Reports that ctenophores are ancestors of all animals hide uncomfortable findings for evolution about the comb jelly’s genome.
Comb jellies (sometimes called sea walnuts) are amazing animals of the sea, flashing like Christmas lights with their cilia-driven light organs (12/19/05). Possessing muscles and complex nerve cells, they are not true jellyfish; despite the resemblance, they are classed in a phylum of their own (Ctenophora). The genome of a comb jelly has been published, and, as usual, it creates puzzles for evolution. You wouldn’t know it from the headlines, though.
- Was Your Ancestor a Ball of Jelly? Evolution Study Surprises Experts. The question of whether sponges or comb jellies were the first animals to evolve continues to stir the waters (National Geographic).
- Your Cousin Was a Comb Jelly (Science Now).
- My Oldest Sister Was a Sea Walnut? (Science Magazine).
- First ever animals were made of jelly, not sponge (New Scientist).
- Aquatic Comb Jelly Floats Into New Evolutionary Position (Science Daily).
- Ctenophores Semaphore Information About Earliest Animals (Live Science).
Hidden beneath the jolly headlines is a conundrum: comb jellies are more complex than sponges, but are now being called ancestral to simpler animals. Science Now explains:
… the genome of one of these comb jellies, as they are commonly called, suggests they have a pivotal place in animal history. The DNA sequence of the sea walnut, Mnemiopsis leidyi, puts these creatures at the base of the animal tree of life, researchers report online today in Science. That base is also populated by sponges, jellyfish, and their other cnidarian relatives, and organisms called placozoans. By comparing the genomes of these four groups of organisms and other animals, researchers conclude that ctenophores branched off first, not sponges as many have thought. Yet ctenophores have muscles and nerve cells, cell types that sponges lack, suggesting that animal evolution did not proceed smoothly from the simple to the more complex. Instead, the ancestor to all these animals may have had a more complex nervous system that sponges and cnidarians lost, and the mesodermal tissue that gives rise to muscles may have arisen independently in ctenophores.
This turns Darwin’s concept of evolution upside down. It simply cannot be (see also 4/11/08). But for today’s evolutionists who can imagine two dozen animal body plans emerging suddenly without transitional forms (the Cambrian Explosion), a few more conundrums are like adding another trillion to the national debt. After awhile, it doesn’t seem to matter.
One of the co-authors was mildly puzzled; Andy Baxevanus told National Geographic, “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.” But the tree-building software gave them a “shock” that “caused quite a stir among experts in the field.” Some refused to believe it. New Scientist says “The finding may force us to reconsider our understanding of early animal evolution.” Joseph Ryan (NIH) was one:
This challenges the two basic tenets of animal complexity, says Ryan: that animals started out simple, and that once they evolved complex traits they stayed that way.
According to Science Daily, Ryan sees two uncomfortable choices, both seemingly miraculous:
“With our whole-genome sequencing data in hand, it is now clear that the cell types that make up muscles and nervous systems were either lost in some animal lineages or that, despite the complexity of these cells, they very well may have evolved multiple times.“
The first “miracle” would be to suppose that complex cell types for muscles and nerves evolved in an unknown, primitive ancestor, leaving no trace. The second “miracle” is even more incredible, imagining those cell types evolving multiple times independently. The original paper in Science leaves the dilemma unresolved:
It appears that much of the genetic machinery necessary for a nervous system was present in the ancestor of all extant animals. This pattern suggests that a less elaborate nervous system was present in the metazoan ancestor and was secondarily reduced in placozoans and sponges. The alternative is that neural cell types arose independently in both the ctenophore lineage and the lineage that led to cnidarians and bilaterians, which might explain some of the unique aspects of the ctenophore nervous system….
The implications of these findings go well beyond the rearrangement of the branches of the metazoan tree of life, arguing for a new way of thinking regarding the emergence and/or conservation of what heretofore were considered to be unique and indispensible biological features. Likewise, theories on the evolution of animal multicellularity have to be reevaluated.
To understand the implications of this finding, we have to remember that multicellularity was a big step in evolution that occurred over 550 million years ago. At the time there was an explosion of forms, as life explored the limitations and possibilities of having a body made up of different types of cells….
As sea walnuts glow when disturbed, so does this study shed light on some interesting assumptions about animal evolution.
The first experiments in multicellularity [i.e., by microbes] were not simple collections of cells without structures or communication. Genes responsible for cell signalling were present even before the evolution of multicellular animals. This suggests single celled organisms were communicating with each other before they decided to organise themselves into bodies with different types of cells.
Second, the three cell layers of well-known animals including ourselves is not unique nor is it a latecomer to animal evolution. The earliest multicellular animals evolved their own form of mesoderm independently, with unique genes allowing sophisticated biological organisation.
Third, the ancestor of all animals had a nervous system which coordinated bodily functions. The nervous system was subsequently lost in the lineages that led to Porifera and Placozoa, but survived in the Cnidarians and the Bilaterians.
Finally and most profoundly, the shape of the evolutionary tree of all animals has taken on a new shape. The earliest branch of the animal tree belongs to Ctenophora, now confirmed to be the sister lineage to all other animals.
So don’t confuse comb jellies with jellyfish.
I think of the Ctenophores as a semaphore, signalling some profound truths to us (in a blue green glow) across the vastness of time about animal origins and biological organisation.
Miracles of design are apparently easier to achieve with active planning agents, like microbes. Some, however, might argue that piling on additional miracles to explain one miracle is a bit like telling more lies to cover up an initial fib. Adding to this story the conundrum that modern-looking ctenophores appear in the Cambrian Explosion (4/03/07), readers can decide whether the proffered explanations constitute “understanding of early animal evolution.”
Here is dazzling proof that (1) evolutionists believe in miracles and (2) no amount of falsification, no matter how obvious, will ever dislodge their undying faith in Darwin. Yet these are some of the same churlish people who lambaste advocates of intelligent design. For an example, look at the angry comments by some PBS viewers incensed that a local affiliate station aired Illustra’s beautiful new un-Darwinian documentary, Flight: The Genius of Birds. Compare their prideful, hateful rhetoric with those who thought the film was good. Example: “This is just disguised propaganda of people who can’t deal with the reality of science and what it means to their beliefs. It is dangerous pseudo-science. I thought this was a nature show only to find I am being preached to using wishful thinking and opinion in place of science.” Question: whose viewpoint used religious arguments?
The situation looks grim for convincing hot-headed dogmatists to follow the evidence honestly. It is the challenge that must be faced despite the heat. If you are nothing more than a comb jelly, all bets are off for a civilization you would want to live in.
For relief, go learn about the beauty and design of comb jellies. They are really remarkable creatures, putting on the most amazing psychedelic light shows of the sea.