Billions of Missing Links: Hen's Eggs
Note: This is one of a series of posts excerpted from my book, Billions of Missing Links: A Rational Look at the Mysteries Evolution Can't Explain.
When it comes to citing examples of purposeful design, nearly every author likes to point out the hen's egg. It's really quite remarkable. Despite having a shell that is a mere 0.35 mm think, they don't break when a parent sits on them. According to Dr. Knut Schmidt-Nielsen,
A bird egg is a mechanical structure strong enough to hold a chick securely during development, yet weak enough to break out of. The shell must let oxygen in and carbon dioxide out, yet be sufficiently impermeable to water to keep the contents from drying out.Under microscopy, one can see the shell is a foamlike structure that resists cracking. Gases and water pass through 10,000 pores that average 17 micrometers in diameter. Ultimately, 6 liters of oxygen will have been taken in and 4.5 liters of carbon dioxide given off. The yolk is its food. All life support systems are self-contained, like a space shuttle.
All hen's eggs are ready to hatch on the twenty-first day. Every day is precisely preprogrammed. The heart starts beating on the sixth day. On the nineteenth day the embryo uses its egg tooth to puncture the air sac (beneath the flat end) and then takes two days to crack through the shell.