Fly dreams and the boundaries of evolutionary science

Jan 02, 2014 by John Hewitt report
Fly dreams and the boundaries of evolutionary science
Jean-Baptiste Lamarck
Credit: Wikipedia

In 2002, Secretary of state Donald Rumsfeld made a statement regarding weapons of mass destruction that today is still well known. He famously parsed the evidence (or lack thereof) into "known knowns, known unknowns, and unknown unknowns." In squeezing virtually all that it can from the ideas of Darwin, evolutionary biology has produced a mountain of facts and ideas that fall squarely in the realm of Rumsfeld's first two categories.

However those mechanisms that first generated life, and by implication continue to refashion it as fast as we try to comprehend, are still unknowns of a nature we have scarcely imagined. Strict adherence to the concepts of random genetic mutation followed by natural selection thrusts up a steep barrier to a full understanding of variation in the natural world. In order to push beyond this cusp, scientists have now turned to the ideas of Lamarck. The latest installment in the genetic saga of individual experience has just been published on the arxiv preprint server by Harvard neurosurgeon Ziv Williams.

Ziv's new results were obtained with flies, and they shadow the recent provocative data on murine (mouse) inheritance of ancestral fears. The latter study raised the roof on what is now possible in a scientific experiment. In demonstrating not only a mechanism for sperm-specific transmission of acquired traits from the father, but also precision modification of neural circuitry, that report set the bar extremely high for what might be proved in a study—and also for what might be swallowed by the larger community.

With mice, it is possible to isolate the mechanism of transmission of a particular experience to the father's sperm by doing in vitro insemination. While that is not so simple in flies, there is one big advantage to working with them—experiments can be more easily done at high n factor (number of flies). This is critical for discerning complex, but often weak, effects. The principle that information of a hereditary nature ratchets only in the direction from to somatic (body) cells is known as Weismann's barrier. It is expected that any breakdown of this evolutionary diode (such as feedback from somatic to germ cells) would be a weak effect because the bandwidth for transmission of experience to germ cells would, at first glance, appear to be severely limited.

It should be pointed out that many genetic therapies now on the table are based on treatment of . If heritable changes to the genome can be introduced via predictable breaches in Weismann's barrier, as many now presume exist, that is something we probably want to know more about. We need look no further than plants to see that in germ lines can be produced as a result of genetic changes in somatic lines. Here somatic cell lineages (vegetative meristems) may be old enough to have accumulated many mutations subject to since seed germination.

Neurobiologists are more interested in those heritable skills or experiences that can be packaged quickly into the germ line, almost perhaps, instantaneously. In many species, sperm are produced at a tremendous rate and practically speaking, they turn over daily. For his fly experiments, Ziv paired different odors with either an aversive or an appetitive stimulus, and trained them over the course of a few days to make the proper associations.

The aversive stimulus was an electrified copper grid which presumably was distasteful enough to be seen as a non-lethal assault, but not so powerful as to prevent any formative interactions. Electrical shock may not be the cleanest stimulus (after all we know from the experiments of Miller and Urey that electricity of sufficient voltage can spawn amino-acids from gases), it seems to have what it takes to make a good impression. The appetitive stimulus in this case was of an appetitive nature—corn meal and sugar. While the opposite of shock may not be a sugar snack, the pair do provide a clear choice between good and evil.

If precise mechanisms of inheritance are to be attributed to specific details of a stimulus, then the particulars of the odors themselves (3-octanol (OCT) or 4-Methylcyclohexanol (MCH)) are important in these studies. Other experiments, like those in mice, used acetophenone because a fair bit is already known about the receptors and circuitry involved in detecting it. Using a T-maze setup, Ziv was able to show that after the parents had mastered associations of odors with good and evil, the offspring of those flies later showed heightened sensitivity to them as well. However, for whatever reason, the effect was only strong with the MCH stimulus, and in the aversive pairing. Not only that, but the response to MCH was the opposite from the response that the parents had learned: the offspring preferred to move toward MCH instead of avoiding it.

Ziv suggests that since the sensitivity to MCH was inherited, but the seemingly useful response (avoidance) was not, there is no inheritance of change at the neural circuit level going on. While that may be a fair enough conclusion, we really can't make any sweeping conclusions at this point as to what is really going on. Ziv, like other explorers of Lamarckian inheritance, merely offers his controlled study with error margins in the same spirit as nearly every other scientific study put on the charts. If we take any of them at face value, we take all of them.

Scientists look for inheritance of specific experiences because they can be quickly inserted into animal, and then later measured to clear effect. To further probe these behavioral phenomena, Ziv suggests that olfactory processes could be blocked at various stages in the adults. Reversibly altering specific pathways using dominant temperature-sensitive transgenes like UAS-Shi for example, would perhaps be one way to do this.

Ultimately scientists want to look beyond transient effects and explore the inheritance of actual physical characteristics, like longer necks in giraffes or bigger hands in farmer's sons. Opponents may argue that any significant results that one might obtain would merely uncover previous genetic pathways already built into the organism. In a way we have the same bottleneck that sensory neurobiogists decry when they try to account for the massive compression of information in a visual stimulus through the retina, and unto the digital output of the optic nerve spike train. However if we figure the entire retina, or the entire body, as a molecular computing volume down to the samllest scale, rather than just considering a few membrane-constrained channels, we hint at the source of power.

Explore further: New clues to memory formation may help better treat dementia

More information: arxiv.org/ftp/arxiv/papers/1312/1312.7331.pdf

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davidivad
5 / 5 (3) Jan 02, 2014
i think it is amazing what we are finding out about the complexities of genetics. genes are complex enough through regular genetics, and now we are studying epigenetics only to find it is even more complex and continuously changing. i often wonder if my late nights in front of the computer screen drinking massive amounts of coffee will become a menace for my children.
johnhew
2.5 / 5 (2) Jan 02, 2014
Seems to be a fair amount of resistance still to Lamarck, as judging by kneejerk votes of 1/5 for this kind of thing, even when the big journals like Nature Neuro just put Lamarck on their cover and told their followers that it is okay now.
Torbjorn_Larsson_OM
5 / 5 (2) Jan 02, 2014
@johnhew: Careful, non-evolutionary epigenetics is Lamarckian, while evolution is certainly not, so Lamarckism is not "okay now" anymore than earlier. Those who writes so has a quixotean agenda.
johnhew
2 / 5 (3) Jan 02, 2014
Thanks for the comment Lars. Let me ask you a question, how many mutations would it take for me to have offspring that could inflate their eye stalks? I'll tell you how many -- no amount of mutation. You would play around in an infinity of infinite universes subbing out a's and g's and never get it. You need more powerful whole body mechanisms, and mates and culture that are keen on them. http://dsc.discov...alks.htm
thingumbobesquire
1 / 5 (1) Jan 03, 2014
The attempt to define evolution as a directed and causal series of inheritance of traits, points at a larger issue that unfortunately hampers progress in science itself. That issue is the zealous quasi-religious adherence to a doctrine of stochastic probability. This is really a question of ontology that has played out over at least several millenia. When Heraclitus ironically cited change as the only constant substance of reality, this was succinctly brought into human consciousness. Einstein's quip that God doesn't shoot pool was of a piece. Leibniz' critique of Newton's dead clock winding ontology in his debate with Clarke, likewise. A vision of a mission that directs scientific inquiry must govern how we proceed. Such is the eradication of disease, the establishment of a defense in space against future impacts from comets and asteroids, and finally evolving an energy regime of controlled thermonuclear fusion. One must start from the standpoint of necessary human evolution.
_ilbud
not rated yet Jan 03, 2014
Tsk always with the religitards and their nonsense.
orti
2 / 5 (1) Jan 03, 2014
Your pathetic slam of Rumsfeld might be more effective if you knew his title.
orti
3 / 5 (1) Jan 03, 2014
"However those mechanisms that first generated life, and by implication continue to refashion it ..."
Isn't that backwards? Evolutionists see that life is adaptable and extrapolate back to its being self creating. Does this article get anything right?
johnhew
not rated yet Jan 03, 2014
If you can understand how the brain first develops for example, then you have some start as to understanding how it continues to change in adult life, and to what perturbations and modifications it would stable against. Not sure how well that works in reverse. Does not the same hold true for programming the universe?
I supported search for WMD and would not slam Rumsfeld for anything but lack of stance against torture. Maybe you can help us with the proper title.
Surly
not rated yet Jan 03, 2014
@johnhew: He was Secretary of Defense, not of State.

This article's starry-eyed, unfocused on the actual research, and suggests a rather loose understanding of how epigenetics works. With that said, it's not nearly as bad as when you mistook Eugene McCarthy's hypothesis for something well-supported.
johnhew
not rated yet Jan 03, 2014
Thanks Surly. Stay tuned here on the McCarthy work, there will be results to come.
I want to suggest it may also be starry-eyed to draw the constraint Lamarck = epigenetics.
Epigenetics, at least as we now know it is but a minor subset of the full suite of mechanisms available for Lamarck to operate.
orti
not rated yet Jan 04, 2014
He was Secretary of Defense (not state (Colin Powell's role)) at the time.
Does anyone know what "mechanisms that first generated life" other than by extrapolation from recent observations?