What came first, the chicken or the egg?

[Darwin123]

The original question was dealt with. The oviparous mode of reproduction existed before chickens (or birds) evolved. That's all that needs to be said or can be said. The current discussion (which I think is relevant and more interesting) is about what the drivers of the evolution of viviparous (live birth) reproduction in mammals might have been. In what ways does this represent a useful adaptation for mammals? Do you have anything useful to contribute regarding this?

There is a link to a reference at the end of this post. I don’t know how reliable the following source is. However, it claims that the earliest known skeletons of mammals show that they bore immature live young. The link has a cladogram of mammal evolution, where the different nodes are numbered.
This reference presents the hypothesis that both viviparity and milk secretion started in the middle to early Jurassic. Node 3 in the diagram shown in the link branches off in the early to middle Jurassic. This would place viviparity, milk secretion and the evolution of angiosperms (i.e., flowers) at nearly the same time.
http://nimravid.wordpress.com/2008/02/26/extinct-mammal-groups/
“Since the mammaliaforms evolved from egg-laying therapsids and the monotremes still preserve egg-laying, it’s likely that the early mammals reproduced by laying eggs up until node 3 on the diagram. The skeletal structure of the multituberculates suggests that they bore immature live young similar to those of the marsupials. Since the monotremes produce milk, but secrete it through pores, it’s likely that nipples evolved at node 3 or sometime after. This may have happened as late as the divergence of the eutherians and marsupials, but probably came earlier. Some researchers think that milk secretion originally evolved as a means of hydrating the thin, leathery shells of basal mammals’ eggs, and was only secondarily used as a means of feeding hatchlings. With viviparity there would be a strong selective drive towards formation of a nipple to more efficiently feed the young. Evidence for this hypothesis will be found if it is discovered that monotremes secrete milk to coat their eggs.”

Hey, there is a correlation between viviparity and flowers! The first pollen is found from about the time that some mammals developed viviparity.
Suppose that viviparity has some sort of causal correlation with flowers! Maybe the birds took to the trees too soon, before there were fruit trees. They had to nest in gymnosperms, which are basically pine trees. The pine needles protected the eggs from egg predation.
The early mammals were feeding on pollinators for the angiosperms, which mostly lived in river valleys as small weeds. The flowering plants did not provide as much protection against egg predation as pine trees. So some mammals were more likely to develop viviparity than birds.
I present this hypothesis just for amusement. It is only slightly more serious than the lame joke that started this thread.
It does appear that a lot of innovations occurred during the Jurassic period. The evolution of the stapes in the middle ear started this period. Viviparity started this period. Milk secretion started this period. Birds started flying during the Jurassic period. And yes, flowers started during the Jurassic period.
Birds, bees, flowers, and mammals. All during the Jurassic. And it doesn't appear that the dinosaurs noticed anything!

 

[Darwin123]

I think it's not so much losing oviparity but the transformation to viviparity. Even humans produce eggs. I think we are pretty sure the process begins with egg retention followed by a progression toward a placental viviparity. We also now believe that both early reptiles and mammals had a common amniote ancestor, which makes mammals very old indeed, but still later than the previous glacial period (the Karoo (Permian) ~260-350 mya). It's reasonable to believe that the early mammals were oviparous and that monotremes are a surviving remnant of oviparous mammals. I agree with you that viviparous mammals need not have been very numerous for a long time, perhaps just developing in those regions with seasonal sub-freezing temperatures. If there was a major short cold period at the KT boundary, many oviparous mammals may have been killed off.

I conjecture another reason viviparity may have evolved. Maybe some early mammals live in an area that was “highly disturbed”. The region was prone to catastrophic events or rapid erosion that were very local. An example would be the inner banks of a river, where the erosion is very large.
Laying an egg in such a disturbed region would be very risky. If an egg were layed on the inner banks of a river, the egg could be washed away during a flood. So a viviparous animal in such a disturbed environment would have an advantage over oviparous animals living in such an environment.
Viviparous behavior could have first evolved in cold regions, to prevent the eggs from being “frozen” or “maimed” by the cold. However, the access of disturbed regions could explain how it spread out of cold areas.
This conjecture places mammals right next to early angiosperms. Early angiosperms were weeds that specialized in disturbed regions. Most angiosperms grow quicker than other plants because angiosperm leaves can draw water and carbon dioxide faster than other leaves. In the Mesozoic, most angiosperms lived in temporary areas where they had to grow quickly.
So I have this image of mammals grazing on flowers on an inner bank of a riverbed. The riverbed is eroding away. A pregnant mammal frantically runs to get to the next inner bank. The flower “tries” to grow and seed quicker. The “flower” may even trick the pregnant mammal to carry a seed.

Here is a 2004 article that shows that both birds and mammals helped to spread seeds from the earliest angiosperms. Also, this 2004 article makes the point that the earliest angiosperms grew in river valleys in areas of great erosion.
http://www.life.umd.edu/faculty/wilkinson/BIOL608W/Tiffney2004.pdf
“(c) the Mesozoic was dominated by large herbivorous
dinosaurs, possible sources of diffuse, whole-plant dispersal; (d) simultaneously, several
groups of small vertebrates, including lizards and, in the later Mesozoic, birds
and mammals, could have established more specific vertebrate-plant associations, but
supporting evidence is rudimentary; and (e) the diversification of small mammals and
birds in the Tertiary established a consistent basis for organ-level interactions, allowing
for the widespread occurrence of biotic dispersal in gymnosperms and angiosperms.”
“Angiosperms appeared and diversified in the later portions of the Early Cretaceous
through the Late Cretaceous. The initial radiation involved shrubby or
perhaps herbaceous plants growing in disturbed sites, particularly along rivers
(Wing & Boucher 1998, Friis et al. 1999).” There are viviparous plants. The seeds germinate while attached to the mother plant. One such plant is the mangrove. Interestingly, the mangrove lives in highly disturbed regions.
http://en.wikipedia.org/wiki/Mangrove
“In this harsh environment, mangroves have evolved a special mechanism to help their offspring survive. Mangrove seeds are buoyant and therefore suited to water dispersal. Unlike most plants, whose seeds germinate in soil, many mangroves (e.g. red mangrove) are viviparous, whose seeds germinate while still attached to the parent tree.”This is a 1960 article that claims that angiosperms evolved in the early Creteceous.
http://earth.geology.yale.edu/~ajs/1960/ajs_258A_11.pdf/284.pdf
It is concluded that no bona fide remains, either megafossil or microfossil, have yet been described from rocks older than early Cretaceous sediments.

However, here is an article from 1999 that claims that there are Jurassic microfossils.
http://www.sciencedirect.com/science/article/pii/003466679290167F
“Two species of angiosperm-like pollen are described from an outcrop of lower Oxfordian Oxford Clay at Normandy, France. An Oxfordian age is established by ammonites (Quenstedtoceras mariae zone) and substantiated by associated age-diagnostic dinoflagellates. The angiosperm-like taxa are determined to be in place by their state of preservation and unique morphology.”

 

[turbo]

Which came first? The chicken or the soup? Just teasing. Egg laying critters were around long before there were any birds that could be identified as "chickens".

 

[Cerlid]

The original question was dealt with. The oviparous mode of reproduction existed before chickens (or birds) evolved. That's all that needs to be said or can be said. The current discussion (which I think is relevant and more interesting) is about what the drivers of the evolution of viviparous (live birth) reproduction in mammals might have been. In what ways does this represent a useful adaptation for mammals? Do you have anything useful to contribute regarding this?

Well I think the question generally means what came first chicken eggs or chickens. Of course eggs non chicken ones came first no one would claim they did not, your interpretation of the question does not really answer anything, it is I think just stating the obvious. Scientists tend to be more precise and the argument is better argued by looking at evolution of chicken and egg than pretending the issue resolves around whole species. So yes the question has been answered, as it was meant to be, not on the issue of eggs not of the chicken species. Incidentally I read an interesting article about this in a science magazine. It decided basically what I said before.

Clearly live birth is favoured by evolution in some conditions, to the extent that even some lizards give birth to live young. Look at why and there will be your answer although it is clearly more complicated than that; in the lizards case it is because the environment is often very cold, so that eggs may not ever hatch if young were not born live. The same thing applies to any reason live birth exists, it's not that hard to work out why many species give birth to live young, it's simply because environment favours it. All you need to do is work out what the selection pressures were and one very obvious one I have given you, the fact that eggs require incubation, but the environment is often not that forgiving is an obvious place to start. Temperature and reliance on it. Natural selection would favour a species that could live and breed in many environments over one that was only suited to a warm one. So why did the dinosaurs die out? Why did mammals survive, it seems somewhat easy to understand why given that abrupt changes environment favour young that are already developed enough to be motile, to move to a more favourable environment, and do not die when it gets too hot or cold because of that. Deversification is key, the more a species is able to adapt to adverse conditions the more likely it is to survive. Eggs have absolutely no ability to change their position in unfavourable conditions quite often, although not always particularly in the sea, but even then they cannot chose where they end up, live animals can jump out of the fire and to somewhere that isn't a frying pan.

"It is not survival of the fittest that denotes what it is most likely to survive, but survival of those most able to adapt."

Paraphrasing Charles Darwin.

Personally I am not sure why this discussion even exists, as we can list many reasons why live birth although somewhat energy intensive, has a pay off beyond simply producing inactive unadaptable, intrinsically at least motionless and unreactive eggs. Further having live young means the adult is at the scene to protect live births where as eggs may well have no protection at all. It seems at least to me fairly obvious why mammals are if not dominant most widespread. Well beyond the asexual bacteria et al but one can argue that being single celled is not really that much of an adaptation that will matter at least to things we value.

 

[SW VandeCarr]

Personally I am not sure why this discussion even exists, as we can list many reasons why live birth although somewhat energy intensive, has a pay off beyond simply producing inactive unadaptable, intrinsically at least motionless and unreactive eggs. Further having live young means the adult is at the scene to protect live births where as eggs may well have no protection at all. It seems at least to me fairly obvious why mammals are if not dominant most widespread. Well beyond the asexual bacteria et al but one can argue that being single celled is not really that much of an adaptation that will matter at least to things we value.

The discussion exists because chickens don't die from complications of pregnancy. Before the 20th century 1000-2000 women per 100000 live births died from complications of pregnancy. Even today it's about 14 per 100000 live births in the US. Placental viviparity is complicated and prone to many more difficulties for the mother (morbidity as well as mortality) than oviparity. In the past, pregnancy was treated almost as a disease with women being confined for months. Yes, eggs need to be watched as do the hatchlings. But the mammalian young also need to be nurtured and protected after birth for periods of a year or longer. In the case of humans, it's now officially up to 26 years under US tax law. The egg needs to be incubated and protected, but birds have developed efficient ways to accomplish this.

Of course there's nothing we can do about this except perhaps by using surrogates for those women who have the money and want to go to the beach. Nevertheless, the costs of viviparity in humans far exceed the benefits IMO. If we laid eggs, there would be easy inexpensive ways for us to protect them and keep them warm.

http://www.digitalhistory.uh.edu/historyonline/childbirth.cfm

 

[RabbitWho]

!

THAT'S a chicken!?

What the heck is this then?

http://www.brolliesgalore.co.uk/acatalog/pic_G_tartan_lyndsey.jpg

 

[Allawonder]

Well, from the statement, I don't see why we all seem perplexed: the chicken came first in 'What came first, the chicken or the egg?' Anyway, nice discussion so far... LOL!

 

[Cerlid]

The discussion exists because chickens don't die from complications of pregnancy. Before the 20th century 1000-2000 women per 100000 live births died from complications of pregnancy. Even today it's about 14 per 100000 live births in the US. Placental viviparity is complicated and prone to many more difficulties for the mother (morbidity as well as mortality) than oviparity. In the past, pregnancy was treated almost as a disease with women being confined for months. Yes, eggs need to be watched as do the hatchlings. But the mammalian young also need to be nurtured and protected after birth for periods of a year or longer. In the case of humans, it's now officially up to 26 years under US tax law. The egg needs to be incubated and protected, but birds have developed efficient ways to accomplish this.

Of course there's nothing we can do about this except perhaps by using surrogates for those women who have the money and want to go to the beach. Nevertheless, the costs of viviparity in humans far exceed the benefits IMO. If we laid eggs, there would be easy inexpensive ways for us to protect them and keep them warm.

http://www.digitalhistory.uh.edu/historyonline/childbirth.cfm

Yeah but surely if you think about live birth over the whole animal kingdom you can come up with a few reasons why it is better than laying eggs, that was my point. Let's try thinking about why live birth favours species not why it might disadvantage one species, and as it turns out it didn't anyway. 7 billion of us, we live in more environments than any other mammalian species on every continent, and we show a remarkable evolutionary fitness, despite our need to wipe each other out on a massive scale, we're very good breeders because of live birth, because of the socialisation that brings and because of the protection that brings to our offspring.

Cherry picking humans, and humans who happen to rule the world as a species at that seems reaching a little, but if you want to discuss how bad off we are then let's do that. Whilst I agree it seems that us developing such large heads, and such wide shoulders, and walking upright may at first of seemed a massive disadvantage but all those things gave us the ability to use our hands freely, to be wise, and to develop medicine. The fact that you are even typing this on a mass communication device, just asserts every dominance the human race has gained. And that's evolution for you, it is blind, but sometimes seemingly dumb evolutionary trails lead to seemingly massive advances in a species that mean their only threat of extinction is themselves, unlike every other species on the planet who's major threat is us.

I don't genuinely see why we have been disadvantaged by live birth given a holistic view; and more importantly given the dominance of live birthing animals general I don't see why they have either as a whole. Hence I don't see the issue. Eggs don't work as well to produce diversity, unless they are internal and not laid in a fashion that means they are subject to predators etc, except in smaller ecological niches. It's evolution baby, when it works and well, and when it favours sexual reproduction and a species, then it is unquestionable that it is better, it would not exist if it was not.

 

[tiny-tim]

from http://en.wikiquote.org/wiki/Evolution …

A hen is only an egg's way of making another egg. ​

(Samuel Butler, in Life and Habit, 1877).

 

[Darwin123]

from http://en.wikiquote.org/wiki/Evolution …

A hen is only an egg's way of making another egg. ​

(Samuel Butler, in Life and Habit, 1877).

Not if its a shark's egg!

 

[jojay99]

Parents of 1 species don't give birth to offspring of different species

Not true. Otherwise, we should all be single cell organisms.

 

[Darwin123]

Regardless of the changes in allele frequencies in populations over time, it's scientifically undisputed that birds evolved from reptiles and reptiles laid (and continue to lay) eggs. So, with respect to chickens (which are birds), the egg came before the chicken.

EDIT: My question is why mammals had to develop a new way. The avian egg is relatively simple and quite elegant IMO. The mammalian way is too complicated, messy and unnecessarily hard on the mother. Has a chicken ever died from the complications of pregnancy?

Most mammal females do not have the same level of difficulty giving birth as humans. Humans are an unusual species of mammal in terms of their difficulty in giving birth.
Human babies have big skulls which can hardly fit through the pelvic opening of the mother. This is why human mothers usually have only one baby at a time. Twins are much more difficult. Triplets still more.
Modern technology helps the offspring of multiple births to survive. Before incubators and milk bottle formulas, even a premature baby had difficulty surviving. You hear a little in ancient stories about twins. You seldom hear about triplets and quadruplets.
A dog can give birth to more than five puppies at once. Often, four or more will survive. So can mice, pigs and other mammals. How often have you heard of a dog dying in childbirth? Have you ever heard of cats or pigs dying in childbirth?
Hyenas are eutharia that have very small babies. How many hyena have died in childbirth? The marsupials have very small babies. Who ever heard of a kangeroo dying in childbirth?
Laying a large egg is at least as risky as giving live birth to a small baby. Yet, the kiwi lays a large egg and the marsupials give birth to small babies.
Our evolution has not caught up with the growth of our brains. Women die in childbirth because the human brain is proportionally larger than that of other mammals.
Taking the human species out of the discussion, live birth isn't much more dangerous than egg-laying. There is as much mystery concerning why all birds lay eggs as there is concerning the fact that most mammals give birth live.
Since there is so many niches that have both egg layers and live bearers, the answer must be in the early history of both classes of animals: the birds and the mammals. Egg laying is the most common mode of operation. However, somehow it didn't work out for the common ancestor of all marsupials and eutharia. The question is why most mammals out of all the vertebrates are usually live bearers.
The answer is probably historical. There may have been an environmental factor where living bearing animals have a large advantage.
The links previous posted on live-bearing squamata seem rather suggestive. Most live bearing squamata live in cold climates. It makes sense to me that some of the early mammals may have lived in cold climates. Their warm bloodedness is consistent with that hypothesis.
While we may never know the answer, I think that it is a plausible conjecture. Some Mesozoic species of mammal living near the North or South pole may be the most recent common ancestor of all the eutharia and marsupials.
I would suggest that paleontologists start to look for Mesozoic mammal fossils in a region that used to be near the North or South pole. There are deposits of dinosaur fossils in such areas. I hope they find mammal fossils there. Paleontologists, start looking for the little fossils in these Mesozoic polar regions!

 

[bobze]

Not true. Otherwise, we should all be single cell organisms.

Yes, it is true. A change in species happens at the level of a population, when we have changes in allele frequencies within the population. It doesn't happen with individuals. That is a common misconception. There is no "first organism" born of a species one day.

We're not single celled organisms, because populations changed overtime. Not because a new species ever arose through one individual.

 

[SW VandeCarr]

Most mammal females do not have the same level of difficulty giving birth as humans. Humans are an unusual species of mammal in terms of their difficulty in giving birth.

A dog can give birth to more than five puppies at once. Often, four or more will survive. So can mice, pigs and other mammals. How often have you heard of a dog dying in childbirth? Have you ever heard of cats or pigs dying in childbirth?

Humans may well have more potential complications of pregnancy than other mammals, but all mammals are subject to ectopic pregnancies, infections, fetal-maternal incompatibility, especially with free breeding animals, as well as other problems. Dogs are not immune.

http://www.pethealthandcare.com/dog-health/dog-pregnancy-problems.html

If you google veterinary medicine, problem pregnancies, you will find references to canine, feline, equine and bovine pregnancies. Cattle ranchers are very familiar with problem pregnancies in their herds.

 

[Ken Natton]

There is no "first organism" born of a species one day.

This of course is the heart of the point. As others have pointed out, the egg, as meant in the question, appeared some vast time period before anything even vaguely resembling a modern chicken. But the clear assumption underlying the question is that it is possible to identify the first chicken, or even the first egg. Neither assumption has any foundation whatever.

 

[RabbitWho]

I read somewhere (why can I never remember where?) that difficult childbirth is a trade we made when we started standing upright, that it changed the shape of our hips in a way that makes childbirth a pain in the hiney.

 

[checkbox]

Assuming we are talking about a 'modern' chicken and a 'modern' chicken egg, the answer would seem to be: the egg.

Rationale: two creatures both 99.999% (etc) genetically similar to modern chickens, but in different ways, mated. The result is an egg that now contains 100% 'modern' chicken DNA.

 

[Ken Natton]

Assuming we are talking about a 'modern' chicken and a 'modern' chicken egg, the answer would seem to be: the egg.

Rationale: two creatures both 99.999% (etc) genetically similar to modern chickens, but in different ways, mated. The result is an egg that now contains 100% 'modern' chicken DNA.

Hmmm. You're still not getting it, checkbox. You are assuming that all living chickens are gentically identical. They are not. All living chickens, like all living humans, are mutants.

 

[QuantumHop]

A chicken is just an egg's way of making another egg

 

[Jimmy Snyder]

If I remember correctly from my HS health course, it was the rooster.

 

[Pythagorean]

If I remember correctly from my HS health course, it was the rooster.

 

[BlackTentacle]

The chicken and and egg are just metaphors for DNA and Protein. The proteins can catalyse reactions as enzymes. They are both essential for life and you can not have one without the other. So how did life arise from the primordial soup without pre-existing DNA and proteins? The answer was a molecules that could perform both roles of replication and of catalysing reactions called RNA - ribonucleic acid; as opposed to deoxyribonucleic acid - DNA and RNA.

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

 

[Ryan_m_b]

The chicken and and egg are just metaphors for DNA and Protein.

Actually the chicken and egg riddle predates knowledge of DNA and protein by over two thousand years. Aristotle is known to have used it to question the nature of the origin of life.