prove me wrong ? No.

Everyone has their own beliefs, and you should respect ours. If to you the creator of us is God, hooray you. To us the Big Bang THEORY is a reasonable option and you should not go against that because whatever we believe is none of your concern

Tim Morris
Tim Morris

@Gordon Gekko Why exactly does existence even need a why? You are speaking from a huge bias, if you think there is some reason behind existence. The idea of a deeper meaning, like a creator, or a reason for existence, is just man's urge to rationalize everything.


Gotta love all the bible trolls scouring Nat Geo and ranting on impotently. Your argument is incredibly ignorant, I doubt you even understand evolution at all. You mostly said "science is hard, therefore there must be a reason", if you understood evolution, you would not think that it was a guess. Life is complicated, but thinking there must be a profound reason for existence is ignorant, and small minded.

Bernardo Fajardo
Bernardo Fajardo

@Gordon GekkoExcuse me... What? Do you realise this is a scientific place. I'm not gonna fight because what you believe. But, saying that science is simply a guess?

Obviously scientifics can't reproduce evolution, the Big Bang, etc. Simply because they'll need millions of years. That's why they have to make hypothesis and theories.

But, if you claim you're right... Why can't we see the act of creation?

Nothing made the universe, cause before the Big Bang there was nothing... No space, no time, the Big Bang was the begining of all.

And evolution, well you'll better remember that we were born of risen apes, not fallen angels.

Noel Bernard
Noel Bernard

@Gordon Gekko May be Evolution is a dimension that is not  necessarily available to your intellect ....

Christopher Lawman
Christopher Lawman

@Azul Waterz Lol. It does look a bit like a vagina. Not one that I would want to go anywhere near though!

craig hill
craig hill

@Azul Waterz They all were. They multiplied thru parthenogenesis. The ancestor of all living critters was female. Males came much later, when parthenogenesis was not enough to develop complex beings and avoid genetic imperfections from the single parent mother, who created males to mate with females, bringing more variation, and therefore health, into these complex creatures. 

Truth be told, the greatest hoax of all time is the notion of the single male creator. Which, when you think about it biologically, is preposterous.


Gordon Gekko
Gordon Gekko

@Noel Bernard@Gordon Gekko And tell me who's intellect is it available to? Certainty quite possible in your fairy-tale mind, I'm sure.

Evolution is NOT proven science. It is an idea offered by a naturalist who had no expertise in biology or the profound mechanisms of complex life. Evolution is a GUESS looking for proof.

And what proof did Darwin have to suppose his idea in any rational way except guessing, assumptions and assertions.

Darwin used more accurately “formal fallacy logic”, based on false (groundless) proposition or premise in order for his hypothesis to have legs.In a word “BS” And thus was born the gospel of evolution.

Evolution and creationism are of themselves based upon beliefs.

And we all choose between these two beliefs... Creationism vs Darwinism (aka: evolution). Both are doctrine based upon beliefs... both have schools of evangelical zealots whom preach their dogma to followers of their faith & cause, both have erected institutions & monuments that declare truth & enlightenment is ours, and both have called each other blasphemes of their science or their God.

Sorry Noel and all you other Darwinism/Evolution believing fanatics, aka: atheists.You are no less a religion then those who believe in Creationism. Atheism IS a belief, it IS a religion.


Noel Bernard
Noel Bernard

@Gordon Gekko Great spirits have always encounted violent opposition from mediocre minds .  


Albert Einstein

Noel Bernard
Noel Bernard

@Gordon Gekko The more you know , the more you know that you don,t know ,the less you know , the more you THINK that you know everything ....

Gallilé


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