Re: What other single species has caused a mass extinction (except possibly, as you say, the first oxygen producer)?

Something like that happens whenever there is a Genetic Takeover.

For example, probably at one point only one individual used DNA. Now all known life on Earth is descended from that individual - and all the RNA-based organisms have gone extinct.

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In fact I can only think of one sense in which multicellular organisms dominate:"A probably tiny initial lineage soon came to dominate the tiny tiny tiny tiny fraction of life on Earth that we humans find interesting to look at."

What other single species has caused a mass extinction (except possibly, as you say, the first oxygen producer)?

The relevant inequalities, it seems to me, are not of genetic or even memetic fitness but of power, as vague as that is.

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On that page, Gould says, among other things:

"total bacterial biomass (even at such minimal weight per cell) may exceed all the rest of life combined, even forest trees, once we include the subterranean populations as well"

- http://www.stephenjaygould.org/library/gould_bacteria.html

...but he offers no figures in support of this - and even if there were any, it would not support the assertion under discussion - since that refers to "unicellular organisms" and "orders of magnitude".

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Tim, Gould actually explicitly says that plant biomass is dominant; did you read the link or my comment?? From the perspective of diversity, however, bacteria (and maybe viruses) are clearly present in vast numbers. I could probably find some pop sci books if you want that kind of reference, but I don't know any off the top of my head. Metagenomics probably has the single best set of scientific references for the vast diversity of non-eukaryotes; here are some references, in increasing order of technical detail:


Sogin et al., http://www.pnas.org/cgi/con...

Venter's work, e.g.: http://www.sciencemag.org/c...; http://www.plosone.org/arti...

Note that in the Sargasso Sea work (Venter Science reference), approximately as many or more proteins were sampled from the Sargasso Sea as had previously been known from all previous bacterial work.

The Sogin work is particularly straightforward and surprising: by the standard (though arguable) definition of species in bacteria, there is a shocking amount of bacterial diversity present in the ocean. We still don't have a good upper OR lower estimate on the number of bacterial species, but every time we look at a new microbial niche we find 10s or 100s of thousands of different species.

The real problem, of course, is that this is an active area of research, so I can't give you hard and fast numbers: the field of microbial diversity is still figuring out the broad outline of what is out there and what it means. Heck, "diversity" by any of the old definitions (16s RNA, for example) may be the wrong way to think about true diversity, because there's at least some evidence that many of these bacteria don't do radically new things. (Many of them do, of course, but many of them don't :).


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Market processes may reduce this inequality even further - compared to the resources applied to invention, it seems far more resources are subsequently dedicated to "democratization" of demand.

To illustrate, if 1500 military export markets were well-developed, Zulu armies would certainly be cheaply kitted with firearms and stirrups by the time the British got round to visiting.

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Gould offers practically no support for the claim that unicellular organisms like bacteria and algae outmass other life forms on earth by orders of magnitude.

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Thanks for the welcome, HA!

Tim, here's a discussion of the biomass issue:


It seems pretty up-to-date. It's tough to find good research-level discussions of this stuff because it's in introductory textbooks in microbiology now, but Gould comes through!

From the perspective of diversity, we *know* that there are many more species and varieties of bacteria than any other type, class, or group of organisms; that's been evident for well over a decade and has been confirmed most spectacularly by the recent metagenomic studies by (among many others) Venter and the JGI. (The only possible exception is viruses, which occupy an uncomfortable niche in the biological hierarchy.)

Gould says that plant biomass outweights bacteria, which is no doubt correct. Diversity-wise, however, bacteria are far more "successful" than animals or plants.

As for Robin's generalizations -- I think the emergence of multicellularity certainly counts as a dramatic singularity event! (As does the CNS, probably, if he ever properly dates it :)


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Tim and Richard, my post today may address your issues.

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Re: "unicellular organisms like bacteria and algae outmass other life forms on earth by orders of magnitude."


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the divorcing of wealth production from amount of childrenThat's a restatement of the question, not an explanation. Perhaps you meant that children used to produce wealth, which would be misleading because the young were always net consumers of the previous generation's production (when the elderly become less productive they also consume less).

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Titus, great to see someone of your expertise posting here. My sense is we could use more biologists and biological scientists (particularly of your caliber) to balance out the amount of engineers and social scientists commenting freely on biological topics.

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Robin, I can't find the full text anywhere; any links?

I am particularly skeptical of the claim that "Then for the next half billion years animal brain sizes doubled roughly every thirty million years". We estimate the vertebrate lineage -- the first lineage where we can clearly pinpoint a central nervous system that is ancestral to mammalian CNS -- to have originated approx 350 mya. Brain sizes in vertebrates vary considerably, so it would be hard to reach any conclusions about average brain sizes and intelligence until you hit the mammals, a very distinct subset of the vertebrates which appeared approx 200 mya.

While I am not an evolutionary neuroscientist, I suspect the strongest argument could be made by limiting oneself to the primates, which appeared approximately 100 mya.

Anyway, I buy your general argument on intuitive grounds, but I think the ancient brain size argument is not defensible. If the most recent citation you have available is 1991, then it doesn't take into account the amazing amount we've learned about the evolution of the nervous system within the deuterostomes in the last 10 years, which undercuts the idea that a CNS is basal to bilaterian animals.


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Dare we hope this pattern will continue?

This sentence makes me curious about your terminal values, Robin. Two questions if I may:

(1) Under your system for valuing things, is it intrinsically bad for an individual in a population of replicators to have more descendants than another individual?

(2) Is it intrinsically bad for a human now living to have exert greater influence over the future than another human now living?

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Jeff I know they dominate in mass, but I thought perhaps not in metabolism - do you have contrary info on that?

Titus, see H. Jerison's '91 book "Brain Size and the Evolution of the Mind."

Eliezer, I look forward to your posts; see also my post tomorrow.

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Your statement "...for the next half billion years animal brain sizes doubled roughly every thirty million years, but species only lasted about one to twenty million years" is an ... interesting one. I am somewhat acquainted with evolution and evo devo research, and I cannot imagine where you found this generalization about brain sizes (or how anyone would support it with actual evidence). Do you have a citation, or an explanation of how this estimate was arrived?

I can *guess* that someone took the evolutionary lineage of humans and tried to guesstimate brain sizes of our ancestors from the fossil record, but that's pretty hand wavy. It also assumes that you get to cherry pick humans as the cream of the evolutionary crop, while (if using biomass, or species abundance) either microbes or insects would take the prize.

Anyway, I'm interested in how you arrived at this statement...


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Re: "most of the future population of the galaxy might end up descending from modern humans"

They probably will not be entirely descended from us. Some of the more basic chemical tricks originally discovered by bacteria are also rather likely to persist indefinitely.

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