That's not a Missing Link! - the vocabulary of "Intermediate Forms"

    Have you ever wondered about the phrase "missing link"?   This is the first
article I've read that does a good job of explaining the misunderstanding regarding
"missing link" fossils ... versus, say, "transitional forms".  But even that phrase
causes problems - - because it implies that one population of extinct animal
"transitioned" into this other fossil form!  Sometimes that slightly different 
fossil comes from a different lineage, but shows perfectly what the common
ancestor  or eventual descendant could have looked like!

“Not that “transitional form” is without its own problems. The phrase can sometimes inadvertently cast an evolutionary cousin as an ancestor through popular translation. But it at least highlights that the organism in question helps inform what paleontologists have identified as a major shift in life’s history.”

Some scientists are moving towards “Intermediate Form” which has fewer implications that one creature led directly to another. Sometimes it is years before experts know enough to know whether a new fossil is on a direct lineage (ancestor or descendant) - - or actually belongs to a related lineage, but demonstrates what a plausible Intermediate Form would look like between one known fossil and another!

How many times have you read “Life is really a tree, not a chain.” Haven’t you ever wondered ‘what difference does it make’?!

Well, here it is!:
“To me, the idea of a ‘missing link’ implies a linear chain of one species evolving into another, evolving into another, and so on,” says Smithsonian Human Origins Program anthropologist Briana Pobiner. That isn’t the pattern we see [in the random fossils we find]. Instead. . . :

Evolution “produces a tree-like branching pattern with multiple descendants of an ancestor species existing at the same time, and sometimes even alongside that ancestor species.”

“Paleontologists often prefer the term . . . “Intermediate Form,” because [it] impl[ies] … these species are parts of an ever-changing continuum. This isn’t just a matter of splitting hairs; terminology shapes our ideas and the way dramatic changes in the course of life are interpreted. Before (and even after) Darwin, naturalists sometimes saw species as part of a ranked hierarchy in which newer forms were somehow better than what came before. “Sloppy words lead to sloppy thinking,” as Pyenson says.”

“In some sense, every species i[s] a[n] [Intermediate] Form from its ancestor because it retains many ancestral traits but has enough unique traits to be a separate species,” Pobiner says."

"And given that every species alive today has fossils related to its ancestry, that’s a lot of [Intermediate] fossils. More often, Pobiner says, “paleontologists often use this term when talking about larger anatomical or ecological shifts that occurred during the history of life.”

For the sake of avoiding confusion in the public mind - - don’t think “missing link”, and try to avoid “transitional forms” - - and focus on “Intermediate Fossils”. While it is rare to know for sure that one fossilized life form literally represents an earlier or later population of Transition - - all similar fossils are Intermediate!

**[Note on Edits - - to better drive the point home, some sentences quoted from the article were edited to more consistently use the terminology of Intermediate Forms and Fossils.]

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I dedicate this new thread to you and our discussions about this issue last year!

Oh dear! So I’m going to get the blame??!! :innocent: Anyway, thanks.

Yeah, I completely agree that defining terms carefully is essential for understanding. And I applaud you for trying to clarify this.

But I still find “intermediate forms”, like “transitional forms”, to be more philosophical than scientific. When everything is an intermediate form, of what value is any term like this except to assert a particular interpretation of the data? Too often scientists have been wrong. Tiktaalik is a good example, where its discovery hailed it as a missing link (transitional form, intermediate form), but then tetrapods were found earlier. So the definition has to be loose enough that it can be argued the data fits, but it lacks the clarity and reproducibility we normally expect of science.

Anyway, we’ll see how this thread flies!

Thanks to @gbrooks9 for starting a thread on this topic since it is one that I have seen many people get wrong. The very first rule to remember is that transitional is not the same as ancestral. Those are two different but related terms. Wiki actually has a decent definition:

“A transitional fossil is any fossilized remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group.[1] This is especially important where the descendant group is sharply differentiated by gross anatomy and mode of living from the ancestral group. These fossils serve as a reminder that taxonomic divisions are human constructs that have been imposed in hindsight on a continuum of variation. Because of the incompleteness of the fossil record, there is usually no way to know exactly how close a transitional fossil is to the point of divergence. Therefore, it cannot be assumed that transitional fossils are direct ancestors of more recent groups, though they are frequently used as models for such ancestors.[2]”–Wiki

Darwin himself addressed this very topic in Origin of Species:

“In looking for the gradations by which an organ in any species has been perfected, we ought to look exclusively to its lineal ancestors; but this is scarcely ever possible, and we are forced in each case to look to species of the same group, that is to the collateral descendants from the same original parent-form, in order to see what gradations are possible, and for the chance of some gradations having been transmitted from the earlier stages of descent, in an unaltered or little altered condition.”–Charles Darwin, “Origin of Species”

DNA evidence is the only evidence that can point to direct ancestry, and obviously this is missing from all but the most recent fossils (e.g. Neanderthals). Therefore, all fossils are assumed not to be direct ancestors of any living organism, even though they could be. A good example of scientists adhering to this principle is found in the figures in the Tiktaalik paper:

All of those intermediate forms are shown as branches on a tree and none are shown as direct ancestors of modern vertebrates.


The value is in the mixture of characteristics found in intermediate fossils since that informs us of the evolutionary history of these features.

Since Tiktaalik was never considered to be a direct ancestor to any living vertebrate, I don’t see how that is a problem. Tiktaalik is considered to be a side branch of the main vertebrate line, and that branch preserved less derived features found in its ancestors that were in the direct vertebrate lineage. Just in case you missed the Darwin quote in my previous post:

“In looking for the gradations by which an organ in any species has been perfected, we ought to look exclusively to its lineal ancestors; but this is scarcely ever possible, and we are forced in each case to look to species of the same group, that is to the collateral descendants from the same original parent-form, in order to see what gradations are possible, and for the chance of some gradations having been transmitted from the earlier stages of descent, in an unaltered or little altered condition.”–Charles Darwin, “Origin of Species”



It’s good to see you once in a while here on BioLogos. But I wonder if you are mis-interpreting the point of having a term like “Intermediate Form” or “Intermediate Fossil”. In an earlier time, when scientists were intoxicated by the idea of having the entire animal kingdom unveiled before them, there was a misplaced zeal in using terminology that over-stated the value of a newly discovered fossil.

Let’s look at your example of the Tiktaalik. You say “So the definition has to be loose enough that it can be argued the data fits, but it lacks the clarity and reproducibility we normally expect of science.” And you imply that the value of Tiktaalik fossils is now lessened.

Here is what the Wiki article says: "Tiktaalik provides insights on the features of the extinct closest relatives of the tetrapods. Unlike many previous, more fishlike transitional fossils [<< EEEK!], the “fins” of Tiktaalik have basic wrist bones and simple rays reminiscent of fingers. . . . the proximal series can be directly compared to the ulnare and intermedium of tetrapods. The fin was clearly weight bearing, being attached to a massive shoulder with expanded scapular and coracoid elements and attached to the body armor… The bones of the forefins show large muscle facets, suggesting that the fin was both muscular and had the ability to flex like a wrist joint. . . .
The more robust ribcage of Tiktaalik would have helped support the animal’s body any time it ventured outside a fully aquatic habitat. Tiktaalik also lacked a characteristic that most fishes have—bony plates in the gill area that restrict lateral head movement. This makes Tiktaalik the earliest known fish to have a neck, with the pectoral girdle separate from the skull. "

As you can see, regardless of other “Intermediate Fossils” that are even older than the Tiktaalik, the unique combination of features in the Tiktaalik still make it an important category of fossils to study!

@Marty, as you will recall, when I first started examining this issue of “Transitional” fossils, I too was surprised that many of these extinct animal populations considered Transitional were not necessarily common ancestors of other similar fossils, nor ancestors of others. So when the article linked above went to the effort of explaining that even the term “Transitional” has pitfalls, I had to enthusiastically agree.

But now it would seem you don’t even like the term “Intermediate”. If I am correctly detecting your tone, I think it goes too far. And it would be good for YECs to come to understand the limits of how the term Intermediate is used - - so they can stop banging their heads against the wall on the older issue of “Transitional”.

Re-read the lines of text from the Tiktaalik article. It systematically reviews the differences in the fossil not normally found in animals conventionally classified as fish. This is a reproducible truth. The important milestones represented in Tiktaalik fossils, once confirmed, are always going to be important - - because of how well we know what it takes to be a fish - - vs. what it takes to be a land-loving tetrapod.

You conclude:
“But I still find “intermediate forms”, like “transitional forms”, to be more philosophical than scientific.”

Does Tiktaalik’s unique trait of a fish with a neck invoke philosophy? I don’t think so. It invokes anatomical truths, that will not change. If anything, the insistence that the adjective “Transitional” implies too much is the philosophical assertion. And for it to be answered, one has to decide if the term should be used even if the writer goes well out of his way to point out that the fossil is not a direct descendant or common ancestor of extinct populations that produced other (similar) fossils.

Yes, sometimes what was called a Transitional fossil was, in fact, a fossil from a cousin population…maybe even a fairly distant cousin branch. But every example of diversity within the animal Kingdom is a valuable indicator of how new forms come and go - - bringing with them some traits from the past, and show-casing new traits never seen before. Sometimes to see how a living form had to compromise to include a new feature is instructive in and of itself.

Marty, I think we all must honestly apply due diligence to what exactly is meant when the term “Intermediate Forms” is used. We must be clear that in many cases, it is Intermediate because of what it is showing (and will always show) … not because we know whether it is a descendant or ancestor of similarly shaped fossils.
To ask for more than this, @Marty, doesn’t seem fair, or necessary.

The value, in any area of biology, lies in what one can conclude from relationships between the things being compared. In natural history (aka evolution), the value of the term is very clear: it identifies X as being between A and B, in some sense that must be separately defined, and thereby establishes that the difference between A and B is not absolute (or quantal) but relative (or continuous).

Such distinctions (binary/quantal versus relative/continuous) are important in other areas of biology, most notably in developmental biology. Cells of early embryos (and stem cells in adults) often make what appear to be binary “choices” between two alternative cell fates. But are these really binary choices? Or might there be a gradient of options, running from A to B? The discovery of intermediate forms between A and B would be decisive in a situation like that.

In short, it is easy to see the scientific value of identifying (and looking for) intermediate forms, once you identify the context in which the question is being asked.


I was hoping to avoid lots of posts, so I’ll try one more round, but I may have to stop after that. I have a long to-do list!

I’ll grant you that the term is marginally better than transitional, and I appreciate you trying to catch my drift and push back. But remember that my objection is linguistic, not technical. Look up “intermediate” in a dictionary, and you get something like “between two other things.” Well, what two other things is any given intermediate form between?

Darwin said, “Why then is not every geological formation and every stratum full of such intermediate links? Geology assuredly does not reveal any such finely graduated organic chain; and this, perhaps, is the most obvious and gravest objection which can be urged against my theory.”

So Darwin knew what intermediate meant.

And this is also very common: “Fossils or organisms that show the intermediate states between an ancestral form and that of its descendants are referred to as transitional forms.” From

Transitional or Intermediate, these words communicate the narrative of ancestry. If that is not intended, find better words! That’s my point. They co-opt a word with a particular connotation, and then argue it does not have that connotation when used in this context.

But seriously I do appreciate you trying to improve the choice of words. I just don’t think we’re there yet.

Hi T! So which of those is intermediate of which? Or are they all intermediate of something? OK, intermediate of what? This is science right, so if we’re claiming they are intermediate, we should know.

I agree on the need for a term to express this. But why not use “similar forms” or “related structures”? The word “intermediate” implies in itself some kind of linear (and probably ancestral) relationship. Since that is supposedly not what is meant, why not use an accurate English word?

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No, it really doesn’t. Things can be intermediate in size, in color, in age, in height. The word is fine; I think the problem is yours to deal with.



I will allow you a tiny victory … clearly the quote above, where the term “intermediate” introduces the phrase “between an ancestral form and that of its descendants” was certainly a premature expectation of the early writers!

However, in those cases where the situation can be actually proven true (!!), as determined by dating layers and/or finding a tight correspondence between features in the fossil of a proven ancestor and features in a proven descendant sample, then certainly the term “Transitional” should be allowed.

But given the general inclination of writer or reader to miss the nuances, or psychologically introduce nuances where one shouldn’t, when the ancestors and/or the descendants aren’t proven, we have no other word to use but “Intermediate”.

Marty, you will allow a writer some word, yes? Do you have one that you think is more fair and appropriate than “intermediate”?

Re-read the paragraph on the Tiktaalik. The features of the fossil being described are not frivolous comparisons. They illustrate - - by means of another living creature now fossilized - - that new traits (expected of land-roving tetrapods) can appear on a creature that otherwise satisfies many of the anatomical definitions of the earlier forms (more fish-like) - - and they exist on a single creature.

This is not philosophy. This is immutable truth.

You and I are ones doing the philosophy - - the philosophy of semantics, meaning and intention.

As I imply above, you can’t expect us to go silent over someone else abusing terminology. There is something to be said - - and I will be happy to say whatever word you think is best (if you are persuasive) !

I just now realized I missed your objection to Intermediate:

Between any two points, there is always a middle point. It’s the inevitable nature of geometry.
If either of us could manage to get everyone to use Intermediate instead of Transitional, I would consider it a great victory. How exactly do you expect to convince someone to write about “Similar Forms” instead of “Intermediate Forms”?

The intended point of the comparison is to show a form that is not just “similar”… but that it represents a “way point” Between anatomical comparisons. I would certainly never use the phrase “related structures”… because then I would be accused of saying the fossil is closely “related” - - instead of distantly “related”.

In Latin, “Intermediate” is what it’s about… “the middle between” … and so it should be used, until the better substitute is found.


An Anecdote: Recently the Washington Post featured an article about amoeba - - true one celled animals - - that build homes out of tiny bits of shell! They exist today.

But they also existed millions of years ago, during the Eocene! And one form was a giant!!! Now extinct, by carefully enlarging its home as a flat and very perforated disk, it could grow to the size of four centimeters! Can you imagine a one-celled creature the size of four centimeters!

The writer of the science article became very enthusiastic at this point, and mentioned that the ancient Egyptians used them as money. The writer said they were called “Nummulites”, which was a Greek word derived from the word for money! But the author got the story garbled! Herodotus called the fossils Nummulites, because they Looked like money - - not because they were used as money. The pyramids were built with stones that had great numbers of fossilized, giant foraminifera. The story made me wince. And every time you (or I) read an article that incorrectly suggests or implies an intermediate form is “transitional”, we should wince too… and maybe even burn the article !!! Or maybe burn the smart phone we read the article on ?? (make sure it’s someone else’s smart phone!).


[[ Giant homes for Giant one-celled Amoebas!! ]]

Here is the cladogram for reference:

Tiktaalik would be intermediate between earlier lobe finned fish like Panderichthys and later tetrapods like Acanthostega (and Ichthyostega as another example if you want to Google it). It is important to note that I used the phrase “like Pandericthys”. These are model fossil organisms that represent a larger group. It is not correct to say that Panderichthys, Tiktaalik, and Acanthostega are all in a direct lineage with one being a direct descendant or ancestor of the others.

The word of the day in this discussion is cladistics. This is a method of organizing species by their shared evolved features which are called synapomorphies. Features that evolve on one branch are called apomorphies, and they are called derived features. Here is a little diagram of how cladistics works:

Of course, there is no way that I can fully explain cladistics in a forum post, and I would probably get some of it wrong anyway. However, if you are curious about how scientists group and organize species then learning about cladistics is definitely the first step.

When you see scientists talking about derived and ancestral traits they are talking about cladistics. In decades gone past scientists would often use terms like “more evolved” or “higher organisms”, but those terms have been tossed in the dust bin (even though they do still pop up once in awhile). Scientists now view all species as being equally evolved because every living species is a terminal branch of evolutionary lineages that are all the same length with respect to time. Scientists have also tossed out the Victorian Age bias that humans are the highest lifeform, even if we still use terms like Primate and Eutherian that still carry that baggage.


Oh man, I hadn’t thought of that! Good point.

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I think maybe in this situation, @T_aquaticus does a superb job of laying out the answer to the question: “what two other things” !!!

And the more I look at the various Cladograms we can google on the internet (Google the images of cladograms!), the more I see that there is a discipline to using them… a discipline that no doubt seems surreal to Young Earth Creationists. And yet, it is really the responsibility of these protesting factions to spend some time learning what the discipline means, and what it is designed to do…


This image, for example, is less focused on the details than on the idea of positioning all the major vertebrate groups in evolutionary sequence. In this case, not all of the lineages terminate into the present. Different circles are used to distinguish between those that don’t and those that do. But each separate line is showing how early a certain trait appears!


Then there is this image, which starts to invest space into listing and sequencing the “characters” (aka, key characteristics of each clade). Notice this one places primates in the middle… not because birds are more evolved than primates, but because the point of this sheet is to trace the characters (key traits defining clades) that went to producing the Bird lineage!:


This image below is a practice sheet (with the teiminations of each branch at the bottom instead of the top), helping newcomers learn how to construct a Cladogram, and what the terms mean as applied to analyzing each branching of a certain trait (or character):

This final image, which is certainly quite attractive, seems to be designed for beginners, but it is in fact the end result of thousands of comparison … with great rigor and discipline, sequencing hundreds of evolutionary traits that go into the major animal groups that we find alive today on Earth!

Go to this page to see the image in context with the narrative:

The image is put together with the specific purpose of positioning Cetacea (the group to which whales belong) in the midst of all the other mammals that evolved at the same time. I quote the introductory text below in larger font. If a Young Earth Creationist can’t follow the meanings of the words used … I think we have found a fundamental reason why they don’t easily comprehend the value of studying “Intermediate Forms”!

Relationships of Cetacea (Artiodactyla) Among Mammals:
Increased Taxon Sampling Alters Interpretations of Key Fossils and Character Evolution

Figure 5

"Strict consensus of the 48 minimum length trees <= highly quantitative analysis begins with trees!
for the equally-weighted parsimony analysis of 606 characters [traits that define clades] <= 606 traits!
observable in fossils (3,722 steps). <= 3,722 unique fossils, tracking the progress of new traits!

At some point, Marty, someone has to crack a book …

@T_aquaticus inspirational posting!

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Just to help make this clear for beginners, the characteristics that are listed are the shared derived (i.e. evolved) characteristics. These are the synapomorphies, and everything on the tree past that node have that feature.

When we talk about intermediate or transitional forms we are talking about the fossils that have a mixture of characteristics between those terminal groups. Continuing with the examples we have already used, we could focus on ray finned fish and amphibians. The intermediate form would have a mixture of characteristics between ray finned fish and amphibians. Those intermediate forms are Panderichthys, Tiktaalik, Acanthostega, and Ichthyostega since they have a mixture of features of those two groups. I don’t know why, but Ichthyostega is one of my favorites ever since I discovered the webpage devoted to the species over at The Tree of Life Web Project, mostly due to the well preserved front limb that has clear examples of a humerus, radius, ulna, carpals, and phalanges. All of these tetrapod features are found on an organism that also has gill plates and other clear characteristics of fish.

This brings us to the big piece of evidence that has convinced biologists that evolution is true for the last 150 years. It is these phylogenies, and the near absence of any violation of those phylogenies. Just for reference, let’s go to the wonderful clade that @gbrooks9 used earlier:

There is one thing that eukaryotic biology does not do well, and that is transmit DNA horizontally between species. The overwhelming mechanism of inheritance is vertical inheritance, where DNA is passed straight down from ancestor to descendant. Therefore, if a feature evolves in one lineage it can not be transmitted horizontally to another lineage. Looking at the clade above, you have hair evolving in the mammal lineage leading do primates and rodents. You have the crocodile/bird clade diverging away from the mammal lineage before hair evolves in mammals. Therefore, you should not find any bird species that has hair (or mammary glands or three middle ear bones which are other derived characteristics found in mammals). Sure enough, out of the tens of thousands of known living and fossil species of mammals and birds, none have a mixture of derived bird and mammal features.

So not only does evolution predict which intermediate forms you should see, but it also predicts which intermediate forms you should NOT see. Every fossil we find fits these predictions. Every. Single. One. YECs like to argue that there aren’t enough intermediate fossils to evidence evolution, but what they don’t realize is that every single fossil we have is overwhelming evidence for evolution. Biologists look at the data we do have, and it overwhelmingly supports the theory of evolution.

YECs also like to argue that we are simply citing similarities as evidence for common ancestry, but that isn’t true. The evidence is in the pattern of similarities, and it is this pattern which YECs continually fail to either address or explain. If they ever hope to overturn the theory of evolution they need tackle this pattern. If people want to know why YECs are ignored by the scientific community then you only need to look at the fact that YECs fail to address one of the biggest and most prevalent pieces of evidence that supports evolution.


To this we should add:

Using mathematical algorithms (not eye-ball or intuition), we can build cladograms using DNA. These cladograms are highly (though not perfectly) consistent with the cladograms built with paleontological methods.

Biologists: please correct or add nuance as needed. Thanks!
@T_aquaticus @sfmatheson @glipsnort @Swamidass


@T_aquaticus, “props” to ya, man.

These last two paragraphs made beads of sweat break out on my brow … nice delivery!

@Marty, I don’t know who you can convince to do it… but someone on the ID side (someone who opposes the idea of common ancestry) has to volunteer to actually study cladistics!

Once you have an I.D. expert in making cladograms, they can explain to YECs and/or I.D. audienes what he has found!

Hi George. If you’re trying to improve “terms” in order to talk to a YEC about evolution, you’re barking up the wrong tree! You must not talk science to a YEC until they are willing to agree that the Bible does not require 24 hour days. Until then, no evolutionary term is going to be satisfactory!

And just to be clear, I’m not YEC.

At this time, as I said, I think “intermediate” is better than “transitional.” As for my opinion about the term and my linguistic and philosophical concerns, it’s not nearly as big a deal as this thread makes it out to be, but you’ll have to ask me for more clarity when I have more time, maybe six months.

I think it’s great you’re trying to improve terms, and I’m honored you asked my opinion. 'Til next time!




Well stated!!!

The question remains … where is the point of “injection” for alternative ideas. I think a full frontal attempt to prove “the Bible does not require 24 hour days” is pointless.

I’ve been taught that to change a “system of thinking”, changes must be applied at 2 or more locations simultaneously, otherwise a one-point change is going to be resiliently pushed back by the strength of the whole system.

For me, I’ve been contemplating the fossils of the flood as the major point of entry. But I really need a corollary point of entry to help support the first point. Still considering options…

Well, don’t think of it as a frontal assault! Think of it as discussing the Bible, which a YEC holds in highest regard.

I always start with Gen 1:1,2. Clearly those two verses mark both time and creative activity before the “first day” (in vs 3). Since the “first day” is not the “first” time period, why should it be 24 hours?

There’s also the seventh day, which Hebrews 4 says God is still in, and we can still enter on any given day. The author maps every human “today” to the Genesis seventh day. Why then should we map the other Genesis days to human 24 hour days?

Next are Psa 19:1-4 and Rom 1:19,20 where David and Paul argue that God’s nature is plainly seen by all people in what has been made. So what has been made must be faithfully testifying, as God would faithfully testify. If I find they have openness to that idea, then I might bring up perhaps supernova 1987A which appears to be 168,000 light years away. So either God created the appearance of a supernova recently with light in transit to fool us, or it really happened about 168,000 years ago. I have trouble theologically with God intentionally deceiving us like that.

Hope that helps!


Hey… I copy/pasted your last post into an email I sent to my archives on key interpretations. Excellent!

I also thought that all the translations of Verse Romans 8:22 would go quite well with your Hebrew 4 item!
Did you ever read some of the excitement around @Mike_Gantt 's visit and postings? He was very big on Creation terminating after 6 days. I wish I had thought about the alternative versions of Romans 8:22 back then - - to better explain how the meaning of “creation” was intended … instead of the “only way” he interpreted it.

Thanks for the help, @Marty !

Translations for Rom 8:22
For we know that the whole creation groaneth and travaileth in pain together until now.

For we know that the whole creation groans and labors with birth pangs together until now.

For we know that the whole creation groans and suffers together until now.

For we know that all creation has been groaning as in the pains of childbirth right up to the present time.

We know that the whole creation has been groaning as in the pains of childbirth right up to the present time.

For we know that the whole creation groans and suffers the pains of childbirth together until now.

For we know that the whole creation groaneth and travaileth in pain together until now.

For we know that the whole creation groans and travails in pain together until now.

For we know that the whole creation has been groaning together with labor pains until now.

For we know that the whole creation has been groaning together in the pains of childbirth until now.