Chapter 22(1)

What are the three key observations of life?

We will define evolution as __, a phrase Darwin used in proposing that Earth's many species are escendants of ancestral species that were different from the present-day species.

__ can also be defined more narrowly as a cange in the genetic composition of a population from generation to generation.
-- Whether it is defined broadly or narrowly, evolution is viewed in two related but different ways:
------> as a __ and a ____

The __ of evolutionary change is revealed by data from a range of scientific disciplines, including biology, geology, physics and chemistry. These data are facts- they are observations about the natural world.

The __ of evolution consists of the mechanisms that produce the observed pattern of change. These mechanisms represent natural caues of the natural phenomena we observe.

These mechanisms represent natural causes of the natural phenomena we observe. Indeed, the power of __ consists of the mechanisms that produce the observed pattern of change. The mechanisms represent natural causes of the natural phenomena we observe. Indeed, the power of evolution as a unifying theory is its ability to __ and __ a vast array of obserations about the living world.

One philosopher who greatly influenced early Western science, __, viewed species as __. Through his observations of nature, he recognized certain __ among organisms. He concluded that life-forms could be arranged on a ladder, or scale, of increasing complexity, later called the __. Each form of life, perfect and permanent, had its allotted rung on this ladder.

These ideas coincided with the __ account of creation, which holds that species were individually designed by __ and therefore perfect. In the 1700s, many scientists interpreted the often remarkable match of organisms to their environment as evidence that the __ had designed each species for a particular purpose.

One such scientist was __ (1707-1778), a Swedish physician and botanist who sought to classify life's diversity, in his words, _(phrase) _. He developed the two- part, or __, system of naming species.

In contrast to the linear hieararchy of the __, Linnaeus adopeted a nested classification system, grouping similar species into increasingly general categories.

__ did not ascribe the resemblances among species to evolutionary kinship, but rather to the pattern of their creation. However, a century later his classification system would play a role in _ argument of evolution.

Darwin drew many of his ideas from the work of scientists studying __, the remains of traces of organisms from the past. Most are found in __ rocks formed from the sand and mud that settle to the bottom of seas, lakes, and swamps. New layers of __ cover older ones and compress them into superimposed layers of rocks called __.

The __ in a particular __ provide a glimpse of some of the organisms taht populated Earth at the time that layer formed. Later, __ may carve through upper (youbger) strata, revealing deeper (older) strata that had been buried.

__, the study of fossils, was largely developed by French scientist Georges Cuvier (1769-1832). In examining __ near Paris, He noted that the older the __, the more dissimilar its fossils were to current life-forms. He also observed that from one layer to the next, some new species appeared while others disappeared. He inferred that extinctions must have been a common occurrence in the history of life. Yet, Cuvier staunchly opposed the idea of evolution.

To explain his observations, Cuvier advocated __, the principle that events int he past occurred sudenly and were caused by mechanisms different fro those operating in the present. Cuvier speculated that each boundary between strata represented a __, such as a flood, that had destroyed many of species living at that time. He proposed that these periodic __ were usually confined to local regions, which were later repopulated by species immigrating from other areas.

In contrast, other scientists suggested that profound change could take place through the cumulative effect of slow but continuous processes. In 1795, Scottist geologist __ (1726-97) proposed that Eearth's geolgic features could be explained by gradual mechanisms still operating.
-- Eg: valleys were often formed by rivers whearing through rocks and that rocks containing marine fossils were formed when sediments that had eroded from the land were caried by rivers to the sea, where they buried dead marine organisms.

The leading geologist of Darwin's time, __ (1797-1875), incorporated Hutton's thinking into his principle of __, which stated that mechanisms of change are constant over time. He proposed that the same geological processes are operating today as in the past and at the same rate.

Huttons and Lyell's ideas strongly influenced __ thinking, who agvreed that if geologic changeresults from slow, continuous actions rather than from sudden events, then Earth mst be much older than the widely accepted age of a few thousand years. He later reasoned that perhaps similarly slowly and subtle processes could produce substantial biological change. __ was not the first to apply the idea of gradual change to biological evolution.

During the 18th century, several __ suggested that life evolves as environments change. But only one of Darwin's predecesors proposed a mechanism for how life changes over time: French biologist __. Alas, he is primarily remembered not for his vissionary recognition that evolutionary change explains patterns in fossils and the match of organisms to their environments, but for the incorrect mechanism he proposed to explain how evolution occurs.

_ published hishypothesis in 1809, the year Darwin was born. By comparing living species with fossil forms, __ had found what appeared to be several lines of descent, each a chronological series of older to younger fossils, leading to a living species. He explained his findings using two principles.

The first was __, the idea that parts of the body that are used extensively become larger and stronger, while those that are not used deteriorate.
The second principle , __, stated that an organism could pass these modifications to its offspring.

__ also thought that evolution happens because organisms have an innate drive to become more complex. __ rejected this idea, but he thought variation was introduced into the evolutionary process in part through inheritance of acquired characteristics. Today, however, our understanding of genetics refutes this mechanism: There is no evidence that acquired characteristics can be inherited in the way proposed by Lamarck.

__ was vilified in his own time, especially by __, who deniedthat species ever evolve. In retrospect, __ deserves credit for recognizing that the match of organisms to their enviromnments can be explained by gradual evolutionary change and for proposing a testable mechanism for this change.