Scientists: Are we in 6th Great Extinction?

Inspired by this page on the PBS Evolution Project site.

Clearly, we’re having a lot of die-off on this planet right now. I ask the dopers who are in a position to have an informed opinion: Are we in the 6th great mass extinction?

Obviously, I can’t keep people from hijacking. All I can do is emphasize that, even though this thread is in GD, it’s not intended to be an open invitation for laymen to discuss the merits of evolutionary theory. But hey, once you birth a baby it has its own life, I reckon.


I’d say it’s too early to tell, but things are certainly trending in that direction. These mass extinctions can take tens-of-thousands of years, though, so I think it’s very difficult to discern what the real pattern is. It seems unlikely, however, that humanity is capable of curtailing its own impact voluntarily, so it’s certainly reasonable to conclude that unless we suffer some species-specific threat to our survival, our presence, on geological time scales, will have a similar impact to one of the global catastrophes that likely triggered some of the previous mass extinctions.

So far, no. The number of “obvious from just the skeletons and large to boot” species that we have managed to eradicate in recored History isn’t all that many. I say “obvious from just the skeletons and large to boot” because that is what they usuallycan/do track from the fossil record. If a beetle that “differs from it’s cousin subspecies only by the number of spots on it’s carapace” goes into extinction, it is rare we can see that from the fossil record. Sure, a lot of “minor” species are going belly up- but were they always and normally doing that before humans? In other words- maybe those “beetle that differs from it’s cousin subspecies only by the number of spots on it’s carapace” are always going extinct, but they can’t be tracked by the fossil record.

Large species- or species that occupy a large niche at least- is/are what they have been able to track. Other than the arguement that early humans wiped out the Pleistocene fauna (something which is very much disputed by both sides), the number of significant species we have wiped out in recorded history isn’t really all that high. Many of those that were are either subspecies or species that occupied a very small niche (the Dodo occupied a small niche for example).

Offhand, I can think of two- the Carolina Parakeet, and the Passenger pidgeon. I am sure I could find more if I looked 'em up. Stellers Sea Cow was certainly large, but there never seemed to be many. Hmm, the Great Auk, also, I suppose.

However, we have brought to the edge many more species- the Atlantic Cod, the American Bison, many of the whales- and others. Thus- there is a distinct possibility that we will enter such an age, or perhaps we have entered it already…

Not yet, no. It’s estimated that the last mass extinction at the K-T boundary wiped out 85% of all species worldwide, short of nuclear war I don’t see how we could match that.

However, we are certainly shovelling species off the face of the planet at an alarming rate. We do this by changing a species’ environment faster than it can adapt (e.g. deforestation), or by hunting them to extinction. Human caused extinction isn’t a new phenomena, for example when the Maoris reached New Zealand they ate the Moa out of existance, but our ability to change the environment has increased dramatically with modern technology.

I think human population will be the biggest factor in determining the level of extinctions. If our population continues to grow were going to need every scrap of available land for food and resources. If war, disease or cultural factors keep our population in check I’d expect the current rate of extinctions to level off.

Consensus certainly seems to be that Man played a major role int he eradication of megafauna in North America. Certainly in Australia.

But the factors that are leadning to the mass extinction are several:

  1. We are changing the global environment at a rate much brisker than genetic diversity and adaptation can allow individual species to keep up with. Global warming, etc.

  2. We are isolating species population from each other. Without a critical mass together survival is doomed (I can dig up an interesting reference for the ongoing demise of American Gingo based on this factor - Science- if requested)

  3. We are introducing species from one part of the world to other parts of the world where they eliminate inidigenious flora and fauna.

Together this is more significant than nuclar warfare.

Life on this planet will survive. Every extinction has been followed by greater diversity … eventually. And the bacteria will always live on. It is and always has been the Age of the Bacteria.

…and cockroaches! Don’t forget the cockroaches! :smiley:

I think this is what’s usually meant when I hear about a man-made mass extinction. The destruction of megafauna that coincided with the rise of humans was huge. Here is an incomplete list

While it isn’t a sure thing, the fact that so many species of the types of animals that humans hunt and/or compete with died out on seperate continents at the same time that humans arrived on those continents is pretty evocative of a wave of human caused extinctions.

Here is an incomplete list of mammals and birds that have become extinct during historical times (which when you think about it, is a very short period on a geologic timescale, I have no trouble beliving that we’re keeping pace with some of the past mass extinctions ). It also seems likely that we’ll see quite a few endangered species whose populations are down to a few individuals give up the ghost in the next few decades.

As to whether we can actually equal the mass-extinctions of past epochs, as others have said, we’ll have to see how global warming, population growth and habitat destruction play out.

A correction and details:

My example of ginkgo was incorrect … it was American Ginseng, and it is felt to be representative of many understory plants. The predicted demise to be is a consequence of both habitat fragmentation and the increase in population of animals that graze on it, in this case the deer which has increased significantly as a consequencxe of the disappearence of its main predators. And as the understory plants go, so will go some of the species that rely on them. It was Science Feb 11 2005:

I prefer to think we are merely shifting the environment to the advantage of those species that evolve quickly!

As a matter of fact, we should have thought of this sooner, that way the “quick adapters” would be in full gear by now and we could screw the environment with reckless abandon!

Well, you seriously do have a point. What does it really matter?

We are the ultimate quick evolver. Short term? We have the ability to adapt by culture and technology. We will likely survive any foreseeable future. Maybe in a poorer and uglier world with more disease and starvation, etc. but we will likely adapt somehow. Long term? On a scale of significance the niches emptied will eventually be filled again. Maybe it will take a few hundred thousand years or so, or even a million, but so what?

Viruses and Bacteria?

I reckon I don’t have as much faith as you do in our technology. If the oceans rise, the jet stream and gulf stream significantly reconfigure, deserts continue to expand, and toxins permeate our environment <not as a result of species extinction, I know, but these are potential causes of it> I just don’t see our technology being that effective against it.

For me, mere survival of the species isn’t the goal. I’m more concerned with my kids having a life worth living.

As Woody Allen said when asked how he’d like to live on in the hearts of his fans, “I’d rather live on in my apartment.”

I think most biologists who study ecology (and I’m one) would agree that we are in the midst of a major extinction event, triggered by human activity, that began about 11,000 years ago, and which will continue over the next several centuries at least, if not millenia. Where exactly the toll will be by the time it’s over relative to the “Big Five” major extinctions is uncertain, but many biologists feel that it will be the greatest since the end of the Cretaceous.

This extinction event has had several phases:

  1. Megafaunal extinctions, particularly in Australia and the Americas, at the end of the last Ice Age about 11,000 years ago. Most of these were probably due to human over-hunting and other impacts such as burning.

  2. Extinctions on oceanic islands over the past few thousand years, especially in Polynesia and Madagascar, as they were colonized by humans and their commensals such as rats. Archeological evidence suggests that thousands of species of birds may have become extinct on Pacific Islands during this time.

  3. Further extinctions due the spread of Europeans throughout the world starting 500 years ago, causing even more extinctions on oceanic islands due to the introduction of predators such as cats and mongooses, and extinctions in mainland areas due to hunting with firearms and habitat alteration.

  4. Within the past century, massive habitat destruction and alteration due to the exponential increase of the human population, coupled with the global spread of invasive species due to human introductions, has caused the extinction or extreme reduction of many species in continental areas as well as on islands.

The recent and projected rate of extinction of known species is many time greater than the calculated extinction rate over previous periods. From here:

Bolding mine.

We do not know exactly what the impact has been on many other species, such as insects, marine organisms, and plants, since many of them have never even been described. However, it is likely that there has been a significant impact there as well.

And the trend continues. Many of the species that still survive today are “living dead” - they have been reduced to such small numbers in such small areas that their long-term survival is very unlikely. Others are slowly but surely succumbing to the effects of invasive species. It may take several centuries more before they actually become extinct, but without massive intervention, the outcome is certain.

Frankly, I find this attitude utterly incomprehensible. The fact that the world is becoming a poorer, uglier, and less interesting place certainly matters to me. I think that it will also be a source of great regret to future generations that such a thing was allowed to take place.

Ah, but you are taking a very self-centered view. Unless you subscribe to particular religious views the world was not created for your enjoyment. Long term there are homeostatic mechanisms at work. If we can’t manage to regulate our own behaviors in such ways that prevent such medium term catestrophic outcomes then the world will correct it for us. Again, eventually. Of course from my POV as a human and a parent I’d like to avoid such outcome as my grandchildren and their grandchildren would be paying the price for generations to come. But life on the planet has “all the time in the world” to recover.

Glad to hear that. But of course the ultimate argument for trying to preserve the Earth’s current biodiversity that it is for our own benefit: whether you subscribe to the economic arguments (of which there are many), scientific arguments, or purely aesthetic arguments (because it makes the world a more pleasant and interesting place.)

There was a thread here not long ago about humans “destroying the planet.” We are of course not destroying the planet. The Earth doesn’t care whether it has 10 million species or is inhabited by nothing more than humans, rats, and bacteria. If we destroy the Earth’s current biodiversity in the manner of the K-T fireball most of it will be regenerated within a mere 10 million years or so (if we let it come back). But that’s a little too long for me. YMMV.

A slight quibble (speaking as a geologist)

You’ve got to be very careful when comapring what’s going on today with the evidence of the fossil record. The evidence from tha past is very, very incomplete. We have (AFAIK) no records of what happened on small islands during previous extinction events, so using what is going on today in these areas doesn’t really help in comparisons.

Quite true. In fact, we lack a lot of details about previous Great Extinctions. For one thing, we have very little information about what happened to most of the smaller organisms. We have no idea of how many species of insects may have become extinct in the Cretaceous-Tertiary or the Permian-Triassic events, for example.

In fact, life on small islands is pretty vulnerable in the first place. Major extinction events in the past probably wiped out life on islands even more severely than they did on land.

So far, the current extinction event has preferentially affected species on islands to a much greater extent than it has those in continental areas. However, even in continental areas it’s sufficiently severe to be of great concern.

I just want to thank all of y’all for the calm, rational, and highly informative posts here. I was afraid it might become the target of a DoS attack (“Dips**ts on Soapboxes”), but it has not.

Great post.

I’ve been meaning to ask in GQ: At what point are animals and other species considered “genetically instinct”, eg. the min. number of reproductive animals needed in order for a specie to survive? Not an easy question, but is there a number?

Actually, it’s easy: one fertilized female.

One species that has come back from the ultimate brink is the Chatham Island Black Robin of New Zealand. It was reduced to only five individuals, which included only one breeding pair. An intensive rescue campaign by the New Zealand Wildlife Service has now built the population back up to 250 individuals, but every one is descended from one single female.

Species can survive extreme population bottlenecks, but the reduction in genetic diversity does often weaken them, and may make their long term survival more problematic. It doesn’t, however, inevitably mean they will become extinct. The problem is greatest if the population remains at a very small size over a long period of time, in which case severe inbreeding will cause problems. There is less of a problem if a population can expand again rapidly after going through a bottleneck. However, many of the species that are now on the verge of extinction today will not be able to expand even if protected because most of their habitat is gone.

Cheetahs seem to have gone through a severe bottleneck in the relatively recent past. They are all so similar genetically that they can receive skin grafts from other cheetahs without rejecting them. However, when the species range extended throughout most of Africa and much of Asia this wasn’t such a severe problem. It is becoming much more so now that the population has been greatly reduced and fragmented.