Birds egg, what came first? by professor Marcos Eberlin
Birds’ Eggs MOLECULAR OXYGEN (O₂) is necessary for life nearly from the moment of conception to convert nutrients into energy. No O₂, no life. A human baby needs O₂ even before the lungs start to work. As the fertilized human egg grows inside the mother’s womb, the mother provides the baby with enough O₂ through the umbilical cord.
A bird embryo, in contrast, does not develop in its mother’s womb. It is totally separated from its mother and isolated inside a capsule: the egg. From the outside, an egg looks more like a coffin than a cradle, enclosed by a hard, sealed, calcium carbonate (CaCO₃) shell. But an egg (Figure 6.3) is much more complex than it looks.13 But eggs, of course, are not coffins; they are self-contained cradles, full of weird and wonderful tricks to provide the chick with all it needs, from mechanical protection to a finely tuned package of food (the yolk and the egg white).
An egg is like a spaceship that contains all it needs, with one exception: O₂. At first glance, death by suffocation would seem to be inevitable. But the baby bird stays inside, maturing well, for weeks. How does it get oxygen? And how does it expel the carbon dioxide (CO₂) that results from converting nutrients into energy? If too much CO₂ were to accumulate inside, it would suffocate the baby animal. How does the chick selectively and efficiently get O₂ in and CO₂ out? NPR has a short online vide on the subject that I highly recommend.14 Here we will summarize much of what’s described and depicted there.
Figure 6.3. The biology of bird and reptile reproduction is unique, and scientists have long wondered how the highly sophisticated egg in the system originated.
Eggs have a hard yet water- and air-permeable shell, strong enough to bear the weight of an incubating mother. The shell contains thousands of tiny pores, each less than a thousandth of an inch across—too small to be seen with the naked eye. A chicken egg, for instance, has more than 7,000 tiny pores. These minuscule pores are perfectly calibrated to maintain the integrity of the whole structure. They deter invaders while allowing O₂ from fresh air to come in and waste CO₂ to get out. If the pores were either too big or too small, birds would have gone extinct. But just having pores is not enough. Two remarkable selective membranes are located directly under the chicken egg’s shell, which cooperate in a highly synchronized fashion. When the female sits on eggs to incubate her young, the eggs are usually warmer than the surrounding air. As an egg cools down, its contents shrink slightly, pulling the two inside membranes apart at the perfect moment. The shrinking sucks in air from the atmosphere, forming a small sac containing mostly nitrogen (N₂) but also sufficient O₂.
The baby bird then somehow “senses” that precious O₂ has entered the egg. To reach it, the chick develops a delicate network of capillaries in a precisely orchestrated genetic and metabolic process. These capillaries are perfectly engineered to move O₂ into and CO₂ out of the bird’s blood. This network grows out of the chick’s abdomen and presses up against the membranes, making close contact with them. The two membranes of the egg also allow selective permeation via proper exchange of O₂ and CO₂. It is a high-tech masterpiece of air treatment and control. The egg pores are engineering masterpieces for another reason. They allow water molecules to move in and out of the shell. The water slowly evaporates, creating more empty space to fill with air. When the baby is ready to hatch, it punctures the inflated air sac to take his first breath while still inside the egg.
The egg tooth is yet another marvel of engineering. This tooth is a small horn-like projection that begins developing on the upper beak on the seventh day inside the egg. Hatching takes place twenty-one days after the egg is laid. As the time for hatching nears, it becomes hard and sharp so the chick can use it for breaking through the inner membrane to reach the air cell located in the egg’s blunt end.15 The air sac between the shell and inner membrane has just the right amount of oxygen to allow the chick to begin employing its respiratory system for up to three days before hatching. Using this air reservoir, the baby fills its lungs and gets strong enough to punch holes through the hard egg shell. The chick’s claws and beak aren’t yet strong enough to break through the hard eggshell, so the egg tooth and the air sac are essential.16 Without the egg tooth and the air sac, the chick would die inside the egg.
The baby bird also needs something else to make the first crack in the shell (called “pipping”). To break holes though the membranes and the hard shell, a pipping muscle swells on the backside of the bird’s neck to press the beak against the shell. Punching an initial hole through the shell is so tiring that the chick rests for as much as eight hours afterward. Then, as Gail Damerow explains, the reinvigorated chick rotates itself counterclockwise, chipping the shell with its egg tooth “thousands of times, until it has broken the shell about three-quarters of the way around, creating a shell cap at the blunt end of the egg.”17 This highly choreographed action of breaking an egg shell can take up to five hours. The chick knows when it is done and pushes against the shell cap with its head. After about forty minutes of labor, it finally breaks the shell cap loose. The newborn bird is exhausted again, and takes another rest. Finally, it gives one strong kick to escape the egg shell.
The egg tooth is essential for the escape. But notice too that the chick’s mother hasn’t had the chance to teach the chick how to do any of this, and yet somehow it knows. (If it didn’t, it would die.) This know-how also is part of what apparently must be foreseen and delivered in advance. The chicks of some bird species, such as megapodes, don’t have an egg tooth. Their egg shells are much softer, so they have no need to develop the nutrient-demanding tooth. They hatch feet-first to kick their way out, using sharp claws that have been ingeniously covered by jelly-like caps to avoid injuries. These jelly-like caps, like the egg tooth, fall off soon after the chick hatches. There is an amazing synergy of action between the baby chick inside its egg and the mother outside. The mother hen “knows” she must incubate the egg for a few weeks, keeping it warm and turning it around several times a day. After about seventeen days of incubation beneath the mother hen, the chick starts to peep. Peeping signals the mother hen that the chick is almost ready to leave the egg.
As soon as she hears the message, the hen begins to peck holes in the rounded end of the shell. More air gets in, allowing the chick more oxygen and thus strength for hatching. From this point on, the chick will use its egg tooth to break the shell, ratcheting his body around in a very coordinated process until it can break free.
Though this is the commonest way for chicks to hatch, in a few species the chick splits the side of the egg and emerges through an untidy hole. The required amount of pecking varies, and appears pre-programmed to match the hardness of the egg and endurance of the chick must incubate the egg for a few weeks, keeping it warm and turning it around several times a day. After about seventeen days of incubation beneath the mother hen, the chick starts to peep. Peeping signals the mother hen that the chick is almost ready to leave the egg. As soon as she hears the message, the hen begins to peck holes in the rounded end of the shell. More air gets in, allowing the chick more oxygen and thus strength for hatching. From this point on, the chick will use its egg tooth to break the shell, ratcheting his body around in a very coordinated process until it can break free. Though this is the commonest way for chicks to hatch, in a few species the chick splits the side of the egg and emerges through an untidy hole. The required amount of pecking varies, and appears pre-programmed to match the hardness of the egg and endurance of the chick.
Thomas Wentworth Higginson, a nineteenth-century author, abolitionist, and women’s rights activist, once declared, “I think that, if required on pain of death to name instantly the most perfect thing in the universe, I should risk my fate on a bird’s egg.”19 Multiple levels of foresight appear required to orchestrate such a perfect thing as an egg. As with other cases, the suggested evolutionary scenarios explain the benefit of having an egg and a chicken to provide it, but ignore the specifics of how this most exquisite system could have originated one small, blind step at a time over many generations.
Which Came First?
THE AGE-OLD question is: Which came first, the chicken or the egg? It takes a chicken to make an egg, but it takes an egg to make a chicken. Without a chicken there would be no egg, but chickens that laid only partly evolved, not-fully-functional eggs would go extinct in a single generation—bye-bye, birdy.
A fully functional egg must be planned in advance, with correctly sized pores, inner membranes, and an expandable air sac. The chick must be programmed to connect itself via a network of blood vessels to the membranes, and to make its air sac slowly expand so the chick can exercise its new lungs before breaking the walls of its prison. The egg must also be loaded with just enough food for the chick to mature. The chick must have the strong and well-designed egg tooth and know how to chip out of its shell. The chick and the hen also must coordinate their behavior. If any of these intricate steps, behaviors, and structures were overlooked, birds would not survive long enough for natural selection to develop anything new. Birds and their eggs are, indeed, striking cases for foresight and planning in nature.
Eberlin, Marcos. Foresight: How the Chemistry of Life Reveals Planning and Purpose . Discovery Institute. Kindle Edition.
Please watch as well the video about the egg at the link below;
