Humble beginnings of the brain?: New research suggests that the genetic blueprints for our big brains might be present in this simple acorn worm. But not all invertebrate researchers agree.
Image: Ariel Pani
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Our earliest invertebrate ancestors did not have brains. Yet, over hundreds of millions of years, we and other vertebrates have developed amazingly complicated mental machinery. "It must have evolutionary roots somewhere, but where?" wrote Henry Gee, an editor at Nature, in an essay published in the journal's March 15 issue. (Scientific American is part of Nature Publishing Group.)
Years of study of common invertebrate lab subjects, such as amphioxus (Branchiostoma lanceolatum) or nematodes, have yielded scant evidence as to the origins of the big, centralized brains we all develop as embryos. Until, that is, researchers turned their gaze to the humble acorn worm (Saccoglossus kowaleskii).
These unlovely, simple little worms live most of their brainless lives buried in deep-sea beds. Researchers have probed the genetic patterns of their developing larvae and think they might have discovered a set of signals similar to the ones we use to build our central nervous system. The findings are reported online in the same issue of Nature.
But not everyone in the invertebrate community is convinced that the early antecedent to the vertebrate brain has been discovered. And these little worms seem to be stirring up controversy in the quest to find the beginnings of our own brains.
Complexity from simplicity
All of our features—from our brains to our bones—emerged from elaboration on the simplest of genetic patterns found in primitive gunk. But scientists have been keen to find out just how far back they can trace key developments, such as the signals that spurred our central nervous system to develop.
"The vertebrate brain is really exquisitely complex and elaborate," says Ariel Pani, a graduate researcher at Stanford University and co-author of the new paper. The brain is prompted into being during development by a long chain of genetically determined signals. "There are particular developmental processes in vertebrates that seem to be absent in other species"—or at least those that have been most commonly studied, such as the amphioxus, Pani notes. Thus, many scientists had presumed that these genetic tools had only emerged with the vertebrate line itself.
That is where members of the hemichordate group, such as S. kowaleskii, can broaden the view into our joint invertebrate past. The last common ancestor this worm had with vertebrates probably lived more than 500 million years ago. So is it possible that this ancient ancestor already contained the genetic groundwork for big brains—and that this ability has since been lost in more common invertebrate subjects?
Lean foundations
The path from a few cells to a full brain has taken hundreds of millions of years in evolutionary time. But during embryonic development, the elaborate process takes just days or months. During an animal's embryonic phase, clusters of proteins—called signaling centers—help spur the creation of different parts of the body. Three major signaling areas in vertebrates—the anterior neural ridge, the zona limitans intrathalamica and the isthmic organizer—are responsible for starting off the major divisions within the central nervous system, such as separating the mid and hind parts of the brain.
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Add CommentHave nematodes not evolved in the past 500 million years? If they have, perhaps 500 million years ago they did not possess the same signalling mechanisms that they have today. On the other hand, some complex organisms, such as alligators and sharks, do not seem to have appreciably changed over perhaps hundreds of millions of years. Not to stir up any creationists, but how do some species avoid significant evolutionary developments resulting from random mutations while others develop dramatic changes? Unlike perhaps nematodes, it seems apparent that the common ancestors of modern ape species did not survive...
Reply | Report Abuse | Link to thisRandom mutation is only part of the process. Many species seem to be exquisitely well adapted to their niche, and being so well adapted, there is likely less advantage to smaller incremental changes. The mud in the sea floor is a fairly consistent, and even though they are by no means stagnant, the worms are as well. A truly dramatic change or mutation, would seem to be far less likely to be beneficial in such a specific environment. Under those circumstances, Natural selection and pressures seem to have less to work on.
Reply | Report Abuse | Link to thisThe human brain is still evolving/reorganizing along molecular-biology lines that depend on diet (eg, acetylcholine, calcium, etc) and stimuli. It began with basic microbial instinct, still operative today in bacteria sending out enzymes to snip off bactericidal drug-molecule tails and/or to thicken their cell walls defensively. We need less studies on nematodes and more insight into human cognition, neuroglia and smart molecules.
Reply | Report Abuse | Link to thisComplexity is a fuzzy word without a proper definition. An atom is complex, a molecule is complex, a macromolecule is complex, a cell is complex, a cluster of cells are complex etc etc. There is no complexity. There is only interference of particles/strings/waves reflected as a measurement of carbon-X entangled states observed via whatever tools are developed. Unless the origin of carbon interference is defined, predicted and measured, the above string of words hold no true scientific 'VALUE'.
Reply | Report Abuse | Link to thisThis makes sense. Since nerve tissue comes from ectoderm, sensory tissue could have moved from the outside of the animal to the inside. Once there, it could have become nerve tissue.
Reply | Report Abuse | Link to thisGenerally, I share your opinion with one exception:
Reply | Report Abuse | Link to thisNatural selection probably had a hard job preventing the species from genetic decaying.
I'm not sure if I understand 'genetic decay,' but as my understanding is only of the most basic kind, I'll answer anyway.
Reply | Report Abuse | Link to thisGenetic decay, or chemical damage, transcriptional errors, and even radiation damage, are always present.
If the mutation is positive, and it can be acted on by selection, then it will be reproduced. If it is detrimental it will likely be eliminated. If it is benign or nonsensical, it may be removed through genetic drift. The negatives tend to act pretty quickly on any reproducing organisms, where the positives have a chance to effect the species.
What we need to remember here, are the large numbers of species in the fossil record, that seem to have survived for millions of years, recognizable, and relatively intact. The simple principal of genetic reproduction, along with the elimination of most undesirable 'decay' in the genome, leaves us with the observations that life is fairly robust; and, that each new copy gets a chance to prove its viability. Yes, catastrophic mutations can occur, as well as insurmountable environmental
events, but the basic pattern of life seems to manage long expanses of time well enough.
Coffey3C@Gmail.com
Too many assumptions. This creationist isn't "stirred up," but I defy anyone to "connect the dots" in this argument.
Reply | Report Abuse | Link to thisOkay, I'll play. I won't even point out that a creationist connecting dots, is sort of an oxymoron.
Reply | Report Abuse | Link to thisWhat do you define as dots, and how would you like
them connected?
In general the invertebrate animals explored many modes of sensory and motor response. This ranged from many segmented limbs, single and double wing sets, social insects and lone predators, to multiple simple eyes, compound eyes and other varieties on sensing and responding to the environment. All this exploratory variety converged on a quadruped limb structure tethered to an autonomic nervous system that reflects emotional behaviour patterns into cerebral awareness. In other words the vertebrates have a greatly enhanced capacity to independently reflect and tailor emotional behaviour patterns according to the needs of circumstance. The reptilian and lower mammalian brains are represented in the Limbic lobe of the human brain such that we sense our vertebrate ancestors emotional intentions and even modify similar patterns of behaviour using the newer cortical hemispheres to which we owe our intellectual capacity. This is not consistent with random mutation and natural selection. There are no six legged lizards or four winged birds. A whole new skeletal, visceral and sensory-motor integration was born anew with the vertebrates with further discrete steps toward conscious creative abilities. The vertebrates had no need to re-explore the invertebrate terrain.
Reply | Report Abuse | Link to thisThese are clearly discrete hierarchical steps up evolutions ladder. Hierarchical order is not consistent with random order and it is evident to some degree in how genes are expressed. For example the Hox genes hierarchically order developmental patterns in both invertebrates and vertebrates but with considerable elaboration in the latter. Heritable epigenetic factors also regulate gene expression along with a host of non-coding RNAs. Most of this is inconsistent with neo-Darwinian theory. Although there is a place for random order it is not the whole picture. See the article http://www.cosmic-mindreach.com/Gene_Expression.html and others on the website for more on this.
But why stop at one species of worm to look for traces of nervous origins? Plants respond to sensory stimuli too, some rapidly such as the Venus Flytrap. But roots also seek out moisture and flowers turn toward the sun. Even bacteria have some degree of sensing and responding to their environment. The point is that forever flogging this hopelessly simplistic Darwinian theory is as mindless as thumping a Bible.
An oxymoron is a person who engages in mindless vilification of an opponent rather than address the scientific issues. Someone who has to be told what the dots represent, and how they should be connected.
Reply | Report Abuse | Link to thisSo, here's how it all works. The dots can be defined as all fossil data relating to unobserved past historical events. How they are connected depends on whether evolution happened a particular way, and not another way, or even whether evolution happened at all.
The great advantage of hypothetical theories relating to unobserved and unrepeatable past events is that these dots can be elastically joined in many and varied ways, as there is no possible way of ever "empirically" verifying what actually happened. What "supposedly" happened in the past therefore depends on the particular presuppositions, inferences, assumptions, conjectures and speculations made.
Scientists interpret the data, and join the dots, differently. The supporters of the "evolutionary continuum" model advocate that the fossil record shows the gradual evolution of life from goo to you. The supporters of "punctuated equilibrium" advocate the sudden appearance of complex life-forms, and the "stasis" of creatures throughout the fossil record.
However, the principle factor to be remembered is that the underlying evolutionary assumption must always prevail. Meaning, the evolutionary hypothesis must always be assumed to be a "fact" from the outset, until "proved wrong". This ensures that all the dots are elastically interpreted, with the dots joined in such a way as to always "prove" evolution is true. Thus, evolutionary presuppositions, explanations, inferences, assumptions, predictions, conjecture, and speculations will always support this overriding naturalistic premise, allowing no other - particularly alternative creationists interpretations.
While the Nobel Committee may not regard science based on "explanations" and unverifiable "inferences" as the real thing, or of the same caliber as testable, repeatable, verifiable and publicly observable empirical science, the scientific community largely thinks otherwise.
Are you serious ???
Reply | Report Abuse | Link to thisRelearn Darwin and Pavlov...
(“Reversible marks on the genome allow honeybees to swap between lives as nurses and foragers.”?
Flip From Head- To Feet- Standing…)
(New Science of Consciousness ? Look underneath the AcademEnglish verbiage…)
Genetics Is Progeny Of Culture
It evolves from survival challenges, from natural selection challenges !!!
I.
Adnauseam Genetics Is Progeny Of Culture
Darwin and Pavlov: it is culture, the ubiquitous trait of all mass formats’ reaction to circumstances, that modifies genetic expressions…
A.
Update Comprehension Of Culture-Genetics
http://universe-life.com/2012/07/20/update-comprehension-of-culture-genetics/
The neural system, including the brain, was evolved by unicells communities (cultures) to react to, exploit, the environments for survival-natural selection.
B.
Tree's leaves genetically different from its roots
http://www.nature.com/news/tree-s-leaves-genetically-different-from-its-roots-1.11156#/comments
C.
The cultures of the roots and leaves, their survival reactions to and exploitation of circumstantial environments, are different, hence their different genetics.
Common sense is the best scientific approach. Plain and simple.
II.
Genome Evolves By Culture, Natural Selection, Not Randomly
A.
Rate of de novo mutations and the importance of father’s age to disease risk
http://www.nature.com/nature/journal/v488/n7412/full/nature11396.html
B.
RNA nucleotide genes are ORGANISMS, life’s primal ORGANISMS.
Genomes are template ORGANISMS evolved by the RNAs for carrying out their - RNAs’ - natural-selection tasks.
All life’s activities originate and evolve for the survival of the RNAs.
THIS is Darwinian evolution.
C.
Modified RNAs expressions are NOT random mutations. Some of them are caused accidents, but not random. Apply Darwinism to them.
There is no randomness in the universe that evolves from all inert mass, singularity, to all moving mass, energy, and probably back again.
Now, after a century of strangled Enlightenment, it’s time to restructure science plans, policies and budgets.
The viable future of humanity is not with natural selection, but with scientism, the follow up of Enlightenment.
Dov Henis (comments from 22nd century)
http://universe-life.com/
Tags: genetic mutations, RNA genes life’s primal organisms, genomes template organisms, natural selection