The Largest Living Systems

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For anyone who studies evolution, it is important to realize that there are characteristic evolutionary patterns. For example, evolution tends towards greater complexity (although not always). Evolution also has a variable speed (which is often contingent on the environment). And a study recently published in PNAS indicates that evolutionary processes generally select for species-level living systems with universal size distribution. Science Daily summarized the importance of this universal size distribution well:

Flocks of birds, schools of fish, and groups of any other living organisms might have a mathematical function in common [… researchers] showed that for each species studied, body sizes were distributed according to the same mathematical expression, where the only unknown is the average size of the species in an ecosystem.

For the researchers of this study, these apparent universal size distribution may be useful for understanding how systems of living matter operate. However, this study made me think of the role of size in evolutionary processes. Specifically, what causes different living systems to evolve different sizes? And what living system has evolved the largest overall size?

The role of size in evolutionary processes has always been a contentious issue for evolutionary theorists. Central to the issue of size has been the idea that natural selection tends to drive the evolution of larger and larger overall size, regardless of whether the living system is a bacterium, a hydra, or a chimp. This observed trend has been labeled Cope’s rule after Edward Cope, a 19th century paleontologist who first proposed the trend. The late evolutionary theorist Stephen J. Gould disregarded Cope’s rule as a “psychological artifact”, however recent studies have provided empirical evidence to support the general pattern.

Paleontologist Joel Kingsolver supports the idea that evolution tends to favour large body size, stating that:

In 80 percent of the studies, there’s consistent selection favouring larger size.

Disappointingly, the theory to explain this pattern is still underdeveloped. In fact, Kingsolver contends that there may not be any universal driver of larger body size:

My guess is that it’s a mix of particular reasons for particular speices. You may be able to make through lean times better than someone who’s smaller. Females that are larger are able to produce more eggs. If males are competing for females, larger size is often favoured.

Paleontologist and science blogger Brian Switek echoed a similar perspective recently in an article about large dinosaur body size:

The evolutionary driving forces behind the evolution of truly huge body size are not clear, and likely differed from one group to the next.

Although evolutionary theory explaining the drive behind selection for larger body is underdeveloped, we do have a better idea of proximate determinants of body size. For example, many theorists have demonstrated that mode of locomotion and reproduction are both important factors either constraining or enabling large body size.

As Brian Switek discussed at length recently, the monstrous sauropod infraorder was able to “sidestep” the costs and risks that constrain mammalian size by “externalizing birth and development.” The size distribution of sauropods dwarfed the size distribution of all other known terrestrial organisms to ever exist.

So of these supermassive sauropods, what species holds the title of largest? The answer to this question was far more difficult to find than I originally thought. Michael Stevens from VSauce recently claimed that Giraffatitan was the largest known “with certainty of a complete skeleton”. Estimates of Giraffatitan come from one skeletal sample, and was thought to be 72-74 feet in length and weigh ~30-40 tons. Compare that to the largest known African elephant which weighed ~12 tons.

However, there is general consensus in the paleontological community that there were larger sauropods than Giraffatitan. Thankfully, I had some help from Brian Switek to better understand the contemporary debate:

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According to Switek Argentinosaurus and Supersaurus
are the leading contenders for heavyweights in the dinosaur world. The longest known of these giants was a Supersaurus that is estimated to be 108-111 feet long. The heaviest was a Argentinosaurus estimated to have weighed 73 tons. They were the giants of the gigantic sauropoda order.

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But we can’t forget about a living clade of animals that has experienced an explosive increase in size distribution: cetaceans. The largest (by far) of our mammalian cousins is the blue whale. And the blue whale is not just a contender for largest living animal, they are also contenders for largest animal of all time. In fact, in terms of absolute weight, it doesn’t appear to be close at all. Whereas Argentinosaurus weighed 73 tons, the largest known blue whale weighed over 200 tons! More than double the weight of the largest known dinosaur! But to be fair, blue whales don’t have to worry as much about the crushing weight of Earth’s gravity. The battle is much closer when we compare length: Supersaurus was between 108-111 feet and the largest known blue whale was ~110 feet.

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Blue whale Balaenoptera musculus = heaviest of all time?

The SV-POW paleontology blogger team made a brilliant point that we should suspect that Supersaurus was on average longer than blue whales because we are comparing with biased sample sizes:

A huge sample of blue whales included none longer than 110 feet, while our comparatively pathetic sample of sauropods has already turned in one animal (Supersaurus) that may have just edged that out, and another (A. fragillimus) that – assuming it was really as big as we think – blows it out of the water.

In case you were wondering, A. fragillimus is estimated to have been between 130-200 feet long! It completely blows my mind that a terrestrial organism can reach those sizes on our planet (just imagine how big they would have been if they had evolved on a planet the size of Mars!).

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The red image represents A. fragillimus, potentially the longest organism ever

In case you were wondering, no primate species has ever been a contender for largest living system. The primate order is comparatively small, with the largest contemporary species (gorillas) weighing between 300-400 lbs (or about 0.15-0.2 tons!). Even if we consider extinct species, no primate has ever even been a contender for largest land mammal. The largest, Gigantopithecus, weighed approximately 1,200 lbs (or about 0.6 tons). Of course, I think Gigantopithecus is aptly named (and I think sympatric populations of Homo erectus would agree); but they are only aptly named in comparison to our relatively puny order. Primate size has probably always been constrained by underdeveloped quadrupedalism and selection for long-term infant dependence.

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Reconstruction of Homo erectus and Gigantopithecus in Southeast Asia

However, it is interesting to know that all species body sizes (from prokaryotes to sauropods) are distributed according to a potentially universal power law. This universal describes how ecology influences average species size, while genetics contains variability around that average. In the future, I’ll be interested to see whether evolutionary theorists can better describe the adaptive pressures selecting for larger size. It is useful to have a grasp on the proximate causes of body size, but the ultimate causes will be necessary to better describe how living systems develop over time.

What do you think about the evolution of large size?  Let Cadell know on Twitter!

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“Earth-like”

Earth-Like Planets

The search for an Earth analogue is heating up. And although we may have to wait for the James Webb Space Telescope to see another Earth, indirect methods are bringing us closer and closer to finding an Earth-like exoplanet every month. These findings are also bringing us closer to estimating the number of Earth-like planets in the Milky Way (e.g., study 12).

The latest research, and for some the most exciting, was the discovery of Kepler-62e. Kepler-62e is a planet located approximately 1,200 light years away from Earth in the Kepler-62 star system. This system is composed of a smaller and cooler star than our Sun, and is accompanied by five known planets, two of which are rocky worlds in the stars habitable zone.

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From the limited data available to astronomers at this point in the detection process, Kepler-62e has been touted as the “most Earth-like” planet known to date. In fact, by utilizing the Earth Similarity Index (ESI) equation Kepler-62e scores a 0.82 (scale: 0-1.0). That score matches the unconfirmed exoplanet candidate Gliese 581 g (Figure 1).

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Figure 1 – Current Potential Habitable Exoplanets

ESI is calculated using data on the mean radius, bulk density, escape velocity, and surface temperature of an exoplanet. In the popular science media a high ESI (~0.80-1.00) is code for “Earth-sized planet within the habitable zone.” In essence that is what everyone means when they say “Earth-like.” But a growing number of scientists, myself included, are beginning to realize that we are getting way ahead of ourselves. At the moment we have no way of understanding an exoplanet’s geophysical history, present state, or the dynamics of the entire star system. Astronomer Phil Plait recently tempered enthusiasm re: Kepler-62e by stating there are too many unknowns to call it Earth-like yet:

Kepler-62e could have a thick CO2-laden blanket of air, making its surface temperature completely uninhabitable, like Venus. Or it might not. We just don’t know yet, and won’t for quite some time.

In short, more data on Kepler-62e could radically alter its ESI number from 0.82 to 0.44! And that is not even factoring in data on how a radically different solar system would affect Kepler-62e’s development and present state.

This frequent, and perhaps cavalier, use of the term “Earth-like” has caused some astronomers concern. Astrobiologist Caleb Scharf recently forced us to consider what is meant by “Earth-like” when used in the context of exoplanet discovery:

Utterance of [Earth-like] can evoke all sorts of images. It may make us think of oceans, beaches, mountains, deserts, forests, fluffy clouds, fluffy bunnies, warm summers, snowy winters, the local pub, or the fabulous hubbub of the local souk. But this is typically far from the meaning attached by scientists. It can simply indicate a planet with a rocky surface, rather than a world with a thick gaseous envelope. It can mean a world that is roughly the same mass and density as Earth. It can mean a planet orbiting a star like the Sun. Or it can just mean that we got bored of saying things like ‘a two-Earth mass object in a close to a circular orbit around a roughly 4 billion year old main-sequence star that is similar in mass to the Sun’.

For me, Scharf adequately articulates the complexity in this galactic search. He also reminds me that we still must be humbled by what we can’t know at this point in time. Our estimates on the number of Earth-like worlds are going to be in constant flux this century because our data will be imperfect. All we need to do is remind ourselves of Earth’s history to know our current data are insufficient to label an exoplanet “Earth-like”. Despite the fact that our planet’s orbit and size have been relatively static, it has gone through phases (and will go through future phases) that we would consider inhospitable.

On a final note, we must also remember that our planet has the current temperature, chemical composition, and general climate it does because of the biosphere. Life, as far as we know, creates an “Earth-like” world. So perhaps, moving forward, the term “Earth-like” should be reserved for planets that we can tell are operating in a Gaia-like way. By that I mean that we should only call a planet Earth-like if the light elements (e.g., carbon, nitrogen, sulphur, and nitrogen) are being dominated and controlled by biology.

What do you think about our search for another Earth?  Let Cadell know on Twitter!

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We Are Not Aquatic Apes

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Anthropology is a subject that has attracted its fair share of anti-intellectual theorists before. These anti-intellectuals are scientists from other areas of scientific inquiry that attempt to propose their own theories about who we are and where we came from despite having no formal anthropological training. Consequently, these people are usually a massive headache because they have no idea what they are talking about. Dr. Jonathan Marks did a great job elucidating why anthropology may attract this type of anti-intellectualism in a recent podcast I did with him.

Either way, I woke up yesterday to an infuriating article published in the Guardian: Big brains, no fur, sinuses… are these clues to our ancestors’ lives as ‘aquatic apes’? The article gave an international platform to several scientists that support the Aquatic Ape Hypothesis/Theory (AAH/T). This hypothesis proposes that there was a, as yet unidentified, aquatic phase of human evolution causing our ancestors to develop bipedalism, big brains, subcutaneous fat, sinuses, and lack of fur. Supporters of the AAH believe that these features are all indicative of an ancestral past spent living primarily in deep creeks, river banks, and the sea.

But there is one major problem: there is no evidence to support it. No evidence is usually a problem in science. No ancestral hominids have ever been found that lived in an aquatic environment.

The theory was first developed in 1960 by Sir Alister Hardy. Since then its supporters have generally been from biology. The AAH has received little to no serious consideration from the anthropological community. And nor should it. Paleontologist Chris Stringer accurately acknowledged in the Guardian article that:

[T]he whole aquatic ape package includes attributes that appeared at very different times in our evolution. If they were all the result of our lives in watery environments, we would have to have spent millions of years there and there is no evidence for this – not to mention crocodiles and other creatures would made the water a very dangerous place.

These are all very important points. If the AAH is valid we would have spent millions of years in a watery environment and we should suspect all features of the “aquatic ape package” to have evolved together, not at separate times. But this is not what paleoanthropology has taught us about our past. We know that our hominid ancestors lived primarily in woodlands 6 million years ago, and primarily in savanna landscapes 3 million years ago. Furthermore, two of the most important features that the AAH attempts to explain, bipedalism and encephalization, developed millions of years apart from each other.

Paleoanthropologist John Hawks has previously deconstructed why no anthropologists take the AAH seriously. He accurately pointed out that the AAH’s single assumption does not explain why we retained these “aquatic characteristics”:

Certainly it makes sense that hominids would develop new anatomies to adapt to such an alien [aquatic] environment. But once those hominids returned to land, forsaking their aquatic homeland, the same features that were adaptive in the water would now be maladaptive on land. What would prevent those hominids from reverting to the features of their land-based ancestors, as well as nearly every other medium-sized land mammal? More than simple phylogenetic inertia is required to explain this, since the very reasons that the aquatic ape theory rejects the savanna model would apply to the descendants of the aquatic apes when they moved to the savanna. […] It leaves the Aquatic Ape Theory explaining nothing whatsoever about the evolution of the hominids. This is why professional anthropologists reject the theory.

And yet anti-intellectuals still get a credible platform to spout nonsense about our aquatic past. Perhaps I could contain my disappointment if it all remained academic. However, ecologist Dr. Michael Crawford claims that our brain growth was solely because our aquatic ancestors had a diet rich in Docosahexaenoic acid (DHA), which is found in seafood. So he then makes the dangerous (and ridiculous) argument that:

[W]ithout a high DHA diet from seafood we could not have developed our big brains. We got smart from eating fish and living in water. More to the point, we now face a world in which sources of DHA – our fish stocks – are threatened. That has crucial consequences for our species. Without plentiful DHA, we face a future of increased mental illness and intellectual deterioration. We need to face up to that urgently. That is the real lesson of the aquatic ape theory.

Using an unsupported theory of human encephalization to claim that lack of fish in someone’s diet will lead to mental illness and intellectual deterioration is just anti-intellectual pseudoscience. Considering how far evolutionary theory has progressed in the past few decades, it is disappointing to see these scientists employ it so poorly. The Aquatic Ape Hypothesis is nothing more than an unsupported adaptive story. It has not been supported by evidence, and I find it highly unlikely that it ever will be.

In 2009, John Hawks thought the AAH fit the description of pseudoscience. In 2013, it still fits the description. We have never been aquatic apes.

What do you think of the AAH?  Let Cadell know on Twitter!

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Extreme Evolution

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The coelacanth is the oldest living species of lobe-finned fish. In fact, it is so old that it has acquired the nickname “living fossil.” The distinction is probably more an artifact of the history of science than of the coelacanth’s ancientness. In the early 20th century scientists believed that the coelacanth went extinct 70 million years ago (15 million years before the K-T mass extinction!). So when a live specimen was discovered off the coast of South Africa it came as a major shock. Upon first analyzing the fish, South African chemistry professor JLB Smith famously wrote the cable:

MOST IMPORTANT PRESERVE SKELETON AND GILLS = FISH DESCRIBED

Since this discovery scientists have been perplexed by this Lazarus taxon. How has the coelacanth managed to persevere over the past 300 million years without changing at all?

This question really gets at the heart of a bigger evolutionary conundrum: does evolution have a uniform speed? Or is the speed of evolutionary change intrinsically variable?

Evolutionary theory pioneer Stephen J. Gould was one of the first to propose that evolutionary change varied tremendously. In order to explain this change he proposed the idea of punctuated equilibrium. This theory proposed that species change is largely contingent on environmental change. Gould recognized that morphological stasis could be correlated with ecological stasis. Therefore, he reasoned that massive ecological changes would prove to be the major drivers of rapid selection over the scale of evolutionary time.

This contradicted dominant theory in the 1970s because all theorists embraced phyletic gradualism: the idea that evolution was steady state with gradual transformations changing lineages. In reality, both punctuated equilibrium and phyletic gradualism are not mutually exclusive. We know now that some species can change quickly (in evolutionary terms) in response to major ecological pressures. However, change can also occur gradually over millions of years in response to more subtle ecological changes.

This brings us back to the “living fossil”: the coelacanth. Has this species really remained unchanged for nearly 300 million years? Is it really a “living fossil”? If so, its history would be a remarkable example of how an organisms environment can stabilize selection.

A recent study published in Nature finally gave us some insight into this decades-old evolutionary mystery. In this study the first genome sequence for the coelacanth was reported. The data revealed what had been obvious to many, the coelacanth’s protein-coding genes are evolving slower than any other known animals. One of the researchers in this study, Kerstin Lindblad-Toh explained that:

We often talk about how species have changed over time, but there are still a few places on Earth where organisms don’t have to change, and this is one of them. Coelacanths are very likely specialized to such a specific, non-changing, extreme environment – it is ideally suited to the deep sea just the way it is.”

However, Lindblad-Toh was also quick to emphasize that the term “living fossil” is unscientific and not an accurate representation of a extant species:

It’s not a living fossil; it’s a living organism, it doesn’t live in a time bubble; it lives in our world, which is why it’s so fascinating to find out that its genes are evolving more slowly than ours.

Here is where we can highlight an interesting (and extreme) example of just how variable evolutionary change can occur. Our species, Homo sapiens sapiens, have evolved very quickly. Let’s put this in comparison by comparing our evolution to our slowly evolving coelacanth cousins. Coelacanth fossils have been found that stretch back to the mid-Paleozoic. This is approximately the time the last supercontinent, Pangaea, first formed. That means the coelacanths emerged 70 million years before the entire Dinosauria clade.

In contrast, our genus, Homo, is approximately 2 million years old. Over this period of time our brain has tripled in size. That is unparalleled evolutionary change. I have written extensively about our genetic origins in the past so I won’t repeat myself here. However, I do want to emphasize that one of the drivers of this change has been ecological disequilibrium. Recent studies by several geoscientists have convincingly demonstrated that the East African savanna was characterized by rapid environmental change during a 200,000 year period approximately 2 million years ago. Clayton Magill, a graduate student involved in one of these studies elucidated how these changes could have stimulated punctuated equilibrium-like effects on human brain growth:

Changes in food availability, food type, or the way you get food can trigger evolutionary mechanisms to deal with those changes. The result can be increased brain size and cognition, changes in locomotion and even social changes – how you interact with others in a group. We show that the environment changed dramatically over a short time, and this variability coincides with an important period in our human evolution when the genus Homo was first established and when there was first evidence of tool use.

Since that period environmental change has played a tremendous role in the creation of our species genotype and phenotype. As modern humans exploded throughout the world, we were forced to adapt quickly to previously alien environments. Most of this adaptation was made possible by our unique ability to drive cultural and technological evolution. However, pertinent contemporary phenotypic differences within our species, like skin colour variation, were also caused by biological adaptation to extreme differences in environmental conditions.

Exploring evolutionary change in the coelacanth and humans represent two major biological evolutionary extremes. Both organisms perfectly encapsulate Stephen J. Gould’s theory of punctuated equilibrium. Ecological pressure can either strongly stabilize selection or drive rapid changes over relatively short periods of time. However, I do want to emphasize that these are the extremes. For many species, phyletic gradualism is king because ecology will change, but it will change slowly.

And don’t forget, today is DNA Day! A time to celebrate the discovery of the molecular backbone of all life on our terraqueous globe! Without the discovery of DNA our knowledge of our own evolutionary past would be relatively impoverished, and this article would not have been possible!

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#DNAday

What do you think about extreme evolution?  Let Cadell know on Twitter!

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Redefining The Singularity

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The technological singularity has quickly become one of the most controversial concepts. It represents a theoretical future period in time when superintelligence emerges through technological means. During a recent conference on the future of artificial intelligence (A.I.) futurist Anders Sandberg proposed that this concept has three major commonalities:

  • accelerating change
  • prediciton horizon
  • intelligence explosion

The term was popularized by computer scientist Vernor Vinge in 1993. He recently expounded on the creation of the concept and the reasoning behind it:

the spectacular feature of A.I. was not making something as smart as a human, but creating minds that were more intelligent than humans. That would be a different type of technological advance. That would change the thing that is the top creative element in technological progress, and since it would be beyond human intelligence, there is a certain unknowability about what would happen beyond that point. Therefore, I came up with the metaphor with the singularity as it is used with blackholes in general relativity reflecting this fact that there is not much information you can imagine beyond the point in time when super-human intelligence comes into place.

Several theorists have hypothesized about how the singularity will happen, when it will happen, and how it will change human nature. In 2007, artificial intelligence expert Ben Goertzel published a paper in Artificial Intelligence outlining the main scenarios proposed by futurists thus far. They included everything from a Sysop scenario where a highly powerful benevolent A.I. effectively becomes a “system operator” to a Skynet scenario where A.I. is created, improves itself, and malevolently enslaves or annihilates humanity. I am definitely most closely aligned with the Kurzweilian scenario. I believe that humanity will create advanced A.I. that can create better, more advanced A.I. However, I also believe that we will intimately merge with technology. By the end of this process humanity will essentially be post-biological in nature. I suspect that it will not be an abrupt or particularly chaotic transition. It will happen gradually over the span of decades (in some ways it has already started happening).

Either way, I am writing this post because I would like to start an important discussion on the term “singularity.” Although I have referred to myself as a “singultarian” and count myself as a Kurzweilian-defender, I find the term singularity problematic. As Vinge stated the term singularity is used to suggest unknowability beyond a certain technological event horizon. However, I posit that this “technological event horizon” is not an actual future reality. I believe that there will come a time when humans are no longer the “top creative element of technological progress” but a “singularity” will not happen. What I mean is that if we keep using the term “singularity” it may start to metaphorically resemble the carrot and stick idiom:

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If humans start artificially enhancing their own intelligence in the 2030s and developing relationships with advanced A.I., the approaching decades (e.g., 2040s-2050s) currently predicted to play host to the singularity will start to become clearer to us than they currently are (i.e. they will not be a technological singularity).

Vernor Vinge has admitted this much stating that:

If you became one of the supersmart creatures, things would not be any more unintelligible to you than the current world is to un-enhanced humans.

Furthermore, we cannot remain intellectually comfortable with the term singularity if we are starting to make predictions of a post-singularity world. Several futurists, including Ray Kurzweil, have already started proposing probable post-singularity developments. But making these predictions completely contradicts the metaphorical validity of the term. If the singularity metaphor proved useful we should find ourselves facing a literal information blackhole. But I don’t think that is what we find ourselves facing.

As a futurist, I feel like we need a new term to better describe what we mean when we say technological singularity. I do not yet know what term would fit best. The term “infinitely self-generating technology” has a nice ring to it. However, I can already think of a host of reasons why that term is problematic.

What do you think?  Let Cadell know on Twitter!

Life Before Earth?

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A few days ago biologists Alexei Sharov and Richard Gordon published a paper that sent shock waves throughout the academic community. In their paper titled Life Before Earth they propose that life originated before the formation of our planet. But just in case that wasn’t radical enough, they further state that:

adjustments for potential hyperexponential effects would push the projected origin of life even further back in time, close to the origin of our galaxy and the universe itself.

In my last post I discussed the transition from non-life to life. However, no where in that article did I discuss the timing of that transition. The dominant view at present is that life originated ~3.5 billion years ago. This estimation comes from direct and indirect evidence of prokaryotic (single-cell organism) activity in Western Australia and South Africa. Although it is hard to prove empirically, most biologists are confident that life on Earth did not exist before this period. This is because between 4.6-4.0 billion years ago Earth can best be described as a chaotic hellscape of magma oceans and planetesimal collisions (i.e., not the best place for RNA replication).

But this latest paper by Sharov and Gordon claims life existed before earth (before even the formation of our galaxy). To be precise they calculate the time of origin for life to be 9.7 ± 2.5 billion years ago. For context our galaxy is ~8 billion years old, and our solar system and planet is 4.6 billion years old.

How could this be?

The authors propose that biologists have neglected to acknowledge the “cosmic time scale” of life. In their paper they posit that in terms of genetic complexity life has grown exponentially (they measure genetic complexity by the number of non-redundant functional nucleotides). Prokaryotes, eukaryotes, worms, fish, and mammals were included in the authors study sample and genetic complexity was plotted on a logarithmic scale (Figure 1). With these data they found that genome complexity doubled every 376 million years. They conclude that if genome complexity doubles at this rate prokaryotic complexity could not have been achieved by 3.5 billion years ago. Both Sharov and Gordon blame biologists of presuming a rapid primordial evolution in order to fit the time scales required by our planet’s age.

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Figure 1

Within this new proposed framework the authors suggest that this exponential doubling time is an inherent evolutionary process accelerating quickly with new, more efficient forms of information storage than genomes (e.g., highly complex brains, language, books, computers, internet). Now I am definitely someone that believes exponential growth is an inherent property of evolutionary processes. I am also someone that thinks evolutionary processes generally tend towards greater and greater levels of system complexity (even though recent research has demonstrated that this is not always the case). However, more than doubling the time of the origin of life proposes a radical re-imagining of life and our universe. Such a proposition demands tremendous evidence. I commend Sharov and Gordon for proposing a bold idea and approaching the evolution of life from a novel perspective, but they did not provide us with tremendous evidence.

Biologist PZ Meyers was first to point out that they cherry picked their data. They did not include many organisms that would have completely thrown off their logarithmic scale. Furthermore, even if the logarithmic scale with all organisms plotted remained unchanged it would not be scientific to assume you can project it back to single nucleotide replicators that existed 9.7 billion years ago. Finally, biologists have only started to understand what is and what is not functional within the human genome. Therefore, we cannot assume that measuring genome complexity based off of our current understanding of functional non-redundant nucleotides is useful.

Unfortunately the claim that life originated 9.7 billion years ago might destroy the credibility of both the paper and the authors. I say unfortunately because within this paper the authors actually make a profound claim that I agree with:

The Drake Equation of guesstimating the number of civilizations in our galaxy may be wrong, as we conclude that intelligent life like us has just begun appearing in our universe. The Drake Equation is a steady state model, and we may be at the beginning of a pulse of civilization. Emergence of civilizations is a non-ergodic process, and some parameters of the equation are therefore time-dependent.

Recently I wrote about why I think it is highly probable that we are the first intelligent civilization to develop in our galaxy. My main reasons for thinking this are:

A) Our universe was not always well-suited for the evolution of life

B) Biological evolution requires billions of years of planetary stability

C) Biological evolution can produce trillions of species without ever selecting for high-intelligence and civilization

There are actually many more reasons why I think this is likely so I suggest reading my entryIntelligent Life in the Milky Way if you want to know more about it. Either way, my line of reasoning is certainly in line with Sharov and Gordon’s assertion that “intelligent life like us has just begun to appear in the universe.” Although they come at it from a slightly different perspective, I obviously find this assertion profound and compelling.

In the end I think Life Before Earth is worth a read if you are interested in learning more about Sharov and Gordon’s claims; but I am personally not sold. Biologists may never know the precise historic pathway of inanimate to animate matter and the specific materials present on the prebiotic earth, but I still think a 3.5 billion year origin for life is more likely than a 9.7 billion origin.

In the future biologists do need to demonstrate how biological evolution was able to produce highly complex prokaryotic genomes in a relatively short period of time. There could be a number of currently unknown reasons for this that do not require a single-nucleotide replicator with pre-galactic origins.

That is not to say that life could not have originated completely or partially from space. The idea that asteroids with complex organic compounds seeded our planet during the late-heavy bombardment 4 billion years ago is quite possible. But positing the chemical compounds necessary for life existed 9.7 billion years ago requires more evidence than a logarithmic scale with cherry picked data points.

What do you think?  Let Cadell know on Twitter!

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From Non-Life to Life: The Unity of Evolutionary Processes

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The origin of life. If there is a more controversial (or complex) scientific problem I have yet to encounter it. Well… the origin of everything, or why there is anything at all is perhaps a little more controversial and complex. But the origin of life is certainly in the top 5. I know it is a scientific problem that has consistently perplexed me. But I shouldn’t feel too bad because it seems to have stumped even the brightest scientific minds. However, a study by chemists Addy Pross and Robert Pascal published in Open Biology last month seems to have laid out one of the most impressive working hypotheses I have seen to explain the transition from non-life to life. The paper is boldly titled: The origin of life: what we know, what we can know and what we will never know. It is open access and a tremendous read.

For several decades evolutionary theorists have been working hard to extend the concept of biological evolution into the realms of physics, chemistry, culture, and technology. In my mind this extension is imperative because it will help us more clearly understand major system transitions and the processes that drive change in our universe. The most important of these major system transitions is the transition from non-life to life. We know that biological evolution via well-understood mechanisms (e.g., selection, mutation, gene flow, genetic drift, etc.) allows for the existence of a complex and diverse biosphere. But we do not know how inorganic matter becomes organic matter.

In the recent publication by Pross and Pascal, they first outline what they feel we will never know about this transition: a) the precise historic pathway of inanimate to animate and b) the specific materials present on the prebiotic earth. I agree with them and I can’t overstate how important it is that they recognize this. I feel like attempting to re-create the environment of prebiotic earth is the biggest theoretical and methodological flaw scientists make when investigating the transition from non-life to life. Those experiments are admittedly interesting, but they are not falsifiable.

What we need to do is build an understanding of the relationship between chemistry and biology. Pross and Pascal believe that they have successfully elucidated this relationship. They state that:

In the context of the [origin of life] debate, there is one single and central historic fact on which there is broad agreement – that life’s emergence was initiated by some autocatalytic chemical system.

Adding that:

It follows that the study of autocatalytic systems in general may help uncover the principles that govern their chemical behaviour, regardless of their chemical detail. Extending Darwinian theory to inanimate chemical systems: The recognition that a distinctly different stability kind, dynamic kinetic stability (DKS), is applicable to both chemical and biological replicators, together with the fact that both replicator kinds express similar reaction characteristics, leads to the profound conclusion that the so-called chemical phase leading to simplest life and the biological phase appear to be one continuous physicochemical process, as illustrated in scheme 1.

lifeF1.medium.gif

Under this working framework it does not necessarily matter what organic molecules were present on the prebiotic earth. What matters is that we can understand how replicating systems work, whether they be chemically based, biologically based, or some grey zone between these two replicating worlds.

A theory to unite how replicating chemistry forms the basis of biological systems has been long in coming. Addy Pross suspects there has been such a lack of progress on this unification because chemists have a much better grasp on the static “regular” chemical world. However, he contends that there are “two chemistries”: one static and one dynamic. And both of these worlds produce stability (i.e., persistence over time) in very different ways.

Pross believes that there is enough empirical evidence from the study of systems chemistry to conclude that replicating molecules can persist via Dynamic Kinetic Stability (DKS). This type of chemical stability is vastly different than regular chemical stability. With regular chemical stability molecules lack reactivity. A good example of this is the molecule H2O, which is a hydrogen-oxygen mixture that forms a stable bond over time (it persists as a “thing” and we call that thing water). This hydrogen-oxygen mixture can form rivers, lakes, and oceans that can persist as a stable entity for an indefinite amount of time. However, replicating chemistry has a different type of stability that must operate on the population level because they are highly reactive. DKS essentially is the product of a group of replicating molecules that can be stable over time as a “population” even though their individual members are constantly changing (which is very different from how a “population” of H2O molecules achieve stability). These systems tend to drift from less stable to more stable over time non-randomly. The quantitative level of stability for the replicating system is dependent on a) its overall size and b) the amount of time it has existed. Again, this is very different from something like water that can possess the same level of stability regardless of its size or how long it has existed.

If this is difficult to conceptualize you could apply the same concept of a biological species and it should come into clear focus. Think of the human species. We have persisted for over 150,000 thousand years as a single biological system, and yet our individual members are always changing (at least for the time being #singularity). Other biological systems have achieved even greater stability. For example, cyanobacteria have remained essentially unchanged for 2.5-3.5 billion years. This ancient form of life, a dynamic system, has achieved greater stability than Mount Everest! And within this analogy resides the key to the discoveries within modern systems chemistry: replicating chemical systems essentially “behave” in the same way that replicating biological systems do. This means that abiogenesis – chemical process by which the simplest life emerged from inanimate beginnings – may have an underlying physicochemical continuity with biological evolution that had previously been unrecognized. A non-random selection for stability and complexity.

For me this research is incredibly fascinating for two reasons: 1) systems chemistry reveals that evolution operates at deeper, more fundamental levels of reality via potentially analogous mechanisms and 2) we are now theoretically able to build models of understanding that the origin of life is a non-random evolutionary process.

This research has very deep implications for how common we should expect life to be in our universe. If life is a product of replicating chemical reactions that acquire stability and increase in complexity via selection mechanisms, we should expect molecular life to be ubiquitous.

This discovery could represent a critical reformation of how we understand and conceptualize the universe. If studies of systems chemistry had revealed that at the molecular level there was only random chemical reactions, then our existence would begin to look extremely bizarre. I mean really, really bizarre. The chances of random chemical processes leading to the complexity we find at even the simplest biological levels is essentially zero. Pross and Pascal eloquently end their paper stating as such:

There is good reason to think that the emergence of life on the Earth did not just involve a long string of random chemical events that fortuitously led to a simple living system. If life had emerged in such an arbitrary way, then the mechanistic question of abiogenesis would be fundamentally without explanation — a stupendously improbable chemical outcome whose likelihood of repetition would be virtually zero. However, the general view, now strongly supported by recent studies in systems chemistry, is that the process of abiogenesis was governed by underlying physicochemical principles, and the central goal of [origin of life] studies should therefore be to delineate those principles.

I am very excited to see what future studies in systems chemistry reveal about these underlying principles. I am already formulating my hypotheses! It seems likely to me that the basic evolutionary mechanisms that have been so profoundly useful for describing all life, will also help us explain how other dynamic systems change over time. And hopefully this research will not always remain theoretical. Although we cannot recreate the prebiotic Earth, but if we ever go to Europa or peak at another Earth maybe we will be able to see the transition from non-life to life first hand.

It is an exciting time to be alive!

What do you think about the non-life to life transition?  Let Cadell know on Twitter!

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