There are two basic life-cycle patterns among animals. Many animals have complex life cycles with two or more very distinct stages; metamorphosis is the usual term for the often-radical changes that ...

For over 100 years, biologists have wondered why animals display different types of life cycles. Some species, like us humans and most vertebrates, develop directly into a fully formed—yet ...

From tadpole to frog caterpillar to butterfly and pup to wolf children will learn about the life cycles of animals the different stages of development and the average life spans of a variety of ...

Analysis of the DNA and proteins of a range of animals has revealed that sperm’s molecular toolkit arose in our single-celled ancestors, perhaps more than a billion years ago ...

Slow orbital changes caused pulses in Earth's oxygen cycle 500 million years ago, which spurred explosions of animal life.