98-102

3. THE FOUR GREAT LINKAGE GROUPS OF DROSOPHILA
AMPELOPHILA 103-118
a. Group I. 104-109
b. Group II. 109-112
c. Group III. 112-115
d. Group IV. 115-118

4. LOCALIZATION OF FACTORS IN THE CHROMOSOMES 118-142
a. The Evidence from Sex Linked Inheritance 118-137
b. The Evidence from Interference 137-138
c. The Evidence from Non-Disjunction 139-142

5. HOW MANY GENETIC FACTORS ARE THERE IN
THE GERM-PLASM OF A SINGLE INDIVIDUAL? 142-143

6. CONCLUSIONS 144

CHAPTER IV
SELECTION AND EVOLUTION

1. THE THEORY OF NATURAL SELECTION 145-161

2. HOW HAS SELECTION IN DOMESTICATED ANIMALS
AND PLANTS BROUGHT ABOUT ITS RESULTS? 161-165

3. ARE FACTORS CHANGED THROUGH SELECTION? 165-187

4. HOW DOES NATURAL SELECTION INFLUENCE
THE COURSE OF EVOLUTION? 187-193

5. CONCLUSIONS 193-194

INDEX 195-197

* * * * *

CHAPTER I

A REVALUATION OF THE EVIDENCE ON WHICH THE THEORY OF EVOLUTION WAS BASED

We use the word evolution in many ways--to include many different kinds of
changes. There is hardly any other scientific term that is used so
carelessly--to imply so much, to mean so little.

THREE KINDS OF EVOLUTION

We speak of the evolution of the stars, of the evolution of the horse, of
the evolution of the steam engine, as though they were all part of the same
process. What have they in common? Only this, that each concerns itself
with the _history_ of something. When the astronomer thinks of the
_evolution_ of the earth, the moon, the sun and the stars, he has a picture
of diffuse matter that has slowly condensed. With condensation came heat;
with heat, action and reaction within the mass until the chemical
substances that we know today were produced. This is the nebular hypothesis
of the astronomer. The astronomer explains, or tries to explain, how this
evolution took place, by an appeal to the physical processes that have been
worked out in the laboratory, processes which he thinks have existed
through all t