Teamed with genetics, Darwin's explanation of how species change through time has become the rock on which biology stands. Which makes the water flea quite the skunk at this party.That "somehow", as Begley correctly notes, is called a "genetic switch", and the notion that a primitive species like the water flea might use one to determine whether offspring develop "helmets" makes perfect sense -- in the context of Darwinian evolution and the genetic theory of inheritance.
Some water fleas sport a spiny helmet that deters predators; others, with identical DNA sequences, have bare heads. What differs between the two is not their genes but their mothers' experiences. If mom had a run-in with predators, her offspring have helmets, an effect one wag called "bite the mother, fight the daughter." If mom lived her life unthreatened, her offspring have no helmets. Same DNA, different traits. Somehow, the experience of the mother, not only her DNA sequences, has been transmitted to her offspring.
That gives strict Darwinians heart palpitations, for it reeks of the discredited theory of Jean-Baptiste Lamarck (1744–1829). The French naturalist argued that the reason giraffes have long necks, for instance, is that their parents stretched their (shorter) necks to reach the treetops. Offspring, Lamarck said, inherit traits their parents acquired. With the success of Darwin's theory of random variation and natural selection, Lamarck was left on the ash heap of history. But new discoveries of what looks like the inheritance of traits acquired by parents -- lab animals as well as people -- are forcing biologists to reconsider Lamarckism. [minor format edits, bold added]
Clearly, a water flea without a helmet would be ill-adapted to survive in an environment rich in predators. Perhaps not so clear is the fact that a water flea with a helmet has at least one disadvantage to one that does not: That helmet has to come from somewhere. The superior armament will cost it more food. In an environment where there are no predators, then, a helmet-less water flea has an advantage in needing less food.
What solution is best? Predators aren't always a problem for water fleas, so a species that saddled itself with unneeded armament would be wasting precious food. (And, I suppose, creationists would pounce on that as an example of how God was telling puny man that He was in charge.... What Intelligent Designer would fail to sign His work?)
But predators sometimes are a problem. Gosh, perhaps an organism that could either have a helmet or not have one as needed would have an evolutionary advantage! I am no expert on water fleas, but something tells me that they don't live too long, so its best bet as a species would be -- oh, I don't know -- to evolve the capacity to turn the helmet gene(s) on or off from one generation to the next. (News flash: Genetic switches, as "gene regulatory proteins", are encoded in the DNA by genes.)
Well! I'll be switched! That's exactly what happened!
But Begley either does not understand this fully or she is an active, dishonest opponent of the theory of evolution, as we see in another example:
Since 1999 scientists in several labs have shown that an experience a mouse mother has while she is pregnant can leave a physical mark on the DNA in her eggs. Just to emphasize, this is not a mutation, the only way new traits are supposedly transmitted to children. Instead, if mother mouse eats a diet rich in vitamin B12, folic acid or genistein (found in soy), her offspring are slim, healthy and brown -- even though they carry a gene that makes them fat, at risk of diabetes and cancer, and yellow. It turns out that the vitamins slap a molecular "off" switch on the obesity/diabetes/yellow-fur gene. [minor format edits, bold added]Yes, a genetic switch has been thrown, and it affects the physical appearance of offspring. But without the genetic code already in place (including both the regulated genes and the switch proteins other genes encode), neither the range of possibilities nor the switching mechanism we're busy distracting ourselves with would even exist.
In Begley's defense, some of the scientists she draws upon seem not to understand how to hold new data or complicated theories such as evolution and genetics in their proper context, and Francis Crick's foolish decision to refer to his theory of inheritance as the "Central Dogma of Molecular Biology" has not helped. On the other hand, the fact that the phenomenon of epigenetic inheritance has been known about for quite some time indicates that further research was warranted -- on Begley's part.
There is no great controversy here. Epigenetic inheritance, far from being a reason to resurrect older, discredited or -- worse -- arbitrary theories of speciation, actually serves as further evidence in support of Darwinian evolution and molecular biology. Begley just insulted the guest of honor by calling it a skunk!
-- CAV
So Darwin specifically didn't understand the mechanisim of inheritance b/c it hadn't been discovered yet. He knew that there was one, he didn't know what it was. So this can't be some sort of refutation of Darwin, per se.
ReplyDeleteWhat it is is a creationist tactic. Namely to refer to the science of Evolutionary Biology as "Darwinian Evolution" as though Darwin wrote a Biblical tome which has been blindly followed ever after.
Fundamentalist Christians assume that their Biblical literalism is the way that the world works and when they see that other people "believe" in evolutionary theory they draw the assumption(whether honestly or no) that those who accept this idea of how the world works do so on the same faith-basis as they accept the Bible.
They have little or no idea of the scientific method, of the willingness to start with evidence and draw conclusions accordingly. And of the idea that new evidence requires the revision of theories to better fit the facts.
Genetics first began to provide a scientific explanation for change over time and speciation. More recently, the effect of development on GENES has refined our understanding of how characteristics come about and are passed on. But even if we discovered that ALL genetic inheritance was a function of developmental factors this would not change or refute the heart of the theory that Darwin put forth, namely that speciation is a function of change over time by means of natural selection that favors living things which are better adapted to their environments.
All excellent points. Thanks for weighing in.
ReplyDeleteGus -- Oddly, misuses of epigenetic inheritance seem to be all the rage these days. Okay, so I only noticed one other example by Art DeVany this past week. But still! I've never heard of it before, so it must be a trend. :-)
ReplyDeleteWould it be accurate say that epigenetic inheritance only makes sense in the broader context of well-established evolutionary theory, so it cannot be grounds for calling that theory into doubt?
In any case, it is an cool little mechanism.
Shooting from the hip here, I think so, and it seems like using epigenetic inheritance to attack modern biology is an example of the fallacy of the stolen concept.
ReplyDeleteYou could not even HAVE a concept of epigenetic inheritance were the genome not the primary basis for determining an organism's physical characteristics.
Not one to want to give any credence to creationist argument, but I must admit biologists are stubbornly holding on to concepts such as central dogma, when clearly the environment can directly affect "switch" genes (as well as other epigenetic genes) in situations where there "would" have been Darwinian significance, but less unhelmeted water fleas die with this direct-from-the-environment switch, which clearly short-cuts the usual surviving-progeny-only feedback, which is still the only way environmental inputs are said to affect inheritable traits as described by the central dogma.
ReplyDeleteIt should be survival of the fittest+with the best epigenetic (or neo lamarckian) shortcuts.
Marco,
ReplyDeleteThanks for your comment, but you are partially missing my point.
The ability of this species to adjust its phenotype from one generation to the next is STILL due, although indirectly, to information encoded by its genome. In that sense, the central "dogma" has not been violated.
Also, no biologist I know of would claim that the environment acts directly to change the genome of any species to its advantage.
The environment CAN cause random genetic mutations (which can also occur due to natural processes within an organism).
All natural selection can do is reveal that some kind of advantage obtains to an organism that happens to have some mutation in some contexts.
Random mutations and natural selection work together, slowly, over time.
Gus
Your argument doesn't sound right to me. You indicate that this ability to have a trait 'switch on' is not unlikely. But this sounds like a dramatic change to me... the offspring of the affected fleas look radically different - they basically have a new appendage because of an experience their mother had. This seems like too radical a change to me for something already developed in the genetic code to just 'switch on'. What other examples are there in nature of this kind of thing happening? This sounds really really unique and would need a deeper explanation than the argument being provided by either yourself or Begley....
ReplyDeleteAnon,
ReplyDeleteThe genetic switch is itself a protein. Proteins are encoded by genes.
Yes, the switch takes effect after it is triggered by the mother's experience, but that does not alter the fact that the switch was already encoded in the genome.
Many apparently mind-boggling things like this actually have simple explanations like this.
Gus
So this is a question more than a comment.. Wouldn't developmental changes such as the throwing of protein switches themselves be instances(at least some of the time) of natural selection?
ReplyDeleteAlso.. I mangled my last paragraph in my first comment.. it should say something like.. "Genetics first began to provide a scientific explanation of the mechanism that causes change over time and speciation...."
Absolutely. That's essentially my point.
ReplyDeleteYour question reminds me of another example which is less exotic than the water flea: Consider the fact that caterpillars and moths have radically different bodies, and yet the same DNA.
All glory and all power to the all wise objects that supposedly "cause" "evolution" to supposedly "happen".
ReplyDeleteThose brilliant objects of yours sure know how to protect the creatures that it supposedly makes. Where is this brain that supposedly knows how to create such great wonders??? Three known levels of correction of "mutations" and now this ability to pass on traits to offspring without natural selection or mutation. That is a wonder indeed!!! Your object god really knows how to make things - NOT. You delude yourself to no end.
And who created God? As you say, complex beings can't just "happen".
ReplyDeleteer... Something on the order of 99.999...% of all beings that were ever alive aren't anymore. It's not that mutation does such a fabulous job of keeping life around, it's just that it has done just good enough so far.
ReplyDeleteNot that I actually got the point of that as it was somewhat garbled..
Clay,
ReplyDeleteThat was just some Christer who wandered by after Google-searching "water flea helmet" and then got his paties in a wad when he saw that, no, the "argument" was not persuasive.
Just emotional vomit, that.
Gus