Instinctual actions - in contrast to actions based on learning which is served by memory and which provides individually stored successful reactions built upon experience - have no learning curve, they are hard-wired and ready to use without learning, but do depend on maturational processes to appear.
Biological predispositions are innate biologically vectored behaviors that can be easily learned. For example in one hour a baby colt can learn to stand, walk, and run with the herd of horses. Learning is required to fine tune the neurological wiring reflex like behavior. True reflexes can be distinguished from instincts by their seat in the nervous system; reflexes are controlled by spinal or other peripheral ganglion, but instincts are the province of the brain.
In a situation when two instincts contradict each other, an animal may resort to a displacement activity.
A good example of an immediate instinct for certain types of bird is imprinting. This is the behaviour that causes geese to follow around the first moving object that they encounter, as it tends to be their mother. Much work was done on this concept by the psychologist Konrad Lorenz.
The Baldwin effect functions in two steps. First, phenotypic plasticity allows an individual to adjust to a partially successful mutation, which might otherwise be utterly useless to the individual. If this mutation adds to inclusive fitness, it will succeed and proliferate in the population. Phenotypic plasticity is typically very costly for an individual; learning requires time and energy, and on occasion involves dangerous mistakes. Therefore there is a second step: provided enough time, evolution may find an inexorable mechanism to replace the plastic mechanism. Thus a behavior that was once learned (the first step) may in time become instinctive (the second step). At first glance, this looks identical to Lamarckian evolution, but there is no direct alteration of the genotype, based on the experience of the phenotype.
The term "instincts" has had a long and varied use in psychology. In the 1870s, Wilhelm Wundt established the first psychology laboratory. At that time, psychology was primarily a branch of philosophy, but behavior became increasingly examined within the framework of the scientific method. This method has come to dominate all branches of science. While use of the scientific method led to increasingly rigorous definition of terms, by the close of the 19th century most repeated behavior was considered instinctual. In a survey of the literature at that time, one researcher chronicled 4000 human instincts, meaning someone applied the label to any behavior that was repetitive. As research became more rigorous and terms better defined, instinct as an explanation for human behavior became less common. In a conference in 1960, chaired by Frank Beach, a pioneer in comparative psychology and attended by luminaries in the field, the term was restricted in its application. During the 60's and 70's, textbooks still contained some discussion of instincts in reference to human behavior. By the year 2000, a survey of the 12 best selling textbooks in Introductory Psychology revealed only one reference to instincts, and that was in regard to Freud's referral to the "id" instincts.
Any repeated behavior can be called "instinctual." As can any behavior for which there is a strong innate component. However, to distinguish behavior beyond the control of the organism from behavior that has a repetitive component we can turn to the book "Instinct"(1961) stemming from the 1960 conference. A number of criteria were established which distinguishes instinctual from other kinds of behavior. To be considered instinctual a behavior must a) be automatic, b) be irresistible, c) occur at some point in development, d) be triggered by some event in the environment, e) occur in every member of the species, f) be unmodifiable, and g) govern behavior for which the organism needs no training (although the organism may profit from experience and to that degree the behavior is modifiable). The absence of one or more of these criteria indicates that the behavior is not fully instinctual. Instincts do exist in insects and animals as can be seen in behaviors that can not be changed by learning. Psychologists do recognize that humans do have biological predispositions or behaviors that are easy to learn due to biological wiring, for example walking and talking.
If these criteria are used in a rigorous scientific manner, application of the term "instinct" cannot be used in reference to human behavior. When terms, such as mothering, territoriality, eating, mating, and so on, are used to denote human behavior they are seen to not meet the criteria listed above. In comparison to animal behavior such as hibernation, migration, nest building, mating and so on that are clearly instinctual, no human behavior meets the necessary criteria. And even in regard to animals, in many cases if the correct learning is stopped from occurring these instinctual behaviors disappear, suggesting that they are potent, but limited, biological predispostions. In the final analysis, under this definition, there are no human instincts.
Instincts in humans can also be seen in what are called instinctive reflexes. Reflexes, such as the Babinski Reflex (fanning of the toes when foot is stroked), are seen in babies and are indicative of stages of development. These reflexes can truly be considered instinctive because they are generally free of environmental influences or conditioning.
Additional human traits that have been looked at as instincts are: sleeping, altruism, disgust, face perception, language acquisitions, "fight or flight" and "subjugate or be subjugated". Some experiments in human and primate societies have also come to the conclusion that a sense of fairness could be considered instinctual, with humans and apes willing to harm their own interests in protesting unfair treatment of self or others.
Other sociologists argue that humans have no instincts, defining them as a "complex pattern of behavior present in every specimen of a particular species, that is innate, and that cannot be overridden." Said sociologists argue that drives such as sex and hunger cannot be considered instincts, as they can be overridden. This definitory argument is present in many introductory sociology and biology textbooks, but is still hotly debated.