New Monadology Codicil

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Let’s reiterate: How do you draw the boundary between one computation and the other? – since, after all, these are just shapes traced within light cones in the sum of the relevant neural networks? There is no especially principled way to do this from the inside of experience. The choice itself changes us. We can choose to believe in a single brain changing from moment to moment. But then we realize that belief in a single brain is arbitrary since timeless causality is flowing from what might be called “other brains” in the naive ontology. The unenlightened are given the Koan: How would you draw the line for souls after mix-matching half of my brain with half of my neighbor’s brain?  – And then connecting the other two halves, all the while keeping every half functioning.

Of course, I who understand, know that a competitive exclusion principle need not apply here, since the two “souls” aren’t competing to exist. It’s not that one blanks out and the other remains. Experience is intrinsic to myself. No things are traveling and seeking to remain.

If I am a physicalist, so I believe that the empirically-tested theories of physics provide an undergirding for my perceptual tools as opposed to the other way around, then this suggests that what I really experience is a solipsistic ascent that is already perfectly adaptive, but that I must sort of forget this in order to be perfectly adaptive.

I developed this idea while processing signaling theory and uniform-cost search. Uniform-cost search is a relevant model because that is how an algorithm checks to see if a new path is better than an older one, and it is easy to see that uniform-cost search is optimal in general. Since new and older don’t exist anywhere except in the timeless algorithms themselves, I argue that we are always in a better path, because otherwise we would not constrain our anticipation by the density that arises when we apply the Born Rule to infinite amplitude. The algorithm that I identify with is occurring in the absence of a physical time.

Signaling theory dynamics have long subsumed biology by the point that we are social mammals that partake in Mind. There, you find that humans are deceived about their hidden motives in order to function. Since my being is a functional role, I am permanently deceived about where I am going in order to get there.

In short: Uniform-cost search selects a node for expansion only when an optimal path to that node has been found and therefore swallows Mind by sacrificing Hilbert-Space drafts.

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Oscillation converges towards the most rational behavior. The most rational behavior is not that which is most Spock-like necessarily, but that which is most capable of tenseless survival with regards to the unknown-source-of-the-Born-Rule/the-unknown-selector-of-binding-in-Relativity’s-fabric.

I am not some crisp cut of physical events that I can point to and say, “Ah there I am.” I can only choose to become truer (by debunking the solidity of closed individualism for instance) and equipping it strategically instead.

Hidden Motives In The Eternal Block

I’m going to begin this post by going meta. I accept the Hansonian creed: Politics is not about policy, medicine is not about health, laughter is not about jokes, and food is not about nutrition. Conversation, including this post, also has hidden motives. Although we like to talk about conversation as if it was about imparting information and finding out useful things, more plausibly it’s about showing off your backpack of tools and skills in context.

In a rich society like ours, somewhere around 90% of our behavior is signaling. The other 10% are things that don’t impress anyone but must be done anyway, such as scratching your ass.

As we’ve become richer, we’ve become more forager-like. If our descendants get poor again, they’ll probably need stronger social norms again, to get them to resist temptations to act like foragers and do what is functional in their world. Their morality would probably rely on a wider more-conservative-like range of moral feelings.

Forager values include more freedom. This is expressed through more travel, less routine, lack of grandiose responsibilities, lack of religion (though not necessarily a lack of spirituality), greater equality, more promiscuity, less war etc. It generally seems that society is moving in this direction, and that we like this trend. This makes sense because we were foragers all along, and happened to have our bodies hijacked by the memetic virus of agriculture. This lead to some selection for agriculturalist traits: propensity for religion, submissiveness, more feminine men, etc. But the selection on genes has simply not occurred for long enough to make us well-adapted to the agriculturalist way (with some demographics worse at it than others).

Agriculture lead to the industrial revolution and this lead to riches. Now that we are rich, we can afford the luxury of becoming our true selves, children, once again.

It is not some natural tendency of humans to make linear moral progress. Rather, it is abundance which purchases this period in which sophisticated values such as humanism and its mutations can arise.

Gene drift is the method for evolution in the absence of natural selection pressure. So too in the memetic landscape. We can afford to evolve via meme drift in the absence of a tangible and immediate threat of starvation, invasion, or pestilence.

It is in this space, sometimes called dreamtime, that I believe we can do enough self-awareness of hidden motives, enough meta-cognition, to see far beyond what we have seen in the foggy haze of survival-mode and naive-signaling-mode.

We cannot disembody our behavior from the biological substrate. This is the case for all moments of being a behavior of a biological organism. Therefore, my seeking truth is a form of signaling. Yet it is at least a more sophisticated signaling, one which acknowledges a single level of self-reflective recursion and no more.

An actor who breaks the fourth wall commits an act of violence against his fellow characters, elevating himself thus. The drama will never be the same for him or for the audience but he will succeed at being remembered.

This is the spirit of insight. It is that which is remembered because it contains the attributes of being both true and useful. This definition of insight is detailed in the Enlightened One’s speech in the Buddhist Suttas, it is detailed in the silicon seams of technological invention, it is detailed in your living flesh riding aboard a deadly planet.

The content here presented then, is not 1st-order signaling, but a 2nd-order signaling which attempts to achieve enough fame to enter the rolls of history in memory. The following endogenously generated probe is true. It elevates contents in the “background” to prominence. But is it useful? –That remains to be seen.

Most people have the idea that time flows.

However, special relativity eliminates the concept of absolute simultaneity and a universal present: according to the relativity of simultaneity, observers in different frames of reference can have different measurements of whether a given pair of events happened at the same time or at different times, with there being no physical basis for preferring one frame’s judgments over another’s.

This also applies to the cells in the brain running massively parallel computations. All the parts of the computations exist in an eternal block.

If, due to the generalized-anti zombie principle, we identify consciousness with a specific subset of these computations and not as an epiphenomena, then it is the case that experience is forever. The fabric of spacetime is imbued with all the flavors of qualia that were ever traced by these computations.

What’s more, there were no line-segment souls anywhere. It is not physically the case that consciousness begins at some arbitrary point of conception and then travels like a Newtonian sphere with a persistent identity to some other point-location where it encounters a Death Event due to all the issues with closed individualism. Instead, we find ourselves everywhere and everywhence but cannot know this from most human indices.

Computations can also have “longer temporal-grain” than what seems intuitive to humans. Consider that the processing for shape occurs at one cluster of spacetime points and the processing for color occurs at another cluster in the future light cone, and no further processing is needed to bind them into an experienced red circle. By Occam’s Razor, we should assume that this kind of “spooky action at a distance” or “phenomenal binding without glue” also occurs with computations across vaster swaths of the eternal block.

More complex algorithms can be built on top of computations with lower specificity. Brain events in a toad hopping off a mushroom may be a building block for parties across the multiverse.

There is no competitive exclusion principle for independent souls or consciousnesses because independent souls/consciousnesses don’t exist. However, we should still expect a natural selection underlying the distribution of our anthropic mass. We should expect more mindspace to be designed by superintelligences than by the relatively dumber processes that bootstrap them.

For the vast majority of our existence we should therefore expect ourselves to exist directly within or caused by that which is most competitive at creating conscious experiences. Whether this is mainly due to the linkage disequilibrium between superintelligences’ utility functions or due to which conscious computations are more populous due to their sheer structure.

An analogy which may be useful in some respects but obfuscating in others: In the textbook classification of life, viruses and bacteria vastly outnumber Chordates, not to mention humans. Similarly, in the framework for life depending on self-modeling conscious computations, some conscious computations may be very simple but vastly outnumber those intentionally designed due to their sheer ease of creation and symbiosis (these simple computations may be remembered/experienced widely by fitting like keys into many of the relevant algorithmic keyholes).

 

 

 

Natural Selection Doesn’t Work When Considering QI Experiences vs. Arbitrary Experiences

Given the pervasiveness of epistasis, adaptation via changes in genetic makeup becomes primarily a search for coadapted sets of alleles–alleles of different genes which together significantly augment the performance of the corresponding phenotype. It should be clear that coadaptation depends strongly upon the environment of the phenotype. The large coadapted set of alleles which produce gills in fish augments performance only in aquatic environments. This dependence of coadaptation upon characteristics of the environment gives rise to the notion of an environmental niche, taken here to mean a set of features of the environment which can be exploited by an appropriate organization of the phenotype. (This is a broader interpretation than the usual one which limits niche to those environmental features particularly exploited by a given species.) Examples of environmental niches fitting this interpretation are: (i) an oxygen-poor, sulfur-rich environment such as is found at the bottom of ponds with large amounts of decaying matter–a class of anaerobic bacteria, the thiobacilli, exploits this niche by means of a complex of enzymes enabling them to use sulfur in place of oxygen to carry out oxidation; (ii) the “bee-rich” environment exploited by the orchid Ophrys apifera which has a flower mimicking the bee closely enough to induce pollination via attempted copulation by the male bees; (iii) the environment rich in atmospheric vibrations in the frequency range of 50 to 50,000 cycles per second – the bones of the mammalian ear are a particular adaptation of parts of the reptilian jaw which aids in the detection of these vibrations, an adaptation which clearly must be coordinated with many other adaptations, including a sophisticated information-processing network, before it can improve an organism’s chances of survival. It is important to note that quite distinct coadapted sets of alleles can exploit the same environmental niche. Thus, the eye of aquatic mammals and the (functionally similar) eye of the octopus exploit the same environmental niche, but are due to coadapted sets of alleles of entirely unrelated sets of genes. (iv) the environment rich in depressive emotion – the aesthetic of Neon Genesis Evangelion are a particular adaptation in qualia-space which aids in the detection/exploitation of the depressive environment.

The various environmental niches E ∈ ε define different opportunities for adaptation open to the genetic system. To exploit these opportunities, the genetic system must select and use the sets of coadapted alleles which produce the appropriate phenotypic characteristics. The central question for genetic systems is: How are initially unsuited structures transformed to an observed range of structures suited to a variety of environmental niches ε? To attempt a general answer to this question, we need a well-developed formal framework. The framework available at this point is insufficient, even for a careful description of a candidate adaptive plan τ for genetic systems, unlike the case of the simpler artificial system. A fortiori, questions about such adaptive plans, and critical questions about efficiency, must wait upon further development of the framework. We can explore here some of the requirements an adaptive plan τ must meet if it is to be relevant to data about genetics and evolution.

In beginning this exploration we can make good use of a concept from mathematical genetics. The action of the environment E ∈ ε upon the phenotype (and thereby upon the genotype A ∈ α) is typically summarized in mathematical studies of genetics by a single performance measure μ called fitness. Roughly, the fitness of a phenotype is the number of its offspring which survive to reproduce. This measure rests upon a universal, and familiar, feature of biological systems: Every individual (phenotype) exists as a member of a population of similar individuals, a population constantly in flux because of the reproduction and death of the individuals comprising it. The fitness of an individual is clearly related to its influence upon the future development of the population. When many offspring of a given individual survive to reproduce, then many members of the resulting population, the “next generation,” will carry the alleles of that individual. Genotypes and phenotypes of the next generation will be influenced accordingly. This is especially important in light of a big universe. If we assume that consciousness is not epiphenomenal, but instead described fully as a slice in the causality of Platonia, then understanding the fitness of degraded experiences barely holding above water by the grace of quantum immortality becomes important.

Fitness, viewed as a measure of the genotype’s influence upon the future, introduces a concept useful through the whole spectrum of adaptation. A good way to see this concept in wider context is to view the testing of genotypes as a sampling procedure. The sample space in this case is the set of all genotypes α and the outcome of each sample is the performance μ of the corresponding phenotype. The general question associated with fitness, then, is: To what extent does the outcome μ(A) of a sample A ∈ α influence or alter the sampling plan τ (the kinds of samples to be taken in the future)? Looking backward instead of forward, we encounter a closely related question: How does the history of the outcomes of previous samples influence the current sampling plan? The answers to these questions go far toward determining the basic character of any adaptive process. But the question is incredibly complicated when we want to measure fitness of experiences, which necessarily exist in an eternal object, and are themselves eternal. How can bounds even be drawn on them?

The answer to the first question, for genetic systems, is that the future influence of each individual A ∈ α is directly proportional to the sampled performance μ(A). This relation need not be so in general – there are many well-established procedures for optimization, inference, mathematical learning, etc., where the relation between sampled performance and future sampling is quite different. Nevertheless, reproduction in proportion to measured performance is an important concept which can be generalized to yield sampling plans – reproductive plans – applicable to any adaptive problem (including the broad class of problems where there is no natural notion of reproduction). Moreover, once reproductive plans have been defined in the formal framework, it can be proved that they are efficient (in a reasonable sense) over a very broad range of conditions.

A part of the answer to the second question, for genetic systems, comes from the observation that future populations can only develop via reproduction of individuals in the current population. Whatever history is retained must be represented in the current population. In particular, the population must serve as a summary of observed sample values (performances). The population thereby has the same relation to an adaptive process that the notion of (complete) state has to the laws of physics or the transition functions of automata theory. Knowing the population structure or state enables one to determine the future without any additional information about the past of the system. (That is, different sampling sequences which arrive at the same population will have exactly the same influence on the future.) The state concept has been used as a foundation stone for formal models in a wide variety of fields.

An understanding of the two questions just posed leads to a deeper understanding of the requirements on a genetic adaptive plan. It also leads to an apparent dilemma. On the one hand, if offspring are simple duplicates of fit members of the population, fitness is preserved but there is no provision for improvement. On the other hand, letting offspring be produced by simple random variation (a process practically identical to enumeration) yields a maximum of new variants but makes no provision for retention of advances already made. The dilemma is sharpened like a fine chef’s sushi blade by two biological facts: (1) In biological populations consisting of advanced organisms (say vertebrates) no two individuals possess identical chromosomes (barring identical twins and the like). This is so even if we look over many (all) successive generations. (2) In realistic cases, the overwhelming proportion of possible variants (all possible allele combinations, not just those observed) are incapable of surviving to produce offspring in the environments encountered. Thus, by observation (1), advances in fitness are not retained by simple duplication. At the same time, by observation (2), the observed lack of identity cannot result from simple random variation.

As Karl Popper observed (before changing his mind eventually, to be fair): natural selection is generalizable to everything: the cosmos, biology, cultural ideas. However, it is my contention that its explanatory power breaks down when considering the competition between Moloch consciousness (i.e. self-aware processes in humanity, transhumanity, and all other arbitrary organisms and AIs across the multiverse) and simple consciousness (that range of most simple experience – whether that ends up being Quantum Torment-flavored or something like unity with Brahman). In other words, once computational specificity/complexity degrades past a certain point, it is unclear how anything is differentially “reborn” since degradation of specificity involves becoming an identical configuration to many “others” (and hence not other in any strictly meaningful sense). The action of the environment upon the phenotype seems to slip past some kind of event horizon.

So How Does DNA Replication Work?

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DNA goes to RNA goes to protein.

And DNA goes to itself.

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DNA is replicated, it makes RNA, and RNA is used to make protein.

So the first step of that is “How does DNA give rise to more DNA?”

Well… How do you find an enzyme? How do you do biochemistry?

Assay!

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You’ve got to grind up the cell. You’ve got to choose a cell in which you are likely to find an enzyme, grind it up, break it into different fractions, and test each fraction. That’s all biochemists do, right?

So what cell might have the enzyme we’re looking for? What cells might be able to copy DNA?

How about ALL CELLS

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Lets use a simple cell. What’s a simple cell?

Lets use bacteria!

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So lets take some bacteria. We’ll grind it up. Fractionate it into different fractions. We’ll see if one of those fractions has the ability to copy DNA.

If we’re going to run an assay, we have to give it a substrate. What substrate would you like to give it? What do you think it needs?

It better have some free nucleotides. Otherwise how could it make DNA?

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What else? Are you going to ask it to make DNA all by itself?

We want something that can copy one of the strands of the double helix. So what should we give it?

Half a helix. A strand of DNA. The strand to be used as a template. So lets give it a template strand.

So we’ll take a template strand of DNA. Here’s my template strand of DNA:

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It has a sequence in there. A’s, T’s, G’s, and C’s, each with a phosphate.

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G – phosphate, A – phosphate, T – phosphate, A – phosphate, A – phosphate, A – phosphate… I won’t write them any longer.

Each one’s got a phosphate in there. That’s the way it goes.

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Alright. That’s the template.

We need floating around in the solution: some trinucleotides. Okay we’ve got some nucleotides floating around.

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And now will this enzyme work?

We have an enzyme. We’ll try different fractions and see if it’s able to just install the right letters in the right place.

No. It turns out it needed one more thing. And the person who discovered this, Arthur Kornberg, thought of it.

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It needed a head start. It needed a primer.

So the primer goes phosphate – C, phosphate – T, phosphate – A, phosphate – T, phosphate – T, phosphate – T.

So this is the 5′ end of DNA.

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Remember the phosphate is hanging of the 5′ carbon, right? What’s in the other end. Let’s see. It ends in the hydroxyl 3′ end of the ribose.

Since this is antiparallel. This strand is going 5′ phosphate to 3′ hydroxyl. You’re going to need to know 5′ and 3′.

So there you go. If you hand it a primer to give it a head start, and you hand it a template, and you hand it some nucleotides – you then assay different fractions, and see “is one of them capable of extending this strand by putting in an A, putting in a T, putting in a C, putting in a C, putting in a G, blur-dur-dup?”

And… Arthur Kornberg discovered an enzyme that could do this. And the biochemists went nuts. They thought, “Wow, this is so cool.” Kornberg was able to discover an enzyme that could accomplish this.

The enzyme polymerizes DNA. Coincidentally, what is the enzyme called?

DNA polymerase. Excellent.

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Now, notice what it does. It takes this triphosphate:

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Puts it in here:

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And joins it into a sugar-phosphate chain.

Where does it get the energy for that synthesis?

Hydrolysis of the triphosphate, right?

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It’s the hydrolysis of the triphosphate. That’s the energy.

What direction is the synthesis proceeding?

It starts here at the 5′ end

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and it moves, adding to the 3′ end.

So it’s 5′ to 3′ direction. That’s the direction it moves. It adds to the 3′ end. Adds the free nucleotides to the 3′ end.

Why not do it the other way?

PHOSPHATE!!!

You see, suppose we were going the other way. Suppose the primer was this way: 3′ to 5′.

As we added each base, the triphosphate would be on this strand, right?

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And we’d be adding to the 3′ end here:

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That means the energy supplied by the triphosphate would be on the growing strand, rather than in the free nucleotides.

Why would it be a terrible idea to put your energy source on the growing strand?

You know those triphosphate bonds are pretty unstable. They hydrolyze by themselves at some frequency. If you’re a free nucleotide and the triphosphate hydrolyzes, big deal. That free nucleotide loses its triphosphate. But what if I’m the growing strand and I lose my triphosphate? Heh.. heh…. there goes my chain.

So you know, life’s not stupid. It doesn’t do it that way. It does it this way. No one has ever found a polymerase that goes that way. They find them all going this way for just that reason.

That was why life evolved it that way. Because you want your triphosphates – those hydrolyzable triphosphates – to be floating around freely rather than invest the energy.

Just think about that. It’s kind of a cool thing. It helps us remember which way it’s going and why it is, and how it is. And it’s kind of interesting.

Alright, so Kornberg wins the Nobel Prize for this.

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Good stuff. Very deserved.

But you know, there’s some questions.

Where does the primer come from in life? Kornberg gave this test tube a primer. But suppose I’m replicating some DNA.

So lets suppose I have a double strand of DNA

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Now just open it up here:

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→5′ to 3′

and

← 5′ to 3′

I need to get, like, a primer here.

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Then the primer can be extended by polymerase. Well, where does the primer come from?

It turns out there is an enzyme specially devoted to making those primers. Kornberg didn’t know it but there is an enzyme.

And by coincidence it is called, primase.

Exactly. Primase makes the primer.

You need a primer here, and the primer is made by primase. Once primase makes a primer, polymerase can chug along and do it just fine.

Let’s check out the other strand.

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Primer here. Polymerase chugs along. But now as this double helix opens up, what happens over here?

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The synthesis is going this way ←. So what do I have to do here?

Another primer. We need another primer.

Then as it opens up more, what do I need?

Another primer.

So the two strands are experiencing a very different kind of replication. In one case, one primer in the 5′ to 3′ direction is enough to keep going. In the other strand, as it keeps opening up, you’ve gotta keep making primers.

[Memes -> Genes, Media -> Drugs] Yields Dystopia

Cultures do not exert their effects in isolation of one another, but interact together in complex networks. In the coming years, sophisticated methods will be developed to leverage culture-culture interaction (CCI) network structure to improve several stages of the media discovery process. Network based methods will be applied to predict media targets, media side effects, and new propagandistic indications. Previous network-based characterizations of media effects focused on the small number of known media targets, i.e., direct binding partners of media. However, media affects many more memes than its targets – it can profoundly affect the civilization’s memeplex.

For the first time, we use networks to characterize memes that are differentially regulated by media. We found that media-regulated memes differed from media targets in terms of function, regional localizations, and neural properties. Media targets mainly included receptors on the plasma membrane of civilization (the software interface), down-regulated memes were largely in the nucleus (the older generation) and were enriched for memetic binding, and memes lacking media relationships were enriched in the extracellular region of civilization (the isolated sub-cultures). Network topology analysis indicated several significant graph properties, including high degree and betweenness for the media targets and media-regulated memes, though possibly due to network biases. Topological analysis also showed that cultures of down-regulated memes appear to be frequently involved in memeplexes. Analyzing network distances between regulated memes, we found that memes regulated by structurally similar media were significantly closer than memes regulated by dissimilar media. Finally, network centrality of media’s differentially regulated memes correlated significantly with media toxicity.

Parabiosis, Drugs Targeting Genes, Susskind, Feynman, and MUH

I’m sorry holy quest, but I must unload my burdened back if I must go on. There is much fun [?useless?] knowledge begging me to be released.

I found out about Kristen Fortney through correspondence with Michael Rae from the SENS Research Foundation (the people on the Manichaean mission to fight the evils of our own metabolism, and the only real rationalists as far as I’m concerned.)

Anyway, I’ve been interested in SENS since I was 16 and pretty much memorized Aubrey de Grey’s speech by heart (he gives the same one every time). But yet I had never heard of Fortney’s work until recently. She seems pretty excited about some of her colleagues’ work eliminating senescent cells, since it has been shown that mice live 30% longer when these are specifically removed. And if you know anything at all about biology, you know that 30% lifespan increase in mammals is ridiculously huge – especially when it was caused by a single intervention.

However, I didn’t read that paper, and took her word for it. (She mentioned it in a podcast.) I did read a paper of her own like 2.5 times. It was about building representations of networks of protein-to-protein interactions with nodes and edges. I learned some interesting things about DNA up-regulation and down-regulation. Apparently, most drugs affect the expression of all genes in a roundhouse-kick fashion. They don’t tend to be specific enough to work on single genes coding for the protein of interest who’s expression level we want to tweak. And Fortney et al. attribute this failure of control to the reason why most drugs have many unintended side-effects and therefore this helps explain the abysmally low number of drugs approved by the FDA in recent times. However, Fortney et al. are not trying to fix this gene targeting problem. They are instead working at the protein interaction level, and just accepting that a ton of genes will be differentially regulated by a single drug. The idea was something about setting off random walks on the node graphs and seeing which paths are treaded the most by a given drug interaction. Maybe whatever abstract analysis tool they were discussing in the paper is actually a little useful, and I don’t claim to have 100% fully understood their work, but as a student of biology and chemistry, my picture of the territory is one of such hopeless complexity that I doubt too much use will come from all this.

Direct interventions, like teasing out why parabiosis (infusion of young blood to old blood) works, and then working to develop antigens and other small molecules sounds more promising (and profitable), at least for now. Luckily she, and many others, are also interested in this area.

Oh but in case you’re getting too giddy for the forever-dancefloor, the effects of old blood on young mice is more devastating than young blood is rejuvenating.

And you know who needs rejuvenation… Leonard Susskind.

We need imaginative, effective theoretical physicists like him around. He famously debated Stephen Hawking about information loss in black holes, and won. It’s kind of sad that his call to fame to the public is only through connection to someone who happened to have more celebrity status.

Yeah Stephen Hawking is cool… and I’m going to let you finish, but Leonard Susskind is largely responsible for fleshing out the holographic principle.

And to those who believe that the holographic principle is “metaphysical” and “unscientific” while Newton’s mechanics are “physical” and “scientific,” you are guilty of attempting to derive the nature of molecules from the taste of the orange juice.

The validity of a theory should not be inferred from whatever particular queasy feel one gets from the sound of a word. ‘Holographic’ means nothing. The claim is precise and mathematical. Only in that ring should the assessment take place.

And by the way, Susskind’s father was a plumber. His father had no idea what a physicist was and initially believed Susskind was planning to be a pharmacist. Kind of inspiring huh? A Jewish plumber, but a plumber nonetheless.

Speaking of… umm, physicists (regardless! of their socially constructed ethnicity). How about that dead chap Feynman. Is he still alive in other regions of the the wave function that never collapses? Infinitely so?

I wonder what he would think about Max Tegmark’s mathematical universe hypothesis.

He would probably consider it rubbish. I get the impression that he had a distaste for ‘pure mathematics,’ given his reaction to the P vs. NP problem.

But he was also not the type to simply internalize the canonical lexicon. He was a mover, a changer, someone who truly valued knowing. It is evidenced by the fact that he was already performing engineering feats as a child; his development of the path-integral formulation; the quirkily simple diagrams that initially perplexed Bohr and Dirac; his criticism of the Brazilian physics education; his interest in the hallucinations produced in a deprivation tank. All of this suggests that he was willing to be different.

He was willing to go wherever reality lead. Including to the arms of prostitutes and the creation of atomic bombs.

But Platonism? That might be too much, even for him.

 

 

 

 

Seedless Plants

Colonization of land by plants fundamentally altered the history of life on Earth. A terrestrial environment offers abundant CO2 and solar radiation for photosynthesis. But for at least 500 million years, the lack of water and higher ultraviolet (UV) radiation on land confined green algal ancestors to an aquatic environment. Evolutionary innovations for reproduction, structural support, and prevention of water loss are key in the story of plant adaptation to land. The evolutionary shift on land to life cycles dominated by a diploid generation masks recessive mutations arising from higher UV exposure. As a result, larger numbers of alleles persist in the gene pool, creating greater genetic diversity. Long before seeds and flowers evolved, the seedless plants covered the Earth. Here, I consider the evolutionary innovations in seedless plants during the first 100 million years of terrestrial life.

Origin of Land Plants

Green algae and the land plants shared a common ancestor a little over 1 BYA and are collectively referred to as the green plants. DNA sequence data are consistent with the claim that a single individual gave rise to all green plants. The green plants are photoautotrophic, but not all photoautotrophs are plants. The definition of a green plant is broad, but it excludes the red and brown algae. All algae–red, brown, and green–shared a primary endosymbiotic event 1.5 BYA. But sharing an ancestral chloroplast lineage is not the same as being monophyletic. Red and green algae last shared a common ancestor about 1.4 BYA. Brown algae became photosynthetic through endosymbiosis with a eukaryotic red alga that had itself already acquired a photosynthetic cyanobacterium.
Plants are also not fungi, which are more closely related to metazoan animals. Fungi, however, were essential to the colonization of land by plants, enhancing plants’ nutrient uptake from the soil.
One of the most significant evolutionary events in the billion-year-old history of the green plants is the adaptation to terrestrial living.

Land plants evolved from freshwater algae

Some saltwater algae evolved to thrive in a freshwater environment. Just a single species of freshwater green algae gave rise to the entire terrestrial plant lineage, from mosses through the flowering plants (angiosperms). Given the incredibly harsh conditions of life on land, it is not surprising that all land plants share a single common ancestor. Exactly what this ancestral alga was is still a mystery, but close relatives, members of the charophytes, exist in freshwater lakes today.
The green algae split into two major clades: the chlorophytes, which never made it to land, and the charophytes, which are sister clade to all land plants. Together charophytes and land plants are referred to as streptophytes. Land plants, although diverse, have certain characteristics in common. Unlike the charophytes, land plants have multicellular haploid and diploid stages. Diploid embryos are also land plant innovations. Over time, the trend has been toward more embryo protection and a smaller haploid stage in the life cycle.

Land plants have adapted to terrestrial life

Unlike their freshwater ancestors, most land plants have only limited amounts of water available to them. As an adaptation to living on land, most plants are protected from desiccation–the tendency of organisms to lose water to the air–by a waxy surface material called the cuticle that is secreted onto their exposed surfaces. The cuticle is relatively impermeable, preventing water loss. This solution, however, limits the gas exchange essential for respiration and photosynthesis. Gas diffusion into and out of a plant occurs through tiny mouth-shaped openings called stomata (singular, stoma), which allow water to diffuse out at the same time. Stomata can be closed at times to limit water loss.
Moving water within plants is a challenge that increases with plant size. Members of the land plants can be distinguished based on the presence or absence of tracheids, specialized cells that facilitate the transport of water and minerals. Tracheophytes have specialized transport cells called tracheids and have evolved highly efficient transport systems: water-conducting xylem and food-conducting phloem strands of tissue in their stems, roots, and leaves. Some plants that grow in aquatic environments, including water lilies, have tracheids. Aquatic tracheophytes had terrestrial ancestors that adapted back to a watery environment.
Terrestrial plants are exposed to higher intensities of UV irradiation than aquatic algae, increasing the chance of mutation. Diploid genomes mask the effect of a single, deleterious allele. All land plants have both haploid and diploid generations, and the evolutionary shift toward a dominant diploid generation allows for greater genetic variability to persist in terrestrial plants.

The haplodiplontic cycle produces alternation of generations

Humans have a diplontic life cycle, meaning that only the diploid stage is multicellular; by contrast, the land plant life cycle is haplodiplontic, having multicellular haploid and diploid stages. Most multicellular green plants have this haplodiplontic life cycle. Many multicellular green algae and all land plants have haplodiplontic life cycles and undergo mitosis after both gamete fusion and meiosis. The result is a multicellular haploid individual and a multicellular diploid individual–unlike in the human life cycle, in which gamete fusion directly follows meiosis.
Many brown, red, and green algae are also haplodiplontic. Humans produce gametes via meiosis, but land plants actually produce gametes by mitosis in a multicellular, haploid individual. The diploid generation, or sporophyte, alternates with the haploid generation, or gametophyte. Sporophyte means “spore plant,” and gametophyte means “gamete plant.” These terms indicate the kinds of reproductive cells the respective generations produce.
The diploid sporophyte produces haploid spores (not gametes) by meiosis. Meiosis takes place in structures called sporangia, where diploid spore mother cells (sporocytes) undergo meiosis, each producing four haploid spores. Spores are the first cells of the gametophyte generation. Spores divide by mitosis, producing a multicellular, haploid gametophyte.
The haploid gametophyte is the source of gametes. When the gametes fuse, the zygote they form is diploid and is the first cell of the next sporophyte generation. The zygote grows into a diploid sporophyte by mitosis and produces sporangia in which meiosis ultimately occurs.

The relative sizes of haploid and diploid generations vary

All land plants are haplodiplontic; however, the haploid generation consumes a much larger portion of the life cycle in mosses and ferns than it does in the seed plants–the gymnosperms and angiosperms. In mosses, liverworts, and ferns, the gametophyte is photosynthetic and free living. When you look at mosses, what you see is largely gametophyte tissue; the sporophytes are usually smaller, brownish or yellowish structures attached to the tissues of the gametophyte. In other plants, the gametophyte is usually nutritionally dependent on the sporophyte. When you look at a gymnosperm or angiosperm, such as most trees, the largest, most viable portion is a sporophyte.
Although the sporophyte generation can get very large, the size of the gametophyte is limited in all plants. The gametophyte generation of mosses produces gametes at its tips. The egg is stationary, and sperm lands near the egg in a droplet of water. If the moss were the height of a sequoia, not only would vascular tissue be needed for conduction and support, but the sperm would have to swim up the tree! In contrast, the small gametophyte of the fern develops on the forest floor where gametes can meet. Tree ferns are especially abundant in Australia; the haploid spores that the sporophyte trees produce fall to the ground and develop into gametophytes.
Having completed an overview of plant life cycles, we next consider the major groups of seedless land plants. As we proceed, you will see a reduction of the gametophyte from group to group, a loss of multicellular gametangia (structures in which gametes are produced), and increasing specialization for life on land.

All algae acquired chloroplasts necessary for photosynthesis, but green algae diverged from red algae after that event. A single freshwater green alga successfully invaded land; its descendant eventually developed reproductive strategies, conducting systems, stomata, and cuticles as adaptations. Green plants include all green algae and the land plants, whereas the streptophytes include only the land plants and their sister clade, the charophytes. Most plants have a haplodiplontic life cycle, a haploid form alternates with a diploid form in a single organism. Diploid sporophytes produce haploid spores by meiosis. Each spore can develop into a haploid gametophyte by mitosis; the gametophyte form produces haploid gametes, again by mitosis. When the gametes fuse, the diploid sporophyte is formed once more.

Bryophytes: Dominant Gametophyte Generation

Land plants began diverging 450 MYA. Bryophytes are the closest living descendants of these first land plants. Plants in this group are also called nontracheophytes because they lack the derived transport cell called a tracheid.
Fossil evidence and molecular systematics can be used to reconstruct early terrestrial plant life. Water and gas availability were limiting factors. These plants likely had little ability to regulate internal water levels and likely tolerated desiccation, traits found in most extant mosses, although some are aquatic.
Algae, including the Charales, lack roots. Fungi and early land plants cohabited, and the fungi formed close associations with the plants that enhanced water uptake. The tight symbiotic relationship between fungi and plants, called mycorrhizal associations, are also found in many existing bryophytes.

Bryophytes are unspecialized but successful in many environments

The approximately 24,700 species of bryophytes are simple but highly adapted to a diversity of terrestrial environments, even deserts. Most bryophytes are small; few exceed 7 cm in height. Bryophytes have conducting cells other than tracheids for water and nutrients. The tracheid is a derived trait that characterizes the tracheophytes, all land plants but the bryophytes. Bryophytes are sometimes called nonvascular plants, but nontracheophyte is a more accurate term because they do have conducting cells of different types.
Scientists now agree that bryophytes consist of three quite distinct clades of relatively unspecialized plants: liverworts, mosses, and hornworts. Their gametophytes are photosynthetic and are more conspicuous than the sporophytes. Sporophytes are attached to the gametophytes and depend on them nutritionally in varying degrees. Some of the sporophytes are completely enclosed within gametophyte tissue; others are not and usually turn brownish or straw-colored at maturity. Like ferns and certain other vascular (tracheophyte) plants, bryophytes require water (such as rainwater) to reproduce sexually, tracing back to their aquatic origins. It is not surprising that they are especially common in moist places, both in the tropics and temperate regions.

Liverworts are an ancient phylum

The Old English word wyrt means “plant” or “herb.” Some common liverworts (phylum Hepaticophyta) have flattened gametophytes with lobes resembling those of liver–hence the name “liverwort.” Although the lobed liverworts are the best known representatives of this phylum, they constitute only about 20% of the species. The other 80% are leafy and superficially resemble mosses. The gametophytes are prostrate instead of erect, with single celled rhizoids that aid in absorption like roots but are not organs.
Some liverworts have air chambers containing upright, branching rows of photosynthetic cells, each chamber having a pore at the top to facilitate gas exchange. Unlike stomata, the pores are fixed open and cannot close.
Sexual reproduction in liverworts is similar to that in mosses. Lobed liverworts may form gametangia in umbrella-like structures. Asexual reproduction occurs when lens-shaped pieces of tissue that are released from the gametophyte grow to form new gametophytes.

Mosses have rhizoids and water-conducting tissue

Unlike other bryophytes, the gametophytes of mosses typically consist of small, leaflike structures (not true leaves, which contain vascular tissue) arranged spirally or alternately around a stemlike axis; the axis is anchored to its substrate by means of rhizoids. Each rhizoid consists of several cells that absorb water, but not nearly the volume of water that is absorbed by a vascular plant root.
Moss leaflike structures have little in common with leaves of vascular plants, except for the superficial appearance of the green, flattened blade and slightly thickened midrib that runs lengthwise down the middle. Only one cell layer thick (except at the midrib), they lack vascular strands and stomata, and all the cells are haploid. However, mosses do have stomata on the capsule portion of the sporophyte generation and because of that are the basal land group with stomata.
Water may rise up a strand of specialized cells in the center of a moss gametophyte axis. Some mosses also have specialized food-conducting cells surrounding those that conduct water.

Moss reproduction

Multicellular gametangia are formed at the tips of the leafy gametophytes. Female gametangia (archegonia) may develop either on the same gametophyte as the male gametangia (antheridia) or on separate plants. A single egg is produced in the swollen lower part of an archegonium, whereas numerous sperm are produced in an antheridium.
When sperm are released from an antheridium, they swim with the aid of flagella through a film of dew or rainwater to the archegonia. One sperm (which is haploid) unites with an egg (also haploid), forming a diploid zygote. The zygote divides by mitosis and develops into the sporophyte, a slender, basal stalk with a swollen capsule, the sporangium, at its tip. As the sporophyte develops, its base is embedded in gametophyte tissue, its nutritional source.
The sporangium is often cylindrical or club-shaped. Spore mother cells within the sporangium undergo meiosis, each producing four haploid spores. In many mosses at maturity, the top of the sporangium pops off, and the spores are released. A spore that lands in a suitable damp location may germinate and grow, using mitosis, into a threadlike structure, which branches to form rhizoids and “buds” that grow upright. Each bud develops into a new gametophyte plant consisting of a leafy axis.

Moss distribution

In the Arctic and the Antarctic, mosses are the most abundant plants. The greatest diversity of moss species, however, is found in the tropics. Many mosses are able to withstand prolonged periods of drought, although mosses are not common in deserts.
Most mosses are highly sensitive to air pollution and are rarely found in abundance in or near cities or other areas with high levels of air pollution. Some mosses, such as the peat mosses (Sphagnum), can absorb up to 25 times their weight in water and are valuable commercially as a soil conditioner or as a fuel when dry.

The moss genome

Moss plants can survive extreme water loss–an adaptive trait in the early colonization of land that has been lost from vegetative tissues of tracheophytes. Desiccation tolerance and phylogenetic position were among the traits that led researchers to sequence the genome of the moss Physcomitrella patens as being the first land plant that is not a tracheophytes. Although the moss genome is a single genome bracketed by Chlamydomonas and the tracheophytes, many evolutionary hints are hidden within it. Evidence indicates the loss of genes associated with a watery life, including flagellar arms, were lost in the last common ancestor of the land plants. Genes associated with tolerance of terrestrial stresses, including temperature and water availability, are absent in Chlamydomonas and present in moss. For example, the plant hormone abscisic acid (ABA) is important in stress responses in moss and other land plants and genes needed for ABA signaling are not found in algae.

Hornworts developed stomata

The origin of hornworts (phylum Anthocerotophyta) is a puzzle. They are most likely among the earliest land plants, yet the earliest hornwort fossil spores date from the Cretaceous period (65-145 MYA), when angiosperms were emerging.
The small hornwort sporophytes resemble tiny green broom handles or horns, rising from filmy gametophytes usually less than 2 cm in diameter. The sporophyte base is embedded in gametophyte tissue, from which it derives some of its nutrition. However, the sporophyte has stomata to regulate gas exchange, is photosynthetic, and provides much of the energy needed for growth and reproduction. Hornwort cells usually have a single large chloroplast.

The bryophytes exhibit adaptations to terrestrial life. Moss adaptations include rhizoids to anchor the moss body and to absorb water, and water-conducting tissues. Mosses are found in a variety of habitats, and some can survive droughts. Hornworts developed stomata that can open and close to regulate gas exchange.

Tracheophyte Plants: Roots, Stems, and Leaves

Tracheophytes, also known as vascular plants, first appeared about 410 MYA. The first tracheophytes with a relatively complete record belonged to the phylum Rhyniophyta. We are not certain what the earliest of these vascular plants looked like, but fossils of Cooksonia provide some insight into their characteristics.
Cooksonia, the first known vascular land plant, appeared in the late Silurian period about 420 MYA, but is now extinct. It was successful partly because it encountered little competition as it spread out over vast tracts of land. The plants were only a few centimeters tall and had no roots or leaves. They consisted of little more than a branching axis, the branches forking evenly and expanding slightly toward the tips. They were homosporous (producing only one type of spore). Sporangia formed at branch tips. Other ancient vascular plants that followed evolved more complex arrangement of sporangia.

Vascular tissue allows for distribution of nutrients

Cooksonia and the other early plants that followed it became successful colonizers of the land by developing efficient water water- and food-conducting systems called vascular tissues. These tissues consist of strands of specialized cylindrical or elongated cells that form a network throughout a plant, extending from near the tips of the roots, through the stems, and into true leaves, defined by the presence of vascular tissue in the blade. One type of vascular tissue, xylem, conducts water and dissolved minerals upward from the roots; another type of tissue, phloem, conducts sucrose and hormones throughout the plant. Tracheids are the cells in the early vascular plants that conducted water in xylem tissue. Vascular tissue enables enhanced height and size in the tracheophytes. It develops in the sporophyte, but (with a few exceptions) not in the gametophyte. A cuticle and stomata are also characteristic of vascular plants.

Tracheophytes are grouped in three clades

Three clades of vascular plants exist today: (1) lycophytes (club mosses), (2) pterophytes (ferns and their relatives), and (3) seed plants.  Advances in molecular systematics have changed the way we view the evolutionary history of vascular plants. Whisk ferns and horsetails were long believed to be distinct phyla that were transitional between bryophytes and vascular plants. Phylogenetic evidence now shows they are the closest living relatives to ferns, and they are grouped as pterophytes.
Tracheophytes dominate terrestrial habitats everywhere, except for the highest mountains and the tundra. The haplodiplontic life cycle persists, but the gametophyte has been reduced in size relative to the sporophyte during the evolution of tracheophytes. A similar reduction in multicellular gametangia has occurred as well.

Stems evolved prior to roots

Fossils of early vascular plants reveal stems, but no roots or leaves. The earliest vascular plants, including Cooksonia, had transport cells in their stems, but the lack of roots limited the size of these plants.

Roots provide structural support and transport capability

True roots are found only in the tracheophytes. Other, somewhat similar structures enhance either transport or support in nontracheophytes, but only roots have a dual function: providing both transport and support. Lycophytes diverged from other tracheophytes before roots appeared, based on fossil evidence. It appears that roots evolved at least two separate times.

Leaves evolved more than once

Leaves increase surface area of the sporophyte, enhancing photosynthetic capacity. Lycophytes have single vascular strands supporting relatively small leaves called lycophylls. True leaves, called euphylls, are found only in ferns and seed plants, having distinct origins from lycophylls. Lycophylls may have resulted from vascular tissue penetrating small, leafy protuberances on stems. Euphylls most likely arose from branching stems that became webbed with leaf tissue.
About 40 million years separates the appearance of vascular tissue and the wide euphyll leaf–a curiously long time. The current hypothesis is that a 90% drop in atmospheric CO2 360 MYA allowed for the increase in leaf size because of an increase in the number of stomata on a leaf. Large, horizontal leaves capture 200% more radiation than thin, axial leaves. Although beneficial for photosynthesis, larger leaves correspondingly increase leaf temperature, which can be lethal. Stomatal openings in the leaf enhance the movement of water out of the leaf, thereby cooling it. The density of stomata on leaf surfaces correlates with CO2 concentration, as the stomatal openings are essential for gas exchange. As the atmospheric CO2 levels dropped, plants could not obtain sufficient CO2 for photosynthesis. In the low-CO2 atmosphere, natural selection favored plants with higher stomatal densities. Higher stomatal densities favored larger leaves with a photosynthetic advantage that did not overheat. Leaves up to 120 mm wide and 160 mm long have been identified in the fossil record form that time period.

Seeds are another innovation in some tracheophytes phyla

Seeds are highly resistant structures well suited to protecting a plant embryo from drought and to some extent from predators. In addition, almost all seeds contain a supply of food for the young plant. Lycophytes and pterophytes do not have seeds.
Fruits in the flowering plants (angiosperms) add a layer of protection to seeds and have adaptations that assist in seed dispersal, expanding the potential range of the species. Flowers allow plants to secure the benefits of wide out-crossing in promoting genetic diversity. Before moving on to the specifics of lycophytes and pterophytes, review the evolutionary history of terrestrial innovations in the land plants.

Most tracheophytes have well-developed vascular tissues, including tracheids, that enable efficient delivery of water and nutrients throughout the organism. They also exhibit specialized roots, stems, leaves, cuticles, and stomata. Many produce seeds, which protect and nourish embryos.

Lycophytes: Dominant Sporophyte Generation and Vascular Tissue

The earliest vascular plants lacked seeds. Members of four phyla of living vascular plants also lack seeds, as do at least three other phyla known only from fossils. As we explore the adaptations of the vascular plants, we focus on both reproductive strategies and the advantages of increasingly complex transport systems.
The lycophytes (club mosses) are relic species of an ancient past when vascular plants first evolved. They are the sister group to all vascular plants. Several genera of club mosses, some of them treelike, became extinct about 270 MYA. Today, club mosses are worldwide in distribution but are most abundant in the tropics and moist temperate regions.
Members of the 12 to 13 genera and about 1150 living species of club mosses superficially resemble true mosses, but once their internal vascular structure and reproductive processes became known, it was clear that they are unrelated to mosses. The sporophyte stage is the dominant (obvious) stage; sporophytes have leafy stems that are seldom more than 30 cm long.
The lycophyte Selaginella moellendorffii is the first seedless vascular plant with a fully sequenced genome. A few clues to the evolution of vascular plants, hidden in the genome, emerged in comparisons with genomes of flowering plants. Genes that play an important role in establishing leaf polarity in flowering plants are not found in Selaginella, indicative of independent origins of leaflike structures in different vascular plant lineages. Genome differences also reflect differences in developmental pathways leading to reproductive maturity in the sporophyte generation in lycophytes and flowering plants.
Comparing predicted proteins in the Chlamydomonas (green alga), Physcomitrella (moss), and Selaginella with 15 angiosperms revealed 3814 gene families that all the green plants share–the essential instructions for building a green plant. About 3000 new genes were acquired in the transition from the single-celled green alga to the multicellular moss, but only 516 genes were added in the transition from nonvascular to vascular plants. This is a first step in sorting out the evolutionary steps that led to the vascular plants.

Lycophytes are basal to all other vascular plants. Although they superficially resemble bryophytes, they contain tracheid-based vascular tissues, and their reproductive cycle is like that of other vascular plants; however, they lack vascularized leaves.

Pterophytes: Ferns and Their Relatives

The phylogenetic relationships among ferns and their near relations is intriguing. A common ancestor gave rise to two clades: One clade diverged to produce a line of ferns and horsetails; the other diverged to yield another line of ferns and whisk ferns–ancient-looking plants.
Whisk ferns and horsetails are close relatives of ferns. Like lycophytes and bryophytes, they all form antheridia and archegonia. Free water is required for the process of fertilization, during which the sperm, which have flagella, swim to and unite with the eggs. In contrast, most seed plants have nonflagellated sperm.

Whisk ferns lost their roots and leaves secondarily

In whisk ferns, which occur in the tropics and subtropics, the sporophytic generation consists merely f evenly forking green stems without roots. The two or three species of the genus Psilotum do, however, have tiny, green, spirally arranged flaps of tissue lacking veins and stomata. Another genus, Tmesipteris, has more leaflike appendages. Currently, systematists believe that whisk ferns lost leaves and roots when they diverged from others in the fern lineage.
Given the simple structure of whisk ferns, it was particularly surprising to discover that they are monophyletic with ferns. The gametophytes of whisk ferns are essentially colorless and are less than 2 mm in diameter, but they can be up to 18 mm long. They form symbiotic associations with fungi, which furnish their nutrients. Some develop elements of vascular tissue and have the distinction of being the only gametophytes known to do so.

Horsetails have jointed stems with brushlike leaves

The 15 living species of horsetails are all homosporous. They constitute a single genus, Equisetum. Fossil forms of Equisetum extend back 300 million years to an era when some of their relatives were treelike. Today, they are widely scattered around the world, mostly in damp places. Some that grow among the coastal redwoods of California may reach a height of 3 m, but most are less than a meter tall.
Horsetails sporophytes consist of ribbed, jointed, photosynthetic stems that arise form branching underground rhizomes with roots at their nodes. A whorl of nonphotosynthetic, scalelike leaves emerges at each node. The hollow stems have silica deposits in the epidermal cells of the ribs, and the interior parts of the stems have two sets of vertical, tubular canals. The larger outer canals, which alternate with the ribs, contain air, and the smaller inner canals opposite the ribs contain water. Horsetails are also called scouring rushes because pioneers of the American West used them to scrub pans.

Ferns have fronds that bear sori

Ferns are the most abundant group of seedless vascular plants, with about 11,000 living species. Recent research indicates that they may be the closest relatives to the seed plants.
The fossil record indicates that ferns originated during the Devonian period about 350 MYA and became abundant and varied in form during the next 50 million years. Their apparent ancestors were established on land as much as 375 MYA. Rainforests and swamps of lycopsid and fern trees growing in the Eastern United States and Europe over 300 MYA formed the coal currently being mined. Today, ferns flourish in a wide range of habitats throughout the world; however, about 75% of the species occur in the tropics.
The conspicuous sporophytes may be less than a centimeter in diameter (as in small aquatic ferns such as Azolla), or more than 24 m tall, with leaves up to 5 m or longer in the tree ferns. The sporophytes and the much smaller gametophytes, which rarely reach 6 mm in diameter, are both photosynthetic.
The fern lifecycle differs from that of a moss primarily in the much greater development, independence, and dominance of the fern’s sporophyte. The fern sporophyte is structurally more complex than the moss sporophyte, having vascular tissue and well-differentiated roots, stems, and leaves. The gametophyte, however, lacks the vascular tissue found in the sporophyte.

Fern morphology

Fern sporophytes, like horsetails, have rhizomes. Leaves, referred to as fronds, usually develop at the tip of the rhizome as tightly rolled-up coils (“fiddleheads”) that unroll and expand. Fiddleheads are considered a delicacy in several cuisines, but some species contain secondary compounds linked to stomach cancer.
Many fronds are highly dissected and feathery, making the ferns that produce them prized as ornamental garden plants. Some ferns, such as Marsilea, have fronds that resemble a four-leaf clover, but Marsilea fronds still begin as coiled fiddleheads. Other ferns produce a mixture of photosynthetic fronds and nonphotosynthetic reproductive fronds that tend to be brownish in color.

Fern reproduction

Ferns produce distinctive sporangia, usually in clusters called sori (singular, sorus), typically on the underside of the fronds. Sori are often protected during their development by a transparent, umbrella-like covering. (At first glance, one might mistake the sori for an infection on the plant.) Diploid spore mother cells in each sporangium undergo meiosis, producing haploid spores.
At maturity, the spores are catapulted form the sporangium by a snapping action, and those that land in suitable damp locations may germinate, producing gametophytes that are often heart-shaped, are only one cell layer thick (except in the center), and have rhizoids that anchor them to their substrate. These rhizoids are not true roots because they lack vascular tissue, but they do aid in transporting water and nutrients from the soil. Flask-shaped archegonia and globular antheridia are produced on either the same or a different gametophyte.
The multicellular archegonia provide some protection for the developing embryo.
The sperm formed in the antheridia have flagella, with which they swim toward the archegonia when water is present, often in response to a chemical signal secreted by the archegonia. One sperm unites with the single egg toward the base of an archegonium, forming a zygote. The zygote then develops into a new sporophyte, completing the lifecycle.
The developing fern embryo has substantially more protection from the environment than a charophyte zygote, but it cannot enter a dormant phase to survive a harsh winter the way a seed plant embryo can. Although extant ferns do not produce seeds, seed fern fossils have been found that date back 365 million years. The seed ferns are not actually pterophytes, but gymnosperms.

Ferns and their relatives have a large and conspicuous sporophyte with vascular tissue. Many have well-differentiated roots, stems, and leaves (fronds). The gametophyte generation is small and lacks vascular tissue.