Starting with the single sensory beings, to the five sensory beings, all living beings have the four basic instincts of hunger, fear, reproduction and sleep. These instincts are an inseparable part of the living being from the time it comes to the womb to the time of its death. Based on these instincts, all its activities occur. Until ultimate liberation, they (the four basic instincts) are always present. It is only after the realization of 'The Self', that one can remain Asang (Separate), which means that these instincts can no longer affect Him (the awakened One).

Every living being wanders within the four realms of existence, they are the Celestial realm (Devgati), the Infernal realm (Nark gati), the Animal and Plant realm (Tiryanch gati) and the Human realm (Manushya gati) and these four basic instincts exist in all these realms, though in different magnitudes.

Instincts form the nature of a living being. They are in the form of tubers of the mind. They develop, as soon as the right circumstances gather.

Aahaar (Hunger)

Every being has the thought of eating and cannot do without it. Eating is essential, and a compulsory part of a living being's life. A living being is verily the diet of another living being. Nothing that lacks life can be eaten. “Jeevo Jeevasya Bhojanam.” A jeev (living being) is the bhojan (diet) of another jeev. 

What makes a Cow come running towards a container full of food? It is the instinct of hunger.

 It is through this instinct that a living being feels the sensation of hunger. In the Animal and Plant realm, this instinct is most powerful, whereas in the celestial realm, it is the least active instinct.

Maithun (Sexual Intercourse for reproduction)

This instinct causes the thought of sexuality. 

During the monsoons, this instinct becomes highly active in the animal and plant realm which causes them to participate in reproduction. During the rest of the year, animals do not think of sexual activity. 

In the human realm, one is continuously absorbed in sexuality due to the intellect (buddhi). The beings of Kalyug (the last part of the time cycle, characterized by ignorance and suffering) have a huge tuber of pride and a very powerful instinct of sexuality.

 The instinct of sexuality is most active in the human realm.

Nindra (Sleep)

Sleep is necessary for the body. Getting tired and restlessness are scientific circumstantial evidences which cause sleep. Upon eating more than what is required by the body, laziness of the mind (pramad) increases, which causes one to sleep. So, every living being must sleep but the duration of sleep is different for each being.

In the celestial world, this instinct of sleep is very powerful. It is said that the sleeping period of one Dev (celestial being) equals innumerable human life spans!

Bhay (Fear)

When a puppy, sitting in the middle of the road, hears the honk of the horn of a car, it immediately gets up and starts walking away. What makes it do that? It is the instinct of fear, which causes the fear of death. Had the instinct of fear not been present, then it would not budge at all and a major traffic problem would occur! Upon hearing sudden and weird noises, the whole body gets startled. These reflexes are due to this instinct of fear. The fear of death is due to the instinct of fear. If animals do not have this fear, they will not move off the road, and this will cause a major traffic jam ! When you honk, the knowledge (gnan) of fear immediately arises in these animals. It is due to the fear of death that they remain steadfast or cautious or straightforward. (Ane etle toh darek jeev pansaro chale chhe!) 

This instinct of fear is most active in the infernal realm (hell). One constantly has the fear of death in hell. All the circumstances to activate this instinct are present there. For example, intense darkness, extreme abhorrence etc..