1

Which one of the following statements is accurate?

a. Natural selection works on variation already present in a population.

b. Natural selection works on non‐heritable traits.

c. Individuals evolve through natural selection.

d. Organisms evolve structures that they need.

e. None of the statements are true.

Speciation and Macroevolution

• Describe the patterns found in the study of macroevolution.

• Explain the concept of exaptation and describe an examples. 

• Explain why mass extinctions can be seen as times of great opportunity 

• Define the biological species concept. Explain its limitations when applied to all types of living organisms. 

• Describe the different types of pre‐zygotic and post‐zygotic reproductive isolating mechanisms. 

• Explain the process of allopatric speciation. 

• Explain what a cladogram or phylogenetic tree, what information does it provide and how can it be constructed

Website: http://evolution.berkeley.edu/

2

Are these two groups of fliestwo populations of the same species

or are they two different species?

What is a species?

‐ population or groups of populations

‐members can potentially interbreed in nature

‐ AND produce fertile offspring

‐ appearance is not important

3

Fly scenario• An event splits the original 

population in two

• Generations later…

• An other event brings the groups

together

But they are not interbreeding!!!

• Speciation has occurred

• Speciation: process by which new species 

come into being

New species originate as modified descendants of other species

Process of SpeciationStep 1: Genetic Isolation

gene flow between 

two populations is interrupted 

(populations become 

genetically isolated from each other)

Step 2: Populations diverge genetically

genetic differences gradually accumulate 

between the two populations 

Step 3: Reproductive isolation

Some of these genetic differences (traits) 

will be reproductive barriers

(traits that prevent two individuals from interbreeding with each other) 

4

Genetic differences  phenotype differences reproductive barriersReproductive barriers

before the zygote forms or after the zygote forms

What can cause speciation?

Geographical barrier 

(Allopatric speciation)

5

Many geological and climatic events can produce geographic barriers causing speciation

But only 1% are alive today because of…

If we reconstruct the speciation events over this time….

Over the last 3. 8 billions of years

Microevolution and

Speciation

has resulted on all the species that have ever existed

6

Through descent with modification over 3.8 billion years

all organisms are genetically related

Macroevolution: evolution above species level

Reconstructing the speciation events over the history of life

Trunk is one species over some time

Speciation happens and the tree splits

Continuing through time reveals new branching

7

How do scientists reconstruct these speciation events? 

Systematists are the detectives of life’s history

Evidence:Observable charactersneed to be derived (unique) and shared

Result:Produce a tree-like diagram Called phylogeny or cladogram

How to interpret a cladogram?

Who is more closely related to B?A or C

If a new trait appears in green line, who A, B or C have it?

8

Evolution is NOT aclimb up a ladder of progresswhere organisms are always getting better

It is important to remember that:

Humans did not evolve from chimpanzees

Humans and chimpanzees

are evolutionary cousins and

share a recent common ancestor

that was neither chimpanzee nor human.

Humans are not "higher" or "more evolved"

than other living lineages.

Since our lineages split,

humans and chimpanzees

have each evolved traits

unique to their own lineages.

Importance of reconstructing evolutionary histories

We can observe large scale patterns through out life’s history

We can organize species based on 

their relationships

9

Macroevolution patternsStasis:

Some species don't change much for a long time 

Rapid change:

Example

Coelacanth (discovered 1930)

Unchanged during the last 80 million years

Macroevolution patternsExtinction:

is the disappearance of 

an entire species

from the face of the Earth

Mass extinctions:

events that have

wiped out anywhere from 

50% to 95% species

Adaptive Radiation :

event in which a group of species

rapidly diversifies

99% of species that have existed are extinct today

10

Macroevolution PatternsConvergent evolution:

Unrelated species develop similarities

due to adaptation to similar environments 

Analogous characters

similar looking structures

due to adaptation to similar environments 

not due to common ancestry 

skeleton made of cartilage

skeleton made of bone

use gills to get oxygen from the water in which they swim

go to the surface and breathe air in through their blowholes

don't nurse their young

do nurse their young

don't have hair

do have hair —they are born with hair around their "noses"