The nanostructure of chicken egg shells is an evolutionary masterpiece. While the shell is pretty robust during its first days, it gets much thinner by the end of breeding, facilitating it for the chick to hatch. This is due to a developmental process. To set up the chicks' skeleton, the inner calcium layer of the shell gets broken down and reused to build the bones. Pretty cool!

The ostrich is the largest living species of bird — and the fastest. Females only mate with one male, but males fertilize several females. The dominant female lays her eggs on a communal nest, followed by all the others — there are around four secondary females with up to 15 eggs each. The weakest eggs will then be discarded by the dominant female, who will incubate them together with the male.

Kiwis are not only peculiar, in that they are flightless, they are also the symbol of a whole country — New Zealand. They are also worth admiring for laying the largest egg of any species in the world — in relation to body size. Weighing up to half a kilogram, the egg occupies nearly the entire body of the bird, interfering with movement and even breathing. Newborn chicks are quickly independent.

Other parents can't compete with the arduous annual journey of Antarctica's emperor penguins. These animals travel 50-120 kilometers (31-74 miles) to reach their breeding colonies. The female can only lay one egg per year, which makes hatching a truly significant event. The Oscar prize-winning documentary "March of the Penguins" makes us feel as if we were walking in the penguin's shoes.

Considered the biggest birds that ever existed — 3 meters tall and weighing half a ton — elephant birds became extinct four centuries ago. However, one of its impressive eggs was found in 2015, and its size honored its reputation: at 200 times bigger than a chicken egg. This image compares the egg with an adult kiwi skeleton. If you decide to pick this one up, you had better be careful!

Chicken eggs are present in our daily lives. So we rarely ask: 'Which came first, the snake or the egg?' We often don't realize that many other animals hatch from eggs — or are "oviparous." Reptiles such as snakes are among them. Although the majority of snakes abandon their eggs after laying, the female python never leaves them until they hatch — as in the photo above.

Sea turtles have lately been struggling to lay their eggs due to several factors such as climate change, illegal trade or tourism. They swim long distances to reach beach spawning grounds, and exit the water to lay eggs in the sand. But if they are disturbed by humans — through light or sound, for instance — they could go back to the ocean without laying any eggs.

At first sight, the image of this midwife toad may be unpleasant, until we understand that what it is carrying on its back are only eggs and not some strange disease. The animal is an exception among toads and frogs: Midwife toad mating doesn't take place in water, but rather on land, and the male is the one in charge of carrying the eggs around for 30 days before laying them.

The Komodo dragon would have been little during the time of the dinosaurs — but today, the largest species of lizard is nearly considered to be a monster. Its mating represents the antithesis of an evening full of gentle caresses. The winner of a violent fight between males jumps on a resisting female to try and copulate without getting hurt. Despite their roughness, they do produce cute babies!