Wednesday, February 01, 2012

The Egg Came First

It is only natural that, when confronted with timeless and confounding questions, your friends should turn to you, the philosopher. Sooner or later, then, they will ask you which came first, the chicken or the egg. You must be prepared to discuss this issue in pedantic depth or lose your reputation for intimidating scholarly acumen. Only after understanding this issue will you be prepared for even deeper and more troubling questions such as "Is water wet? Or is water only something that makes other things wet?"

The question invites us to consider a sequence of the following sort, stretching back in time: chicken, egg, chicken, egg, chicken.... The first term of the series can be chosen arbitrarily. The question is the terminus. If one assumes an infinite past and everlasting species, there may be no terminus. However, the cosmological assumptions behind such a view are highly doubtful. Therefore, it seems, there must be a terminus member of the series, temporally first, either a chicken or an egg. The question which came first is often posed rhetorically as though it were obvious that there could be no good epistemic grounds for choice. However, as I aim to show, this appearance of irresolvability is misleading. The egg came first.

Young Earth Creationist views merit brief treatment. If God created chickens on the Fourth Day along with "every kind of winged creature", then the question is whether He chose to create the chicken first, the egg first, both types simultaneously, or a being at the very instant of transition between egg and chicken (when it is arguably either both or neither). The question thus dissolves into the general mystery of God's will. Textual evidence somewhat favors either the chicken or both, since God said "let birds fly above the earth" and the Bible then immediately states "and so it was", before transition to the Fifth Day. So at least some winged creatures were already flying on the Fourth Day, and one day is ordinarily insufficient time for eggs to mature into flying birds. Since chickens aren't much prone to fly, though, it's dubious whether such observations extend to them, unless God implemented a regular rule in which winged creatures were created either mature or simultaneously in a mix of mature and immature states. And in any case, it is granted on all sides that events were unusual and not subject to the normal laws of development during the first Six Days.

If we accept the theory of evolution, as I think we should, then the chicken derives from a lineage that ultimately traces back to non-chickens. (The issues here are the same whether we consider the domestic chicken to be its own species or whether we lump it together with the rest of gallus gallus including the Red Junglefowl from which the domestic chicken appears to be mostly descended.) The first chicken arose either as a hybrid of two non-chickens or via mutation from a non-chicken. Consider the mutation case first. It's improbable (though not impossible) that between any two generations in avian history, X and X-1, there would be enough differentiation for a clean classification of X as a chicken and X-1 as a non-chicken. Thus we appear to have a Sorites case. Just as it seems that adding one grain to a non-heap can't make it a heap, resulting in the paradox that no addition of single grains could ever make a heap, so also one might worry that one generation's difference could never (at least with any realistic likelihood) make the difference between a chicken and a non-chicken, resulting in the paradox of chickens in the primordial soup.

Now there are things philosophers can do about these paradoxes. Somehow heaps arise, despite the argument above. One simple approach is epistemicism, according to which there really is a sharp line in the world such that X-1 is a non-heap and X is a heap, X-1 is a non-chicken and X is a chicken. On this view, our inability to discern this line is merely an epistemic failure on our part. Apparent vagueness is really only ignorance. Another simple approach is to allow that there really are vague properties in the world that defy classification in the two-valued logic of true and false. On this view, between X, which is definitely a chicken, and X-N, which is definitely a non-chicken, there are some vague cases of which it is neither true nor false that it is a chicken, or somehow both true and false, or somewhere between true and false, or something like that. There are also more complicated views, too, than these, but we needn't enter them, because one key point remains the same across all these Sorites approaches: The Sorites cases progress not as follows: X chicken, X-1 egg, X-2 chicken, X-3 egg, X-4 chicken.... Rather, they progress in chicken-egg pairs. From a genetic perspective, since the chicken and egg share DNA, they form a single Sorites unit. Within this unit, the egg clearly comes first, since the chicken is born from the egg, sharing its DNA, and there is a DNA difference between the egg and the hen from which that egg is laid. For a ridiculous argument to the contrary, see here.

If we turn to the possibility of speciation by hybridization, similar considerations apply.

A much poorer argument for the same conclusion runs as follows: Whatever ancestor species gave rise to chickens presumably laid eggs. Therefore, there were eggs long before there were chickens. Therefore, the egg came first. The weakness in this argument is that it misconstrues the original question. The question is not "Which came first, chickens or eggs?" but rather "Which came first, the first chicken or the first chicken egg?"

However, the poverty of this last argument does raise vividly the issue of how one assigns eggs to species. The egg-first conclusion could be evaded if we typed eggs by reference to the mother: If the mother is a chicken, the egg is a chicken egg; if the mother is not a chicken, the egg is not a chicken egg. David Papineau succinctly offers the two relevant considerations against such a view here. First, if we type by DNA, which would seem to be the default biological standard, the egg shares more of its DNA with the hatchling than with its parent. Second, as anyone can see via intuitive armchair reflection on a priori principles: "If a kangaroo laid an egg from which an ostrich hatched, that would surely be an ostrich egg, not a kangaroo egg."

(HT: Walter Sinnott-Armstrong, who in turn credited Roy Sorenson.)

Update, Feb. 2:
In the comments, Papineau reveals that he has recanted in light of considerations advanced by Mohan Matthen in his important but so far sadly neglected "Chicken, Eggs, and Speciation" -- considerations also briefly mentioned by Ron Mallon in his comment. Although I find merit in these remarks, I am not convinced and I believe Papineau has abandoned the egg-first view too precipitously.

Matthen argues that: "Speciation occurs when a population comes to be reproductively isolated because the last individual that formerly bridged that population to others died, or because this individual ceased to be fertile (or when other integrating factors cease to operate)" (2009, p. 110). He suggests that this event will normally occur when both soon-to-be-chickens and soon-to-be-chicken-eggs exist in the population. Thus, he concludes, a whole population of chickens and eggs is simultaneously created in a single instant. In assessing this view let me note first that depending on the size of the population and its egg-laying habits, this view might suggest a likelihood of chickens first. Suppose that in a small population of ancestral pre-chickens the last bridge individual dies outside of laying season; or suppose that the end of an individual's last laying season marks the end of an individual's fertility. If there are no out-of-season eggs at the crucial moment, then chickens came first.

More importantly, however, Matthen's criterion of speciation leads to highly counterintuitive and impractical results. Matthen defines reproductive isolation between populations in terms of the probability of gene transfer between those populations. (Also relevant to his distinction is the shape of the graph of the likelihood of gene transfer by number of generations, but that complication isn't relevant to the present issue.) But probability of gene transfer can be very sharply affected by factors that don't seem to create comparably sizable influences on species boundaries. So, for example, when human beings migrated to North America, the probability of gene transfer with the ancestral population declined sharply, and soon became essentially zero (and in any case in excess of the probability of gene transfer between geographically coincident hybridizing species). By Matthen's criterion, this would be a speciating event. After Columbus, gene transfer probability slowly rose and by now gene transfer is very high between individuals with Native American ancestry and those without. Thus, by Matthen's criterion, Native Americans were for several thousand years a distinct species -- not homo sapiens! -- and now they are homo sapiens again. If the moment of change was Columbus's first landing (or some other discrete moment), then the anchoring of a ship, or some other event, perhaps a romantic interlude between Pocahontas and John Smith, caused everyone on the two continents simultaneously to change species!

More simply, we might imagine a chicken permanently trapped in an inescapable cage. Its probability of exchanging genes with other individuals is now zero. Since Matthen allows for species consisting of a single individual, this chicken has now speciated. Depending on how we interpret the counterfactual probabilities, we might even imagine opening and shutting the door repeatedly (perhaps due to some crazy low-probability event) causing that individual to flash repeatedly back and forth between being a chicken and being a non-chicken, with no differences in morphology, actual behavior, location, or sexual preference during the period. On the surface, it seems that Matthen's criterion might even result in all infertile individuals belonging to singleton species.

There are both philosophical and practical biological reasons not to lightly say that individuals may change species during their lifetimes. One consideration is that of animal identity. If I point at an individual chicken and ask at what point the entity at which I am pointing ceases to exist, there are good practical (and maybe metaphysical) reasons to think that the entity does not cease to exist when a single feather falls off, nor to think that it continues to exist despite being smushed into gravy. The most natural and practical approach, it seems, is to say that the entity to which I intend to refer (in the normal case) is essentially a chicken and thus that it continues to exist exactly as long as it remains a chicken. Consequently, on the assumption that the individual pre-chicken avians don't cease to exist when they become reproductively isolated, they remain non-chickens despite overall changes in the makeup of the avian population. (These individuals may, nonetheless, give birth to chickens.) Nor does it seem that any important scientific biological purpose would be served by requiring the relabeling of individual organisms, depending on population movements, once those organisms are properly classified. Long-enduring organisms, such as trees, seem best classified as members of the ancestral population they were born into, even if their species has moved on since. Long-lived individuals can remain as living remnants of the ancestral species -- a species with temporally ragged but individual-respecting borders. The attractiveness of this view is especially evident if we consider the possibility of thawing a long-frozen dinosaur egg.

Matthen argues as follows against the those who embrace either an egg-first or a chicken-first view: The first chicken would need to have descendants by breeding with a non-chicken, but since by definition species are reproductively isolated this view leads to contradiction. This consequence is easily evaded with the right theory of vagueness and a suitable interpretation of the reproductive isolation criterion. On my preferred theory of vagueness, there will be individuals of which it's neither determinately true nor determinately false that they are chickens. We can then define reproductive isolation as the view that no individual of which it is determinately true that it is a member of species X can reproduce with an individual of which it is determinately false that it is a member of species X. As long as all breeding is between determinate members and individuals in the indeterminate middle, the reproductive isolation criterion is satisfied. (This is not to concede, however, that species should be defined entirely in terms of reproductive isolation, given the problems in articulating that criterion plausibly, some of which are noted above.)

Second update, Feb. 3:
The issues prove even deeper and more convoluted than I thought! In the comments section, Matthen has posted a reply to my objections, which we pursue for a couple more conversational turns. Although I'm not entirely ready to accept his account of species, I see merit in his thought that the best unit of evaluation might be the population rather than the individual, and if there is a first moment at which the population as a whole becomes a chicken population (rather than speciation involving temporally ragged but individual-respecting borders), then that might be a moment at which multiple avians and possibly multiple avian eggs simultaneously become chickens and chicken eggs.

An anonymous reader raises another point that seems worth developing. If we think of "chickens" not exclusively in terms of their membership in a biologically discriminable species but at least partly in terms of their domestication, then the following considerations might favor a chicken-first perspective. Some act of domestication -- either an act of behavioral training or an act of selection among fowl -- was the last-straw change from non-chickenhood to chickenhood, creating the first chicken. But this act was very likely performed on a newly-hatched or adult bird, not on an egg, since eggs are not trainable and hard to discriminate usefully among. Therefore the first entity in the chicken-egg sequence was a chicken, not an egg. For some reason, I find it much more natural to accept the possibility that a non-chicken could become a chicken mid-life if chickenhood is conceived partly in terms of domestication than if it is conceived entirely as a matter of traditional biological species. (I'm not sure how stable this argument is, however, across different accounts of vagueness.)

54 comments:

jeyshu said...

My god, this is beautiful. I can only aspire to such levels of pedanticism.

Ron Mallon said...

You suppose that a chicken couldn't be of a different species than the egg from which it hatched. However, if we type species according to the classic species concept (whereby individuals of a species are members of reproductive isolated populations), this is false. An egg could be an egg member of a population, hatch, and then the population undergoes a speciation event and voilĂ ! chickens! (On the assumption that each population has both birds and eggs at all time, and that both split populations contain birds and eggs, this gives you the conclusion that chicken eggs and birds came about simultaneously. Mystery solved!)

Anonymous said...

This is an untopic. The answer is: neither. There is no chicken. It's a highly arbitrary human taxonomic invention. I'm done, goin' back to watch more Breaking Bad.

Kenny said...

Even better on that last point, surely the egg is the same individual of the species as the chicken that hatches from it. Each chicken comes from one and only one egg, and so it makes sense to individuate egg-chicken pairs that way. Approximately half of all chickens lay zero eggs, and the other half lay many many eggs, so it would be ridiculous to individuate the pairs that way.

Eric Schwitzgebel said...

Ron, you might well be right about that. I was having worries along those lines myself just now. I'll think about it more and amend the post if I find myself still agreeing with you after a day or two.

Part of the issue here is how externalistically one individuates chickenhood. I can imagine someone insisting that even on very externalistic criteria of chickenhood, once a chicken always a chicken. Species might individuate in a temporally ragged but individual-member's-species preserving way. So, for example, imagine an animal that lives for a million years while all the other members of its lineage have ordinary life spans. Maybe we want to say that it is still the species it was born despite the fact that none of its contemporaries are?

Also, since "chicken" isn't a biological term, one might even argue (despite my own way of putting things above) that there's some important slippage between chickenhood and the biological definition of a species. Is there any scenario, for example, on which the drumstick on my plate becomes non-chicken by virtue of something that happens to a population of birds outside the room?

The issue gets deeper and more convoluted....

Brandon N. Towl said...

I have nothing to add about chickens. I'll only note that, in high school, I independently came up with the "water not being wet" debate-- without having been touched by the taint of philosophy, oddly enough.

I drove my fellow teammates on the swim team slightly crazy with that one.

clasqm said...

Refreshing to see you give equal time to the young Earth Creationists. But what about the Deists? God created the self-replicating molecule and then retired to the cosmic equivalent of Florida. Fit THAT into a General Theory of Gallo-Ovo-Primogenesis!

David Papineau said...

Readers of this blog may wish to know that I have changed my mind on this fundamental topic, for the reasons cited by Professor Mallon. Indeed chickens could well have come first, if the crucial speciation event fell outside the laying season. I was in fact awoken from my dogmatic slumbers some while ago by Professor Mohan Matthen of Toronto University. I refer you to his definitive paper 'Chicken, Eggs and Speciation' in Nous 2009.

Eric Schwitzgebel said...

Thanks, David! Somehow I missed that important article. I'll have to check it out.

Eric Schwitzgebel said...

Brandon: The sign of a natural-born philosopher!

Clasqm: As long as the deist accepts evolutionary theory, the sorites egg-chicken pair argument should apply (caveat the Mallon-Matthen worry). Is there reason to think otherwise?

Mohan Matthen said...

Hi Eric,

Thanks for mentioning and discussing my article.

I am having some difficulty with your counter-example. Looking back on my paper, I see I didn't stipulate explicitly that for any two populations P and P', there is a non-zero chance that a (copy of any) gene from a P-genotype will end up on the same genome as one from a P'-genome. But this is what I was assuming. (No inescapable cages: but I'll come back to this.)

Consider the population of humans that migrates to N. America. There is a non-zero chance that genes from this population will recombine with one from the ancestral population. (Somebody may make the return trip.) But this probability is low, by comparison to recombining with locally available genes. (As well, the probability of the NorAm-Europe recombination doesn't rise in a straight line, but I will join you in disregarding my brilliant innovation.)

It follows that the North American population is now different from the European one. But not that the North American population belongs to a different species. Speciation occurs when the probability of inter-population recombination falls to zero. (P=0) (I was thinking that P=0 only when changes in the "fertilization system" of one or other population ruled out inter-mating.)

Now, you might say: the probability of inter-species recombination isn't zero, exactly—it's some tiny number. I would have to concede that point and mumble stuff about "normal channels" etc. Perhaps I would say: probability of inter-population recombination through normal fertilization system is zero. Does your counter-example still work against such a reformulation, assuming that such a reformulation is possible?

As for the inescapable cage, i.e., the cage from which escape is literally impossible (P=0), I would say: Yes, that counts as speciation. But as regards the inescapable-when-shut-but sometimes-open cage —— well P is not zero!

I am sure I have not got your counter-example straight though.

Eric Schwitzgebel said...

Thanks for the thoughtful reply, Mohan!

I don't think you can require a probability of flat-out zero for interpopulation transfer as a criterion for species individuation, even with a qualification about normal channels of fertilization. Practically, my understanding is that some hybridizing species can transfer genes at low rates through normal reproductive channels despite being generally (and hence justifiably?) classified as distinct species. Reproductive isolation between species is sometimes not utterly complete. More fancifully, we can imagine the non-actualized possibility of a sterile hybrid of two species undergoing further genetic change that allows it to mate again with members of one or the other population. The mere unactualized future possibility of such a hybrid renders non-zero the probability of gene transfer between the populations, thus again resulting in implausibly large lumpings of species. (If you want to rule out transfer that requires future genetic change, perhaps this example can also be run using unactualized but remotely possible changes in developmental environment that would result in a phenotype no longer reproductively isolated.)

There's also the issue of whether you would be comfortable with allowing each infertile individual to be a singleton species. I'd think this would be difficult to accept given its sharp divergence from ordinary classification procedures, but your final remark about the caged chicken makes me wonder if you would in fact accept it after all. Maybe you could dodge this worry somehow by appealing to inclusive fitness, that is, transferring genes by means of relatives? But to make that worked there would probably need to be some reason to rule out super-duper-inclusive fitness that transcends species boundaries (one species passing down most of its genes by collective suicide on behalf of a related species).

BTW I think you were understanding the cage example aright, despite my unclarity. There were two versions, p = 0, and p = very low.

Mohan Matthen said...

Thanks Eric. I agree with your reservations about P=0: that has to be an idealization. And so the real, true, unidealized position has to be that species don't really exist, that they are idealizations. Or possibly that species overlap.

But this doesn't tell us which comes first, the chicken or the egg. As far as the idealized world of species goes, I'll stick to my answer that eggs can at best be joint-first, since you can't have population-separation without some existent organisms.

SK said...

Hi,

I read your interview on 3AM Magazine and I am interested in contributing to your research of the stream experience. I am pretty philosophical sound myself and I have found myself at times questioning my vision. I have worn corrective lenses for quite some time and have had corrective eye surgery (PRK) 2 years ago. I also have some input on dream experience (vision/clarity) as well.

Anonymous said...

My understanding is that chickens are just domesticated jungle fowl, so they don't constitute a species. They might, after so many years of selective breeding, now constitute one or more subspecies of jungle fowl, but I don't think that's relevant to their chickenness, and in any case it's even harder to find the beginnings of subspecies than those of species.

If this is correct, then the first chicken was just the first domesticated jungle fowl. The answer to the all-important question now rests on whether an egg from a wild bird can be domesticated. If so, then the egg may have come first, but if not, then the chicken did.


I also question whether eggs and chickens are in fact different things. An egg surely doesn't die when it hatches, and if the egg continues to exist after hatching then it is surely identical to the resulting chicken, so the question is whether the process of hatching destroys the egg. An egg does lose an important part - its shell - in hatching, but then babies lose their placentas in being born and we think the baby-placenta combo is the same organism as the newborn in that case. So I can't see why eggs shouldn't be thought to survive hatching in the form of a baby chick.

Anonymous said...

To expand on that last point - if chickens just are eggs, then likewise eggs are chickens, and so neither comes first, because the relation 'comes before' is irreflexive. If chickens are eggs, then they must always come at precisely the same time as eggs. I.e., it's a tie for first.

Eric Schwitzgebel said...

SK: Sure! Email me at eschwitz at ucr dot edu.

Mohan: Yes, that makes sense. As an idealization, your view is appealing and has the consequence you suggest. Since I'm inclined toward vagueness in general, the Sorites-type solutions appeal to me, but there's a way of thinking about it such that the relevant Sorites unit is the population, and then the light might dawn gradually over the chicken-egg population as a whole. (That would still entail the unfortunate consequences of mid-life species change, however.)

Eric Schwitzgebel said...

Anon Feb 2: That's an interesting point you raise about domestication. I could see it being deployed into a chicken-first argument. Maybe domestication requires some behavioral modification or human selection, and the final last straw of behavioral modification or human selection would presumably a modification of or selection of a chicken, not an egg. So then although wildfowl would be egg-first, chickens might be chicken-first! I'll have to ponder this one further.

On your second point, why can't we talk about egg-stages and chicken-stages of the same individual, so that the question becomes whether the first chicken-egg individual started as an egg-stage or a chicken-stage. Then we get egg-first, right?

Mohan Matthen said...

Eric and Anon Feb 2:

Population splitting can occur by evolutionary change—that's how sympatric speciation occurs. Domestication can be seen as speciation of this sort. If this is right, it's pretty straightforward to apply the Matthen-Ereshefsky Population Structure Theory to the case.

Baron P said...

"Within this unit, the egg clearly comes first, since the chicken is born from the egg, sharing its DNA, and there is a DNA difference between the egg and the hen from which that egg is laid."
Not true. The mother has already acquired the characteristics of the chicken that were then copied as strategic instructions via the RNA/DNA of the creature that develops in the egg.

Wesley Buckwalter said...

Some additional data to consider:

http://youtu.be/rEypxTLo2bk

Baron P said...

More simply, evolutionary changes take place in the chicken, not in the egg, or at somewhere between it and the chicken.

Baron P said...

Even if it's argued that mutations can occur within the egg, they'd still be within the unborn chicken.

Eric Schwitzgebel said...

Wes: More evidence for egg first! I'm not sure about the generalizability of those results, however, or the face validity of that particular operationalization of the issue.

Eric Schwitzgebel said...

Baron P: I'll accept that there's some DNA tranfer back from the developing fetus into the mother's body, but such DNA doesn't play the same huge phenotype-shaping role as that same DNA plays for the chick. So it seems to me that it's reasonable to carve a joint between individuals on that basis.

Your point about mutations within the egg being in the unborn chicken inside the mother resembles the recent argument I alluded to (in good fun, I hope) as "ridiculous" in the post. The weakness in that argument, I think, is that the relevant entities of evaluation are laid eggs and hatchling-to-adult chickens. A mutation in the genetic material that helps govern the formation of the egg inside the chicken does not plausibly change the species of the hen carrying the embryo (consider especially the case of embryos that never mature into laid eggs). It's the egg, not the mother, that is the entity that crosses the line between pre-chickenhood and chickenhood.

Mohan Matthen said...

Baron P:

I find this confusing: "evolutionary changes take place in the chicken, not in the egg, or at somewhere between it and the chicken."

How can an evolutionary change occur in a chicken or egg? Perhaps, you are counting a mutation as an evolutionary change (perfectly reasonable)—but that always occurs "between a chicken and an egg". (That was Roy Sorenson's reason for saying that the egg came first.)

Baron P said...

The genetic change ordinarily starts with a mutation of the genetic functions and their structures within the chicken, whether the chicken is yet to produce its egg or not. There has been no argument that the mutations occur while material is within the eggshell, but as I said, it may turn out to be possible. As chickens in particular pass on some acquired traits epigenetically.
But even you neo-Darwinians should know that the mutations occur within the body content of the chicken, not without, whether by stochastic means or the adaptive mutation process.
You say: "It's the egg, not the mother, that is the entity that crosses the line between pre-chickenhood and chickenhood."
That's both meaningless and patently ridiculous, since the substance in the egg is still a growing, not evolving, chicken. Otherwise you might as well argue that no pre-chicken has by that measure to be the same species as its mother.

Baron P said...

And nobody seems to have yet considered that if it was a chicken in the egg, it had a chicken father, so that its phenotype had elements of both, but nevertheless was still within the chicken species. And the father contributed a share of its strategic functions, but didn't make the egg that held it. The egg, remember, that contained, but didn't make, the replicating chicken

Eric Schwitzgebel said...

Baron P, I do accept that animals don't have to be the same species as their mother. That's kind of the point, really, isn't it? (See, e.g., the Papineau quote.) On the relevance of the father's species, I explicitly discuss that issue, contrary to your apparent statement that nobody has considered it, in my first update in light of Matthen's response. I don't want to be dismissive, but I feel that you're not reading very carefully.

Brian Erst said...

I am neither a geneticist nor a philosopher of science, but it seems to me that the answer to the chicken/egg problem lies in how you concieve speciation to occur.

We can think of speciation as occurring for two different reasons - a change in the expression of existing alleles or the introduction of a new mutated allele. I suspect that the former is what causes the vast majority of speciation events, while the latter is the dominant popular view of how they occur. The former leads to a "chicken" view, while the latter seems to lead to an egg view.

If we have a population of proto-chickens that are now physically isolated and local selection pressures leads to the selection or loss of alleles that cause that population to become genetically isolated (unable or extremely unlikely to interbreed with the original population), then the speciation event takes place when the last bridge individual dies. The new allele set can no longer migrate out of this population. Chickens came first. (The same allele sorting could theoretically happen in more than one population - leading to two populations that could interbreed with each other but not the parent population.)

The introduction of a new mutated allele doesn't really change this view. If the mutation occurs in a single gamete or egg, it can't be the cause of the speciation, because the single individual would die out without offspring. The introduction of this new gamete into the local population might cause a new selection pressure against another set of alleles, so that over a short span of time the newly introduced allele crowds out a set of alleles that allow for interbreeding. Once again, there will be a last bridge individual that has a set of alleles that allowed it to breed with the "old" population and a set that allows it to breed with the "new" population. When that individual dies, the new population becomes chickens. Mutation-driven speciation would be extremely unlikely to occur multiple times, so it might be considered a "harder" speciation, especially if it causes the loss of an allele that is absolutely required by the original population.

Baron P said...

And as to the Sorenson paper cited, he writes: "Given Mendel's theory of inheritance, the transition to chickenhood can only take place between an egg-layer and its egg. For a particular organism cannot change its species membership during its lifetime. It is genetically fixed. However, evolutionary theory assures us that organisms can fail to breed true. So although it is indeterminate as to which particular egg was the first chicken egg, we can know that whichever egg that may be, it precedes the first chicken -- whichever that may be."

Which, I say again, is irrelevantly ridiculous, as even with this odd theory, the change would have taken place before the egg was made to embrace and protect the embryo.

But then Sorenson writes: "The egg's precedence is a biological rather than a logical necessity. Given Lamarck's theory of acquired traits, the chicken could have come first."
Unfortunately, he leaves the question pretty much at that. Some might then conclude that he has said the egg came first, except that he has given us some better reasons why it wouldn't have.

Baron P said...

Eric, I admit that I didn't read your update carefully, but perhaps you did not read what I wrote carefully as well. It may have been your point that animals can be of a different species than their mother, but it's still not mine. The change is an arbitrary one, determined by us humans as a way to draw a line that probably in nature can't be drawn.
(And didn't Papineau just write here that he now feels chickens could come first?)

Kyle said...

This is simply a matter of definition. If a chicken egg is defined as an egg containing a chicken, then the egg came first. If it is defined as an egg laid by a chicken, then the chicken came first. It's really that simple, isn't it?

Baron P said...

So an egg that contains a chicken did not need, by definition, to have been laid by a different chicken?

Kyle said...
This comment has been removed by the author.
Kyle said...

No, it did not. Evolution allows for a chicken to grow in an egg that was laid by a beast one step away from what we consider a chicken. It all simply hinges on the definition of "chicken egg", after which the answer is very easy.

Anonymous said...

"If a chicken egg is defined as an egg containing a chicken, then the egg came first."

If a non-chicken can become a chicken, through speciation or domestication, then there can be a chicken that was not hatched from an egg containing a chicken, so the above conditional is false.

I am fairly sure that, throughout the above discussion, there is only one sense of 'chicken egg' being used, which is something like 'egg containing only chicken DNA'.

Kyle said...

Speciation does not take place over the course of one individual's lifetime, so an individual non-chicken cannot become a chicken. The speciation step would be when a non-chicken lays an egg containing a chicken, in which case it hinges on the definition of "chicken egg".

If "chicken egg" indeed means something like "egg containing only chicken DNA", and if speciation requires multiple generations, then the answer has to be that the egg came first.

If you can domesticate an individual non-chicken into a chicken over the course of its lifetime, then the answer has to be that the chicken came first.

Baron P said...

"Evolution allows for a chicken to grow in an egg that was laid by a beast one step away from what we consider a chicken."
There are over 200 breeds that we nevertheless regard as chickens, so how do you define a step away from all of them? Better, what book on evolution do you read?

Brian Erst said...

Baron, what if what we call a "chicken" spontaneously reappears in the original population - if "chicken" is just a subset of a larger population, but eventually gets split?

Let's take a population of jungle fowl that has three subpopulations - white, brown and black. White is the dominant allele and can interbreed with brown and black. Brown and black are recessive alleles - both can interbreed with white and their own allele, but brown/black offspring are sterile. The brown population is what we'd call "chickens" - the brown allele is tightly coupled with increased egg laying and docility - while the others are what we'd call "jungle fowl". But as long as white fowl exist, "chickens" spontaneously arise from the "jungle fowl" group whenever a white/brown mates with another white/brown.

Now, a new predator species moves into the area and selectively kills white fowl. Suddenly, brown chickens and black jungle fowl are the only ones left - and they can't interbreed. Where once there was one species, there now are two. Genetic information can no longer be exchanged and they begin to drift apart - the browns become more "chicken-y" and the blacks become more "fowl-y".

Kyle said...

The evolution book I read says that speciation works through minuscule genetic differences between mother and child; do tell if yours differs. Minuscule change is change nonetheless, so wherever you draw the line for "chicken", and whatever breed you choose, the first chicken wasn't born from a chicken.

Baron P said...

Brian, what does that have to do with anything concerning the functional role of eggs? In any case it takes a significant group to similarly adapt to the new traits before you change the species' genotypes - even when we resort to directed evolutionary breeding.
Kyle, your book is way out of date.

Kyle said...

Baron P, if an individual almost-chicken can become a chicken over the course of its lifetime, voilĂ ! The chicken came first.

If an individual cannot change species, and a "chicken egg" is an egg with solely chicken DNA, the egg must have come first.

There are really only so many possibilities, and each has a distinct solution.

Baron P said...

Life forms evolve functions and forms through learning from experiences and each other, and that learning occurs not just in their brains but elsewhere in their bodies. Assisted by the advantage of accident, we engineer our own adaptive mutations as it were.
They occur gradually in our forms, but since we experience life less in our eggs than in our maturity, the adaptation occurs when we are best able to react to our environment - which is not when protected from it by an eggshell.

Baron P said...

Kyle said...

*If an individual cannot change species, and a "chicken egg" is an egg with solely chicken DNA, the egg must have come first.*

Are you in that case arguing that the first chicken came from an egg, but not a chicken egg? Since a chicken egg could only have been laid by a chicken?

And thus that the dinosaur-like ancestors of chickens did not evolve chickens until they had laid them in a more dinosaurian egg? And that the chicken then evolved the chicken egg? So a dinosaur egg certainly came before a chicken, but the chicken egg came after?

But that leads back to whether there was a first egg or first chicken ancestor. I tend to think the ancestor developed the egg after the cell division process became ineffective for evolving multicellular beings. What do you think?

Of course if you're assuming that the bona fide chicken egg came before the chicken, then the dinosaurs that evolved and laid the chicken had to evolve the chicken egg first and have it there before the chicken evolved during or after the laying of the egg, How to evolutionarily select the chicken egg before the chicken is of course a question.

Kyle said...

Baron P,

If a chicken egg must be laid by a chicken, yes, the first chicken came from an almost-chicken egg.

If a chicken egg must only contain chicken DNA, the first chicken egg (that is, the first egg to contain a chicken) came from an almost-chicken.

The way I see it, again, it hinges completely on how to define the chicken egg.

Baron P said...

So that the first bona fide chicken egg came from a chicken, no?

Anonymous said...

Chicken could be a mushroom or tree.
Egg is only egg.
This is evolution.

Baron P said...

If an egg can't lay itself, there had to be a first layer of the first egg.
Unless the first egg was, perhaps, the god of its limited purpose. Eggs all the way down in other words.

David said...

If the question is merely "Which came first, the chicken or the egg?", then obviously the egg came first. Dinosaurs were laying eggs millions of years before chickens (or any bird) had evolved.
If the question is the implied "Which came first, the chicken or the CHICKEN egg?", then...as pointed out...the answer hinges solely on your definition of what a "chicken egg" is.

Baron P said...

If "obviously the egg came first," why the conundrum?

And why wouldn't the answer lie "solely" as much on a definition of a chicken as on its egg?

And again, have chickens really separated entirely from dinosaurs?

Wumpus said...

The crux of the chicken-and-egg riddle is: if A is necessary for B and B is necessary for A, how did the whole thing begin?

All chicken and egg questions involve semi-hemi-demi chickens and semi-hemi-demi eggs. They both start as non-chickens and non-eggs. Slowly, they co-evolve into their current state.

The answer should not be chicken or egg. It should be. They gradually co-evolved.

Richard said...

So, it seems:

If the chicken is the first chicken, then by definition it can’t have a chicken predecessor.
So, either it is its own predecessor (eg via a mid-life species change) or the egg is.

Are there examples of mid-life species change?

Eric Schwitzgebel said...

That's a thorny issue! If species are partly defined by reproductive isolation, then there might be mid-life species changes by changing the degree of isolation.