Two new Homo fossils are described in this week's Nature, and here they are.
This is KNM-ER 42700. It's a very well preserved brain case, it has been dated to 1.55 million years ago, and it has been positively identified as belonging to Homo erectus. It's a little unusual in being particularly small, but otherwise, definitely H. erectus.
a, Anterior, b, left lateral, d, superior and e, inferior views of KNM-ER 42700 (scale bar, 5 cm).
This is KNM-ER 42703. It's a broken maxilla, or upper jaw, and it has been dated to 1.44 million years ago — it's over 100,000 years more recent than the KNM-ER 42700. This specimen has been identified as Homo habilis.
f, Anterior, g, occlusal and h, right lateral views of KNM-ER 42703 (scale bar, 2 cm).
This is very cool and there are some interesting things to learn about human evolution from them. Unfortunately, one fact seems to be dominating the news about them, and is being consistently misinterpreted: the H. erectus specimen is older than the H. habilis specimen, yet the most common models of human evolution have H. habilis giving rise to H. erectus which in turn was the progenitor of H. sapiens. Even the Nature news summary makes a big issue of this difference.
Anthropologists have tended to see the evolution of Homo species as a linear progression, beginning with H. habilis and passing through H. erectus before ending up with modern humans.
And further, it gets twisted and accentuated yet further in the popular press, with articles claiming that Finds test human origin theory and
Evolution doubt after fossil find.
These are all wrong (I think; I don't hang out with anthropologists much—they don't really see evolution in that simplistic and linear fashion, I hope?). These discoveries do not put any seriously held theories in doubt. They do nicely demonstrate that a linear progression is not to be seriously held.
Just as your mother's life most likely substantially overlapped with your own, the persistence of a parental species so that it overlaps in time with its daughter species is not a challenge to evolution at all. That's the case here; the authors certainly do not regard this work as casting any doubt on the evolution of humans at all. Here's their conclusion:
Although some characters previously regarded as diagnostic of
H. erectus differ from H. habilis simply on the basis of overall cranial
size, the two taxa are nonetheless
metrically and nonmetrically distinguishable throughout their
lengthy co-occurrence through time. Moreover, during this period
of nearly half a million years the dento-gnathic morphology of
H. habilis shows relatively little change. The long period of sympatry
suggests the existence of some form of niche differentiation between
H. erectus and H. habilis, one that may have included foraging or
dietary differences. Taken together, these new fossil data highlight
that an anagenetic relationship between the two taxa is implausible.
As the earliest secure evidence of Homo is found outside the known
region of overlap, it is nonetheless possible that H. erectus evolved
from H. habilis elsewhere, and that the Turkana basin was a region of
secondary contact between the two hominin taxa.
To translate,
-
The two species are anatomically distinct, and they don't see signs of a blending between the two.
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The two species were sympatric, or living in the same territory at the same time. This suggests that they probably had different lifestyles, or conflict would have driven out one or the other.
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They did not have an anagenetic relationship, that is, one species did not gradually and imperceptibly change into the other. The Homo lineage had branched at some earlier date.
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That branch occurred elsewhere and earlier, and the H. habilis→H. erectus→H. sapiens line of descent is still tenable; it's just that KNM-ER 42703 would then be a member of a dead-end branch that did not leave descendents in modern times (of course, KNM-ER 42700 is probably also not a direct ancestor — it's representative of a population that may have led to us.)
Experience tells me that this concept, that individual fossils can't be arranged in a simple, linear, lineal relationship, is going to be very hard for many people to grasp, and is going to fuel quite a few creationist shouts of triumph in the near future, and the media aren't helping. It's misplaced. Evolution predicts a great many branches, with only a few twigs here and there preserved in the fossil record, exactly as we see in this discovery.
Spoor F, Leakey MG, Gathogo PN, Brown FH, Anton SC, McDougall I, Kiarie C, Manthi FK, Leakey LN (2007) Implications of new early Homo fossils from Ileret, east of Lake Turkana, Kenya. Nature 448:688-691.
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I read some articles about this, too, after seeing some of the screaming stupid headlines. I thought the same thing: the creationists are going to love this.
But then I thought, really, what is there for them to love? They don't believe in carbon dating, they think fossils have been planted to fool us, or some kind of nonsense - so how can they use this stuff to further their point? It should be irrelevent to them.
Thanks for taking this on, PZ. I was waiting for this since I saw the "Evolution Theory in Doubt" headlines on Yahoo! news this morning.
It seems to me that, given the extensive body of evidence suggesting a habilis->erectus->sapiens link, that the most likely explanation for this finding is:
1. habilis existed on its own
2. an isolated subset of habilis formed a founder population OR was subject to a new set of selection pressures
3. the isolated subset of habilis evolved into erectus
4. the erectus population grew out, and eventually occupied the same geographical location as habilis
I'm only a humble molecular biologist, so perhaps someone with a better grasp of anthroloplogy will tell me I'm off my rocker, but this sounds like a perfectly tenable explanation, which is consistent with the already-existing data, no?
I'm taking bets on how long it takes before it gets misrepresented by creationists. My bet was 18 hours from publication.
Wow, KNM-ER 42700 is just a wonderful looking fossil.
I'm a little confused. Meave Leakey is quoted in the articles as saying "Their co-existence makes it unlikely that Homo erectus evolved from Homo habilis." You state that "The Homo lineage had branched at some earlier date." My question is, at the time of the branch would that species be considered Habilis, or did habilis and erectus both evolve from an earlier common ancestor?
I think newspaper editors are remarkably stupid, but that's just my opinion to drive traffic to my own site and drum up publicity for articles that have nothing to do with a particular headline.
Make your own inferences...
How do you know they were homo's?
@Michael. As far as I remember that's one of the standard speciation models, so no, you're not off your rocker.
NickM wrote: *But then I thought, really, what is there for them to love? They don't believe in carbon dating*
It doesn't matter if they believe in carbon dating this time. We don't use 14C to date anything older than about...I dunno, 60-70,000 years bp. Of course, out of ignorance they'll try to use that point to support their side: "the scientists *themselves* say that cannot date fossils millions of years old using carbon dating. Well, then how can they say these new hominins are around one and half million years old?"
Man, is this going to be one of those "if we came from monkeys, why are there still monkeys" arguments? How silly, it's nothing we haven't been dealing with for years anyway. So my bet would be more like 18 minutes, factician, not hours.
The right wing
How do you know they were homo's?
If you'd seen the women back then, you'd be a Homo too!
Zing!
hey, more to add to the "shoebox."
Your hope is correct, PZ. Anthropologists don't see hominin evolution in such a simplistic and linear fashion, at least, not anymore. It used to be thought that the human lineage was more or less a single march from A. africanus through H. habilus, H. erectus, H. neanderthalensis, to us, but now it seems the African plains were overrun with human ancestors, in-laws, and second cousins twice removed.
Taz: I think either of those scenarios is reasonable. The difference is the branching pattern... I wish I could draw a picture. In the first case it would be more like a straight line with a branch coming off at an angle (Sort of like the letter K without the bottom leg). In the second it would look more like the letter Y.
@Josh - Sorry for the display of ignorance - how then do the scientists determine the age of really old fossils, if not by carbon-dating? And why is carbon dating not effective for really old objects? Generally, I try to google and look up stuff in wikipedia - but in this case if you could steer me to a website that answers these questions, I'd appreciate it.
One of those blue bars in that diagram is going to have to be extended. Africa 1.5 million years ago was a crazy busy place for our clade, wasn't it?
This is why scientific reporting should be made by SCIENTISTS and not pseudojournalists who don't know jack about science.
I was reading something not long ago how they've changed the "Out of Africa" hypothesis to the "Out and In and Out again" hypothesis. :)
The Meave Leakey comment brings to mind the book "Lucy," in which Johanson characterized Louis Leakey as having a sort of obsession with the idea that there was an as-yet-undiscovered Homo lineage going back far, far into time, and not wanting australopithecines et al. to be in the line leading up to us. I haven't read enough of the Leakey family's work to know whether Johanson's characterization was really fair or not, but the idea of cutting habilis, with its more-australopithecus-like-characteristics, out of the line might be that view of the facts rearing its head again. I really can't understand how a paleontologist can possibly make a statement like that--obviously habilis could be the ancestor of erectus AND have co-existed with erectus, and as zuckerfrosh points out, the contrary view really is nothing more than the "how come there are still monkeys?" argument, moved back a million years or two.
NickM: here's a suggestion, a book I reviewed called Bones, Rocks, and Stars. It's all about dating methods.
Carbon dating is limited because carbon isotopes have short half-lives -- the isotopes measured will have all decayed after many tens of thousands of years. Other methods use other radioactive isotopes that have much longer half-lives and so persist over a greater range of time.
An "If I Ruled The World" moment:
If I ran a news company, I'd instruct the people in charge of hiring and such to toss out the resumes of people without a degree in something other than journalism. Real experts only. Real experts without journalism experience will be trained in journalism on the job.
Nick: No worries...by far most people don't realize that we don't use 14C for anything really old (my apologies to all of you Holocene-centrists out there with the *really old* comment). Carbon 14 only has a half-life of 5700 or so years and so it is of limited use (if we're taking really deep time) in dating rocks or other material. For older stuff, we use different radioactive isotopes with much longer half-lives.
Generally, Wikipedia makes me wanna punch people, especially with science. The USGS has a really good page:
http://geology.wr.usgs.gov/wgmt/common/geochronology.html
I have issues on occasion with talk origins, but they have a pretty good overall view of dating in the broad sense:
http://www.talkorigins.org/faqs/dating.html
Tom @Thoughtsic.com , don't be an idiot. There are some very high quality science journalists out there. Fact is, if all science reporting was left up to science 1.) the public wouldn't understand most of it 2.) the scientists wouldn't get as much research done and 3.) the coverage would lack objectivity. Scientists aren't immune from pimping their the importance of their own research, and if you think otherwise, you don't know enough scientists. Dedicated science journalists translate the science into language the public can understand and provide an objective stance on research.
The problem is that most newspapers no longer keep a stable of dedicated science journalists. NYT does, and their science coverage is, by and large, pretty good as a result. I will agree that your average general assignment reporter will muck up the science nine times our of ten, but I would argue that he never should have been assigned the story in the first place, and I would certainly argue that your solution wouldn't work.
...which should be plenty to accurately date anything you might find in God's 6,000 year old world, you heathen! ;^)
I think the thing I found most interesting about the Nature paper is the notion that H. erectus looks to be substantially more sexually dimorphic than we previously thought...if so, and if that character really is not derived and is thus 'primitive,' it suggests that H. erectus is perhaps not as similar to modern humans as previously thought.
I was incredibly perplexed by the reporting of this story, since they seemed to think that this was a revolutionary find. The article I read made it sound like it was a death knell for habilis evolving into erectus, and it's obvious (even to a Physicist) that it doesn't.
Bill: Laughing my ass off. Excellent Point. Thanks for making me spit water all over my monitor, jackass... ;)
Crap, that screed would have come off better without the grammatical mistakes. Let's see here...
"Fact is, if all science reporting was left up to scientists"
"Scientists aren't immune from pimping their the importance of their own research"
You know, I have no real training in journalism or science, but I swear I could do a much better job at it than the people doing it now.
The only problem is getting a job as a science writer without any experience or qualifications beyond a passionate layman's interest.
stogoe
It's harder than you think... People have a terribly mistaken impression that reporting is an easy thing to do. It's easy to do poorly, yes, but it takes an awful lot of work to be a good journalist, science writing or otherwise.
This is precisely why I'm jumping from the biology ship (where I've spent the last decade) to pursue science education... would you be shocked to know that most science educators are NOT actually scientists? Probably not. But that's the way it is. Sigh.
stogoe
And, if you're actually serious about wanting to break into the profession, several of my colleagues got into science writing with little more than a proven ability to write and a passionate interest in science. And they're damned good reporters. So if you're feeling up to it, call up an editor or e-mail one, pitch them a story idea, send them a writing sample and get cracking. They don't care if you don't have a journalism degree. If you have a good idea and can write, they'll let you write about it.
That was my initial thought as well, but then we have the Leakey quote:
I'm struggling to understand why journalists are expected to sort out stuff that scientists haven't sorted out. I notice the usual journalist-bashing, which in some cases is deserved but in other cases is not. But then I've long ceased to expect intelligent commentary from a place dominated by the descendents of Joe McCarthy.
What really bothers me in this episode...
Here we have new evidence which may challenge some of our understandings of human evolution, and may well lead to some fine-tunings of it. This points to the strength of the science: evidence leads to ideas, not vice versa, and changes to the evidence are honestly analyzed to help make the ideas more accurate.
And yet, this is exactly what the creationists will point to as showing the weakness (or they may use stronger words such as failure) of evolution.
And they get away with it. Every time.
You have a point, davidm. Journalists can't be expected to understand the fine points of these things. I think where the outrage comes from is when they take a new finding and just assume it means something really revolutionary, then spin it into an inflammatory headline without checking to make sure they have it right.
Wow. Nice dig there. Jerk.
LOOK AT THE HEADLINES!
You would thing there was some meltdown in the theory of evolution by reading them.
That deserves all the ridicule we can muster.
thing=think
Steve_C,
Was that directed at me? I can't tell.
davidm:
Smooth. The way you slide a general insult into what started out as a reasonable comment. I'm impressed.
And while we're on the topic of crappy headlines, here's a little newsflash: Most of the time, reporters don't write the headlines! Copy editors do. And, unfortunately, copy editors sometimes only spend about .25 seconds skimming the story and coming up with the headline. So, complain about the headlines all you want, but realize that the reporters aren't responsible for them.
KNM-ER 42700 (erectus) is dated to 1.55 million years ago (Mya), while KNM-ER 42703 (habilis) is dated to 1.44 Mya. I don't have access to the Nature article.
Does anyone know if in the article the authors mention the uncertainty in those ages?
"Their coexistence makes it unlikely that Homo erectus evolved from Homo habilis."
An article that I read this morning (either NYT or WSJ, sorry don't have them in front of me) made reference to the possibility of an earlier, undiscovered common ancestor from a period of time that is sparsely represented in the fossil record. That hypothesis suggests that the relationship may be more along the lines of "cousin" species than "parent-daughter" species.
Yeah, I was going to point out that this was a case where the scientists are contributing to the confusion, but when davidm slithers in with his usual kneejerk defense of media failure, I lost all interest in doing so.
Most people are relatively stupid.
not "stupid evil" or "stupid dumb" -- just stupid. Meaning they read the headline - say "ah" then read the article with the headline as the guiding framework. Anything that doesn't fit the predefined framework gets ignored (the 600 pound gorilla that nobody sees)
I need to communicate with *lots* of different communities with different client organizations. I spend a *lot* of time on the headline (or subject line, if email).
When I don't take this time - it doesn't matter how clear or internally consistent I make the the overall message - if the headline suggests something different, then that's what people will remember and *know*.
I am lucky in that I *do* get to write my own headlines.
As MarkP says - that's the job of the sub (and don't you DARE tell him his headline doesn't make sense).
Gah. Please, PZ, don't let davidm ruin it for the rest of us journalists!
An apt observation, John.
Personally, I wouldn't waste my time sticking around a place where I had "long ceased to expect intelligent commentary", and find myself reduced to mere petty sniping--yet, for some unexplained reason, he still does.
Guess he just doesn't know how to quit us.
oops -- this is what happens when you write too quickly (at least I don't do this in my job!!!!)
MarkP should say MikeP. Sorry Mike!
and that's usually the job of the sub in traditional media
No problem, tony. I know how it goes.
Thank you for the enlightening discussion. Much appreciated!
Changcho, here is the discussion of the stratigraphy from the paper (I deleted the superscripts for cited references):
"Both hominins were found during fieldwork in 2000 at Ileret (north-eastern Kenya). They lie between the KBS Tuff (1.869 +/- 0.021 Myr)and the Chari Tuff (1.383 +/- 0.028 Myr); the age of the Lower Ileret Tuff (1.527 +/- 0.014 Myr) provides additional chronological control. We estimate an age of 1.54 Myr for the Main Ileret Caliche, and 1.60 Myr for tuff IL02-043, assuming a linear sediment accumulation rate between the KBS Tuff and the Lower Ileret Tuff. IL02-043 correlates with a tuff in Submember J-5 of the Shungura
Formation, so it must be slightly younger than the Morutot Tuff, which has an arithmetic mean age of 1.607 +/- 0.019 Myr.
KNM-ER 42700 was found in situ in 'Area 1' by F.K.M. Almost
fully embedded in a matrix of coarse sandstone and carbonates, only a small area of the right temporal bone and of the right supraorbital torus was exposed. This specimen was recovered from strata above IL02-043, and 1.5 m below the Main Ileret Caliche. Therefore its age is between 1.53 and 1.61 Myr, probably within the interval 1.55 +/- 0.01 Myr, assuming constant sedimentation rates between IL02-043 and the Main Ileret Caliche. KNM-ER 42703 was found by John E. Kaatho in Area 8. It was ex situ, coated in carbonate matrix, on the brown mudstone and sandstone sequences between the Lower Ileret Tuff and the Chari Tuff. Assuming constant sedimentation rates between these dated levels, the probable age is 1.44 +/- 0.01 Myr. This is consistent with
the age of the 'Main fish bed', estimated to have formed at about 1.42 Myr ago, and also with the youngest measured ages
(1.476 +/- 0.013 Myr) of materials from the Okote Tuff Complex at Koobi Fora."
Note: tuff is an extrusive volcanic rock--essentially an ashfall deposit; it can be directly dated.
They talk about sedimentation rates a couple of times herein. The error bars on sedimentation rates in continental environments are often rather large. They cite some references regarding the sedimentation rates, but I haven't looked at them.
PZ: "I think; I don't hang out with anthropologists much--they don't really see evolution in that simplistic and linear fashion, I hope?"
Some biologists see evolution in such a simplistic fashion -- biological anthropologists are no exception. Wolpoff has been fighting with other paleoanthropologists for decades over the overly simplistic "either we are descendants of neanderthals or not" from the mitochondria crowd. For ten years, we've been told that since the modern mitochondria (and Y chromosome) aren't neanderthal, therefore no gene flow existed between the two populations, completely forgetting the last name problem of Pitcairn --- everyone on the island ended up with only a handful of last names.
The recent find of the microcephalin gene derived in modern humans from apparently neanderthal lineage should hopefully put that to rest. But then, you can never underestimate the foolishness of most people in any field.
The habilis skull was found on the surface, not encased in rock, so that may affect the dating some. The dating was done by Ar 39/40 dating of the surrounding rock.
http://www.unews.utah.edu/p/?r=080607-1 has a short FAQ at the end of the press release that discusses many of the issues that came up here.
I wonder how much of our evolutionary analysis is distorted by our anthropocentrism - particularly our idea that we (modern humans) are a terribly distinct species. For starters, we are put into a different genus from our sibling species, which wouldn't be distinct enough, gene-wise, to merit a separate genus for zebras.
Wasn't it a couple of years ago that a Nature paper showed continuing gene flow between anthropecines and pongids until 2.5mya? Isn't the crazy quilt of proto-humans in Africa just a simple example that we aren't looking at clear distinct stable species, but interbreeding specializations with fairly limited genetic differences between the groups.
Of course the phenotypic differences look huge to us, but that's because we are human. Wouldn't dog scientists make big noise about the difference between a Pekinese and a Rottweiler?
Josh, thank you. So +/- 10,000 years for both ages, which means that their uncertainties are an order-of-magnitude smaller than the difference in the ages.
Can I ask a silly layman's question? It is my understanding that fossils are rocks - that the biological material has been replaced by rocks and that what we call a fossil is really some sort of cast of the original material. But is that true of all fossils or only fossils older than a certain age? For instance, the fossils being discussed here: are they rocks or are they bone? Something else? Something in between?
I'm pretty sure dinosaur fossils are all rock, but I guess they've even found some organic material at the core of a Tyrannosaur femur. And I thought they were charting the genome of a Neanderthal... So are all the Australopithecus/Home fossils rocks or bones or...?
I don't think anyone's posted a link to this yet:
http://www.sciam.com/article.cfm?alias=fossils-paint-new-picture&chanID…
I thought it was a good article. There's another one somewhere that I can't find, talking about Stephen J. Gould's idea of human evolution being like a bush, not a linear progression, but I can't find it.
Well, factician (#4) . . .I think we have a winner!
Little Casey Luskin at our favorite creationist website at the DI has waded in with his usual bumbling, incompetent, poorly reasoned tripe.
"What if H.E. Evolved from H.H. then why are their still H.E.!" -- Creationism 1.44 million years ago.
Thanks for the nice post, PZ. I read the media reports with interest but the expert's take is invaluable!
"But it's 1,000,000 BC! The Earth was created in 2000 BC, so that means we don't exist!"
"Don't be silly, Og. How can we be sitting here talking if we don't exist? How could I stoke the fire, like this, if I didn't exist?"
"God must be making us think we exist, in order to test our faith."
"Then...that means the fire doesn't exist either, and I'm tempting the Lord's wrath if I keep acting like it's there." (drops stick)
Let's hope the Mainstream media doesn't get wind that monotremes still exist.
PZ, what I worry about is that it's too easy to blame the media. I suspect at least some of the researchers named as authors have a share in this. The BBC piece on this quotes Fred Spoor as making what strikes me as a really dubious argument, that it is somehow "more complex" and therefore less likely that the simultaneous existence of habilus and erectus means that they didn't have a third completely different linear ancestor species to them both. More complex than some kind of isolation of habilus populations that allowed one to speciate? Why? Etc.
I get a bit frustrated with natural scientists who blame the media for simplifying their work when those same scientists step up to the plate and voluntarily offer quotes that appear to pre-digestively offer up those same simplifications in order to garner a headline. If the Leakeys and Spoor and others just put out a paper that said, "Hey, habilus and erectus cohabited for at least 500k years, and by the way, they seem to have been sexually dimorphic at a level that's more like gorillas and less like sapiens", maybe they wouldn't get column space in the NY Times and the BBC. But then they wouldn't have to postfacto complain that the media got it kind of wrong.
Tim, that's exactly right. Several of the authors have made dubious statements exaggerating the significance of these finds outside the context of the paper (which makes restrained and appropriate interpretations only); the Nature news article then pushes the envelope a bit with its reporting; then the general media blows it still further out of proportion; and the creationists just go nuts and say incredibly stupid things about it.
There's actually some interesting sociology of science going on right here in a single day. It's like watching a game of telephone being played out right in front of us.
I don't hang there either, but paleoanthropologist John Hawks calls out the media reaction as "Man bites dog".
And worse:
And then he goes into dating changes and the "Out and In and Out again" story of LM. (Comment #19.)
"You see, this is interesting stuff! It's like a Plio-Pleistocene soap opera -- complete with twins separated at birth, old characters being killed in Amazonian plane crashes and mysteriously returning disguised as someone else."
I wish he would write some press releases.
And wouldn't this quilt or bush be generally more likely than a linear progression, thus confirming the theory more? [I can get that PE or ring species would be expected linear speciation, but this expectation seem to be rather confined in time and space.]
Um, don't you mean whiner?
It's amazed me for years that every chunk of bone dug up in East Africa seems to be greeted with headlines about upsetting the entire picture of human evolution.
On the pattern of evolutionary divergence, sometimes I get the feeling that people talk about species as if they were a particular individual, rather than a large widespread population. (I didn't say that very well, so if it doesn't make sense, just ignore it :-)
I hate to interject this late in the discussion with a quibble, but given the anthropologic nature of this I feel that I can.
I am a layman, but a voracious reader, and consumed with the desire to understand the universe (as long as I don't have to study or take tests).
I am under the impression, given the books that I have read, as well as my sub-rudimentary knowledge of German, that scientists now refer to our recent cousins as "Neandertals", without the "th", as there is no "th" sound in modern German, and the spellings (in German, where the archaic spelling had been preserved) changed in the first half of the last century to reflect what the pronunciation had always been. A lot of the more recent books I have read follow the new(?)spelling rule, but the pronunciation either way is, and always was, "neandertal", without the "th" sound.
autumn, either spelling is currently accepted for the common name, but always neanderthalensis for the scientific name.
The writer Robert J Sawyer has a point:
Not that he's an authority on hominids or anything, but it's a good summary which even talk.origins links to. Too bad his Neanderthal Parallax books are such crap. But I digress...
Re #56, MAx,
Here's a story about 8 million year old fossil cypress trees in Hungary that didn't turn to stone, the wood was preserved.
Very cool IMHO. http://www.bbj.hu/news/news_29502.html
Re #56 Max. Max, I threw out a short discussion this common perception that there is an on/off switch between bone and fossil on the "Hey gang! Want to see something depressing?" on 1 August. In the interests of brevity, I'm not going to copy it here; it was post #98. The short answer is "no, not all fossils are 'rock' as opposed to bone." Like everything else in geology, it is rather more complicated than that.
Thanks, Fernando and Josh. Josh, I read the comment you referenced and that was exactly what I was looking for. So I guess permineralization is a continuous process that can vary in rate depending on the depositional environment and other factors.
I found it hard to get a clear answer on this from Wikipedia or Google. The simplistic assumption that a fossil is a rock seems to be the norm.
Max, Glad it helped. Yeah...permin. is a complicated process involving a lot of factors, the contributions of most of which are poorly understood. Best -Josh
I don't know a single one of my professors (I'm an anthropology student) who would characterize human evolution as a linear march. It worries me that journalists can spout anything they like when a large proportion of the general public seems to see most news sources as equally credible. There are good science writers out there, but many that newspapers (at least where I'm from) seem to employ are just staff writers who aren't particularly versed in the science they're writing about. The result is usually a person who half-understands something who forgoes accuracy for making the story more appealing and easier to digest for the public. I think we've seen how this leads to not only to factual errors but gross misrepresentation of those errors.
Most extreme forms are like:
Low scientific literacy -> minor incongruity -> evolution is false, ergo creationism!
I don't hang there either, but paleoanthropologist John Hawks calls out the media reaction as "Man bites dog".
And worse:
And then he goes into dating changes and the "Out and In and Out again" story of LM. (Comment #19.)
"You see, this is interesting stuff! It's like a Plio-Pleistocene soap opera -- complete with twins separated at birth, old characters being killed in Amazonian plane crashes and mysteriously returning disguised as someone else."
I wish he would write some press releases.
And wouldn't this quilt or bush be generally more likely than a linear progression, thus confirming the theory more? [I can get that PE or ring species would be expected linear speciation, but this expectation seem to be rather confined in time and space.]
Um, don't you mean whiner?