Thursday, 2 August 2018

Mosses on your roof? Here's what you should know...

As an ecologist and bryologist, I've spent a long time studying the little green things we call mosses. If you've never taken a minute to appreciate the beauty and intricacy of these tiny plants, I suggest you do so. The first time I looked at a fresh clump of moss under a micrcoscope I was hooked. Unseen to most, mosses form entire forests on a microscopic level, all within a centimeter or two of the soil or organic material upon which they're growing. These micro-forests contain complete food chains, with primary consumers (herbivores), several different tiers of secondary consumers (carnivores), and of course, the decomposers (mostly fungi). It's a fascinating world!

One of the most common questions people ask me, however, when they discover that I study mosses, is "how do I keep them from growing on my roof?". If you even Google this the phrase "mosses on roof shingles", the entire first page is packed with recommendations from various home-renovation and landscaping contractors on how to get rid of them - there's even a Wikipedia entry for it!

There is an assumption underlying this question though, that the mosses are somehow bad for the roof shingles, when in truth we simply do not know whether this is the case in the general sense - simply put, nobody has really studied the question.

To be sure, mosses may regularly be found growing in places where the shingles are somewhat degraded. But correlation does not equal causation. In other words, the mosses could be responding to the conditions that caused the shingle degradation, rather than causing the degradation themselves. And in some cases, mosses grow in places where there is little to no degradation whatsoever. My working hypothesis is that, while there are likely cases where the mosses contribute (slightly) to the degradation of shingles, most of the impact of mosses will be neutral to slightly beneficial, because (1) degradation is caused by other things, and the mosses are simply responding to those same things, and (2) mosses have several traits that might actually slow such degradation. Allow me to explain further.

Mosses are what biologists refer to as "poikilohydric"; this means they absorb all their water passively from the atmosphere through their leaves and stem. They do not have roots like the large herbaceous plants we're more familiar with. Instead, they have tiny little hair-like appendages called "rhizoids", which help them to stick on their chosen surface. These rhizoids are highly unlikely to cause damage to your shingles, because they don't usually penetrate into the ground. And even if they do find a nice opening, they're physically incapable of growing more than a couple of milimeters into it, because these rhizoids are the size of the fuzz on a piece of synthetic fleece or felt fabric. Simply put, mosses are pretty much physically incapable of doing physical damage to your rooftop in the way that a herbaceous plant does.

Before I go further with discussion of mosses, let's take a step back and address the primary causes of shingle degradation: erosion and fungal digestion.

The primary cause of shingle degradation is almost certainly water and wind-driven erosion for most rooftops. Think about it, where do you first see shingles with the corners and edges turning up? In places where water is channeled (e.g., joints between angled roofs), and where the shingles are more exposed to winds from multiple directions (the apex of the roof). Both of these actions will knock those little sandy particles loose, and these particles will then bounce down over other shingles, knocking other particles loose as they go. So let's start by acknowledging that erosion is the primary source of physical shingle degradation.

Next, we must acknowledge the primary chemical means by which shingles are degraded. Most asphalt shingles are made of 3 main things: recycled cellulose fiber (i.e., old newspapers), tar, and coarse sand. Cellulose fiber is undigestible for most animals (humans included), but fungi LOVE the stuff. There are thousands of species of fungi dedicated to digesting wood fiber. Some prefer certain tree species, others prefer particular parts of the tree. Some are more generalist in their choices, and will go for just about anything that contains cellulose (like paper or shingles). These fungi actually grow vast microscopic webs through the cellulose fibres, slowly breaking down the cell walls and incorporating the carbon from the cellulose into their own bodies. Because cellulose fibres are essentially hollow tubes that have been sealed off, breaking down this cellulose means that something formerly more like rigid PVC pipe is now more like empty paper-towel tubes; the more digested it becomes, the more the mat of cellulose fibre begins to work like a sponge, capturing and holding water tightly. If you've ever had to deal with mould in your house, you know that the continual presence of water can exacerbate the problem, because moisture brings on a whole-other set of fungal colonizers.

Recap: shingles are physically broken down by erosion, and chemically broken down by fungi. 

Now, let's bring the mosses back in - I'll make three points that relate to what mosses may be doing in this rooftop ecosystem: two that suggest the mosses are responding to conditions, and one that suggests they are contributing to the conditions.

The first point in favour of mosses responding to rooftop conditions, but not causing them, is that some mosses produce antimicrobial compounds. These compounds can inhibit the growth of certain bacteria, fungi, and parasites. In fact, certain species (e.g., Sphagnum fuscum) are so good at this that they were extensively used as absorbent wadding for bandages during the world wars. Ecologists have also shown that fallen trees decay more slowly when covered by certain moss species, particularly in peat bogs. To my knowledge, nobody has studied whether the moss species that commonly grow on rooftops will inhibit the growth of shingle-decay fungi, but let's keep our minds open to the possibility at this point. If they do, they would actually be reducing the rate of shingle decay, not contributing to it.

The second point in favour of mosses responding to rooftop conditions, but not causing them, is that by growing over your shingles, these mosses are likely shielding the shingles from erosion. Several scientists are actively studying their role as a critical component of something called a biological soil crust (BSC), which reduces soil erosion in sandy ecosystems (like pine barrens and deserts). By covering up loose soil (or shingles), the mosses block the actions of water and wind. Their presence also leads to the creation of a thin layer of organic compounds, which can act as a type of glue to hold particles in place. So even though mosses may not colonize until shingles are a bit eroded, their presence probably inhibits further erosion.

Now a point in favour of mosses contributing to shingle degradation. (Note that I'm saying "contributing to" instead of "causing", because the mosses wouldn't be there if the roof wasn't already regularly experiencing high moisture levels & erosion, combined with a bit of fungal degradation.)  Since they absorb their water passively from the atmosphere, mosses like it to be wet. They tend to colonize wet spots on your roof before dry spots because of this. But they also enhance their own habitat as they grow. The tendency to form dense, spongey mats, allows them to hold onto rainwater a little bit longer than if they were isolated shoots. So where you have mosses, your shingles may be wet for a little longer than other places on your roof. If an antimicrobial-compound-tolerant species of fungus can colonize your shingles, it will have a habitat that is slightly more wet than other parts of your roof, and may therefore grow a little more quickly through those cellulose fibres than it otherwise would.

So between the first two points, mosses may be reducing shingle degradation on both the physical and chemical front. From the last, they might be slightly enhancing the growing environment for decay-fungi, which would contribute to shingle decay.

Now to answer the question that I'm so frequently (not) asked: Should you attempt to get rid of the mosses on your roof by the use of moss-killing strips or sprays?

Probably not.

Given the arguments I've made above, getting rid of the mosses will be unlikely to increase the lifespan of your shingles, and may actually reduce it instead. Moreover, if your roof shingles are really degraded (e.g., leading to a leaky roof), the problem is not the mosses, it's the degradation of the shingles by cellulose-digesting fungi.

So if you're concerned about mosses degrading your rooftop, but the roof itself seems to be okay (not leaking or obviously coming apart), you can probably rest easy and enjoy the nice green carpet you got for free. You may even enjoy some additional benefits from having mosses on your roof, like increased insulative value and moderated stormwater runoff. This is actually an active area of research for me, so stay tuned to hear more about the benefits of having a mossy-green roof.

If your roof is obviously no longer doing its job (e.g., leaking), you don't have a moss problem, you have a shingle-rot problem: killing or removing the mosses will not solve this, and may even make it worse. In this case, it's probably time to re-shingle and re-seal the roof.

Friday, 18 May 2018

The impacts of anthropocentrism on our thinking about evolution

The impacts of anthropocentrism on thinking about evolution

In evolutionary biology, one of the big myths we are often tasked with dispelling is that that the traits which seem like obvious indicators of success to us are adaptive in the evolutionary sense. I call this an anthropocentric interpretation of evolutionary theory. For example, people have asked me, if evolution leads to survival of the fittest, why aren't humans getting smarter as a species? While the cynic in me wants to respond in the immortal words of Harvey Danger "...that only stupid people are breeding...", and there is an element of truth to this, the question calls for a much more detailed examination of the misconceptions behind the question.

There are actually several assumptions built-in to this question that are either universally false, or at least wrong most of the time. They are: (1) that the human (anthropocentric) definition of success = the evolutionary definition of fitness; (2) that the evolution of humans (and presumably other large vertebrates) is easily measurable over time-scales that are relevant to modern science; and (3) that past selective forces = current selective forces.

Before I explain further, let's re-examine the central tenets of evolution by natural selection:

- More individuals are produced each generation than can survive
- Within populations, individuals vary in their phenotypic traits, and this variation is heritable
- Individuals with beneficial traits are more likely to survive than those with detrimental traits

The first assumption is wrong because for a trait to be considered evolutionarily adaptive (beneficial), it must demonstrably be selected for, or be selected against less than alternative traits. In the context of human evolution, this means that for intelligence to be an adaptive trait, more intelligent people should not only be more capable of gathering resources (e.g., land, wealth, etc.), but also have more mates and produce more children than less intelligent people. Both parts are pretty soundly refuted by scientific research. Once you factor out education level, inheritance, and other influences, most smart people are no better at accumulating wealth than most dumb people.1 In addition, smart people (more specifically, those with high IQ scores) have been shown to produce fewer offspring than dumb ones2. So not only is being smart not an evolutionary advantage, being "dumb" may confer a slight advantage, if differential reproductive output is the primary measure of success.

However, such research also assumes that (1) people with high and low IQ's are on equal footing in other ways, and (2) that our data on IQ and reproductive rates in humans have been of consistently high quality over enough generations to allow for a reliable test, and (3) that the selective advantages have remained consistent over time. So for the time being, we'll have to let this rest with the statement that being smart is probably not an advantage in the evolutionary sense, although it may be in others.

The second assumption, that human evolution occurs over easily measurable time-scales, is in the category of "probably false". From examining fossil skulls of early homonids, anthropologists know that brain volume has increased at very coarse scales (i.e., over millions of years) from our earliest ancestors up until the last 10,000 years or so. Since then, our ancestors brain volume remained static or even declined slightly, although there is some evidence that this is linked to population growth and the impacts of the development of agriculture on human survival, with a slight increase occurring after the industrial revolution3. However, there is much more to human intelligence than brain size. Newer studies have shown that, at best, brain volume is only weakly correlated to intelligence; a much more effective measure is the number of synapses in a brain4, but this is pretty much impossible to measure without modern MRI techniques, so we're mostly outta luck on testing this question. In addition, recent research shows that for large anatomical changes to become widespread in a population, it can take up to a million years!5 Presumably, smaller changes can become widespread in a smaller amount of time, but to expect them to be evident in as short a time as we have had MRI scans for is clearly ridiculous. We actually don't (and probably can't) know whether the intelligence (in the modern sense meaning that which is measured by IQ or similar tests) has changed since our species was separated from our ancestors.

The third and final assumption, that current selective forces are the same as past ones, is almost certainly wrong. As mentioned above, brain volume changed a bit between hunter-gatherer humans and agricultural humans, but that's not the only thing that changed. Hunter-gatherer humans had far more robust skeletons overall. Although recent research6 has shown that this change is mainly just in the phenotype, rather than the genotype, of humans, it does illustrate a point: the environment in which early humans lived was very different than the one in which we now live. Different selective forces were at play. Consequently, the farthest back we should really be looking is the last 10,000 years, when agriculture was becoming more widely adopted. Post-agricultural humans are more anatomically similar to modern humans than pre-agricultural ones were, and therefore probably had more comparable selective forces at play. And I would argue that, realistically, we should be comparing no further back than the industrial revolution, when humans once again went through an abrupt transition towards increasingly sedentary lives.

So in summary, the answer to the question "why aren't humans evolving to be smarter", is that (1) intelligence does not currently seem to confer greater fitness (i.e., survival AND reproductive success), (2) actually testing this question would require brain scans or IQ tests of humans going back MUCH farther than we currently have, because evolution takes a long time, and (3) due to rapid technological changes, we are not operating under the same selective pressures as our human ancestors were, so even if we did have good information dating back a million years, it's unlikely the trend would continue to modern days uninterrupted.

In case this whole thing just went over your head, or the heads of the people you're attempting to explain it to, don't worry. I have a simpler way to explain it.

Remember when you were a teenager, and there were popular kids and jocks and nerds and Jesus freaks and goths and other easily identifiable subcultures in your school? Which ones do you think had the most sex over their lifetimes?  Probably jocks and preps, right? Which ones do you think used the least birth control?  Probably the Jesus freaks, right?

(More sex) + (less birth control) = more babies
and, when it comes to evolution,

more babies = greater fitness

This is assuming, of course, that the babies survive, as they probably would in today's world.

Let me leave the last words to Harvey Danger:

Monday, 7 November 2016

On Remembering and Freedom

I wrote this on Remembrance Day in 2012. 

On my way down to the war memorial today, I was thinking about the way we remember our fallen soldiers from wars past.  We remember them as heroes, as model patriots and gentleman, as people who paid an incredible price for God and country.  It is often said that those who died in the war gave their lives for our freedom.  But what exactly does that mean?  Does it mean we would be living in some sort of prison cells, or as slaves under German occupation, or that we would never have been born at all if Canadian soldiers hadn't fought and died?

The answer to all this is: I don't know.  If anyone is familiar with the Nazi plans for invading the world once they had finished with Britain and the rest of Europe, I'd invite you to leave a comment here for my education (preferrably with references).  But for the time being, given that we joined the war as an ally of Britain, rather than as a country that the Nazi's moved against directly in provocation, let's assume the Nazi's weren't realistically planning on taking over the U.S. and Canada, or at least hadn't thought that far ahead - despite what the various governmental propaganda-makers seemed to indicate.  No, I'm betting that, if Hitler had won the war, he would have realized that a complete occupation of North America was a fools-bet at best, and that he didn't have the resources to do it.

But if Canada and the U.S. weren't directly at risk, what does it mean when we say that these brave soldiers fought, and sometimes died for our freedom? 

Here's where I became stuck for a little while.  On the one hand, if we weren't under a direct threat from the Nazis, we probably could have spared a lot of Canadian blood and grief by choosing a different course of action.  On the other hand, allowing the Nazi's to rule Europe might have led to just as much eventual bloodletting through ethnic cleansing and continued rebel-resistance in France and Britain.  You could say that our soldiers fought, and sometimes died, for the freedom of the many European people who would have fallen under the Nazi occupation.  So you could say that our soldiers fought for freedom in general, but for our freedom?

A crowd of about 6-700 people was gathered around the cenotaph in Rothesay as these thoughts were milling about in my head, all with poppies adorning their coats and hats, all in solemn silence listening to some small children reading In Flanders Fields.  This year one particular passage caught my attention:

...Take up our quarrel with the foe,
to you from failing hands we throw
the torch; be yours to hold it high...

What does that mean to take up their quarrel with the foe?  Of course John McCrae can't have meant that we should keep fighting Nazi's until they're extinguished from the earth - you get the sense that he meant much more than that, that "foe" was something bigger than Hitler and the Nazis.

And then the trumpet played Last Post, and I was reminded of my Grandpa, Walter Haughian, who fought on the Italian front as an artilleryman in WWII.  I started feeling a little ashamed of myself, like in asking whether what he fought for was really my personal freedom was also questioning the legitimacy of the life-long emotional scars he bore as a result of that terrible war.

So I asked myself, what did my Grandpa fight for?  If the rest of his life was any indication, he fought for love - love of his family and friends, love of his country, and love of life in general.  But is this the same thing as freedom?  Yes - allow me to explain.

If you know anything about the Nazi's ideology, much of it was based on a misinterpretation of Darwinian evolution, and a likely intentional misapplication of the objective concept of "survival of the fittest" to the clearly subjective idea that one group of humans can declare itself to be the fittest, and proceed to impose their concept of artificial selection on the species.  Of course, this wasn't how it started - it started as a visceral knee-jerk reaction from a segment of society that blamed their own misfortune on what they referred to as immigrants.  These people (many of whom had lived in Germany for generations) were not ethnically Germanic, and therefore were counted as immigrants who were displacing true Germans from their jobs.  The hard economic times of the 1930's, combined with the sentiments of national shame imbued by the results of WWI, allowed the Nazi party to turn this knee-jerk reaction into a convincing story that was easy to buy into for many hard-working Germans.  Ethnic nationalist pride soon turned into blatant racism and hate, justified by seemingly scientific eugenics and Social Darwinist-type arguments, leading to what we all know today as the Holocaust, where almost five million innocent people were killed because of WHO THEY WERE. 

This is key.

Now ask yourself, where else have we seen people killed for who they are?  A few examples I came up with:

We like to think of ourselves as living in a world that is far more fair and just than it was in the 1940's - and it probably is.  But the truth is people are still persecuted for who they are on a daily basis, and the global media makes this information so accessible that we really shouldn't feel that the world is okay. 

Take up the quarrel with the foe

So who is the foe?  The foe is hate.  It's really simple, when you think about it.  Hate - whether it is justified by someone's conception of science, religion, or economics, whether it is against another country or certain individuals in our own country.  But how do we take up the quarrel?  How do we keep the torch of justice and freedom burning?  Surely we don't all need to enlist?

To you from failing hands we throw
the torch; be yours to hold it high.

What our soldiers gave us, what my Grandpa and John McCrae gave us, is another way.  We can take up this quarrel, without taking on the same burden of death and disaster that they took on themselves, because we have the tools to do it.  To me, the most likely danger to North America from losing WWII came from the possibility of Nazi-sympathizers gaining political power, and forming alliances with Nazi Germany (such sympathizers were quite common in Canada and the United States prior to WWII).  Hitler and the war forced our grandparents to see the rhetoric for what is was - hate speech.  60 years later, when we see a piece of hateful propaganda, we have the perspective of constant ideological conflict and several world wars to help us sift through the rhetoric.  We have the insight to question the motives of those who would sway us towards violence and conflict.  And ultimately, we have the knowledge that in showing love for our fellow-humans, we have held the torch high and banished the seeds of hate that lead to ugly conflict.

The world isn't perfect.  John McCrae knew this, hence his instructions to hold high the torch - to shed light on hate and see it for what it really is.  The freedom they gave us was true freedom - freedom of the heart and the mind - it is up to us to use it, that we may continue to keep the foe at bay.

Francis memes and what the current surge of papal positivity says about us

As a Catholic, I appreciate the positive attention pope Francis is getting in the media - it is certainly a breath of fresh air to hear about his ideas in the news as opposed to the constant (and rightly so) reporting of sex scandals throughout the late 90s and early 2000s.

But I've gotta say the only really different things about Pope Francis that I see are (1) that he rejects many of the 'elitist' formalities of office (whereas his predecessors viewed it as a necessary burden), and (2) he uses common language with a great social media presence, thereby appealing to a much broader swath of society.  It is not news that he (and by implication, the church) accepts much of evolutionary theory, that he criticises corporate capitalism and human greed, that he suggests pollution and other environmental damage is sinful, or that he preaches love and compassion above other considerations (especially those surrounding marriage and divorce).  

All of these things have been true of much of the church leadership for much of the last few decades.  For example, John-Paul II wrote extensively about the importance of philosophy, logic, and the power of the human intellect, especially when it comes to science and technology, and Benedict XVI spoke often about the importance of preserving the environment, how pollution is sinful, and that climate change is a grave problem for humanity that is coupled with our modern lifestyle.  At the core, Benedicts message on caring for the environment (“As we care for creation, we realize that God, through creation, cares for us”), is really no different than David Suzuki's (what we do the the environment, we do to ourselves) minus the theism.  And so I'm inclined to think that, while I agree that Pope Francis seems poised to make more significant changes, the public, in general, are a bit naive when it comes to Catholicism, both in practice and in theory.

The current bandwagon seems to be largely occupied by people who formerly had been (or perhaps still are) persuaded to to think that the Catholic leadership and teachings were universally corrupt and bad.  I'm certainly not defending the entire canon (I could hardly do so effectively as both a layperson and a partial dissenter), and there have definitely been some truly bad people in the church's leadership.   But I would suggest that, if you're going to be critical of of something, you should at least consider the possibility of good and bad simultaneously, rather than simply picking the bits that agree with your world-view.  In this case, my suspicion is that many of us had prematurely jumped on the Pope-critiquing bandwagon in the past.

So if you're one of the people giving Francis a Facebook pat-on-the-back, it might be worthwhile asking yourself whether you are doing so because something has fundamentally changed, or because you just like what he says.  If it's the former, please point out to me what the changes are, because I'm very busy and could use the help.  If it's the latter, I would suggest that you would probably like much of what all recent popes have written or said, and may want to reconsider your (premature) judgement of them.

Alternatively, if you're just being happy and positive, please continue, and enjoy this photo of a cute sloth wearing a papal mitre.

Funny excerpts from student writing

I'm keeping track of these from now on, for my own benefit and that of my teaching freinds, because sometimes you just need a laugh to get you through the marking :)

"These observations were then sketched out and labelled."

-- If you're not sure why this one's funny, do a Google search for "sketched out".

"There were no sperm seen ... due to possible immaturity, therefore I looked at someone else's sperm."

-- The part that I abbreviated does not change the implication. Brings a whole new meaning to the term 'lab partner'.

 "Within a population there will always be strong, intermediate, and weak individuals. If you are weak you will not find a mate (no one will want you) and you will not get food so you will die in what is called 'Natural Selection'."

-- Guess you'd better hit the gym then bro.

Is having kids bad for the environment?

Ever since a friend posted a complaint against mothers who seek attention on Facebook for their 24/7 (often thankless) vocation of child-rearing, I've thought about how environmental reasons factor into the decision to have kids, and have come to the conclusion that most of my friends who cite the current unsustainably large population size of earth as a reason for not having children may not be making the best argument (not that they should have to defend their choice one way or another, but these things do come up from time to time). 

It's not the best argument because it seems (to me) like those who choose not to have kids often also choose to drive 4-8 hours every other weekend so they can enjoy some time away, take more frequent vacations in other coutries via air-travel, or simply buy more than my friends who have kids at home.  In other words, it seems like the extra freedom and financial resources generated by not having children cause us to consume a much larger amount of resources, thereby increasing our environmental footprint.  Although I'm not sure if the resulting environmental footprint would be quite as large as that of feeding and clothing additional mini-humans (probably not by the time they are teenagers), I'm betting that it is certainly not simply the same footprint minus the kids share.  I've always maintained that if you raise your children to be committed to improving sustainability, they may end up decreasing that footprint even more; and I suspect that the hero of many environmentalists, David Suzuki, probably shares that view, givent that he's had 5 children himself. Ultimately, by limiting yourself to one child you are still contributing to a trend of reduced reproductive output in the country.  Perhaps the large population size of the earth and other environemntal arguments are not the best arguments for not having children; but then, why should we have to argue about it at all?

If you get in a discussion about this with someone who thinks everyone should have kids and presses the issue, the best argument is simply "I don't want to have children"; if they press further, you could add "because I don't want to give up my freedom", as usually seems to be the case.  Citing the large population size of the earth is likely to make people that have kids defensive about their own reasons, because it implies they are doing more damage than you (although if that's what you mean to imply, its a great way to do it).  If you have particularly fecund siblings, you could also suggest that your genes are already being passed on abundantly, so you choose to improve your biological fitness in other ways (e.g., getting more exercise, education, or R&R).

Occasionally people with children become somewhat persistent in trying to convince those that don't want them, even suggesting that it is 'selfish' to not have children, while maintaining a 'holier than thou' attitude (although I have also seen this attitude in non-reproducers).  Given the fact that not having children is an evolutionary dead end, and that devoting more time to other people's children (or just other people), as many teachers, professors, and aunties or uncles do is, by definition, altruistic (the opposite of selfish), this is certainly not the case for most.  Although one could argue they are at least a bit more selfish than reproducers, in that they only devote 50% of their time compared to 80% or more of reproducers (to pick two not very well-researched guesstimates), there are selfish reasons involved in both choices: reproducers are selfish in that they want to ensure their own DNA is represented in the next generation (as opposed to that of others), whereas non-reproducers are selfish in that they are not willing (note that this wouldn't apply if you simply couldn't have children) to devote as much time to raising children.

In my opinion, the absolute best of both worlds, and the least selfish option altogether, is adoption, because there is zero increase in population, but you still have a chance to pass on your best, most sustainable ideals for the future.

Being an environmentalist doesn't mean you have to abstain from child-bearing, nor does having children necessarily make you less environmentally friendly (unless, perhaps, you have rabbit-like reproductive tendencies).  Whatever you choose to do, you can also choose to do it responsibly; don't fool yourself into thinking you are somehow more enlightened than those who choose differently.

Human-caused extinctions, values, and religious beliefs

We are currently in the middle of a human-caused extinction crisis (the loss of many species on a Geologically tiny time-scale) that is only projected to get worse over coming decades, as humans continue to homogenize the natural world in order to grow crops, create living spaces, and provide resources for an expanding population.  If you are a religious person, or have some thoughts on how religious people think about this, I'd like to know if you think that religious beliefs either justify these actions or contradict them.  I emphasize some of the Christian perspectives below, but would be particularly interested to hear your point-of-view if you have another faith-background.

In several places in the bible, we are told that all species have intrinsic value (e.g., God created the birds of the sky, fish of the sea, etc... and saw that it was "good").  Yet, the bible also clearly indicates that humans are the 'pinnacle' of creation, and are therefore more important than other species.  It even tells us that we are to "have dominion over them" - which at the very least indicates that we have precedence to displace, if not the priveledge to use and misuse as we please. This is something of a paradox for Christians - some would suggest that, both because because God deemed it to have intrinsic value, and because the diversity of life around us relates directly to our quality of life, it is justifiable to protect that biodiversity from over-exploitation. I think few Christians would argue about the prior argument, but the latter is one that many people disagree with.  As an ecologist, I can say that there is ample evidence for high natural biodiversity having a huge positive impact on human quality of life.  For example, there are well-documented cases of artificially increasing agricultural production through the use of fertilizers, while simultaneously reducing the native microflora and microfauna of the soil, leading to long-term degredation of ecological capacity, including the capacity to produce crops.

From an evolutionary perspective, one could also justify preservation or exploitation: all species evolved from the same elementary life-forms via essentially random processes, and are therefore of equal value, including humans.  We are no more valuable than dogs, gophers, or mushrooms, and therefore do not have the right (whatever that means) to 'play God' and cause these other species to go extinct.  To some extent, this argument ignores that, throughout the geological history of the earth, a small group of highly successful species has often come to dominate ecosystems or even continents, thereby leading to the extinction of many other species.  Indeed, some people have used this justification for the rampant exploitation of natural resources that happens today, suggesting that we are simply following our biologically hard-wired instincts to consume more and increase our genetic inheritance (in theory).  Furthemore, there are clearly different 'levels' of importance (at least ecological importance) for different species - some are simply too rare, too few in number, or too specialized to have much of an impact on the function of the system as a whole.  Although I can assure you that the human species is unique so far in the magnitude of our 'domination', I can't say with certainty that we are or are not following our instincts by causing extinctions, be it from over-use (e.g., passenger pigeons) or from purposeful eradication (e.g., large predators, biting insects).

Now it is clear to most biologists that causing species to go extinct on such a large scale as we currently are is probably not very good for US as a species.  Most of the things we've tried to or successfully gotten rid of have not even been well-understood, and have occasionally caused some pretty serious ripple-effects.  To be sure, there may be some ecological redundancy at larger scales, but most biologists would agree that it's a bad idea to start taking things out and expect that the various ecosystem goods and services will still be available to us later on, particularly given the complexity of these systems. Think of it as playing Jenga while wearing really dark glasses and boxing gloves.

But, despite this view being widely published throughout the scientific literature, and apparently having widespread public support, you don't generally hear priests, reverends, or rhabis telling their congregations to stop eating bluefin tuna or buying new mahogany furniture.  I'm not suggesting they ignore environmental issues - I've heard many preach about responsible consumption, and a couple of years ago the pope actually declared that pollution was a sin - but they seem to ignore that species are being lost at an alarming rate.

Unlike many outspoken scientists, I think religious leaders have great potential to help with the challenges we scientists get to document. But I'm not seeing it yet (at least not at more than a lip-service level), so I'd be grateful if any reading this post could point towards a few examples of local leaders doing so, and perhaps answer a few questions to help me understand all these social and religious complexities.

1) Do you believe that all species have intrinsic value? (in other words, that they have value even if we don't see any particular use for them)
2) Do we have the moral obligation to prevent species from going extinct?
3) How do you justify that belief?
4) If you justify it on religious grounds (even partly), have you ever heard a religious leader speak about it as a problem?