Migration of a single pair of birds to an island can lead to adaptive radiation due to the diverse conditions that promote variations for survival, influenced by factors like food needs, safety, and environmental niches. Additionally, the incompleteness of fossils arises from the rarity of suitable fossilization conditions and destructive forces. Examples include precursors of trilobites in pre-Silurian rocks and transitional whale fossils with both teeth and baleen.

1. ort Answer: 1) Why would migration to an island by a single pair of birds be likely to lead to
adaptive radiation in their descendants?
Solution
1) The law of adaptive radiation by Osborn postulates, "each isolated region, if large and
sufficiently varied in its topography, soil, climate and vegetation, will give rise to a diverse
fauna; the larger the region and more diverse teh conditions, the greater will be the variation of
animals found". Thus, the pair of birds entering an island will be prone to variations in
topography and biological entities leading to adaptations in their features to lead a survival. The
factors which would influence their adaptative radiation are need for food, need for safety, need
for better breeding grounds, absence of enemies, presence of unoccupied environmental niches
and isolation.
2) The incompleteness of fossils is caused by the following factors:
Most of the animals and plants do not get suitable conditions for fossilization. They are
destroyed by destructive forces.
3. a. Precursors of trilobites found in pre-Silurian rocks.
b. Fossils of transitional whale with both teeth and baleen discovered.