Why did it take so long to produce us?

Johninch

I am trying to understand why, if the first life on earth appeared so soon after the Hadean between 4 and 3.5 billion years ago, its development since then has been so slow. The fact that life appeared so soon, suggests that the prevailing conditions were favorable. So why didn’t those conditions lead to a faster evolutionary development? Am I perhaps underestimating the difference in complexity between a self replicating RNA strand and a living cell?

Still, it took 3 billion years to produce just sponges, corals, and anemones, before the first sea-based life forms ventured onto the land, which is a really huge lapse of time. It then took another nearly 500 million years to produce primates. Genus homo has existed for only about 2.5 million years or about 0.06% of Earth’s history, and nearly all of that has been spent living more or less like erect monkeys. Is it not the case that homo sapiens nearly didn’t evolve at all?

Big climatic changes, asteroid impacts and vulcanism can represent setbacks, but they only represent setbacks if there was progress to set back.

There have been many long periods of excellent conditions for intelligent life, but all we ever got was a huge amount of unintelligent diversity, until now, after 4 billion years. If brain based intelligence is only a further development of the sense organs, I wonder why it took so long to evolve large sophisticated brains, considering the advantages of intelligence for survival and proliferation.

Ouabache wrote in another thread (a few years ago):

“Certainly lower life forms (microbes and insects) will adapt more easily to severe stresses on the environment. Because of their shorter life cycles, they respond more quickly to these stresses. This is due to a faster accumulation of beneficial mutations. If the air and land become too inhospitable, life will continue to adapt under water.”

In view of this, I have some questions about evolution:

1. Apart from the reproduction rate, what are the other most important factors which drive the frequency of genetic mutations?
2. If lower life forms mutate faster under stress, does this mean that a certain amount of stress should lead to higher life forms?
3. Why do higher life forms tend to have lower reproduction rates, which is detrimental to their proliferation?
4. In more complex life forms, does the mutation process have a higher or lower chance to be beneficial than in simpler life forms?

I don’t know if the answers to these questions may help to explain why it took so long for us to get here. Otherwise, what is the reason? Or, if no particular reason, could it easily have happened much sooner, in the conditions actually prevailing on Earth, or are we deluded in our thinking that this is the perfect Goldilocks planet?

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Evo

I would suggest that you first read the sticky on Evolution. There area a number of sources linked, read those also.

http://www.physicsforums.com/showthread.php?t=543950

Then if you still have questions, you can fine tune them.

Ygggdrasil

The question takes as its premise that a goal of evolution was to produce intelligent life (i.e. us). This is certainly a very human-centric view of biology. Perhaps when we consider that our bodies carry more bacterial cells than human cells we should rethink which species is the more successful one. Maybe we're nothing more than glorified portable bacterial incubators.

Interestingly you point to asteroid impacts as a setback to "progress" (whatever than means in an evolutionary sense as evolution has no set goal toward which to progress), whereas it seems likely that the asteroid impact that led to the extinction of the dinosaurs allowed mammals to populate the spaces once dominated by the dinosaurs, leading to the diversification of mammalian species. Indeed, there are many instances in the history of the Earth where a mass extinction event has allowed rapid evolutionary change as species once confined to small niches have been allowed to flourish and diversify. So to some extent, the timing of evolutionary "progress" is dependent on completely random events or on changes to environmental factors.

AlephZero

The simple answer is that "us" is what evolution happens to have produced so far. If the process had worked quicker or slower, "us" would be something different from what "we" actually are.

Johninch

You’re both right, I’m taking a human-centric view. I also agree that the Earth wasn’t created for us and neither did evolution have us in mind.

Fact is, WE are the ones who are classing the Earth as a Goldilocks planet.

In my end question which I am driving at is this: if this is a Goldilocks planet, which took 4 bn years to produce us, can we expect similar planets in other solar systems to take as long, or, can we identify the evolutionary factors which have caused the huge delay?

I am viewing this question in connection with the Fermi Paradox.

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mfb

I don't think there was a huge "delay" on earth. Over the whole time, life changed, species aquired more and more useful features and got rid of others.

On the other hand, with just one example of evolving life, it is hard to know the "usual" timescale for human-scale intelligence (if that timescale exists at all). 4 billion years is a obvious choice for a guess, maybe corrected to higher values due to the absence of alien life on earth.
Those catastrophes speed up changes in life.
Just compare yourself to a monkey, and you see many differences as a result of ours and their evolution.

Ygggdrasil

This question is related to a very old yet important question in evolutionary biology: if one were to replay the "tape of life" -- that is, to make identical copies of the primordial Earth and observe them over time -- would we obtain the same result every time? In other words, is evolution deterministic? Will systems with identical or near identical initial conditions follow similar trajectories or will random events cause these trajectories to wildly diverge?

Although we don't have any definitive answers to this question yet, an interesting experiment performed by Richard Lenski (discussed here) provides some insights into these questions. In 1988, Lenski founded 12 populations of genetically identical bacteria in a growth medium that contained only limited amounts of glucose (which the bacteria can use as a carbon source) but plentiful amounts of citrate (which the bacteria cannot use as a carbon source). After 31,500 generations only one of these populations (population #3) evolved the ability to metabolize citrate. The fact that all 12 populations did not evolve identically suggests that evolution does may not proceed deterministically. Furthermore, the study provided evidence that some random, non-adaptive mutations primed that population to evolve the ability to metabolize citrate. Since these mutations likely occurred by chance, these results suggest that the timing of when population #3 was able to evolve the ability to metabolize citrate was essentially stochastic.

Johninch

Many thanks for the link, which I also followed back to the previous thread, leading to Ken Shirriff’s blog and some very interesting information on cell structure and functionality.

It seems I was correct in thinking that the formation of the cell and it’s development was a very big step, considering its complexity now. The timeline of increasing complexity towards the human cell today is however not clear to me - to what extent has the human cell evolved as opposed to being inherited from ancestor species? Or to put it another way, to what extent does speciation depend on cell evolution? Here I mean the evolution of cell complexity other than genetic mutation of the DNA.

I have also been looking at Stephen Jay Gould on Punctuated Equilibrium (PE) versus Gradualism. Here I am not clear whether, when we refer to Darwinism we mean PE or Gradualism. It looks like Darwin changed his mind. Dawkin’s idea of Variable Speedism together with a locational Gradualism, is another possibility. Which theory has the best (fossil or other) evidence?

PE together with mfb’s statement in his post above that “catastrophes speed up changes in life” and as I read elsewhere “the capricious and sudden nature of some environmental changes … make evolution largely unpredictable”, plus the results of Lenski’s experiment, all suggest that the solution to Fermi’s Parodox has an important evolutionary-biological element. On the other hand, Simon Conway Morris said “evolutionary routes are many, but the destinations are limited”. Can I assume from this, that intelligence is a likely destination, even with another chemistry?

My interest at the moment is mainly the evolution of intelligence.

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Ryan_m_b

As far as I'm aware this "classification" isn't to do with the fact that sentient, tool users (us) evolved but that life formed.

As for why we evolved now simplistically the answer is because of our lineage. We could no more have evolved before we did than your great grandma could give birth to your grandson.

dschlink

The formation of life is a big step, which may be relatively likely. The formation of multicellular forms with specialized cells is another big step and might have formed out of biofilms. The third big step is the capture of energy-transforming bacteria (mitochondria) in cells, this is much less likely. As complexity increases, fewer and fewer mutations are beneficial, making each step less likely.

Think of the monkey/keyboard analogy: producing single words is more likely than sentences. Sentences are likely than stories.

mfb

The basic concept how cells work are nearly fixed in mammals (and similar in other groups) - you won't see big differences between muscle cells of a human and muscle cells of a cat, for example. More general, all species use DNA/RNA, and nearly all species use exactly the same genetic code and the same or very similar molecules to read, interpret and copy it.
This is a hint how difficult the evolution of those mechanisms is - most "good" mutations already happened in the past and got included in life, there is nearly no way to improve such basic things now without ruining anything else.
Only in environments where intelligence is useful, even if it evolves in small steps.

DiracPool

My opinion on the OP's question relates to Herbert Simon's book "The sciences of the artifical." One of the books principal arguments is that complex systems evolve through long periods of incremental gestations whereby a given system becomes robust enough to serve as a reliable foundation for the next, more hierarchically advanced but more tenuous addition to the structure to be built on top of it. In other words, if the guys laying the foundation of a building do not have their act together, the framers, the drywallers, and the roofers are superfluous. Therefore, if it takes a team of foundation layers 20 years to get their stuff right, well then the framers and the roofers are just gonna have to wait.

This is the same thing in evolution. In Biology, the cell is king. Its the cell that was hard to make, it took 3 bill years to do so. However, once we got a stable eukaryotic cell, things started happening fast from there starting with the Cambrain explosion.

Johninch

Since looking at the human cell in more detail, I can also see that it was very hard to make and needed a long time. Ok so I accept the 3 billion years for the first multicellular animal, although it’s an incredibly long time just for that, on a goldilocks planet.

Sure once we got the eukaryotic cell, things started happening less slowly than before, but I wouldn’t call 500 million years “fast”.

Still unimaginably long is that genus homo took 5 million years to produce us. There were some further developments necessary, such as increase in brain size and functionality, but after the appearance of homo sapiens 200’000 years ago, what else had to change? Basically nothing, yet for 190’000 years we just wondered around. Then suddenly 10’000 years ago without genetic change, the first civilisations started.

It seems that the species is incredibly sensitive to precise conditions of temperature and climate, far beyond what is catered for in the Drake Equation.
Either the development of intelligent life on Earth was inexplicably slow as was my opening thought, or the Fermi Paradox is no paradox at all – there’s hardly any other intelligent life in the galaxy.

Alternatively, Fermi was correct and the Earth is not the intelligence promoting biological paradise which it is assumed to be.

In this context I am talking about the development of advanced intelligence, which is likely to lead to scientific and technological progress. The only links to the advance of intelligence which I have found relate to health and nutrition and it is stated that there are no genetic links to intelligence in modern man. So is it correct that the biological factors leading to the state of science and technology today compared with say 1’000 years ago are mainly health and nutrition? Has there been intelligence-boosting selective breeding?

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Ygggdrasil

With respect to the development of civilization, it seems like the transition from nomadic hunter-gatherer societies to sedentary agrarian societies was due mostly to geographic and environmental factors, not any genetic changes. See the following discussion for more information: http://www.physicsforums.com/showthread.php?t=657768

mfb

If you could take a baby from 2000 years ago and let it grow up in our current society, you probably would not see any difference to humans born today. Scientific discoveries and cultural changes are dominant on that short timescale.

I don't understand that argument. The galaxy has many planets with an age of 5 billion years (or more).

Johninch

Thanks for the link to the other thread. Seems that my problem with the '190'000 years lack of progress' was well answered there.

Understood, thanks.

I consider that my questions have been substantially answered. Thanks everyone.

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etudiant

Hi Johninch,
Your question has become more topical because of the recent discovery that most stars appear to have planets. As it took minimal time for life to emerge on Earth( at most 200 million years after the Earth cooled enough to allow liquid water), we can assume that most other stars are also surrounded by life bearing planets. By contrast, intelligent life may be less than 100,000 years old on this planet, which suggests it is very rare indeed. ( Of course, there are reputable observers who do not believe intelligent life exists on this planet either, which if true would simple strengthen the argument.)
One conclusion may be that we are essentially alone in a galaxy teeming with life.
Another might be that whatever causes intelligence to arise is not likely to be discovered. It happens so rarely and we have no idea of what to look for.