Facial composite In the U.S. the FBI maintains that hand-drawing is its preferred method for constructing a facial composite. Many other police agencies, however, use software, since suitable artistic talent is often not available. Until quite recently, the facial composite systems used by international police forces were exclusively based on a construction methodology in which individual facial features (eyes, nose, mouth, eyebrows, etc.) are selected one at a time from a large database and then electronically 'overlaid' to make the composite image. Such systems are often referred to as feature-based since they essentially rely on the selection of individual features in isolation.
Small population size precisely three individuals in the effective population), one will become extinct within one generation just because they are all the same sex. If the population remains at this size for several generations, such an event becomes almost inevitable. The environment can directly affect the survival of a small population. Some detrimental effects include stochastic variation in the environment, (year to year variation in rainfall, temperature) which can produce temporally correlated birth and death rates (i.e. 'good' years when birth rates are high and death rates are low and 'bad' years when birth rates are low and death rates are high)