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..