Describe the forms of variability identified by C. Darwin.

C. Darwin identified three forms of variability: definite (group), indefinite (individual) and correlative (correlative). Certain (group) variability is the appearance of the same characters in all individuals and their offspring under the influence of a changed environmental factor. Certain variability is massive. For example, if there is a lack of food, animals lose weight, in colder climates the hair of mammals becomes thicker, leaves of plants under different lighting conditions vary in shape, etc. Certain variability increases the body’s adaptability to specific environmental conditions, but is not transmitted by inheritance. Uncertain (individual) variability – the appearance in an individual individual within the same variety, breed, type of new trait that did not occur in parents. So, within the same breed of rabbits, different coat colors can be observed. This form of variability is the result of the specific influence of the conditions of existence on each individual organism. Relative (correlative) variability – a change in a single organ or part of the body following a change in other parts of the body. For example, with constant exercise of the lower extremities, domestic duck breeds on the femur develop a crest for muscle attachment.