Macroevolution and Species
, changes occurring in the gene pool of a population generation after generation fine-
tune a species for success in its environment. Under certain conditions and a long period of time, the same
type of evolutionary changes can lead to the formation of entirely new species.
1. Evolutionary change of one species into another is called macroevolution, or descent with
modification, and was described by Darwin.
B. While microevolution is easy to see occurring around us, macroevolution is not, but there is much
evidence supporting the hypothesis that macroevolution has occurred.
1. Fossils, the remains, impressions, or traces of life preserved in rock, provide direct evidence of
previous forms of life.
a. fossils are very valuable for understanding previous forms of life on Earth, but unfortunately
fossilization is a rare event that requires specific conditions; hence the fossil record is incomplete and
unsystematic. There are many fossils of some organisms, very few of others, and none at all for the vast
majority of creatures that have lived on Earth.
b. hard parts such as bones, teeth, and shells are most likely to be preserved; only extremely rarely
are conditions right for preserving soft parts like worms, flowers, or leaves.
i. fossilization most often occurred when an organism was covered with mud, water, or volcanic
ash soon after death so that it was not eaten. Anaerobic mud or ash are the best because they slow down
c. microscopic fossils are very important in understanding the history of life on Earth, especially the
plant life. Algae such as diatoms with hard shells, and tough pollen grains fossilize well.
d. fossils show that many organisms previously found on Earth are now extinct.
e. they also illustrate relationships between extinct and living organisms, like the similar bone
structure of birds and archaeopteryx.
f. comparing fossils with their descendants allows us to see how evolutionary changes have
occurred over time. If we understand the environmental changes occurring at the same time we can begin
the evolutionary changes occurred.
i. for example, fossil horses have shown us that over time the horse line grew larger, their paws