Unit B

Module 4 ~ Lesson 3


In this lesson you explored the following essential question:

  • What proof is there that present-day species evolved from ancestral forms?

The Burgess Shale in Yoho National Park is an excellent source of evidence for evolution. If Darwin had access to the fossils in the Burgess Shale, he likely would have had even stronger evidence to support his developing theories. Scientists today have more evidence for evolution than Darwin had.

Scientists have been accumulating evidence of evolution for more than 150 years. Early evidence, such as fossils, led scientists to examine anatomy. Homologous structures, which can be compared between fossils and living organisms, support Darwin's theory that organisms evolve from ancestral forms. Similarities in embryo development (a three-week-old human embryo looks similar to a chicken embryo) also seem to support Darwin's theory.

New discoveries and the advancement of technology allow scientists to look at molecular biology and genetics (such as DNA and the process of cellular reproduction) for evidence of evolution. For example, scientists have found that human DNA is 98.8% similar to chimpanzee DNA. This information indicates that at some point there was a common ancestor for the two animals.

 Lesson Glossary

analogous structures: body parts in different species that have similar functions but evolved separately

biogeography: the study of the past and present geographical distribution of species

embryology: the study of similar features in embryos and evolutionary relationships that may exist

fossils: the remains of past life found in sedimentary rock

homologous structures: body parts in different species that have the same evolutionary origins and structural elements but may have different functions

hypothesis: a statement that provides one possible answer to a question or one possible explanation for an observation

inheritance of acquired characteristics: a theory that characteristics acquired during an organism's lifetime could be passed to its offspring

strata: a layer of rock or soil that has a consistent character and is different from layers above and below it

transitional fossil: the remains or impression of a prehistoric organism that shows intermediary links between groups of organisms and shares characteristics common to these groups

gradualism: the theory that evolution occurs slowly and steadily in a linear fashion

punctuated equilibrium: the theory that suggests that evolutionary history consists of long periods of stasis (stable equilibrium), punctuated by periods of divergence