Question

1. Life is not perfect. One reason for this is because the environment changes and adaptations lag. Which of the following best describes what this statement means.

   		Selection occurs in the parental generation. If the environment changes between generations offspring may no longer be best adapted to their environment.
   		Selection can only work with the genetic material present in a population. When the environment changes, new variation is needed and mutations that result in traits suitable to the current environment will take time to build up in the population.
   		Selection occurs in the parental generation. If the environment changes, parents may need to change their behavior in the new environment. These new adaptations would not have been passed onto previous offspring, resulting in a lag since some generations will not be best adapted to the new environment.
   		Two of the answers best describe this statement.

Rose thorns are modified stems. The ancestors to our modern-day roses did not have thorns to protect them from herbivory. Which of the following would be the reasonable hypothesis for how natural selection drove the evolution of thorns on roses?

		Ancestral rose stems had variable stem textures; from smooth to bumpy. Those with bumpy stems were less palatable to herbivores and so were consumed less frequently. Thus bumpy stemmed individuals reproduced more than smooth stemmed individuals and their offspring exhibited the parental bumpy stem texture.
		Ancestral roses were all smooth-stemmed. A mutation arose that conferred thorn-like structures on rose stems. Individuals with the thorn mutation were less palatable to herbivores and so were consumed less frequently. Thus they reproduced more than smooth stemmed individuals and their offspring exhibited the thorn-like structure trait.
		Ancestral rose stems had variable stem textures; from smooth to bumpy. Those with bumpy stems were less palatable to herbivores and so were consumed less frequently. Thus bumpy stemmed individuals reproduced more than smooth stemmed individuals.
		Ancestral rose stems had variable stem shapes; from rounded to angular Those with angular stems were less palatable to herbivores and so were consumed less frequently.

Answer 1

1. Selection can only work with the genetic material present in a population. When the environment changes, new variation is needed and mutations that result in traits suitable to the current environment will take time to build up in the population.

Genetic variation is an important force in evolution as it allows natural selection to increase or decrease the frequency of alleles already in the population.

2. Ancestral roses were all smooth-stemmed. A mutation arose that conferred thorn-like structures on rose stems. Individuals with the thorn mutation were less palatable to herbivores and so were consumed less frequently. Thus they reproduced more than smooth stemmed individuals and their offspring exhibited the thorn-like structure trait.