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Chapter 26   The Tree of Life: An Introduction to Biological Diversity

Lecture Outline

Overview: Changing Life on a Changing Earth

Life is a continuum extending from the earliest organisms to the great variety of forms alive today.

Organisms interact with their environments.

Geological events that alter environments change the course of biological history.

When glaciers recede and the land rebounds, marine creatures can be trapped in what gradually become freshwater lakes.

Populations of organisms trapped in these lakes are isolated from parent populations, and may evolve into new species.

Life changes the planet it inhabits.

The evolution of photosynthetic organisms released oxygen into the air, with a dramatic effect on Earth’s atmosphere.

The emergence of Homo sapiens has changed the land, water, and air at an unprecedented rate.

Historical study of any sort is an inexact discipline that depends on the preservation, reliability, and interpretation of records.

The fossil record of past life is generally less and less complete the further into the past we delve.

Fortunately, each organism alive today carries traces of its evolutionary history in its molecules, metabolism, and anatomy.

Still, the evolutionary episodes of greatest antiquity are generally the most obscure.

Concept 26.1 Conditions on early Earth made the origin of life possible

Most biologists now think that it is credible that chemical and physical processes on Earth produced simple cells.

According to one hypothetical scenario, there were four main stages in this process:


The abiotic synthesis of small organic molecules (monomers).


The joining of monomers into polymers.

Lecture Outline for Campbell/Reece Biology, 7th Edition, © Pearson Education, Inc. 26-1

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