(a) Yes.
(b) Geographical isolation prevents gene flow between populations of a species whereas asexual reproduction generally involves only one individual. Slowly the separated individuals will reproduce among themselves and generate new variations. Geographical isolation gradually leads to genetic drift. Continuous accumulation of those variations through a few generations may ultimately lead to the formation of a new species.

If complex appearance is parallel with evolution, then humans are more complex than bacteria. But when we take it as total life characteristics, then it is difficult to identify.

DNA sequences are used for studying human evolution. There is no biological basis to the idea of human races. All human beings are a single species but there is a great diversity of human forms and features across the earth. The earliest members of human species Homo sapiens are traced from Africa.
The evidences in support are as follows:
1.Common body plan, structure, physiology and metabolism.
2.Constant chromosome number
3. Common genetic blue print
4. Free inter-breeding

The traits developed in an individual during its life time due to the effect of environmental factors are called acquired traits. These traits are also called somatic variations as they affect the structure and functioning of cells, tissues and organs without influencing the genetic material. Example - colour of seeds, colour of eyes.
A trait which is caused by a change in its gene or DNA is called an inherited trait. In other words, the traits which are passed from parents to their offspring generation after generation are called inherited traits. Example - loss of a finger in an accident.

Only those changes in the DNA or germ cells will be passed on to the progeny resulting in the variations in them. Since acquired characters do not produce any change in the DNA of germ cells, they cannot be inherited.