Is this to blame for the Fermi paradox?

[lpetrich]

Good chart. I've considered the question of bottlenecks of evolution in reference to Drake's equation. One can get a little bit of a clue from how often various features have evolved.

f(life): though we have found a lot of complexity since when FD proposed his equation, we've also found out how much of it likely emerged.

With phylogeny techniques, we've discovered an early split in the prokaryotes, between (ordinary) bacteria and a lot of oddballs that have been named archaea. Eukaryotes are derived from a mishmash of organisms from both of these domains. The inferred Last Universal Common Ancestor likely had:

• A DNA genome alongside its RNA
• RNA-to-protein translation with transfer RNA's and ribosomes
• Electron-transfer energy metabolism
• Chemiosmotic (membrane-pump) energy metabolism
• Lithotrophic metabolism: living off of inorganic compounds
• Autotrophic metabolism: making all of its biological molecules

This is rather complicated, and that's led to the RNA world. In it, RNA was information storage and enzyme. DNA is a modification of RNA for master-copy duty, and proteins were enzyme cofactors that eventually became the whole enzymes. Several enzyme cofactors are plausibly attributed to the RNA world, like several B vitamins.

The main problem with the RNA-world hypothesis is the origin of the RNA. It's difficult to make it prebiotically. One can make the ribose part with the Butlerov formose reaction, starting with formaldehyde, but that reaction produces a big mess of sugarlike molecules with only a tiny bit of ribose. I've seen hypotheses of predecessors like Peptide Nucleic Acids and Polycyclic-Aromatic-Hydrocarbon Nucleic Acids.

Finally, The “Water World” Theory Of The Origins Of Life Revamped | IFLScience -- it can account for both membrane-pump and electron-transfer energy metabolism.

So we may plausibly expect to see such metabolism in ET organisms. But I'm not sure if we can reasonably expect RNA or DNA. I suspect some nucleic-acid-like molecule with a backbone other than our (deoxy)ribose-phosophate one.

 

[lpetrich]

Now f(intelligence). That has required a *lot* of evolution from the LUCA to us.

An important step was liberation from hydrothermal vents and hot springs. That happened by way of oxygen-releasing photosynthesis.

Photosynthesis in general has two surviving inventions.

Bacteriorhodopsin -- halobacteria a.k.a. haloarchaea -- it plugs into membrane-pump (chemiosmotic) energy metabolism, with the b'rhodopsin pumping hydrogen ions outward.

Chlorophyll -- many (ordinary) bacteria -- it plugs into electron-transfer energy metabolism, with the chlorophyll molecules residing in antenna complexes that act much like photovoltaic cells. Only this one has an oxygen-releasing variant.


The emergence of eukaryotic cells is mainly significant for allowing the handling of large genomes. Sizes of genomes of free-living prokaryotes range from 1 megabase pair to 10 Mbp. Eukaryotes' genomes can be much larger, with the champion somewhere around 100 billion base pairs. There may be other ways of handling large genomes, however.


Multicellularity has evolved several times, mostly plantlike, funguslike, and slime-moldlike. Slime molds alternate between separate one-celled organisms and a fruiting body on a stalk that makes spores. These spores then hatch into the one-celled phase again. Animallike multicellularity evolved only once, as far as I can tell. So it may be some planet has multicellular organisms that are all plants, fungi, and slime molds -- no animals.

Most multicellular organisms are eukaryotes, likely from eukaryotic genome handling enabling the evolution of complicated developmental mechanisms. But there are some prokaryotic ones: many cyanobacteria (plantlike), actinobacteria a.k.a. actinomycetes (funguslike), and myxobacteria (slime-moldlike).


Going onto land is a necessity for being able to develop electricity-based technologies. Let's see about that. Plantlike organisms went onto land only once, while animals have done so several times: early amphibians, insects, arachnids, myriapods (centipedes and millipedes), snails, earthworms, leeches, onychophorans, and others. Does that mean that it's easier for animals to do so than plants?


Intelligence generally requires sociality. That has emerged several times across the animal kingdom in various forms and various degrees. Among our closest relatives, there is an interesting correlation between brain size and social-group size that anthropologist Robin Dunbar has discovered. Extrapolated to our species, that leads to "Dunbar's number", about 150. That's the number of people that we can easily keep track of. This has led to the "social brain hypothesis", that our large brains have evolved for tracking fellow members of our species. However, the causality may easily go in the opposite direction: a large brain size that evolved for other reasons could enable a large social-group size.

Another feature that has helped us is manipulative organs. Our hands are very good ones, I think better than most others on this planet with the possible exception of cephalopod tentacles. Dolphins completely lack manipulative organs; to hold something, they have to use the kludge of biting it, like what many of us have seen with dogs and cats.

An important mental feature is, I think, having a concept of self, at least as determined from Gordon Gallup's mirror test. Can one recognize oneself in a mirror? We learn how to do that at 18 months - 2 years, and chimps can learn in adolescence. Elephants, dolphins, orcas, and corvids (crowlike birds), and psittacines (parrotlike birds) have all demonstrated this ability.

However, with the possible exception of dolphins, we are the only species that uses full-scale language, as opposed to individual symbols like individual sounds. For instance, vervet monkeys make sounds that they interpret as warnings about different kinds of predators: "Snake!" "Leopard!" "Eagle!".


So there's a rather sizable gauntlet to run to get to us.

 

[lpetrich]

Now f(communicative).

The first step in that is forming a large-scale society, a society much larger than Dunbar's number. An important step in that is agriculture, because it enables supporting a much higher population density than can be supported by foraging (hunting and gathering).

Our species and its predecessor species had plenty of opportunities to invent agriculture over the Pleistocene. But we did so only in the Holocene, the current interglacial period. It's currently defined as starting at the end of the Younger Dryas cold snap, about 11770 years ago. But after that, several populations independently invented agriculture, with some of the first being Middle Easterners with wheat.

Biologist Peter Turchin has IMO convincingly argued that an important factor in the emergence of large-scale societies has been war -- societies fighting each other, with the winners being the ones who can most successfully organize their fighting of wars. He also has some interesting theories of the rise and fall of societies, especially preindustrial ones with histories that can be long. To summarize:

• Rising phase: united, conquering, but elites eventually pull ahead
• Falling phase: Elites fight each other in civil wars, society may lose territory, ends when the elites get burned out

He's also found a similar cycle for the United States over its history. A peak in the early 19th cy, a trough around 1900 (the Gilded Age), a peak around 1950, and heading to a trough now. He uses data on economic inequality, amount of wages, amount of immigration, people's heights, strife, etc.

He's also found a 50-year two-generation cycle of strife and revolts. One generation revolts against some unjust and troublesome situation, and the next one is unwilling to do so. But the revolt is a distant memory to the one after that, and it revolts. In the US, there was no revolt in the 1820's, but there was one around 1870, one around 1920, and and one around 1970, meaning that the US is due for one around 2020.

This is something of a digression, but I think that it shows that a social order can be unstable.

 

[lpetrich]

Back to the invention of agriculture, one has to ask why in the Holocene and not before. I've seen a speculation that pre-Holocene climates were generally too erratic to permit an agricultural economy to last, while the Holocene has had a relatively stable climate.

Jared Diamond has IMO the best theory for why Eurasian people claim to dominate the world, including settling on other continents and creating Eurasian-style societies there. Lots of interchange of crop plants and domestic animals over Eurasia's east-west extent. The Americas are oriented in the wrong direction. If one wanted to get (say) potatoes from Peru to Idaho, one would have a long way to go in terrain that potatoes don't like to grow in -- potatoes like cool, mountainous terrain. Llamas may have the same problem.

Once that is done, it's necessary to develop theoretical science. The Greco-Roman world almost did so, but it was cut off by the Crisis of the Third Century, some big strife that almost broke up the Roman Empire. It did not revive again for over a thousand years, and that revival was rather slow at first. But it succeeded.

So we have for agriculture either multiple inventions or no invention, depending on the climate's stability, and we have for theoretical science only one invention.

That can make getting to the communicative stage rather difficult.

 

[Crazy Eddie]

^ And even with all of that, it's hardly a foregone conclusion that intelligent life forms would actually evolve BEYOND the communicative stage. High technology and advanced forms of warfare evolved on Earth in only a handful of places, cultivated by advanced Empires that used that technology to conquer their neighbors. If, say, the bubonic plague or a natural disaster had destroyed Europe before they managed to expand to the New World, most of humanity would probably STILL be living in a largely agrarian society.

That's the "Ba'Ku People" outcome in the chart. Aggressive expansion requires technological development and innovation to stay ahead of population growth and changing environments, but if your society places a higher value on long-term stability, you'll have almost no reason to expand to conquer your neighbors, no reason to create a growing economy, little reason to innovate or develop new technologies. Just keep doing the same old thing for generation after generation until something happens that causes you to make a few minor changes every now and again.

 

[lpetrich]

Yes, that can limit the effective value of the lifetime, L, the final term in the Drake Equation. But there are some other potential limiting factors.

Wars. Superweapons like nuclear bombs can make wars very destructive, enough to destroy much industrial infrastructure.

Ecological problems. Global warming is an obvious one here, though it's more disruptive than destructive.

Resource problems. Dependence on non-renewable or inadequately-renewable resources, combined with inability or unwillingess to get renewable substitutes going in sufficient quantity. We have the risk of that scenario, because of lobbying by fossil-fuel interests and economic-Panglossian ideology.

Loss of interest. The Ba'ku scenario. Something like how the last three Apollo missions were canceled because some people thought that they were repetitious. Expensive prestige projects are vulnerable to that, like the Chinese Treasure Fleets.

Social instability. Interstellar communication or interstellar spaceflight may primarily be supported by some faction that then falls out of power or loses influence. The fate of the Chinese Treasure Fleets is a good example of this.

 

[lpetrich]

Some cases of loss of interest in our history:

Treasure voyages - Wikipedia
Chinese treasure ship - Wikipedia
NOVA | Ancient Chinese Explorers
Chinese Treasure Fleets: The Chinese Overseas Expeditions During the Early 15th Century
Between 1405 and 1433, China sent 7 Treasure Fleets into the Indian Ocean, some of them going as far as Africa. But after that, China abandoned those efforts outright. From the last link,

The explanation for this strange action lies in the internal politics of the Empire. The Mandarin bureaucrats generally ran the Empire, but within the Imperial Court the court eunuchs had control. The admiral of the Treasure Fleets was Zheng He (jung huh). Zheng He was a Moslem Chinese who was captured by the army in southwestern China as a boy. His captors castrated him and sold him as a servant for harems. He ended up in the Imperial Court. The eunuchs of the Imperial Court functioned as a separate bureaucracy and the Mandarins were fearful of their power. When the Treasure Fleet expeditions to the Indian Ocean turned out to be successes the Mandarins were so afraid that the power of the eunuchs would be enhanced to the point where they would rival the Mandarins in power that they set to stop the Treasure Fleet expeditions. The Mandarins convinced the Emperor that the Treasure Fleet threaten to contaminate the Empire and must be destroyed.

So the treasure fleets lost because they were (1) expensive and (2) a pet project of a faction that fell out of official favor.


More recently, Apollo program - Wikipedia -- the last three missions were canceled as a penny-pinching measure. Humanity has not gone further from the Earth than low Earth orbit at any time since.

The Apollo program was, in large part, a beat-the-Russians effort. After the Russians had been thoroughly beaten there, some people thought that it wasn't worth continuing.


William Proxmire - Wikipedia and his Golden Fleece Award - Wikipedia -- his attacks on what he considered absurd government spending. He gave one to NASA's SETI efforts, the Search for Extraterrestrial Intelligence.


So if interstellar communication or interstellar spaceflight starts seeming too expensive, that means trouble.

 

[Trekker4747]

You go to the shore and fill a glass with water, you don't see any fish in the water. Does that mean there's no fish in the entire ocean?

Same idea. Only our cup is a thimble and the ocean is the size of the galaxy.

I don't think there's any "paradox" or anything crazy going on out there, I certainly don't think we're the only life in the entire damn universe. I just think the numbers aren't in our favor in finding or knowing about ti and nor is technology really there for us to detect or contact it.

And it may never be possible.

 

[Tim Walker]

On another web site it was pointed out that only one Earthly civilization made the scientific technological leap. The others basically stagnated at an agrarian level.

If a civilization makes the leap, it may be presented with bottlenecks: Self destruction, resource exhaustion, natural disaster.....

 

[RoJoHen]

If only the dinosaurs had thumbs...

 

[lpetrich]

On another web site it was pointed out that only one Earthly civilization made the scientific technological leap. The others basically stagnated at an agrarian level.

That's correct -- I mentioned that for theoretical science in f(communicative). It's the same one that had the Industrial Revolution. In early modern times, Europe's economic development diverged from the rest of the world, and Britain from the rest of Europe, though why these divergences happened is a very controversial issue (Industrial Revolution - Wikipedia, Great Divergence - Wikipedia).

But the Industrial Revolution made it much easier to dominate the rest of the world, and by the turn of the 20th cy., Britain had a world-spanning empire that the Sun never set on. This was despite losing 13 rebellious colonies over 1775 - 1783.

If a civilization makes the leap, it may be presented with bottlenecks: Self destruction, resource exhaustion, natural disaster.....

Like what I'd mentioned. As to major natural disasters, asteroid and comet strikes come to mind, as do large volcanic eruptions.

 

[RAMA]

http://www.centauri-dreams.org/?p=34107

Well this is never good, but hardly conclusive.

RAMA

 

[Gov Kodos]

To paraphrase a wise book, "Space is big. Really big. You just won't believe how vastly, hugely, mindbogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space." In short, we'll likely never get to other stars much less run across an alien civilization.

 

[BillJ]

To paraphrase a wise book, "Space is big. Really big. You just won't believe how vastly, hugely, mindbogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space." In short, we'll likely never get to other stars much less run across an alien civilization.

+1

We're kinda out of the way out on the spiral arm. So it won't much surprise me if we live and die completely alone. Never knowing the answers to our questions.

 

[lpetrich]

We are not *that* out of the way. We are in an arm of the Milky Way called the Orion Arm. The next arm in is the Sagittarius Arm and the next arm out is the Perseus Arm.

 

[BillJ]

We are not *that* out of the way. We are in an arm of the Milky Way called the Orion Arm. The next arm in is the Sagittarius Arm and the next arm out is the Perseus Arm.

We're obviously far enough out of the way, that if there are aliens floating around they haven't found us yet.

 

[RoJoHen]

We are not *that* out of the way. We are in an arm of the Milky Way called the Orion Arm. The next arm in is the Sagittarius Arm and the next arm out is the Perseus Arm.

We're obviously far enough out of the way, that if they are aliens floating around they haven't found us yet.

Or they found us a really, really long time ago. For all we know they killed the dinosaurs.

That's the crazy thing about space and time. Think of how many mass extinctions our planet has had over millions and millions of years. What if they had never happened? Imagine an alien world on a similar evolutionary path...only on their planet the dinosaurs never died off. On their planet the dinosaurs evolved into a space-faring race millions of years ago. Maybe they flew by us back then and never came back.

So many crazy things are possible when you're talking about such grand time spans.

 

[Gov Kodos]

Unlikely, unless those space-dinos skipped fossil fuels during their technological development and left them all for us. Besides, that still wouldn't mean squat to us even if it had happened.

 

[publiusr]

We are not *that* out of the way. We are in an arm of the Milky Way called the Orion Arm. The next arm in is the Sagittarius Arm and the next arm out is the Perseus Arm.

The actual distance to the core of our Galaxy hasn't changed--but with the Milky Way wider than once thought--the outskirt position no longer holds.

So the YOU ARE HERE shirts need the arrow to point farther in--that and the Milky Way looks to be a barred spiral.
That might be how life evolves--in the arms of barred spirals that may allow enough collisions to shake things up.

Ironically, life may not like peacefully resting galaxies--but may favor violent ones instead.

Mixing the pot

 

[Awesome Possum]

Don't all of our broadcasts and radio signals get lost in the background radiation at a certain distance? It could be the universe is full of signals, they're just too weak for us to pick them up.