Extinctions paper: Why grad school is cool, and what creationists don’t get about evolutionary biology

| 92 Comments

Barnosky_etal_2011_Nature_Fig1.jpgThis isn’t exactly about creationism/evolution, but it’s still pretty cool. And I will find a way to tie it in, since I haven’t blogged on PT in, I think, months.

Contrary to what creationists believe, evolutionary biologists don’t sit around in biology departments plotting to overthrow God and morality. We spend our time doing things like statistics and programming and specimen preparation and experimental manipulation and DNA sequencing and field observation, and then give and hear talks and discussions about this research. The main thing we are interested in is not “proving evolution”, it is discovering cool facts and devising hypotheses to explain them, and then devising tests of those hypotheses (typically, statistical tests, something which creationists almost always ignore). In short, it’s like any other science.

This paper is a case in point:

NATURE | REVIEW

Barnosky, Anthony D.; Matzke, Nicholas; Tomiya, Susumu; Wogan, Guinevere O. U.; Swartz, Brian; Quental, Tiago B.; Marshall, Charles; McGuire, Jenny L.; Lindsey, Emily L.; Maguire, Kaitlin C.; Mersey, Ben; Ferrer, Elizabeth A. (2011). “Has the Earth’s sixth mass extinction already arrived?” Nature 471(7336), 51-57. (DOI - Link)

Abstract

Palaeontologists characterize mass extinctions as times when the Earth loses more than three-quarters of its species in a geologically short interval, as has happened only five times in the past 540 million years or so. Biologists now suggest that a sixth mass extinction may be under way, given the known species losses over the past few centuries and millennia. Here we review how differences between fossil and modern data and the addition of recently available palaeontological information influence our understanding of the current extinction crisis. Our results confirm that current extinction rates are higher than would be expected from the fossil record, highlighting the need for effective conservation measures.

It emerged from a seminar course on mass extinctions, taught by Berkeley paleontologist Tony Barnosky. The graduate students included zoologists, anthropologists, computer/modeling types (that’s me), and paleontologists. While reviewing the literature on mass extinction, we got to discussing what it means to say that we are currently “in the Sixth Mass Extinction”. There are different ways to measure extinctions, e.g. by absolute magnitude (mass extinctions have typically been defined as situations where 75% of species go extinct) or by rates of extinction far above the typical background rate. The difficulty with comparing mass extinctions in the paleontological record to the current extinction crisis is that the paleontological record has very coarse resolution compared to human time scales. You are doing very well in paleontology if you can date an extinction event to +/-300,000 years – but this uncertainty in dating an event is much larger than all of recorded human history! In addition, for various reasons it is common in geology, paleontology, and evolution, that the shorter the period of time over which you measure something, the more variability in rate you tend to see, and this variability gets smoothed out when you average over longer time intervals. Thus, extinction events in the fossil record can be “smoothed” by the coarse-resolution data than they may have been in real life. Similarly, the current rate of extinction might, hypothetically, fall within the range of extinction rates that happen in “regular” background extinction, when background extinction is measured at short time intervals.

Since it is pretty important for us to know whether or not our current extinction crisis compares to mass extinction events, we proposed some ways of turning the “apples and oranges” comparison of the fossil and modern data into something more like an “apples and apples” comparison. Basically this can be attempted by looking at both the fossil record and the modern record at a variety of time-resolutions. We can also examine what the future might look like under different scenarios: e.g. what is the extinction rate if all currently endangered species were to go extinct; what is it if all endangered + threatened species go extinct, etc., and how long does it take us to get to a mass extinction under each of these scenarios? Basically our conclusion was that even under the most conservative assumptions, we are still at an extinction rate that is very elevated compared to the fossil background extinction rate. Depending on the scenario, we reach a 75% “mass extinction” (for certain well-studied groups) within a few hundred to a few thousand years, if, as people say, “current rates continue.” This is a geological eyeblink.

Obviously, given the study we made of how extinction rates can be variable, we are not so naive as to predict that a mass extinction will come for sure in a few hundred or a few thousand years. This would be fatalistic and unscientific. Rather, what we say is that we are currently on that path. Taking a different course will require that humans recognize the problem and make decisions to avoid it.

Anyway: this is one small example of the kind of evolution-related research that happens in one department on one campus. It is one of hundreds of evolution articles published by Berkeley researchers each year, and one of tens or hundreds of thousands of such articles published each year around the world. It’s routine. It may seem strange to creationists and other wildly amateur commentators on the field of evolutionary biology, but this is the kind of thing that is going on every day of every week in biology departments. It’s about the furthest possible thing from being some kind of conspiracy or plot against creationism, God, the Bible, morality, etc. It’s just us doing our day jobs, just like all of the other scientists on campus.

References and press

Barnosky, Anthony D.; Matzke, Nicholas; Tomiya, Susumu; Wogan, Guinevere O. U.; Swartz, Brian; Quental, Tiago B.; Marshall, Charles; McGuire, Jenny L.; Lindsey, Emily L.; Maguire, Kaitlin C.; Mersey, Ben; Ferrer, Elizabeth A. (2011). “Has the Earth’s sixth mass extinction already arrived?” Nature 471(7336), 51-57. (DOI | Link)

Drake, Nadia (2011). Scientists try to determine whether life on Earth is quickly heading toward extinction. San Jose Mercury News. San Jose, CA. (Link)

Gibbons, Ann (2011). “Are We in the Middle of a Sixth Mass Extinction?” ScienceNOW. (Link)

Sanders, Robert. (2011). “Has the Earth’s sixth mass extinction already arrived?” Retrieved March 2, 2011, from http://newscenter.berkeley.edu/2011[…]ady-arrived/.

Pappas, Stephanie (2011). 6th mass extinction looms but preventable, study says. LiveScience, MSNBC. (Link)

NSF. (2011). “Earth’s Sixth Mass Extinction: Is It Almost Here?” Retrieved March 2, 2011, 2011, from http://www.nsf.gov/news/news_summ.j[…].mc_ev=click.

92 Comments

I would be very depressing to have to tell the next generation that we’re the dino-killing comet of our time.

I would be curious about comparisons within recorded human history of how human populations stressed their environments and what the socio/political responses and consequences were.

We have records of societies going extinct (e.g., Easter Islanders, Mayans) and even data on what these societies were doing at the time.

Now we are dealing with a situation in which the human footprint is global and is affecting climate as well as thousands of other species. What kind of responses are we seeing from our socio/political systems, and how do these compare with what we know of the past?

Since the human impact on the planet is so large, that might give some idea of where we are headed.

From the physicist’s perspective, we life forms are starting to push the limits of the tiny energy window in which we all survive.

Taking a different course will require that humans recognize the problem and make decisions to avoid it.

My question is slightly off topic, but I find it intriguing. Do we have any right to avoid the problem, in the first place?

I can well imagine what kind of a hellish place a planet in the midst of a mass extinction could be for our descendants, yet trying to avoid such extinction could mean to effectively stop “the next big thing” from happening (whatever it could be). Nature does not care for the future and does not make plans, but we do and we have moral responsibilities and concerns.

Besides: although we are likely going to be the last nail in the coffin for a wealth of species, the extinction trend probably has begun before humanity could make a significant contribution.

After all, the primate branch of the tree of life has already been extensively pruned before modern humanity emerged.

Of course, all of this does not mean that we have any right to ignore environmental concers either: there is a difference between avoiding to fight a wood fire and going to it with a flamethrower.

Mike Elzinga said:

I would be curious about comparisons within recorded human history of how human populations stressed their environments and what the socio/political responses and consequences were.

We have records of societies going extinct (e.g., Easter Islanders, Mayans) and even data on what these societies were doing at the time.

Now we are dealing with a situation in which the human footprint is global and is affecting climate as well as thousands of other species. What kind of responses are we seeing from our socio/political systems, and how do these compare with what we know of the past?

Since the human impact on the planet is so large, that might give some idea of where we are headed.

From the physicist’s perspective, we life forms are starting to push the limits of the tiny energy window in which we all survive.

Mike, just a correction. While Mayan and Aztec civilization prospered and then went “extinct” for a variety of reasons, Mayan culture (and, if I’m not mistaken, Aztec too) is still alive and well, practiced by modern Mayans who live in Mexico and surrounding coutnries in Central America.

Nick,

Congratulations on colloborating on what looks like is an important contribution to our understanding of mass extinctions as seen from both the fossil record as well as the Recent (Holocene) Epoch. Hope you have a .pdf since I’m going to contact you in private about getting a copy.

Appreciatively,

John

Nick, that looks hugely interesting and exciting, but does that mean you’ve raised the curtain on the debate concerning the existence of AME (Anthropogenic Mass Extinction)?

dpr

it is common in geology, paleontology, and evolution, that the shorter the period of time over which you measure something, the more variability in rate you tend to see

Heisenberg.

Well if global climate change is real, what else would you expect to happen?

It has always amazed me how the average creationist can ignore all of the ecological implications of a young earth. If you start with that as a non negotiable presupposition, analyses such as this are impossible. Of course, that just makes it that much easier to ignore the ecological consequences of your actions.

It also amazes me that creationists typically cannot understand the role of death in evolution. It’s almost as if the fact that other organisms die and other species go extinct is a dirty little secret that no one can talk about. EIther they are just afraid to face their own mortality, or they realize on some level that nature is just the way it is whether they like it or not.

Long article about this in this morning’s San Jose (CA) Mercury News at http://www.mercurynews.com/ci_17523[…]=most_viewed

Nick, Question: why “minus bats and endemics?”

Terenzio the Troll said: My question is slightly off topic, but I find it intriguing. Do we have any right to avoid the problem, in the first place?

Doing nothing is as much a course of action as doing something (conservation-wise). So we ARE making decisions about this. The option to not-make-a-decision does not exist in the real world. Instead, our two options are to (i) make conservation decisions consciously and in an informed manner, or (ii) subconsciously/in an uninformed manner.

Terenzio -

To me this paper raises some interesting methodological and definition issues, but let’s just take it for granted that humans are directly responsible for a high extinction rate of other species.

My question is slightly off topic, but I find it intriguing. Do we have any right to avoid the problem, in the first place?

I am a huge proponent of human rights and civil rights, but “rights” are a human invention. We have any rights we choose to give ourselves.

To me it’s a no-brainer that if we respect one another as individuals with worth and dignity, we should make some effort not to damage the common environment that we all share.

I can well imagine what kind of a hellish place a planet in the midst of a mass extinction could be for our descendants, yet trying to avoid such extinction could mean to effectively stop “the next big thing” from happening (whatever it could be). Nature does not care for the future and does not make plans, but we do and we have moral responsibilities and concerns.

I would differentiate between two different types of conservation activity -

1) This rarely actually occurs, but - human efforts to preserve a species which is endangered for reasons other than human activity. A rare example might be cheetah preservation efforts. This type of activity is likely to be unusual, be confined to large, attractive species which are already rare, and probably, be harmless.

2) This is also currently out of style, but - cooperative efforts to modify human behavior in order to reduce potentially harmful changes to the environment which ARE unequivocally driven by human activity. Unfortunately, the current social/political climate in the United States is such that if anything, scorn for the idea of respecting humanity’s common environment and actual deliberate efforts to live in a harmful way, are aspects of a large and popular political movement.

Number “1)”, if it occurs at all, can be seen as aesthetically driven. Number “2)”, which is not happening, would be very desirable.

Besides: although we are likely going to be the last nail in the coffin for a wealth of species, the extinction trend probably has begun before humanity could make a significant contribution.

Do you have a citation for that rather surprising statement?

There is some debate whether the Pleistocene widespread extinction of mammalian megafauna was largely due to humans.

In the last few centuries, I can’t think of many recorded major extinction or endangerment events that weren’t directly or indirectly due to humans.

After all, the primate branch of the tree of life has already been extensively pruned before modern humanity emerged.

Extinctions will occur with or without humans, yet contributing to an excess number of extinctions is potentially a self-destructive aspect of human behavior that might best be modified.

Of course, all of this does not mean that we have any right to ignore environmental concers either: there is a difference between avoiding to fight a wood fire and going to it with a flamethrower.

Yes, to elaborate on what I said above, traditional “conservation” was sometimes informally grounded in an assumption that the biosphere is relatively unchanging without human intervention.

Having said that, even since the days of Teddy Roosevelt, the vast majority of environmental policies have, in fact, protected the common environment all humans live in from extensive damage done to benefit small groups of humans.

Nick Matzke -

Forgive me if some of this is dealt with in the paper, but here are a few interesting issues -

1) Common definition of extinction for field biology and paleontology. For example, let’s say a finely resolved big cat species were to go extinct; Bengal Tiger, for example. That would be noticed as an extinction by field biology. But there would be other tigers, which might not be differentiable as different species by paleontology (putting aside species definition debates). There would be other very closely related big cats that we don’t even recognize as “tigers”. Obviously, just looking at percentage of recognized species is one pretty good way of handling this - arguably that should correct the “more extinctions if you can detect more species” bias. But I wonder if real time observation biases in favor of observing extinctions. This comment does NOT IN ANY WAY reflect any doubt in my mind that humans are provoking an unfavorable decrease in biodiversity with their current behavior. It’s just a technical thought.

2) Proportion of overall multicellular biomass the goes extinct. Although both are likely to be undesirable, replacement of multiple species by a few species, but with no overall decrease of biomass, versus massive short term reduction in multicellular biomass, are different things.

Obviously, I think that your research advances understanding of and further clarifies human impact on the rest of the biosphere.

Nick, looks like an interesting read. Thanks for the tip.

Terenzio the Troll said:

I can well imagine what kind of a hellish place a planet in the midst of a mass extinction could be for our descendants, yet trying to avoid such extinction could mean to effectively stop “the next big thing” from happening (whatever it could be).

Well, fossil fuels are finite, so expending increasing sums of money on extracting what little is left is fast becoming a redundant investment. The “next big thing” could (and hopefully will) easily arise from exploration into alternative, sustainable/renewable energy sources. We’re generally terrible at predicting the future above certain very short time-scales, but it’s pretty safe to say that some research always brings us unexpected benefits.

Nature does not care for the future and does not make plans, but we do and we have moral responsibilities and concerns.

I think we have documented plenty of examples of “Nature” planning for the future. Birds build nests before they lay eggs. Termites build complex air-conditioned structures and farm fungi. Plants invest in seed-banks. Many species (check out ‘semelparous’) exhibit life-history trade-offs that suggest they won’t invest all their energy reserves in a current reproductive event at the expense of future reproductive success. All these traits and behaviours have been selected for over and over again across multiple taxa. And all seem like planning for the future to me.

Hmmmm, I guess I assumed that Global Climate Change driven largely by fossil fuel consumption was the most important driver of the next Mass Extinction. This might not be true. There are a range of other human actions that drive species loss - habitat loss, poisoning and fragmentation, unsustainable harvesting and so on.

But the message remains - it’s worth investing in research that explores alternatives to the way we’ve been doing things, especially when we are confident that past practice was harmful.

harold said: …replacement of multiple species by a few species, but with no overall decrease of biomass, versus massive short term reduction in multicellular biomass, are different things.

I recall a factoid that the biomass of ants, termites, krill and squid are each greater than the biomass of humans. I wouldn’t predict any of those groups going extinct any time soon.

John Kwok said:

Mike, just a correction. While Mayan and Aztec civilization prospered and then went “extinct” for a variety of reasons, Mayan culture (and, if I’m not mistaken, Aztec too) is still alive and well, practiced by modern Mayans who live in Mexico and surrounding coutnries in Central America.

Yeah; understood.

Similar remarks could be said about the fall of Rome and the plunge into the “Dark Ages.”

But the laws of physics and chemistry will not be violated by humans any time soon. Whenever any population outruns the nutrients in the Petri dish, the population dies.

Historically we see a few escaping and finding new niches to fill. But when the Petri dish is the entire planet, this becomes more problematic.

The net influx of energy from the Sun gives hope. The stupidity of our educational and socio/political systems mitigates that hope.

And maybe we aren’t the next best thing anyway.

D. P. Robin said:

Nick, that looks hugely interesting and exciting, but does that mean you’ve raised the curtain on the debate concerning the existence of AME (Anthropogenic Mass Extinction)?

dpr

Exactly, D. P., that’s what Nick and his co-authors have done. At the very least theirs is an excellent initial attempt at trying to quantitfy the current accelerated extinction rate and comparing and contrasting it with what we know for mass extinctions from the fossil record.

Getting the populace at large to respond appropriately to the global implications of articles like Barnosky et al. requires that they pay attention, and that may be insurmountable. As a 35 year biology professor, it seems clear that the major impediment to learning in classrooms is just paying attention. The businessmen who frequent the deli where I breakfst consider all concerns about subjects like extinction rate to be of importance only to a certain core of intellectuals who find that subject personally interesting. Everyone else then is free to ignore it. They pay no attention to protestations about their lack of attention. It’s maddening.

Paul Burnett -

1) The relationship between the size range in which an individual organism is found and the proportion of the biomass made up of that size range of organisms is interesting.

I won’t bother to calculate the mass of an individual here, but it will, of course, tend to be a function of the cube of a single dimension.

A “typical” prokaryotic cell has a diameter of about a few micrometers, with many variable examples http://hypertextbook.com/facts/2001[…]ceWong.shtml. Prokaryotes make up a huge proportion of the biomass. Exempting viruses, I’m not aware of the concept of extinction even being applied to prokaryotic lineages. Study of prokaryotes is overwhelmingly driven by applications, mainly medical, also industrial. “Pure” study of incidental prokaryotes is potentially fascinating but only a tiny fraction of microbiology, although study of extremophiles has had profound impact on biology.

A “typical” unicellular eukaryote is hard to describe, as many plankton species are almost as small as bacteria, for example, whereas many familiar examples like yeast and amoebae are more in the 10 micrometer diameter range, with much variation (very small eukaryotes probably evolved their smaller size). It could be crudely approximated that an “average” unicellular eukaryote has about 100 or so times the mass of an “average” prokaryote, and that’s probably within an order of magnitude. I haven’t heard much use of the concept of extinction applied to unicellular eukaryote lineages, either, even though some of them use sexual reproduction.

I assume there is a greater biomass of prokaryotes than of unicellular eukaryotes, although I am not sure.

Multicellular animals obviously range from not much bigger than a few large unicellular eukaryotes (dust mites have a diameter of about 500 microns) to vast. There is a clear tendency for lineages with smaller individual size to actually make up a greater percentage of the biomass. For example, an individual adult bear of any species is much larger than an individual adult ant of any species, but ant-sized organisms make up a vastly higher proportion of the biomass than bear- sized organisms. Indeed, this relationship appears to be non-linear, proportion of the biomass seems to drop off sharply in animals, as individual size increases. A major outlier is the fairly large biomass of humans.

I’m not sure if it works the same way with plants. The large biomass of trees would seem to argue otherwise.

Clearly, the concept of extinction is mainly applied to large animals, especially mammals and birds, and to a lesser degree to large plants. It’s much harder to define species at all when dealing with microbes (not that’s it’s easy otherwise).

Getting back to the extinction-due-to-replacement versus extinction-due-to-overall-decrease-in-biomass distinction, I will note that any event that had a global effect of markedly reducing availability of solar energy would affect ALL levels of the biomass, except in a few very weird, isolated environments.

Barnosky has done some really interesting work on how much of the global Net Primary Productivity humans have taken over from the rest of life. It’s pretty huge, e.g. most large animals have been made extinct or restricted to parks, and human crops and livestock have taken over that entire ecological space.

He notes that part of what keeps us going well above the natural biomass carrying capacity, based on natural NPP, is fossil fuel input. But that has it’s own problems, and a time limit as well…

Some of you may remember Al Bartlett and his Forgotten Fundamentals of the Energy Crisis.

For those who don’t have the back-of-the-envelope math, it’s worth spending some time with.

Bartlett has also written a paperback book entitled The Essential Exponential! put out by the Center for Science, Mathematics & Computer Education, University of Nebraska, Lincoln.

I don’t know if it is still available in print.

Mike Elzinga said: Bartlett has also written a paperback book entitled The Essential Exponential! … I don’t know if it is still available in print.

Amazon has 4 new and 4 used - http://www.amazon.com/Essential-Exp[…]1&sr=8-5

(Why would the used ones cost 3 times what the new ones cost?)

Paul Burnett said:

Mike Elzinga said: Bartlett has also written a paperback book entitled The Essential Exponential! … I don’t know if it is still available in print.

Amazon has 4 new and 4 used - http://www.amazon.com/Essential-Exp[…]1&sr=8-5

(Why would the used ones cost 3 times what the new ones cost?)

Bartlett also lists it as being available at the University of Colorado Bookstore.

This is a pretty decent introduction to the math for high school and undergraduate students.

Wait a minute! 5 mass extinctions? Are you trying to say there were 5 global floods? And, of course, they all occurred in the last 6000 years.

There I win! I beat FL et al in making the first intelligence-free comment!

And we all know that evolutionary biologists may not sit around in biology departments plotting to overthrow God and morality – it’s standing room only.

;)

The Founding Mothers said:

The “next big thing” could (and hopefully will) easily arise from exploration into alternative, sustainable/renewable energy sources […]

I think we have documented plenty of examples of “Nature” planning for the future. Birds build nests before they lay eggs.

Uhmmm, in hindsight I must reckon my previous comment was ill-phrased and prone to be misunderstood.

With “the next big thing” I was referring to some sort of replacement, well, for us.

Also, with planning for the future I meant that evolution has no goal. I was trying to say that there is no species destined to become our prefigured replacement in the number of sentient creatures, and something “suitable” will eventually evolve after our demise, if chances are right. Even so, our actions might postpone or altogether stop this replacement from happening (think of the dinosaurs stubbornly refusing to become extinct: ok, I know, it’s stupid). Or, at the very least, leave our distant successors a depleted planet to live on.

Well, first of all thank you for your lengthy reply.

Do you have a citation for that rather surprising statement?

Well, I can easily see why you find my assertion startling. I was not assuming or suggesting that humans did not have an hand in the pleistocene/holocene extinctions. Following the trail of my “nail in the coffin” metaphor, I was rather wondering if humans have perchance precipitated an event that was already waiting for the right conditions to happen.

After all, at least for Australia, is still matter of debate if the extinctions were already started when the first men landed there. Sure as hell, they helped a lot afterwards (and they still are).

Africa fared better than the rest of the world till historic times as for extinction rates (ok, this might not count: humans and other megafauna co-evolved there).

As for North America, I was thinking of horses and their relatives: equidae saw a shrink in their diversity well before humans reached America: by that time only the genus equus was left.

Which is the same that happened to our lineage: humans are the only bipedal primates left of a formerly numerous family.

We recognize past mass extinctions because dominant plants and animals were extirpated or greatly reduced in diversity. As a species which thinks itself dominant, isn’t the lesson of earth history that, as the present mass extinction runs its course, we are likely to be in deep trouble?

This yEC says this paper is not doiung any science. In fact its not doing biology. All your info is based on geology presumptions and then you draw some biological conclusions. Biology is about living things and studying them and to study them one must be dealing with a living/or recently living thing. Casts of former living things is not biology. This thread makes a good point for creationism. Further i question that there is anything of the prestige of “science” going on here. This subject can not draw forth much data to work with in order to draw conclusions. It all looks like just more green “science” making speculations . They get paid for this? Are they aware some diseases are still not cured?

Robert Byers said:

Are they aware some diseases are still not cured?

Indeed they are. These diseases are called ignorance and stupidity.

Nick, your paper made the San Jose Mercury News, and in a form that wasn’t so garbled that I couldn’t figure out what it was about. Big science!

We are getting ready to go to El Salvador in 2011, I really enjoy reading about it, I want to know more about the people of El Salvador how they live and where they live

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