Jump to content
Sign in to follow this  
CDarwin

Why did the australopithecines go extinct?

Recommended Posts

When you look at the human fossil record it seems remarkably "progressive." Species further back in time are more like apes and they are "replaced" by species looking remarkably more and more like humans. That seems a problem to me. Why wouldn't some ape-like hominids continue into the "human period," like there are still proper apes around today? Even with environmental change, were there not forest edge environments remaining in Africa for them?

 

Australopithecus and Paranthropus were long lived genera, wide spread, and by all indications well suited to their edge environment. So why was Australopithecus gone after 2 million years ago and Paranthropus after 1?

 

The idea that it was because of competition with Homo doesn't hold water for me. The australopithecines were ecologically seperated from their Homo cousins. It's become something of a cliche, but the the australopithecines had much larger and more robust dentition, in line with a diet heavy in vegetable matter, where Homo was undoubtedly more omnivorous, even occassionally and with increasing frequency exploiting meat. The only substative ecological similarity between Homo erectus and Paranthropus that the two didn't share with every baboon and vervet monkey was that they were both bipedal. Did that really entail an ecological specialization so exclusive that one had to compete the other out?

Share this post


Link to post
Share on other sites
When you look at the human fossil record it seems remarkably "progressive." Species further back in time are more like apes and they are "replaced" by species looking remarkably more and more like humans. That seems a problem to me. Why wouldn't some ape-like hominids continue into the "human period," like there are still proper apes around today? Even with environmental change, were there not forest edge environments remaining in Africa for them?

 

There were many "proper apes" back then. The hominids had split between human(like), chimps, pongids and gorillas before 2 MYA. Among the homo ancestry there were several species, but there were plenty of other apes.

 

http://www.amnh.org/education/resources/rfl/web/hhoguide/family-tree.html

Share this post


Link to post
Share on other sites
There were many "proper apes" back then. The hominids had split between human(like), chimps, pongids and gorillas before 2 MYA. Among the homo ancestry there were several species, but there were plenty of other apes.

 

http://www.amnh.org/education/resources/rfl/web/hhoguide/family-tree.html

 

Mhmm... yeah I know. I'm using the old gradistic classification and refering all bipeds to the Hominidae and all apes to Pongidae, thus "homid" as I'm using it refers specifically to human ancestors. I'm sorry if that threw you.

 

The Homonoids (according the the old scheme) split between the Asian and African apes, then between the gorilla ancestors and the chimp/human ancestors, and then between the chimp and human ancestors, that last split occuring according to molecular evidence around 7 million years ago. I know.

 

My question refers to the lineage that split off and "lead" to humans. Some early members, like the Australopithecines remained fairly "ape-like" in their cranial proportions elements of the post-crania, while developing whole new specializations in the form of their teeth for heavy chewing of vegetal matter in a forest edge environment. This lineage dissapears after entirely after 1 million years and is replaced by consitently more "human-like" species. It is almost is if there were a direction to this evolution. That seems strage to me. Is being like a human really the absolutely best way to survive as a terristrial ape, to the extent that hominids that more closely resembled the modern human condition would universally out compete those that did not?

Share this post


Link to post
Share on other sites

I don't know if this still holds, but at one time it was thought that the rise of modern homo coincided with a reduction in jungle and increase in savannah regions. Heavily specialized traits (like the robust chewing jaw for heavy vegetation) tend to do poorly when the environment undergoes a significant change and selection pressure increases. More generalized traits can usually radiate more easily into new niches.

Share this post


Link to post
Share on other sites
When you look at the human fossil record it seems remarkably "progressive." Species further back in time are more like apes and they are "replaced" by species looking remarkably more and more like humans. That seems a problem to me. Why wouldn't some ape-like hominids continue into the "human period," like there are still proper apes around today? Even with environmental change, were there not forest edge environments remaining in Africa for them?

 

Australopithecus and Paranthropus were long lived genera, wide spread, and by all indications well suited to their edge environment. So why was Australopithecus gone after 2 million years ago and Paranthropus after 1?

 

The idea that it was because of competition with Homo doesn't hold water for me. The australopithecines were ecologically seperated from their Homo cousins. It's become something of a cliche, but the the australopithecines had much larger and more robust dentition, in line with a diet heavy in vegetable matter, where Homo was undoubtedly more omnivorous, even occassionally and with increasing frequency exploiting meat. The only substative ecological similarity between Homo erectus and Paranthropus that the two didn't share with every baboon and vervet monkey was that they were both bipedal. Did that really entail an ecological specialization so exclusive that one had to compete the other out?

 

Perhaps a supervolcano such as the Lake Toba eruption that nearly caused homo sapiens to go extinct 75,000 years ago.

 

I'm not going to try and match known major eruptions with the timeline of australopithecines, but I wouldn't rule out that as a major factor.

 

I think the effects upon evolution of supervolcanoes are greatly downplayed or even ignored. They are like minor Mass Extinction events that happen literally all the time on a evolutionary scale, pushing previously weak or borderline species into extinction.

Share this post


Link to post
Share on other sites

I read somewhere that Homo sapiens was initially a small group of survivors at the edge of the African savannah (~10^6 yrs ago), following major climate change and desertification.

Lots of other Homo species disappeared, due to large changes back in the day (the end of the Pleistocene?). The Holocene is the current interglacial. Also there is evidence that modern humans are descended from Asian ancestors (who left Africa much earlier). Neanderthals went extinct before the interglacial, by about 20k yrs.

Share this post


Link to post
Share on other sites
I don't know if this still holds, but at one time it was thought that the rise of modern homo coincided with a reduction in jungle and increase in savannah regions. Heavily specialized traits (like the robust chewing jaw for heavy vegetation) tend to do poorly when the environment undergoes a significant change and selection pressure increases. More generalized traits can usually radiate more easily into new niches.

 

That's true, but there's always going to be a forest edge. That's the environment the australopithecines were adapted to.

 

I think the effects upon evolution of supervolcanoes are greatly downplayed or even ignored. They are like minor Mass Extinction events that happen literally all the time on a evolutionary scale, pushing previously weak or borderline species into extinction.

 

East Africa was volcanically active, but I think that begs the question. Why were the australopithecines so weak to be knocked off from a super-volcano (really that would be two super volcanoes a million years apart) in the first place?

Share this post


Link to post
Share on other sites

East Africa was volcanically active, but I think that begs the question. Why were the australopithecines so weak to be knocked off from a super-volcano (really that would be two super volcanoes a million years apart) in the first place?

 

During bottlenecks, I think that sometimes it just comes down to luck.

 

Let's say that australopithecines and an early homo species were both reduced to numbers under 1,000 during a supervolcano event (which can erupt anywhere on Earth and cause global catastrophe). At these levels, random events such as one of the last surviving herds of Wildebeest seeking shelter near the homo species' last habitat and providing ample food could be the difference between extinction and survival.

 

Of course, that's just one of many possibilities. A strong possibility, in my opinion, though.

Share this post


Link to post
Share on other sites
During bottlenecks, I think that sometimes it just comes down to luck.

 

Let's say that australopithecines and an early homo species were both reduced to numbers under 1,000 during a supervolcano event (which can erupt anywhere on Earth and cause global catastrophe). At these levels, random events such as one of the last surviving herds of Wildebeest seeking shelter near the homo species' last habitat and providing ample food could be the difference between extinction and survival.

 

Think about what the "australopithecines" were, though. We're talking about two genera spread out over 3 million years all over Africa. You're proposing numerous bottlenecks in numerous populations of numerous species spread out over at least a million years, each accompanied by a super-volcano?

Share this post


Link to post
Share on other sites

I believe the current theories of Homo extinction are focused on climate change as being the proximate cause.

 

The end of an ice age usually means a lot of this occurs, and there have been a few ice ages. And I just realised I made a mistake in another post about the Holocene being the onset of ice-ages (instead of the latest one). They started when the continents got to roughly where they are now, the Cenozoic, the start of which geologic period is marked by the KT boundary, ~65m yrs ago. But we or our predecessors weren't around until the Miocene , I think.

Share this post


Link to post
Share on other sites

I wouldn’t think any vertebrate could be ‘strong’ enough to cope with a sudden super volcanic eruption and its aftermath, if being located in the 'wrong' place. Wouldn’t survival hinge more on the location of australopithecines and their food sources at the time of a super volcanic eruption?

Share this post


Link to post
Share on other sites

A disaster would have a local effect (unless it was real big, say a supervolcano, which is still a theory, isn't it?). So it's down to any survivors. Obviously, there were some of these (in our case).

Share this post


Link to post
Share on other sites
I wouldn’t think any vertebrate could be ‘strong’ enough to cope with a sudden super volcanic eruption and its aftermath, if being located in the 'wrong' place. Wouldn’t survival hinge more on the location of australopithecines and their food sources at the time of a super volcanic eruption?

 

The answer for the australopithecines to "where were they" was "all over Africa." A super-volcano that big would leave a faunal impact, which you don't see.

 

The extinction of the australopithecines wasn't a sudden event like a super-volcano anyway. I think we can move past that notion.

Share this post


Link to post
Share on other sites
The answer for the australopithecines to "where were they" was "all over Africa." A super-volcano that big would leave a faunal impact, which you don't see.

 

The extinction of the australopithecines wasn't a sudden event like a super-volcano anyway. I think we can move past that notion.

 

Well, if it wasn't the aftermath of a super volcano effecting specific food chains and sources, it seems possible that australopithecines where easy meat on two legs for homos? Homos and Australopithecines may have eventually wondered into each others territory, or, Homo hunting parties would actively seek Australopithecines out?

Share this post


Link to post
Share on other sites
The answer for the australopithecines to "where were they" was "all over Africa." A super-volcano that big would leave a faunal impact, which you don't see.

 

The extinction of the australopithecines wasn't a sudden event like a super-volcano anyway. I think we can move past that notion.

 

I think the effects of a supervolcano would very subtle in the geological record. For example, if a supervolcano dropped the average global temperature by 10C for 15 years, it would be very difficult if not impossible to spot. But that would be enough to cause the population of hominids in Africa to plummet to dangerously low levels.

 

And I don't think the existence of supervolcanoes are in questions.

 

http://en.wikipedia.org/wiki/La_Garita_Caldera

 

This eruption ejected 5,000 cubic kilometers of debris. In comparison, the 1883 eruption of Krakatoa ejected 25 cubic kilometers. Krakatoa reduced global temperatures by 1.2 Celsius for a year.

 

Why would it be hard to imagine that an eruption 200 times larger reduced the temperature by over 10 Celsius?

 

That's just an example of one supervolcano. We do not know for certain if eruptions during the existence of hominids were larger or smaller.

 

Either way, I don't think you can "move past that notion" as if it were infeasible. I would consider it infeasible that supervolcanoes didn't have a major effect on the evolution of most species throughout earth's history.

Share this post


Link to post
Share on other sites

LOL... has anyone yet given any support that a supervolcano even occurred during the epoch involved? :doh:

Share this post


Link to post
Share on other sites
That's true, but there's always going to be a forest edge. That's the environment the australopithecines were adapted to.

 

 

But if the forest shrinks, the edge gets smaller and you can't support as large a population. There's more pressure from others competing in similar niches. Now, add in specialization of the diet — what if one of the food sources is diminishing (from the large population or other competition)? Look at the panda for an example of what overspecialization can do.

Share this post


Link to post
Share on other sites
Either way, I don't think you can "move past that notion" as if it were infeasible. I would consider it infeasible that supervolcanoes didn't have a major effect on the evolution of most species throughout earth's history.

 

Alright, I don't mean to be disimissive. The super-volcano alternative just don't seem to fit what we see in Africa for the time, which is gradual faunal change spread all over the continent over millions of years. There isn't any evidence of the sudden destruction of whole lineages. Also, I'm not aware of any evidence of any super-volcanoes errupting around that time.

 

But if the forest shrinks, the edge gets smaller and you can't support as large a population. There's more pressure from others competing in similar niches. Now, add in specialization of the diet — what if one of the food sources is diminishing (from the large population or other competition)? Look at the panda for an example of what overspecialization can do.

 

But the austrolopithecines were't that specialized. They were generally geared toward a more vegatitive diet, but so are a lot of animals. The australopithecine extinctions did coincide with a legitimate environmental shift, the beginning of the Pleistocene and the drying of Africa, so it would be unreasonable to ignore that as an important factor in their extiction. Why were they less competitive than the other animals they might have competed with, though? That would have been monkeys (geladas, baboons, possibly early savannah guenons or late African macaque-like things) mostly, and possibly early Homo.

 

Did the baboon smite Lucy? I think that possible. They probably would have shared similar general diets, though I can't think of anything in the African woodland at the time that might have been able to handle the heavy mastication of the tough, fibrous foods that Paranthropus was exploiting. Well, elephants maybe?

 

I'd also be willing to except the "dumb luck" explanation, that australopithecines weren't able to hang on in a more limited niche like the geladas were after they were usurped by the baboons, but I wonder if there is a better one. Why on earth did the gelaldas lose out? That'd be an interesting quesiton to find an answer to. I believe there's a book on it.

Share this post


Link to post
Share on other sites
LOL... has anyone yet given any support that a supervolcano even occurred during the epoch involved? :doh:

 

I know Wikipedia is not an infallible source, but it lists many known supervolcano eruptions in the last 2 million years. http://en.wikipedia.org/wiki/Supervolcano#Known_eruptions

 

Going back much further becomes difficult because eruptions occured on top of the same calderas multiple times.

 

If the Loba Toba eruption 75,000 years ago wiped out 60% of the human population, why is it inconceivable such an event has occurred more than once, possibly affecting evolution.

 

Again, I'm not claiming this as a fact, just throwing out into the conversation as a possibility. I am not quite sure why people are so critical of it, especially knowing how common and how large these eruptions can be.

Share this post


Link to post
Share on other sites

I don't doubt the existence of supervolcanoes. I don't doubt their commonality in the existence of this planet, nor their effect on the life the planet supported during their eruption.

 

I do doubt the use of this idea as an explanation for the reasons australopithecines went extinct... especially since you cannot even describe a single event that occurred at the right time and the right place... also, the lack of other plant/animal deaths during the same time... also, the fact that homo survived.

 

Also, maybe it was aliens that did it.

 

Come on. If you're going to speculate, at least root it in something valid. Just because you saw a special on discovery channel last week doesn't mean that the topic of said special is the answer to each question you encounter.

 

 

 

 

 

Sorry for my tone... Long day. Lots of pissed off executives who have been drilling me for real explanations and not fluffy speculations without support. Mea culpa.

Share this post


Link to post
Share on other sites
I don't doubt the existence of supervolcanoes. I don't doubt their commonality in the existence of this planet, nor their effect on the life the planet supported during their eruption.

 

I do doubt the use of this idea as an explanation for the reasons australopithecines went extinct... especially since you cannot even describe a single event that occurred at the right time and the right place... also, the lack of other plant/animal deaths during the same time... also, the fact that homo survived.

 

Also, maybe it was aliens that did it.

 

Come on. If you're going to speculate, at least root it in something valid. Just because you saw a special on discovery channel last week doesn't mean that the topic of said special is the answer to each question you encounter.

 

 

 

 

 

Sorry for my tone... Long day. Lots of pissed off executives who have been drilling me for real explanations and not fluffy speculations without support. Mea culpa.

 

...

 

You are equating large volcanic eruptions with aliens, as a factor in evolution, to make my suggestion sound absurd. And stating that I'm getting my information from the Discovery Channel.

 

Can you back those claims up? One would do well to avoid including exaggerated or created statements in other areas than just science.

 

All I was suggesting was that supervolcanoes exacerbated existing selection pressures, and that there is a possibility that these eruptions in conjunction with other advantages homo had, was a factor in the extinction of said species.

 

The reason this possibility came to mind was that the Lake Toba eruption reduced the human population by 60%. If something happened once, if could have happened before. I don't know why people get so cranky over a simple suggestion.

Share this post


Link to post
Share on other sites

Fair enough. So, exactly which supervolcano do you presume wiped out australopithicines? What year?

Share this post


Link to post
Share on other sites

I don't think any supervolcano wiped them out, but it is possible that it reduced them to such a level at a particularly bad time that homo established firm dominance or even finished off their cousin species. I'm not going to get more specific than that, because I do not know.

 

I cannot answer which specific supervolcano was involved if any. The exact date for the extinction of australopithecines is in a fairly large time frame; supervolcanoes occur multiple times every 100,000 years; the circumstances of the extinction of the australopithecines could have been triggered by a supervolcano but the species itself struggled on for many years after before succumbing; scientists certainly do not know every supervolcanic eruption throughout history, especially when you start getting past 1 MYA.

 

The point... it was only a suggestion, and the possibilities are too varied to state any certainty.

Share this post


Link to post
Share on other sites
I don't think any supervolcano wiped them out, but it is possible that it reduced them to such a level at a particularly bad time that homo established firm dominance or even finished off their cousin species. I'm not going to get more specific than that, because I do not know.

 

I cannot answer which specific supervolcano was involved if any. The exact date for the extinction of australopithecines is in a fairly large time frame; supervolcanoes occur multiple times every 100,000 years; the circumstances of the extinction of the australopithecines could have been triggered by a supervolcano but the species itself struggled on for many years after before succumbing; scientists certainly do not know every supervolcanic eruption throughout history, especially when you start getting past 1 MYA.

 

The point... it was only a suggestion, and the possibilities are too varied to state any certainty.

 

You've encapsulated all the problems with your hypothesis in that statement. A) You're still thinking of the Australopithecines, an extensive lineage inhabiting the entire continent of Africa, as a "species." B) You're suggestion simply isn't testable.

Share this post


Link to post
Share on other sites

A) I'm not thinking of them as a species, and I was aware of what I said when I said it. Sometimes speaking in extremely precise terminology wears on the brain when speaking informally on an internet site. If I was writing a paper, I might use my terms more strictly.

 

B) Suggestions need not be testable... because they are suggestions. If someone reads my supervolcano suggestion, thinks on it a bit, and realizes a way to test it, wonderful. If not, no loss.

 

I think you encapsulated what irritates me about many scientifically-inclined individuals: an over-emphasis on terminology and semantics instead of ideas. Overall, I think this may harm science because it shifts focus to precision in communication rather than understanding in communication.

 

You see, humans have this amazing ability to convey meaning perfectly without fully spelling out every word in exact detail. If I said "cars" when referring to vehicles in general, you would understand. If I use "species" when referring to genera, you understand as well.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.