Can the 'hard steps' in the evolutionary history of human intelligence be recast with geological thresholds?

[Jim__]

From phys.org

The timeline of the hard steps in Earth's past that research discussed in this article builds on, reanalyzes and augments. Not shown is the era about a billion years in the future where all life on Earth will become extinct. Credit: Daniel B. Mills
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What took so long for humans to appear on Earth? The Earth is 4.6 billion years old, and life began about 4 billion years ago, yet humans—the only intelligent, technological species we know of in the universe—have existed only for the last 200,000 years. Why didn't we come sooner? What factor(s) delayed our appearance? And what can life's timeline here say about the possibility of other technologically advanced lifeforms in the universe?

One hypothesis of our evolutionary history is the "hard steps" model. In 1983, the Australian physicist Brandon Carter hypothesized that the path to humanity required "successful passage through a number of intermediate steps," each of which was very improbable and difficult given the time that had been available. Originally, Carter saw only two steps—the origin of the genetic code, and "the final breakthrough in cerebral development."

Many researchers have since modified Carter's idea and proposed more than two steps, with the most popular formulation of the model today envisioning five: 1) the creation of single celled life ( "abiogenesis" ), 2) the appearance of photosynthesis that creates oxygen, 3) the emergence of eukaryotic cells from prokaryotic cells, 4) the emergence of complex life, such as multicellular animals, and 5) the rise of Homo sapiens with an established language.

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So the question arises if intelligent, technological animals like us developed on Earth only late in the time available, cutting it close. Would the same fate befall any advanced extraterrestrial life elsewhere in the galaxy? Might they have developed too late in their sun's timespan to get to Earth? The hard steps model thus predicts that technological species such as humans on Earth are exceedingly rare in the universe.

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[PoindexterOglethorpe]

1. For what it's worth,

My Son The Astronomer tells me that many astronomers think we humans actually got here pretty fast, and may well be the first (and so far only) technological civilization in the galaxy.

[hunter]

2. How are humans any different than, say, ants? Or beetles?

What makes us humans so "special?"

In the past people often claimed that humans are special because some omnipotent god created us and watches over us. The universe was very small then.

That's not an acceptable position for scientific research today so now we humans are special because we say we are.

It's likely our species will never have any external confirmation of our supposed "intelligence" or other special qualities. This planet has seen many innovative species come and go. Most species become extinct.

Whether we believe in gods or hypothetical space aliens, we're not looking at the problem from a realistic perspective..

I find studies like this frustrating and fruitless.

wikipedia

[Jim__]

3. Two points that were not clear just based on my excerpt.

The first paper is talking about technological life - life that will have technosignatures - something it expects to be rare based on its model.

The abstract from this paper:

We use the critical step model to study the major transitions in evolution on Earth. We
find that a total of five steps represents the most plausible estimate, in agreement with previous
studies, and use the fossil record to identify the potential candidates. We apply the model to
Earth-analogs around stars of different masses by incorporating the constraints on habitability
set by stellar physics including the habitable zone lifetime, availability of ultraviolet radiation for
prebiotic chemistry, and atmospheric escape. The critical step model suggests that the habitability
of Earth-analogs around M-dwarfs is significantly suppressed. The total number of stars with
planets containing detectable biosignatures of microbial life is expected to be highest for K-
dwarfs. In contrast, we find that the corresponding value for intelligent life (technosignatures)
should be highest for solar-mass stars. Thus, our work may assist in the identification of suitable
targets in the search for biosignatures and technosignatures.

The second paper - the current paper - disagrees with the first paper, and is more generally concerned with evolutionary processes. An excerpt from this paper:

According to Carter, a hard (or critical) step must be both 1) essential to the evolutionary
emergence of any given trait or organism, and 2) improbable with respect to the externally
allotted time (1, 2). Throughout his publications, Carter variously and interchangeably referred to
the “emergence of civilization” (1), “the emergence of intelligent observers such as ourselves”
(2), and “the evolution of what we recognize as intelligent life” (4) as the evolutionary
innovation whose probability was ultimately in question. While the origin of a “scientific
civilization such as our own” (1) and “the emergence of intelligent life” (4) more generally
represent distinct evolutionary events in the history of life on Earth (that is, the origin of human
civilization vs. the origin of Homo sapiens, respectively), the hard-steps model can be applied
equally – as Carter phrased it – to any given “stage of advancement” (1), including “less
‘advanced’ stages of development” (2). While this language, betraying non-Darwinian notions of
evolution as a linear ‘ascent’ from lower to higher degrees of ‘advancement’ (27), is perhaps too
reminiscent of the Great Chain of Being for most modern evolutionary biologists to accept (28),
Carter nevertheless rejected so-called ‘progressive’ notions of evolution (with humans at the top)
as “unduly anthropocentric?? (1). Indeed, like the anthropic principle itself, the hard-steps model
is applicable to humans and non-human entities alike – notably, extraterrestrial organisms (1), as
well as any organism that has existed or will exist on Earth. In the various applications of the
hard-steps model by other authors, the focus has primarily been on humans or H. sapiens (7, 11),
“intelligent life” (9, 18), and “observerhood” (12). Others adopted a more operational approach
relevant to the field of SETI (the search for extraterrestrial intelligence), defining intelligence as
“the building of radio telescopes” (8) or life capable of manufacturing detectable
“technosignatures” (17). In general, “intelligence” has no standard definition, and arguably
agency (the capacity to deliberately change one's environment) and cognition (knowing how to
perform these changes and reflecting on them) are more relevant traits for SETI (29). For our
purposes, we are concerned with the existence of evolutionary transitions and processes (so-
called “steps”) that were both improbable (relative to 𝜏0) and essential to the evolutionary origin
of H. sapiens on Earth (since we are the self-reflective observers communicating about our own
observations). While this effort concerns SETI, it applies equally to understanding evolutionary
timescales on Earth (30), as well as how life in general may unfold on worlds beyond Earth.

[hunter]

4. What can anyone discern from a sample size of one?

SETI is pure fantasy until the moment they say "hello."

Humans have a very poor track record when it comes to recognizing the intelligence and high technologies of others, even within our own species.