Search NOVA Teachers

Back to Teachers Home

Odyssey of Life, Part I—The Ultimate Journey

Classroom Activity

To put in correct order the developmental stages for a fish, chick, pig, calf, and human.

Materials for each team
  • copy of "Timing Is Everything" student handout (PDF or HTML)
  1. Copy and distribute the "Timing Is Everything" student handout. Have students cut out and reassemble the squares in an order that correctly represents three developmental stages of the five animals depicted (fish, chick, pig, calf and human).

  2. When students finish, have them explain the reasoning behind their answers. To conclude, have a discussion about the similarities and differences students see in the embryos. Since these five animals look similar in their early embryonic stages, might all vertebrates look similar in those stages? What might that suggest?

  3. As an extension, have students research how the theory of evolution has been viewed from the 1800s through today.

Activity Answer

stage 1: 8, 2, 4, 10, 3
stage 2: 1, 7, 15, 6, 11
stage 3: 14, 9, 13, 12, 5

Students may think that the embryos only look similar. Point out that the backbones and limbs of all four-limbed vertebrates (also called tetrapods) are identical in embryonic origin and underlying structure. Even though they may differ in final external form and function, the various tetrapod limbs (arms, legs, flippers, wings) are all built from precisely the same sets of embryonic tissues, are supported by the same sets of bones, and are moved by the same sets of muscles. These extensive homologies reinforce the scientific understanding that all tetrapods have descended, with various modifications, from ancient, long-extinct ancestors.

Note: These illustrations are representations—not exact depictions—of the embryonic stages of each of these five animals.
Links and Books


Lewin, Roger. The Origin of Modern Humans. New York: Scientific American Library: Distributed by W.H. Freeman, 1993. Looks at possible preludes to Homo sapiens, various hypotheses regarding the origin of modern humans, the idea of a Mitrochondrial Eve, the archeology of modern humans and the origin of language.

Web Sites

NOVA Online—Odyssey of Life
Includes a cyberdebate about how humans evolved; time-lapse sequences of growing human, pig, chicken and fish embryos; an interview with photographer Lennart Nilsson; an essay about the commonalities among species; and an online activity that reveals what bugs live in, on and around us.

Talk Origins
This newsgroup is devoted to the discussion and debate of biological and physical origins. Most discussions in the newsgroup center on the creation-evolution controversy, but other topics of discussion include the origin of life, geology, biology, cosmology and theology.

The Visible Embryo
Follows human embryological development over 40 weeks, providing in-depth information about what occurs at each stage. Requires Shockwave or QuickTime plug-ins.


The "Timing is everything" activity aligns with the following National Science Education Standards:

Grades 5-8

Life Science

Science Standard C:
Life Science

Structure and function in living systems

  • Specialized cells perform specialized functions in multicellular organisms. Groups of specialized cells cooperate to form a tissue, such as a muscle. Different tissues are, in turn, grouped together to form larger functional units, called organs. Each type of cell, tissue and organ has a distinct structure and set of functions that serve the organism as a whole.

Grades 9-12

Life Science

Science Standard C:
Life Science

The cell
  • Cells can differentiate, and complex multicellular organisms are formed as a highly organized arrangement of differentiated cells. In the development of these multicellular organisms, the progeny from a single cell form an embryo in which the cells multiply and differentiate to form the many specialized cells, tissues and organs that comprise the final organism. The differentiation is regulated through the expression of different genes.

Biological evolution

  • The great diversity of organisms is the result of more than 3.5 billion years of evolution that has filled every available niche with life forms.

  • The millions of different species of plants, animals and microorganisms that live on Earth today are related by descent from common ancestors.

Teacher's Guide
Odyssey of Life, Part I—The Ultimate Journey

Video is not required for this activity