In some certain respect, all members of species are similar or alike. For instance, you have inherited the characteristics of the human race. That makes you look like other human beings. In what ways are you alike? Try to note some characteristics which make you similar to other human beings. The traits which you find most likely common among human beings are called species characteristics.
Although organisms have similarities, they also have their individual characteristics. These characteristics make one an individual member of a species different from another specie. It makes them unique in some ways. These traits basically lead to individual differences. Although you and I are both humans, we are alike and we are different in some ways. We may have two eyes, two ears and other body parts but we may differ in terms of eye color, skin color, structure of earlobes and even hair color.
There are various factors that make people alike but different in some ways. Human possess the individuality that make them different from their brothers and sisters despite the same roots. Heredity can be one reason for variation but it's not everything. There is another factor called environment. Even identical twins can manifest some physical differences if they are brought up in two separate and entirely different environment or circumstances. Environment may affect an individual's growth. If parents are tall, children are most likely to be tall. Moreover, in an environment which limits a child's access to its nutritional needs, the child may appear small and skinny. This only proves that environment affects individual differences.