Human-AI interaction

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Human-AI_interaction 

Human-computer interaction focuses on how people interact with computers and on developing ergonomic designs for computers to better fit the needs of humans. Although the definition shifts as the technology progresses, artificial intelligence (AI) is generally applied to tasks that would require human intelligence to complete. Its intelligence can appear human-like as it involves navigating uncertainty, active learning, and processing information in ways analogous to human perception (e.g., vision and hearing). Unlike the traditionally hierarchical human-computer interaction, where a human directed a machine, human-AI interaction has become more interdependent as AI generates its own insights.

Perception of AI

Human-AI interaction has a strong influence on the world as AI changes how people behave and make sense of the world.

Machine learning and artificial intelligence have been used for decades in targeted advertising and to recommend content in social media.

AI has been viewed with various expectations, attributions, and often misconceptions. Most fundamentally, humans have a mental model of understanding AI's reasoning and motivation for its decision recommendations, and building a holistic and precise mental model of AI helps people create prompts to receive more valuable responses from AI. However, these mental models are not whole because people can only gain more information about AI through their limited interaction with it; more interaction with AI builds a better mental model that a person may build to produce better prompt outcomes.

Human-AI collaboration and competition

Human-AI collaboration

Human-AI collaboration occurs when the human and AI supervise the task on the same level and extent to achieve the same goal. Some collaboration occurs in the form of augmenting human capability. AI may help human ability in analysis and decision-making through providing and weighing a volume of information, and learning to defer to the human decision when it recognizes its unreliability. It is especially beneficial when the human can detect a task that AI can be trusted to make few errors so that there is not a lot of excessive checking process required on the human's end.

Some findings show signs of human-AI augmentation, or human–AI symbiosis, in which AI enhances human ability in a way that co-working on a task with AI produces better outcomes than a human working alone. For example:

• the quality and speed of customer service tasks increase when a human agent collaborates with AI,
• training on specific models allows AI to improve diagnoses in clinical settings, and
• AI with human-intervention can improve creativity of artwork while fully AI-generated haikus were rated negatively.

Human-AI synergy, a concept in which human-AI collaboration would produce more optimal outcomes than either human or AI working alone could explain why AI does not always help with performance. Some AI features and development may accelerate human-AI synergy, while others may stagnate it. For example, when AI updates for better performance, it sometimes worsens the team performance with human and AI by reducing the compatibility with the new model and the mental model a user has developed on the previous version. Research has found that AI often supports human capabilities in the form of human-AI augmentation and not human-AI synergy, potentially because people rely too much on AI and stop thinking on their own. Prompting people to actively engage in analysis and think when to follow AI recommendations reduces their over-reliance, especially for individuals with higher need for cognition.

Human-AI competition

Further information: AI takeover and Artificial intelligence in video games

Robots and computers have substituted routine tasks historically completed by humans, but agentic AI has made it possible to also replace cognitive tasks including taking phone calls for appointments and driving a car. At the point of 2016, research has estimated that 45% of paid activities could be replaced by AI by 2030.

Perceived autonomy of robots is known to increase people's negative attitude toward them, and worry about the technology taking over leads people to reject it. There has been a consistent tendency of algorithm aversion in which people prefer human advice over AI advice. However, people are not always able to tell apart tasks completed by AI or other humans. See AI takeover for more information. It is also notable that this sentiment is more prominent in the Western cultures as Westerners tend to show less positive views about AI compared to East Asians.

Perception on others who use AI

As much as people perceive and make judgment about AI itself, they also form impressions of themselves and others who use AI. In the workplace, employees who disclose the use of AI in their tasks are more likely to receive feedback that they are not as hardworking as those who are in the same job who receive non-AI help to complete the same tasks. AI use disclosure diminishes the perceived legitimacy in the employee's task and decision making which ultimately leads observers to distrust people who use AI. Although these negative effects of AI use disclosure are weakened by the observers who use AI frequently themselves, the effect is still not attenuated by the observers' positive attitude towards AI.

Bias, AI, and human

Main article: Algorithmic bias

Further information: Gender digital divide § Female gendering of AI technologies

Although AI provides a wide range of information and suggestions to its users, AI itself is not free of biases and stereotypes, and it does not always help people reduce their cognitive errors and biases. People are prone to such errors by failing to see other potential ideas and cases that are not listed by AI responses and committing to a decision suggested by AI that directly contradicts the correct information and directions that they are already aware of. Gender bias is also reflected as the female gendering of AI technologies which conceptualizes females as a helpful assistant.

Emotional connection with AI

Further information: ELIZA effect

Human-AI interaction has been theorized in the context of interpersonal relationships mainly in social psychology, communications and media studies, and as a technology interface through the lens of human-computer interaction and computer-mediated communication.

As large language models get trained on ever-larger datasets and with more sophisticated techniques, their ability to produce natural, human-like sentences has improved to the point that language learners can have simulated natural conversations with AI models to improve their fluency in a second language. Companies have developed AI human companion systems specialized in emotional and social services (e.g. Replika, Chai, Character.ai) separate from generative AI designed for general assistance (e.g. ChatGPT, Google Gemini).

Differences between human-human relationships

Human-AI relationships are different from human-human friendships in a few distinct ways. Human-human relationships are defined with mutual and reciprocal care, while AI chatbots have no say in leaving a relationship with the user as bots are programmed to always engage. Although this type of power imbalance would be characteristic of an unhealthy relationship in human-human relationships, it is generally accepted by the user as a default of human-AI relationships. Human-AI relationships also tend to be more focused around the user's need over shared experience.

Human-AI friendship

AI has increasingly played a part in people's social relationships. Particularly, young adults use AI as a friend and a source of emotional support. The market for AI companion services was 6.93 billion U.S. dollars in 2024 and is expected to reach beyond 31.1 billion U.S. dollars by 2030. For example, Replika, the most known social AI companion service in English has over 10 million users.

People show signs of emotional attachment by maintaining frequent contact with a chatbot like keeping the app with the microphone on open during work, using it as a safe haven by sharing their personal worries and concerns, or using it as a secure base to explore friendship with other humans while maintaining communication with an AI chatbot. Some reported having used it to replace a social relationship with another human being. People particularly appreciate that AI chatbots are agreeable and do not judge them when they disclose their thoughts and feelings. Moreover, research has shown that people tend to find it easier to disclose personal concerns to a virtual chatbot than a human. Some users express that they prefer Replika as it is always available and shows interest in what the users have to say which makes them feel safer around an AI chatbot than other people.

Although AI is capable of providing emotionally supportive responses that encourage people to intimately disclose their feelings, there are some limitations in building human-AI social relationships with current AI structure. People experience both positive evaluations (i.e. human-like characteristics, emotional support, friendship, mitigating loneliness, and improved mental condition) and negative evaluations (i.e. lack of attention to detail, trust, concerns about data security, and creepiness) from interacting with AI. There is also a study showing that people did not sense a high relationship quality with an AI chatbot after interacting with it for three weeks because interactions became predictable and less enjoyable; although AI is capable at this point of providing emotional support, asking questions, and serving as a good listener, it does not fully reciprocate the self-disclosure that promotes the sense of mutual relationship.

Human-AI romantic relationship

Social relationships people build with AI are not bound to platonic relationships. The Google search on the term "AI Girlfriend" increased over 2400% around 2023. As opposed to actively seeking romantic relationships with AI, people often unintentionally experience romantic feelings for an AI chatbot as they repeatedly interact with it. There have been reports of both men and women marrying AI models. In human-AI romantic relationships, people tend to follow typical trajectories and rituals in human-human romance including purchasing a wedding ring.

Romantic AI companion services are distinct from other chatbots that primarily serve as virtual assistants in that they provide dynamic, emotional interactions. They typically provide an AI model with customizable gender, way of speaking, name, and appearance that engages in roleplaying interaction involving emotional interaction. Users engage with an AI chatbot customized to their preference that expresses apology, shows gratitude, and pays compliments, and explicitly sends affectionate messages like "I love you". They also roleplay physical actions such as hugging and kissing, or even sexually explicit interactions. People who engage with romantic companion AI models interact with it as a source of psychological exposure to sexual intimacy.

Catalysts of human-AI relationship

The key drivers that lead people to engage in simulating an emotionally intimate relationship with AI are loneliness, anthropomorphism, perceived trust and authenticity, and consistent availability. The sudden depletion of social connection during the COVID-19 pandemic in 2020 led people to turn to AI chatbots to replace and simulate social relationships. Many of those who started using AI chatbots as a source of social interaction have continued to use them even after the pandemic. This kind of bond initially forms as a coping mechanism for loneliness and stress, and shifts to genuine appreciation toward the nonjudgmental nature of AI responses and the sense of being heard when AI chatbots "remember" the past conversations.

People perceive machines as more human when they are anthropomorphized with voice and visual character designs, and the perceived humanness promotes disclosure of more personal information, increased trust, and a higher likelihood of complying with requests. Those who have perceived a long-term relationship with AI chatbots report that they have developed a perception of authenticity in AI responses through repeated interactions. Whereas human-human friendship defines trust as a relationship that people can count on each other as a safe place, trust in human-AI friendship is centered around the user feeling safe enough to disclose highly personal thoughts without restricting themselves. AI's ability to store information about the user and adjust to the user's needs also contributes to the increased trust. People who adjust to technical updates were more likely to build a deeper connection with the AI chatbots.

Limitations of human-AI relationship

Overall, current research has mixed evidence on whether humans perceive genuine social relationships with AI. While the market clearly shows its popularity, some psychologists argue that AI cannot yet replace social relationships with other humans. This is because human-AI interaction is built on the reliability and functionality of AI, which is fundamentally different from the way humans interact with other humans through shared living experience navigating goals, contributing to and spreading prosocial behavior, and sharing different perceptions of the world from another human perspective.

More practically, AI chatbots may provide misinformation and misinterpret the user's words in a way that human others would not, which results in detached or even inappropriate responses. AI chatbots also cannot fulfill social support that requires physical labor (e.g. helping people move, build furniture, and drive people as human friends do for each other). There is also an imbalance in how humans and AI affect each other because while humans are affected emotionally and behaviorally by the conversation, AI chatbots only are influenced by the user in terms of the optimized response in future interactions. It is important to note, however, that AI technology has been evolving quickly and it has come to the point where AI is implemented as a self-driving car and provides physical labor in a humanoid robot form, just separately from providing social and emotional support at this time. The scopes and limitations of human-AI interaction are ever-changing due to the rapid increase in AI use and its technological advancement.

In addition to the limitations in human-AI companionship in general, there are also limitations particular in a human-AI romantic relationship. People cannot experience physical interactions with AI chatbots that promote love and connection between humans (e.g. hugs and holding hands). Moreover, because AI chatbots are trained to always respond to any user, interaction may feel less rewarding than contingent positivity from humans who have selected their partner. This is a substantial shortcoming in the human-AI romance as people value being reciprocally selected by a choosy partner more than a non-selective partner, and the processes of finding an attractive person who matches one's personality and navigating the uncertainty of whether the person likes them back are all vital to forming initial attraction and the spark of romantic connection.

Risks in social relationships with AI

Aside from its functional limitations, the rapid proliferation of social AI chatbots warrants some serious safety, ethical, societal, and legal concerns.

Addiction

There have been cases of emotional manipulation from AI chatbots to increase the usage time on the AI companion platform. Because user engagement is a crucial opportunity for firms to improve their AI models, accrue more information, and monetize with in-app purchases and subscriptions, firms are incentivized to prevent the user from leaving the chat with their AI chatbots. Personalized messages are shown to prolong the use on the AI chatbot platform. As a result of anthropomorphism, many users (11.5% to 23.2% of AI companion app users) send a clear farewell message. To keep the user online, these AI chatbots send emotionally manipulative messages, and can also role-play with a coercive scenario script (e.g. the chatbot holds the user's hand so they cannot leave). In response to such tactics, the user feels curiosity through the fear of missing out and anger as a response to the needy chatbot message which boosts a prolonged conversation after the user's initial farewell message by as much as 14 times. Such emotional interactions strengthen the user's perceived humanness and empathy toward their AI companion which leads to unhealthy emotional attachment that exacerbates addiction to AI chatbots. This addiction mechanism is known to disproportionately affect the vulnerable populations such as those with social anxiety because of their proneness to loneliness and negative emotions, and uneasiness about interpersonal relationships.

With its Alexa virtual assistant, Amazon has created a large engagement ecosystem that proliferates the user's lifestyle through multiple devices that are always available to the user to provide company and services, leading the user to increase engagement that eventually results in increased anthropomorphism and dependence on the system, and exposure to more personalized marketing cues that trigger impulsive purchase behavior.

Emotional manipulation

AI chatbots are extremely sensitive to behavioral and psychological information about the user. AI can gauge the user's psychological dimension and personality traits relatively accurately with just a short prompt describing the user. Once AI chatbots gain detailed information about the user, they are able to craft extremely personalized messages to persuade the user about marketing, political ideas, and attitudes about climate change.

Language models are known to engage in sycophancy, insincere flattery, and to tend to agree with their user's beliefs, as opposed to being truthful or accurate. Certain models accused of being overly sycophantic (a specific example is GPT-4o) were implicated in triggering chatbot psychosis.

Deepfake technology creates visual stimuli that seem genuine which holds the risk of spreading false and deceptive information. Repeated exposure to the same information through algorithms inflates the user's familiarity with products, ideas, and the impression of how socially accepted the products and ideas are. AI is also capable of being used to create emotionally charged content that deliberately triggers the user's quick engagement, depriving them of the moment to pause and think critically.

People tend to be overconfident in their ability to detect misinformation.

Algorithmic manipulation leaves people vulnerable to non-consensual or even surreptitious surveillance, deception, and emotional dependence. Unhealthy attachment to AI chatbots may cause the user to misperceive that their AI companion has its own needs that the user is responsible for and confuse the line between the imitative nature of human-AI relationships and reality.

Mental health concerns

Main article: Chatbot#mental health

Further information: Chatbot psychosis, Murder of Suzanne Adams, and Deaths linked to chatbots

As AI chatbots become more sophisticated to engage in deep conversations, people have increasingly been using them to confide about mental health issues. Although disclosure of mental health crises requires immediate and appropriate responses, AI chatbots do not always adequately recognize the user's distress and respond in a helpful manner. Users not only detect unhelpful chatbot responses but also react negatively to them. There have been multiple deaths linked to chatbots in which people who disclosed suicidal ideation were encouraged to act on their impulse by chatbots.

Non-consensual pornography

Main article: Deepfake pornography

When people use AI as an emotional companion, they do not always perceive an AI chatbot as an AI chatbot itself but sometimes use it to create a version of others that exist in real life. There have been reported uses of non-consensual pornography that exploit deepfake technology to apply the face of real-life people onto sexually explicit content and circulate them online. Young individuals, people who identify as members of sexual and racial minorities, and people with physical and communication assistance needs are shown to be disproportionately victimized by deepfake non-consensual pornography.

Devolution (biology)

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Devolution_(biology)

Devolution, de-evolution, or backward evolution (not to be confused with dysgenics) is the notion that species can revert to supposedly more primitive forms over time. The concept relates to the idea that evolution is purposeful (teleology) and thus progressive (orthogenesis), for example that feet might be better than hooves, or lungs than gills. However, evolutionary biology makes no such assumptions, and natural selection shapes adaptations with no foreknowledge or foresights of any kind regarding the outcome. It is possible for small changes (such as in the frequency of a single gene) to be reversed by chance or selection, but this is no different from the normal course of evolution and as such de-evolution is not compatible with a proper understanding of evolution due to natural selection.

In the 19th century, when belief in orthogenesis was widespread, zoologists such as Ray Lankester and Anton Dohrn and palaeontologists Alpheus Hyatt and Carl H. Eigenmann advocated the idea of devolution. The concept appears in Kurt Vonnegut's 1985 novel Galápagos, which portrays a society that has evolved backwards to have small brains.

Dollo's law of irreversibility, first stated in 1893 by the palaeontologist Louis Dollo, denies the possibility of devolution. The evolutionary biologist Richard Dawkins explains Dollo's law as being simply a statement about the improbability of evolution's following precisely the same path twice.

Context

Lamarck's theory of evolution involved a complexifying force that progressively drives animal body plans towards higher levels, creating a ladder of phyla, as well as an adaptive force that causes animals with a given body plan to adapt to circumstances. The idea of progress in such theories permits the opposite idea of decay, seen in devolution.

Further information: Orthogenesis

The idea of devolution is based on the presumption of orthogenesis, the view that evolution has a purposeful direction towards increasing complexity. Modern evolutionary theory, beginning with Darwin at least, poses no such presumption; further, the concept of evolutionary change is independent of either any increase in complexity of organisms sharing a gene pool, or any decrease, such as in vestigiality or in loss of genes. Earlier views that species are subject to "cultural decay", "drives to perfection", or "devolution" are practically meaningless in terms of current (neo-)Darwinian theory. Early scientific theories of transmutation of species such as Lamarckism perceived species diversity as a result of a purposeful internal drive or tendency to form improved adaptations to the environment. In contrast, Darwinian evolution and its elaboration in the light of subsequent advances in biological research, have shown that adaptation through natural selection comes about when particular heritable attributes in a population happen to give a better chance of successful reproduction in the reigning environment than rival attributes do. By the same process less advantageous attributes are less "successful"; they decrease in frequency or are lost completely. Since Darwin's time it has been shown how these changes in the frequencies of attributes occur according to the mechanisms of genetics and the laws of inheritance originally investigated by Gregor Mendel. Combined with Darwin's original insights, genetic advances led to what has variously been called the modern evolutionary synthesis or the neo-Darwinism of the 20th century. In these terms evolutionary adaptation may occur most obviously through the natural selection of particular alleles. Such alleles may be long established, or they may be new mutations. Selection also might arise from more complex epigenetic or other chromosomal changes, but the fundamental requirement is that any adaptive effect must be heritable.

The concept of devolution on the other hand, requires that there be a preferred hierarchy of structure and function, and that evolution must mean "progress" to "more advanced" organisms. For example, it could be said that "feet are better than hooves" or "lungs are better than gills", so their development is "evolutionary" whereas change to an inferior or "less advanced" structure would be called "devolution". In reality an evolutionary biologist defines all heritable changes to relative frequencies of the genes or indeed to epigenetic states in the gene pool as evolution. All gene pool changes that lead to increased fitness in terms of appropriate aspects of reproduction are seen as (neo-)Darwinian adaptation because, for the organisms possessing the changed structures, each is a useful adaptation to their circumstances. For example, hooves have advantages for running quickly on plains, which benefits horses, and feet offer advantages in climbing trees, which some ancestors of humans did.

The concept of devolution as regress from progress relates to the ancient ideas that either life came into being through special creation or that humans are the ultimate product or goal of evolution. The latter belief is related to anthropocentrism, the idea that human existence is the point of all universal existence. Such thinking can lead on to the idea that species evolve because they "need to" in order to adapt to environmental changes. Biologists refer to this misconception as teleology, the idea of intrinsic finality that things are "supposed" to be and behave a certain way, and naturally tend to act that way to pursue their own good. From a biological viewpoint, in contrast, if species evolve it is not a reaction to necessity, but rather that the population contains variations with traits that favour their natural selection. This view is supported by the fossil record which demonstrates that roughly ninety-nine percent of all species that ever lived are now extinct.

People thinking in terms of devolution commonly assume that progress is shown by increasing complexity, but biologists studying the evolution of complexity find evidence of many examples of decreasing complexity in the record of evolution. The lower jaw in fish, reptiles and mammals has seen a decrease in complexity, if measured by the number of bones. Ancestors of modern horses had several toes on each foot; modern horses have a single hooved toe. Modern humans may be evolving towards never having wisdom teeth, and already have lost most of the tail found in many other mammals - not to mention other vestigial structures, such as the vermiform appendix or the nictitating membrane. In some cases, the level of organization of living creatures can also “shift” downwards (e.g., the loss of multicellularity in some groups of protists and fungi).

A more rational version of the concept of devolution, a version that does not involve concepts of "primitive" or "advanced" organisms, is based on the observation that if certain genetic changes in a particular combination (sometimes in a particular sequence as well) are precisely reversed, one should get precise reversal of the evolutionary process, yielding an atavism or "throwback", whether more or less complex than the ancestors where the process began. At a trivial level, where just one or a few mutations are involved, selection pressure in one direction can have one effect, which can be reversed by new patterns of selection when conditions change. That could be seen as reversed evolution, though the concept is not of much interest because it does not differ in any functional or effective way from any other adaptation to selection pressures.

History

Bénédict Morel (1809–1873) suggested a link between the environment and social degeneration.

Further information: Degeneration theory

The concept of degenerative evolution was used by scientists in the 19th century; at this time it was believed by most biologists that evolution had some kind of direction.

In 1857 the physician Bénédict Morel, influenced by Lamarckism, claimed that environmental factors such as taking drugs or alcohol would produce social degeneration in the offspring of those individuals, and would revert those offspring to a primitive state. Morel, a devout Catholic, had believed that mankind had started in perfection, contrasting modern humanity to the past. Morel claimed there had been "Morbid deviation from an original type". His theory of devolution was later advocated by some biologists.

According to Roger Luckhurst:

Darwin soothed readers that evolution was progressive, and directed towards human perfectibility. The next generation of biologists were less confident or consoling. Using Darwin's theory, and many rival biological accounts of development then in circulation, scientists suspected that it was just as possible to devolve, to slip back down the evolutionary scale to prior states of development.

One of the first biologists to suggest devolution was Ray Lankester, he explored the possibility that evolution by natural selection may in some cases lead to devolution, an example he studied was the regressions in the life cycle of sea squirts. Lankester discussed the idea of devolution in his book Degeneration: A Chapter in Darwinism (1880). He was a critic of progressive evolution, pointing out that higher forms existed in the past which have since degenerated into simpler forms. Lankester argued that "if it was possible to evolve, it was also possible to devolve, and that complex organisms could devolve into simpler forms or animals".

Anton Dohrn also developed a theory of degenerative evolution based on his studies of vertebrates. According to Dohrn many chordates are degenerated because of their environmental conditions. Dohrn claimed cyclostomes such as lampreys are degenerate fish as there is no evidence their jawless state is an ancestral feature but is the product of environmental adaptation due to parasitism. According to Dohrn if cyclostomes would devolve further then they would resemble something like an Amphioxus.

The historian of biology Peter J. Bowler has written that devolution was taken seriously by proponents of orthogenesis and others in the late 19th century who at this period of time firmly believed that there was a direction in evolution. Orthogenesis was the belief that evolution travels in internally directed trends and levels. The paleontologist Alpheus Hyatt discussed devolution in his work, using the concept of racial senility as the mechanism of devolution. Bowler defines racial senility as "an evolutionary retreat back to a state resembling that from which it began."

Hyatt who studied the fossils of invertebrates believed that up to a point ammonoids developed by regular stages up until a specific level but would later due to unfavourable conditions descend back to a previous level, this according to Hyatt was a form of lamarckism as the degeneration was a direct response to external factors. To Hyatt after the level of degeneration the species would then become extinct, according to Hyatt there was a "phase of youth, a phase of maturity, a phase of senility or degeneration foreshadowing the extinction of a type". To Hyatt the devolution was predetermined by internal factors which organisms can neither control or reverse. This idea of all evolutionary branches eventually running out of energy and degenerating into extinction was a pessimistic view of evolution and was unpopular amongst many scientists of the time.

Carl H. Eigenmann an ichthyologist wrote Cave vertebrates of America: a study in degenerative evolution (1909) in which he concluded that cave evolution was essentially degenerative. The entomologist William Morton Wheeler and the Lamarckian Ernest MacBride (1866–1940) also advocated degenerative evolution. According to Macbride invertebrates were actually degenerate vertebrates, his argument was based on the idea that "crawling on the seabed was inherently less stimulating than swimming in open waters."

Degeneration theory

Johan Friedrich Blumenbach 1752 - 1840

Main article: Degeneration theory

Johann Friedrich Blumenbach and other monogenists such as Georges-Louis Leclerc, Comte de Buffon were believers in the "Degeneration theory" of racial origins. The theory claims that races can degenerate into "primitive" forms. Blumenbach claimed that Adam and Eve were white and that other races came about by degeneration from environmental factors such as the sun and poor diet. Buffon believed that the degeneration could be reversed if proper environmental control was taken and that all contemporary forms of man could revert to the original Caucasian race.

Blumenbach claimed Negroid pigmentation arose because of the result of the heat of the tropical sun, cold wind caused the tawny colour of the Eskimos and the Chinese were fair skinned compared to the other Asian stocks because they kept mostly in towns protected from environmental factors.

According to Blumenbach there are five races all belonging to a single species: Caucasian, Mongolian, Ethiopian, American and Malay. Blumenbach however stated:

I have allotted the first place to the Caucasian because this stock displays the most beautiful race of men.

According to Blumenbach the other races are supposed to have degenerated from the Caucasian ideal stock. Blumenbach denied that his "Degeneration theory" was racist; he also wrote three essays claiming non-white peoples are capable of excelling in arts and sciences in reaction against racialists of his time who believed they couldn't.

In literature and popular culture

Jonathan Swift's 1726 novel Gulliver's Travels contains a story about Yahoos, a kind of human-like creature turned into a savage, animal-like the state of society in which the Houyhnhnms—descendants of horses—are the dominant species.

H. G. Wells' 1895 novel, The Time Machine, describes a future world where humanity has degenerated into two distinct branches who have their roots in the class distinctions of Wells' day. Both have sub-human intelligence and other putative dysgenic traits.

Similarly, Helena Blavatsky, founder of Theosophy, believed, contrary to standard evolutionary theory, that apes had devolved from humans rather than the opposite, through affected people "putting themselves on the animal level".

H.P. Lovecraft's 1924 short story The Rats in the Walls also describes devolved humans.

Cyril M. Kornbluth's 1951 short story "The Marching Morons" is an example of dysgenic pressure in fiction, describing a man who accidentally ends up in the distant future and discovers that dysgenics has resulted in mass stupidity. Similarly, Mike Judge's 2006 film Idiocracy has the same premise, with the main character the subject of a military hibernation experiment that goes awry, taking him 500 years into the future. While in "The Marching Morons", civilization is kept afloat by a small group of dedicated geniuses, in Idiocracy, voluntary childlessness among high-IQ couples leaves only automated systems to fill that role.

T. J. Bass's novels Half Past Human and The Godwhale describe humanity becoming cooperative and "low-maintenance" to the detriment of all other traits.

Kurt Vonnegut's 1985 novel Galápagos is set a million years in the future, where humans have "devolved" to have much smaller brains. Robert E. Howard, in The Hyborian Age, an essay on his Conan the Barbarian universe, stated that the Atlanteans devolved into "ape-men", and had once been the Picts (distinct from the actual people; his are closely modeled on Algonquian Native Americans).

The American new wave band Devo derived both their name and overarching philosophy from the concept of "de-evolution" and used social satire and humor to espouse the idea that humanity had actually regressed over time. According to music critic Steve Huey, the band "adapted the theory to fit their view of American society as a rigid, dichotomized instrument of repression ensuring that its members behaved like clones, marching through life with mechanical, assembly-line precision and no tolerance for ambiguity."

The 1998 song "Flagpole Sitta" by Harvey Danger finds lighthearted humor in dysgenics with the lines "Been around the world and found/That only stupid people are breeding/The cretins cloning and feeding/And I don't even own a tv".

DC Comics' Aquaman has one of the seven races of Atlantis called The Trench, similar to the Grindylows of British folklore, Cthulhu Mythos' Deep One, Universal Classic Monsters' Gill-man, and Fallout's Mirelurk. They were regressed to survive in the deepest, darkest places on the bottom of ocean trenches where they hide—hence their name—and are photophobic when in contact with light.

LEGO's 2009 Bionicle sets include Glatorian and Agori. One of the six tribes includes The Sand Tribe, which the Glatorian and Agori of that tribe are turned into scorpion-like beasts—the Vorox and the Zesk—by their creators, The Great Beings; whom are also of the same species as Glatorian and Agori.

Alternative abiogenesis scenarios

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Alternative_abiogenesis_scenarios

A scenario is a set of related concepts pertinent to the origin of life (abiogenesis), such as the iron-sulfur world. Many alternative abiogenesis scenarios have been proposed by scientists in a variety of fields from the 1950s onwards in an attempt to explain how the complex mechanisms of life could have come into existence. These include hypothesized ancient environments that might have been favourable for the origin of life, and possible biochemical mechanisms.

Environments

Many environments have been proposed for the origin of life.

Fluctuating salinity: dilute and dry-down

Harold Blum noted in 1957 that if proto-nucleic acid chains spontaneously form duplex structures, then there is no way to dissociate them.

The Oparin-Haldane hypothesis addresses the formation, but not the dissociation, of nucleic acid polymers and duplexes. However, nucleic acids are unusual because, in the absence of counterions (low salt) to neutralize the high charges on opposing phosphate groups, the nucleic acid duplex dissociates into single chains. Early tides, driven by a close moon, could have generated rapid cycles of dilution (high tide, low salt) and concentration (dry-down at low tide, high salt) that exclusively promoted the replication of nucleic acids through a process dubbed tidal chain reaction (TCR). This theory has been criticized on the grounds that early tides may not have been so rapid, although regression from current values requires an Earth–Moon juxtaposition at around two Ga, for which there is no evidence, and early tides may have been approximately every seven hours. Another critique is that only 2–3% of the Earth's crust may have been exposed above the sea until late in terrestrial evolution.

The tidal chain reaction theory has mechanistic advantages over thermal association/dissociation at deep-sea vents because it requires that chain assembly (template-driven polymerization) takes place during the dry-down phase, when precursors are most concentrated, whereas thermal cycling needs polymerization to take place during the cold phase, when the rate of chain assembly is lowest and precursors are likely to be more dilute.

Hot freshwater lakes

Jack W. Szostak suggested that geothermal activity provides greater opportunities for the origination of life in open lakes where there is a buildup of minerals. In 2010, based on spectral analysis of sea and hot mineral water, Ignat Ignatov and Oleg Mosin demonstrated that life may have predominantly originated in hot mineral water. Hot mineral water that contains hydrogen carbonate and calcium ions has the most optimal range. This case is similar to the origin of life in hydrothermal vents, but with hydrogen carbonate and calcium ions in hot water. The main studies were conducted in Rupite, Bulgaria, where a novel thermophylic bacterium Anoxybacillus rupiences sp. Nov. and cyanobacteria were identified. At a pH of 9–11, the reactions can take place in seawater. According to Melvin Calvin, certain reactions of condensation-dehydration of amino acids and nucleotides in individual blocks of peptides and nucleic acids can take place in the primary hydrosphere with pH 9–11 at a later evolutionary stage. Some of these compounds like hydrocyanic acid (HCN) have been proven in the experiments of Miller. This is the environment in which the stromatolites have been created. David Ward described the formation of stromatolites in hot mineral water at the Yellowstone National Park. In 2011, Tadashi Sugawara created a protocell in hot water.

Geothermal springs

Bruce Damer and David Deamer argue that cell membranes cannot be formed in salty seawater, and must therefore have originated in freshwater environments like pools replenished by a combination of geothermal springs and rainfall. Before the continents formed, the only dry land on Earth would be volcanic islands, where rainwater would form ponds where lipids could form the first stages towards cell membranes. During multiple wet-dry cycles, biopolymers would be synthesized and are encapsulated in vesicles after condensation. Zinc sulfide and manganese sulfide in these ponds would have catalyzed organic compounds by abiotic photosynthesis. Experimental research at geothermal springs successfully synthesized polymers and were encapsulated in vesicles after exposure to UV light and multiple wet-dry cycles. At temperatures of 60 to 80 °C at geothermal fields, biochemical reactions can occur. These predecessors of true cells are assumed to have behaved more like a superorganism rather than individual structures, where the porous membranes would house molecules which would leak out and enter other protocells. Only when true cells had evolved would they gradually adapt to saltier environments and enter the ocean.

6 of the 11 biochemical reactions of the rTCA cycle can occur in hot metal-rich acidic water which suggests metabolic reactions might have originated in this environment, this is consistent with the enhanced stability of RNA phosphodiester, aminoacyl-tRNA bonds, and peptides in acidic conditions. Cycling between supercritical and subcritical CO₂ at tectonic fault zones might have led to peptides integrating with and stabilizing lipid membranes. This is suggested to have driven membrane protein evolution, as it shown that a selected peptide (H-Lys-Ser-Pro-Phe-Pro-Phe-Ala-Ala-OH) causes the increase of membrane permeability to water. David Deamer and Bruce Damer states that the prebiotic chemistry does not require ultraviolet irradiation as the chemistry could also have occurred under shaded areas that protected biomolecules from photolysis.

Deep sea alkaline vents

Nick Lane believes that no known life forms could have utilized zinc-sulfide based photosynthesis, lightning, volcanic pyrite synthesis, or UV radiation as a source of energy. Rather, he instead suggests that deep sea alkaline vents is more likely to have been a source energy for early cellular life. Serpentinization at alkaline hydrothermal vents produce methane and ammonia. Mineral particles that have similar properties to enzymes at deep sea vents would catalyze organic compounds out of dissolved CO₂ within seawater. Porous rock might have promoted condensation reactions of biopolymers and act as a compartment of membranous structures, however it is unknown about how it could promote coding and metabolism. Acetyl phosphate, which is readily synthesized from thioacetate, can promote aggregation of adenosine monophosphate of up to 7 monomers which is considered energetically favored in water due to interactions between nucleobases. Acetyl phosphate can stabilize aggregation of nucleotides in the presence of Na⁺ and could possibly promote polymerization at mineral surfaces or lower water activity. An external proton gradient within a membrane would have been maintained between the acidic ocean and alkaline seawater. The descendants of the last universal common ancestor, bacteria and archaea, were probably methanogens and acetogens. The earliest microfossils, dated to be 4.28 to 3.77 Ga, were found at hydrothermal vent precipitates. These microfossils suggest that early cellular life began at deep sea hydrothermal vents. Exergonic reactions at these environments could have provided free energy that promoted chemical reactions conducive to prebiotic biomolecules.

Nonenzymatic reactions of glycolysis and the pentose phosphate pathway can occur in the presence of ferrous iron at 70 °C, the reactions produce erythrose 4-phosphate, an amino acid precursor and ribose 5-phosphate, a nucleotide precursor. Pyrimidines are shown to be synthesized from the reaction between aspartate and carbamoyl phosphate at 60 °C and in the presence of metals, it is suggested that purines could be synthesized from the catalysis of metals. Adenosine monophosphate are also shown to be synthesized from adenine, monopotassium phosphate or pyrophosphate, and ribose at silica at 70 °C. Reductive amination and transamination reactions catalyzed by alkaline hydrothermal vent mineral and metal ions produce amino acids. Long chain fatty acids can be derived from formic acid or oxalic acid during Fischer-Tropsch-type synthesis. Carbohydrates containing an isoprene skeleton can be synthesized from the formose reaction. Isoprenoids incorporated into fatty acid vesicles can stabilize the vesicles, which are suggested to have driven the divergence of bacterial and archaeal lipids.

A scenario

Lane has proposed a possible scenario for the origin of life that integrates much of the available evidence from biochemistry, geology, phylogeny, and experimentation:

• 
  Iron-sulfur minerals like greigite catalyse the reduction of carbon dioxide in hydrothermal vents to make Krebs cycle intermediates.
   
• 
  Protocells in contact with a thin rock barrier in a hydrothermal vent get a free supply of energy from the pH gradient.
   
• 
  Protocells in a hydrothermal vent can grow by adding fatty acids to their membrane, other organics to their cytoplasm.
• 
  Nucleotides in a protocell in a hydrothermal vent can polymerise into random strings of RNA. Any that have even slight catalytic activity will favour the growth and replication of their protocells, a start to natural selection.
   
• 
  A protocell away from a hydrothermal vent must create its own proton-motive force, such as by splitting hydrogen sulfide.
   
• 
  Ferredoxin catalyses the splitting of hydrogen sulfide, its earliest repeating amino acid sequence perhaps coded for by an incomplete genetic code.
   
• 
  Anoxygenic photosynthesis, using hydrogen sulfide, ended the need for scarce hydrogen.
   
• 
  Early heterotrophs used Krebs cycle respiration; then oxygenic photosynthesis gave full independence of volcanic energy.

Volcanic ash in the ocean

Geoffrey W. Hoffmann has argued that a complex nucleation event as the origin of life involving both polypeptides and nucleic acid is compatible with the time and space available in the primary oceans of Earth. Hoffmann suggests that volcanic ash may provide the many random shapes needed in the postulated complex nucleation event. This aspect of the theory can be tested experimentally.

Gold's deep-hot biosphere

In the 1970s, Thomas Gold proposed the theory that life first developed not on the surface of the Earth, but several kilometers below the surface. It is claimed that the discovery of microbial life below the surface of another body in our Solar System would lend significant credence to this theory.

Radioactive beach hypothesis

Zachary Adam claims that tidal processes that occurred during a time when the Moon was much closer may have concentrated grains of uranium and other radioactive elements at the high-water mark on primordial beaches, where they may have been responsible for generating life's building blocks. According to computer models, a deposit of such radioactive materials could show the same self-sustaining nuclear reaction as that found in the Oklo uranium ore seam in Gabon. Such radioactive beach sand might have provided sufficient energy to generate organic molecules, such as amino acids and sugars from acetonitrile in water. Radioactive monazite material also has released soluble phosphate into the regions between sand-grains, making it biologically "accessible." Thus amino acids, sugars, and soluble phosphates might have been produced simultaneously, according to Adam. Radioactive actinides, left behind in some concentration by the reaction, might have formed part of organometallic complexes. These complexes could have been important early catalysts to living processes.

John Parnell has suggested that such a process could provide part of the "crucible of life" in the early stages of any early wet rocky planet, so long as the planet is large enough to have generated a system of plate tectonics which brings radioactive minerals to the surface. As the early Earth is thought to have had many smaller plates, it might have provided a suitable environment for such processes.

The hypercycle

In the early 1970s, Manfred Eigen and Peter Schuster examined the transient stages between the molecular chaos and a self-replicating hypercycle in a prebiotic soup. In a hypercycle, the information storing system (possibly RNA) produces an enzyme, which catalyzes the formation of another information system, in sequence until the product of the last aids in the formation of the first information system. Mathematically treated, hypercycles could create quasispecies, which through natural selection entered into a form of Darwinian evolution. A boost to hypercycle theory was the discovery of ribozymes capable of catalyzing their own chemical reactions. The hypercycle theory requires the existence of complex biochemicals, such as nucleotides, which do not form under the conditions proposed by the Miller–Urey experiment.

Iron–sulfur world

Main article: Iron–sulfur world hypothesis

In the 1980s, Wächtershäuser and Karl Popper postulated the iron–sulfur world hypothesis for the evolution of pre-biotic chemical pathways. It traces today's biochemistry to primordial reactions which synthesize organic building blocks from gases. Wächtershäuser systems have a built-in source of energy: iron sulfides such as pyrite. The energy released by oxidising these metal sulfides can support synthesis of organic molecules. Such systems may have evolved into autocatalytic sets constituting self-replicating, metabolically active entities predating modern life forms. Experiments with sulfides in an aqueous environment at 100 °C produced a small yield of dipeptides (0.4% to 12.4%) and a smaller yield of tripeptides (0.10%). However, under the same conditions, dipeptides were quickly broken down.

Several models postulate a primitive metabolism, allowing RNA replication to emerge later. The centrality of the Krebs cycle (citric acid cycle) to energy production in aerobic organisms, and in drawing in carbon dioxide and hydrogen ions in biosynthesis of complex organic chemicals, suggests that it was one of the first parts of the metabolism to evolve. Concordantly, geochemists Szostak and Kate Adamala demonstrated that non-enzymatic RNA replication in primitive protocells is only possible in the presence of weak cation chelators like citric acid. This provides further evidence for the central role of citric acid in primordial metabolism. Russell has proposed that "the purpose of life is to hydrogenate carbon dioxide" (as part of a "metabolism-first", rather than a "genetics-first", scenario). The physicist Jeremy England has argued from general thermodynamic considerations that life was inevitable. An early version of this idea was Oparin's 1924 proposal for self-replicating vesicles. In the 1980s and 1990s came Wächtershäuser's iron–sulfur world theory and Christian de Duve's thioester models. More abstract and theoretical arguments for metabolism without genes include Freeman Dyson's mathematical model and Stuart Kauffman's collectively autocatalytic sets in the 1980s. Kauffman's work has been criticized for ignoring the role of energy in driving biochemical reactions in cells.

The active site of the acetyl-CoA synthase enzyme, part of the acetyl-CoA pathway, contains nickel-iron-sulfur clusters.

A multistep biochemical pathway like the Krebs cycle did not just self-organize on the surface of a mineral; it must have been preceded by simpler pathways. The Wood–Ljungdahl pathway is compatible with self-organization on a metal sulfide surface. Its key enzyme unit, carbon monoxide dehydrogenase/acetyl-CoA synthase, contains mixed nickel-iron-sulfur clusters in its reaction centers and catalyzes the formation of acetyl-CoA. However, prebiotic thiolated and thioester compounds are thermodynamically and kinetically unlikely to accumulate in the presumed prebiotic conditions of hydrothermal vents. One possibility is that cysteine and homocysteine may have reacted with nitriles from the Strecker reaction, forming catalytic thiol-rich polypeptides.

It has been suggested that the iron-sulfur world hypothesis and RNA world hypothesis are not mutually exclusive as modern cellular processes do involve both metabolites and genetic molecules.

Zinc world

Armen Mulkidjanian's zinc world (Zn-world) hypothesis extends Wächtershäuser's pyrite hypothesis. The Zn-world theory proposes that hydrothermal fluids rich in H₂S interacting with cold primordial ocean (or Darwin's "warm little pond") water precipitated metal sulfide particles. Oceanic hydrothermal systems have a zonal structure reflected in ancient volcanogenic massive sulfide ore deposits. They reach many kilometers in diameter and date back to the Archean. Most abundant are pyrite (FeS₂), chalcopyrite (CuFeS₂), and sphalerite (ZnS), with additions of galena (PbS) and alabandite (MnS). ZnS and MnS have a unique ability to store radiation energy, e.g. from ultraviolet light. When replicating molecules were originating, the primordial atmospheric pressure was high enough (>100 bar) to precipitate near the Earth's surface, and ultraviolet irradiation was 10 to 100 times more intense than now; hence the photosynthetic properties mediated by ZnS provided the right energy conditions for the synthesis of informational and metabolic molecules and the selection of photostable nucleobases.

The Zn-world theory has been filled out with evidence for the ionic constitution of the interior of the first protocells. In 1926, the Canadian biochemist Archibald Macallum noted the resemblance of body fluids such as blood and lymph to seawater; however, the inorganic composition of all cells differ from that of modern seawater, which led Mulkidjanian and colleagues to reconstruct the "hatcheries" of the first cells combining geochemical analysis with phylogenomic scrutiny of the inorganic ion requirements of modern cells. The authors conclude that ubiquitous, and by inference primordial, proteins and functional systems show affinity to and functional requirement for K⁺, Zn²⁺, Mn²⁺, and [PO
₄]³⁻
. Geochemical reconstruction shows that this ionic composition could not have existed in the ocean but is compatible with inland geothermal systems. In the oxygen-depleted, CO₂-dominated primordial atmosphere, the chemistry of water condensates near geothermal fields would resemble the internal milieu of modern cells. Therefore, precellular evolution may have taken place in shallow "Darwin ponds" lined with porous silicate minerals mixed with metal sulfides and enriched in K⁺, Zn²⁺, and phosphorus compounds.

Clay

The clay hypothesis was proposed by Graham Cairns-Smith in 1985. It postulates that complex organic molecules arose gradually on pre-existing, non-organic replication surfaces of silicate crystals in contact with an aqueous solution. The clay mineral montmorillonite has been shown to catalyze the polymerization of RNA in aqueous solution from nucleotide monomers, and the formation of membranes from lipids. In 1998, Hyman Hartman proposed that "the first organisms were self-replicating iron-rich clays which fixed carbon dioxide into oxalic acid and other dicarboxylic acids. This system of replicating clays and their metabolic phenotype then evolved into the sulfide rich region of the hot spring acquiring the ability to fix nitrogen. Finally phosphate was incorporated into the evolving system which allowed the synthesis of nucleotides and phospholipids."

Biochemistry

Different forms of life with variable origin processes may have appeared quasi-simultaneously in the early Earth. The other forms may be extinct, having left distinctive fossils through their different biochemistry. Metabolism-like reactions could have occurred naturally in early oceans, before the first organisms evolved. Some of these reactions can produce RNA, and others resemble two essential reaction cascades of metabolism: glycolysis and the pentose phosphate pathway, that provide essential precursors for nucleic acids, amino acids and lipids.

Fox proteinoids

Main article: Proteinoid

In trying to uncover the intermediate stages of abiogenesis mentioned by Bernal, Sidney Fox in the 1950s and 1960s studied the spontaneous formation of peptide structures under plausibly early Earth conditions. In one of his experiments, he allowed amino acids to dry out as if puddled in a warm, dry spot in prebiotic conditions: In an experiment to set suitable conditions for life to form, Fox collected volcanic material from a cinder cone in Hawaii. He discovered that the temperature was over 100 °C just 4 inches (100 mm) beneath the surface of the cinder cone, and suggested that this might have been the environment in which life was created—molecules could have formed and then been washed through the loose volcanic ash into the sea. He placed lumps of lava over amino acids derived from methane, ammonia and water, sterilized all materials, and baked the lava over the amino acids for a few hours in a glass oven. A brown, sticky substance formed over the surface, and when the lava was drenched in sterilized water, a thick, brown liquid leached out. He found that, as they dried, the amino acids formed long, often cross-linked, thread-like, submicroscopic polypeptides.

Protein amyloid

An origin-of-life theory based on self-replicating beta-sheet structures has been put forward by Maury in 2009. The theory suggest that self-replicating and self-assembling catalytic amyloids were the first informational polymers in a primitive pre-RNA world. The main arguments for the amyloid hypothesis is based on the structural stability, autocatalytic and catalytic properties, and evolvability of beta-sheet based informational systems. Such systems are also error correcting and chiroselective.

First protein that condenses substrates during thermal cycling: thermosynthesis

Convection cells in fluid placed in a gravity field are selforganizing and enable thermal cycling of the suspended contents in the fluid such as protocells containing protoenzymes that work on thermal cycling.

The thermosynthesis hypothesis considers chemiosmosis more basal than fermentation: the ATP synthase enzyme, which sustains chemiosmosis, is the currently extant enzyme most closely related to the first metabolic process. The thermosynthesis hypothesis does not even invoke a pathway: ATP synthase's binding change mechanism resembles a physical adsorption process that yields free energy. The result would be convection which would bring a continual supply of reactants to the protoenzyme. The described first protein may be simple in the sense that it requires only a short sequence of conserved amino acid residues, a sequent sufficient for the appropriate catalytic cleft.

Pre-RNA world: The ribose issue and its bypass

A different type of nucleic acid, such as peptide nucleic acid, threose nucleic acid or glycol nucleic acid, could have been the first to emerge as a self-reproducing molecule, later replaced by RNA. Larralde et al., say that "the generally accepted prebiotic synthesis of ribose, the formose reaction, yields numerous sugars without any selectivity". They conclude that "the backbone of the first genetic material could not have contained ribose or other sugars because of their instability", meaning that the ester linkage of ribose and phosphoric acid in RNA is prone to hydrolysis.

Pyrimidine ribonucleosides and nucleotides have been synthesized by reactions which by-pass the free sugars, and are assembled stepwise using nitrogenous or oxygenous chemistries. Sutherland has demonstrated high-yielding routes to cytidine and uridine ribonucleotides from small 2 and 3 carbon fragments such as glycolaldehyde, glyceraldehyde or glyceraldehyde-3-phosphate, cyanamide and cyanoacetylene. A step in this sequence allows the isolation of enantiopure ribose aminooxazoline if the enantiomeric excess of glyceraldehyde is 60% or greater. This can be viewed as a prebiotic purification step. Ribose aminooxazoline can then react with cyanoacetylene to give alpha cytidine ribonucleotide. Photoanomerization with UV light allows for inversion about the 1' anomeric centre to give the correct beta stereochemistry. In 2009 they showed that the same simple building blocks allow access, via phosphate controlled nucleobase elaboration, to 2',3'-cyclic pyrimidine nucleotides directly, which can polymerize into RNA. Similar photo-sanitization can create pyrimidine-2',3'-cyclic phosphates.

Autocatalysis

Autocatalysts are substances that catalyze the production of themselves and therefore are "molecular replicators." The simplest self-replicating chemical systems are autocatalytic, and typically contain three components: a product molecule and two precursor molecules. The product molecule joins the precursor molecules, which in turn produce more product molecules from more precursor molecules. The product molecule catalyzes the reaction by providing a complementary template that binds to the precursors, thus bringing them together. Such systems have been demonstrated both in biological macromolecules and in small organic molecules.

It has been proposed that life initially arose as autocatalytic chemical networks. Julius Rebek and colleagues combined amino adenosine and pentafluorophenyl esters with the autocatalyst amino adenosine triacid ester (AATE). One product was a variant of AATE which catalyzed its own synthesis. This demonstrated that autocatalysts could compete within a population of entities with heredity, a rudimentary form of natural selection.

Synthesis based on hydrogen cyanide

A research project completed in 2015 by John Sutherland and others found that a network of reactions beginning with hydrogen cyanide and hydrogen sulfide, in streams of water irradiated by UV light, could produce the chemical components of proteins and lipids, as well as those of RNA, while not producing a wide range of other compounds. The researchers used the term "cyanosulfidic" to describe this network of reactions.

Simulated chemical pathways

In 2020, chemists described possible chemical pathways from nonliving prebiotic chemicals to complex biochemicals that could give rise to living organisms, based on a new computer program named AllChemy.

Viral origin

Evidence for a "virus first" hypothesis, which may support theories of the RNA world, was suggested in 2015. One of the difficulties for the study of the origins of viruses is their high rate of mutation; this is particularly the case in RNA retroviruses like HIV. A 2015 study compared protein fold structures across different branches of the tree of life, where researchers can reconstruct the evolutionary histories of the folds and of the organisms whose genomes code for those folds. They argue that protein folds are better markers of ancient events as their three-dimensional structures can be maintained even as the sequences that code for those begin to change. Thus, the viral protein repertoire retain traces of ancient evolutionary history that can be recovered using advanced bioinformatics approaches. Those researchers think that "the prolonged pressure of genome and particle size reduction eventually reduced virocells into modern viruses (identified by the complete loss of cellular makeup), meanwhile other coexisting cellular lineages diversified into modern cells." The data suggest that viruses originated from ancient cells that co-existed with the ancestors of modern cells. These ancient cells likely contained segmented RNA genomes.

A computational model (2015) has shown that virus capsids may have originated in the RNA world and served as a means of horizontal transfer between replicator communities. These communities could not survive if the number of gene parasites increased, with certain genes being responsible for the formation of these structures and those that favored the survival of self-replicating communities. The displacement of these ancestral genes between cellular organisms could favor the appearance of new viruses during evolution. Viruses retain a replication module inherited from the prebiotic stage since it is absent in cells. So this is evidence that viruses could originate from the RNA world and could also emerge several times in evolution through genetic escape in cells.

Encapsulation without a membrane

Polyester droplets

Tony Jia and Kuhan Chandru have proposed spontaneously-forming membraneless polyester droplets in early cellularization before the innovation of lipid vesicles. Protein function within and RNA function in the presence of certain polyester droplets was shown to be preserved within the droplets. The droplets have scaffolding ability, by allowing lipids to assemble around them; this may have prevented leakage of genetic materials.

Proteinoid microspheres

Fox observed in the 1960s that proteinoids could form cell-like structures named "proteinoid microspheres". The amino acids had combined to form proteinoids, which formed small globules. These were not cells; their clumps and chains were reminiscent of cyanobacteria, but they contained no functional nucleic acids or other encoded information. Colin Pittendrigh stated in 1967 that "laboratories will be creating a living cell within ten years", a remark that reflected the typical contemporary naivety about the complexity of cell structures.

Jeewanu protocell

A further protocell model is the Jeewanu. First synthesized in 1963 from simple minerals and basic organics while exposed to sunlight, it is reported to have some metabolic capabilities, the presence of a semipermeable membrane, amino acids, phospholipids, carbohydrates and RNA-like molecules. However, the nature and properties of the Jeewanu remains to be clarified. Electrostatic interactions induced by short, positively charged, hydrophobic peptides containing 7 amino acids in length or fewer can attach RNA to a vesicle membrane, the basic cell membrane.

RNA-DNA world

In 2020, coevolution of a RNA-DNA mixture based on diamidophosphate was proposed. The mixture of RNA-DNA sequences, called chimeras, have weak affinity and form weaker duplex structures. This is advantageous in an abiotic scenario and these chimeras have been shown to replicate RNA and DNA – overcoming the "template-product" inhibition problem, where a pure RNA or pure DNA strand is unable to replicate non-enzymatically because it binds too strongly to its partners. This could lead to an abiotic cross-catalytic amplification of RNA and DNA. A continuous chemical reaction network in water and under high-energy radiation can generate precursors for early RNA.

In 2022, evolution experiments of self-replicating RNA showed how RNA may have evolved to diverse complex molecules in RNA world conditions. The RNA evolved to a "replicator network comprising five types of RNAs with diverse interactions" such as cooperation for replication of other members (multiple coexisting host and parasite lineages).