1. Speciation

2.
Nature knows no pause in progress and development, and attaches her curse on all inaction.
Johann Wolfgang von Goethe

3. When you learned about biological classification, you were taught that the organisms that closely resemble each other and are capable of breeding in nature are classified in the same species.
Organisms of the same species interbreed to produce fertile offspring.
Sometimes, two different species breed and produce a viable offspring that is infertile.
Therefore, the definition of a species has to also consider the physical appearance and behavioural pattern of individuals and populations.

4. Fun Fact… A mule is produced when a horse and donkey interbreed.
The binomial name for a horse is E. caballus and the binomial name of a donkey is E. asinus. 
They are not the same species, and as a result, mules are infertile.
Anyway… where were we?

5. New species are formed through the process of natural selection which favours beneficial genetic variations by individuals within a population.
The evolutionary process that results in the formation of new species is called speciation.
Many scientists believe that new species have formed and will continue to form in the ongoing process of creation.

6. Remember the definition of evolution involved all living things sharing a common ancestor.
The phylogenetic tree of life, illustrates the divergence of the three domains from a common ancestor.
Some event had to have taken place which resulted in the formation of a new species that are shown as branches.
A phylogenetic tree can be used to show the evolutionary history between organisms that have similar traits.
Using evidence such as genetics, fossil records, biochemistry and anatomy a phylogenetic relationship can be established between organisms.

8. The phylogenetic tree below illustrates the relationship between animals.
From this phylogenetic tree you can interpret that all the animals originated from a common ancestor and that speciation events happened that produced new species.
The evolutionary timeline suggests that birds, dinosaurs and crocodiles are closely related and share a common ancestor.

9. Causes of Speciation
The key to speciation is the evolution of genetic differences between two diverging species.
For a direct split, the species must have genetic differences that cause mating between them to cease or to produce non-viable offspring.
Changes in timing, location or mating rituals may be enough to cause speciation.
There are three modes of speciation that are used to explain the different mechanisms that result in the formation of new species.

11. Allopatric Speciation
Allopatric species occurs when populations become geographically separated from one another.
A lake, canyon, mountain range and road can each represent a physical barrier that can restrict the breeding between populations.
The separation of the population may result in a divergence as different environmental conditions can cause natural selection to operate differently in each of the areas.
Each isolated population can either become extinct or evolve into a different species.
The illustration on the next slide highlights an experiment conducted by Diane Dodd in 1989 that clearly shows allopatric speciation.

13. Parapatric Speciation
In parapatric speciation the population is not separated by a physical barrier, however, the population does not mate randomly.
Individuals are more likely to mate with individuals that are geographically closer within the same population.
This reduces the gene flow across the population.

14. Sympatric Speciation
In sympatric speciation, individuals within a population develop different preferences within the same geographical area.
The behaviour of the individuals isolates them from the rest of the population and their affinity for the new niche leads to speciation.

15. The most important factor in speciation is reproductive isolation.
In all the examples provided above, each population becomes reproductively isolated from one another before speciation can occur.
When the gene flow is limited within a population, genetic divergence can take place so that the original two populations no longer share enough genetic similarities and therefore can no longer interbreed.
Reproductive isolation is accomplished through geographical barriers, behavioural changes in mating rituals, and reproductive barriers like incompatible reproductive parts or offspring infertility.

16. Review Questions!
The _________  tree can be used to show evolutionary history between organisms with similar traits.
Which of the following evidence cannot be used to establish similarities between species?
Physical Anatomy DNA
Eating habits Fossils
True or False? - Species A and B have a common ancestor which is different from C.
Provide one example of an event that could lead to speciation.

17. Answers Phylogenetic. Eating Habits.
The answer is false. All three species have a common ancestor, however, species A and B diverged at the speciation event.
A change in habitat, mating rituals, reproductive life cycle, and geographic separation are events that can lead to reproductive isolation and speciation.

18. Homework Further reading on speciation:
Pay close attention to the example involving apple maggots in the third reading.