Which of the following is the most important precondition for speciation to occur?

(1) Reproductive isolation

(2) A crash of the population size

(3) Adaptive radiation

(4) Random mating

The ultimate source of allelic variations is:

1. Genetic recombinations 

2. Mutation 

3. Genetic drift 

4. Natural selection 

If a new allele suddenly becomes very abundant in a population, most likely it is:

1. mutating rapidly

2. flowing with emigrants

3. strongly selected for

4. a product of assortative mating

Genetic drift occurs when a few individuals of a species colonize an island. This phenomenon is :

(1) the bottleneck effect

(2) the founder effect

(3) assortative mating

(4) random mating 

The unit of evolution is now known to be the:
1. individual
2. family
3. population
4. species

The struggle for existence is a consequence of:

(1) Each organism leaving more organisms than needed to replace itself

(2) Innate competitive tendencies

(3) The inevitable difficulty of coping with climatic conditions

(4) Territories and dominance hierarchies

Darwin believed that a giraffe has a long neck because:

1. a creator designed it that way

2. catastrophes eliminated short neck forms

3. its ancestors stretched their necks to get food

4. ancestral giraffes with longer necks got more food and left more surviving off-springs.

In a sympatric speciation, there is:

In modern terms, selection refers to :

1. Inheritance of dominant characters
2. differential reproduction 
3. a decrease in allele frequency in a population
4. differences in the contribution of various genotypes to the next generation 

In genetic drift, the term "genetic bottleneck" means:

1. reduction in allele frequencies or richness

2. random change in allele frequency by chance alone

3. sudden increase in the number of individuals

4. reproductive isolation of the population