THE PACE OFSPECIATION

Section 25.3

POLL #1

• Speciation- is the evolutionary process in which new species arise.

• The pace of speciation refers to the rate of evolutionary change.

• Scientists want to know this rate to further understand the concepts of evolution and natural selection.

BACKGROUND

• Darwin suggested that evolutionary rates change over different periods of time.

• Scientists who have been examining the patterns of speciation began to investigate two distinct patterns.

• Neither of the two are considered completely flawless and are ways to classify the tempo of speciation.

BACKGROUND(CONT.)

• This theory suggests that new species evolve over long periods of time, but the evolution is constant and continuous.

• This means that species are always evolving in small ways that may not be noticeable at first.

• New species arise from many small changes that accumulated over a long period of time.

GRADUALISM

• This hypothesis on the pace of speciation theorizes that the tempo of change is much more irregular than phyletic gradualism suggests.

• This belief states that there are periods of time where a species can have little to no phenotypic change.

PUNCTUATED EQUILIBRIA

• On the other hand, there are periods of time that the species will have rapid evolutionary change which leads to a new species.

• During the time of little to no change, known as the equilibrium period. Neutral genetic changes are said to accumulate.

POLL #2

FACTORS THAT CHANGE THE PACE OF SPECIATION

• Allopatric speciation, which can also be termed as geographic isolation can effect the pace of speciation.

• When a population of animals migrates away from a larger population a whole slew of new traits may arise relatively quickly.

• If this population continues to develop new traits it may eventually become its own species.

FACTORS THAT CHANGE THE PACE OF SPECIATION

• Environmental shifts can also change the tempo of evolution.

• When an environmental shift occurs that effects a species ability to survive it can drive speciation greatly.

• The alleles that allow a species to survive the environmental shift will be very heavily favored therefore quickening the pace of evolution.

A predator is an enviromental shift. Organisms that could hide from it have a better chance to survive.

Poll #3

• Two theories are needed because both together most accurately explain speciation.

• In many fossil records scientists observe species with long periods of time without any change, but than they have short periods of intense change.

• Scientists hypothesize that the periods of little change are probably small neutral changes accumulating that were described in gradualism.

DAFAQ #1“WHY ARE

TWO THEORIES OF SPECIATION NEEDED?”

THERE ARE ACTUALLY 3*

• Yes, organisms have very different paces of speciation.

• For example, bacteria are said to evolve much, much quicker than humans. This is because bacteria have many more generations than humans do.

• Bacteria can reproduce a lot quicker, scientists say some can every 20 minutes. This is not even comparable to the speed that humans have to reproduce.

• Therefore, bacteria have a much quicker pace of speciation.

DAFAQ #2“DO DIFFERENT SPECIES HAVE

DIFFERENT TIMETABLES OF SPECIATION?”

• This third hypothesis about the pace of speciation almost a hybrid of the previous theories.

• The hypothesis is that a species is relatively stable in terms of evolution for a long period of time, but than undergoes a rapid change that does NOT lead to a new species.

PUNCTUATED GRADUALISM

THE THREE HYPOTHESES