What Is a Life Cycle?

Patrick Colgan is the former executive director of the Canadian Museum
of Nature.

These two books continue the “what is?” theme of The Science of
Living Things series. In What Are Food Chains and Webs?, food chains and
webs are examined in terms of energy flow, ecological niches of species
(such as herbivores), and examples in different communities (such as a
reef). The authors cover a laudably broad range of topics, including
energy pyramids, photosynthesis, carnivorous plants, decomposers, and
cleaner fish. The recommended food web game with a ball of string risks
ending in a tangle.

In What Is a Life Cycle?, life cycles are treated in terms of plant
seeds and animal eggs, metamorphosis, selected animal groups (including
arthropods and vertebrate classes), and overall features of life cycles
(including their fragility in endangered species). Simplification takes
its toll; for instance, young reptiles may be “carbon copies” of
their parents anatomically but not genetically. Eggs are featured
throughout the book, and mating, fertilization, and parental care are
well presented both textually and visually. However, sperm are not
mentioned until the second half of the book and make no appearance on
the two pages dedicated to humans, which feature only females.

In each book, there is a helpful glossary and index. The text in both
books is straightforward if somewhat uninspired. The pleasant drawings
and photographs are effective as illustrations (although the eggs of
three bird species could have been made life-size). Recommended.