Online guidance for the students of Zoology

All Academic content is by Dr. Girish Chandra, PhD (unless otherwise stated), ex Professor, Delhi University


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  • Burst of evolution takes place when animals are put into new environment.
  • Nothing in biology makes sense except in the light of evolutionT. Dobzhansky
  • Contrary to Darwinism, reproduction and not survival is at the centre of evolutionary process.
  • Batrachotoxin, the poison from the skin of South American tree frogs, Phyllobates and Dendrobates, is the most toxic animal secretion known to mankind. Only 200 microgram of it is enough to kill a man.
  • Natural selection requires genetic variations but natural selection also reduces genetic variations by eliminating alleles. Thus evolution by natural selection bites the hand that feeds it.
  • In humans there are at least 4500 genes that cause diseases.
  • The combined length of blood capillaries in human body is about 96,500 kms. If blood has to fill all these capillaries, no blood will be left in arteries and veins. Therefore, body selectively supplies blood to organs that need it most.
  • Natural selection refines and specializes a species to live in its environment but the same specializaion brings its doom when the environment changes. Thus the species also follow the cycle of birth, growth and death.
  • Although chimpanzee genome differs from human genome by hardly 1.5%, yet there have been 40 million evolutionary events that separated chimps from us. Read on the Riddle of Human Origin
  • Biological evolution tracks opportunities but is blind to destinations other than survival – Strickburger. Read on different Ways of Evolution
  • Natural selection causes a change in gene frequency but is not the same as a change in gene frequency. Read details in Hardy-Weinberg’s Law

Latest Articles

KEA – The predatory parrot

The kea (Nestor notabilis) is a parrot-like bird of family Strigopidae, which is about the size of a hen and occurs in the alpine regions of New Zealand. Their extraordinary intelligence is comparable to the primates and hence they are sometimes nicknamed 'mountain monkeys'. Being highly inquisitive, keas are notorious for exploring and manipulating objects often in residential areas where they damage articles such as shoes, car seats sofas, bags etc. with their sharp and curved beak. They are highly intelligent birds with quick learning abilities. Researchers at the Universities of Vienna and Oxford tested the Kea’s problem-solving abilities b...

Methods Of Studying Animal Behaviour

Ethology is the study of animal behaviour to find out natural responses of animals to various environmental stimuli. Some studies are also done in laboratory conditions to elicit measured responses. Therefore, ethology involves laboratory as well as field studies and has strong relationship with other sciences such as ecology, environmental science, neurology, physiology, psychology and evolution. The beginning of modern ethology commenced with the experimental as well as field studies done by the Dutch biologist Nikolas Tinbergen, Austrian biologists Konrad Lorenz and the German Karl von Frisch, who were jointly awarded Nobel Prize in 1973 for t...

Biological Rhythms – Chronobiology

Biological rhythms are self –sustaining natural cycles of animal life history which maintain themselves regardless of the environmental factors. All animals possess innate biological clocks which are driven by the biochemical mechanisms. Erwin Bunning (1936) was the first biologist to carry out extensive work on biological rhythms. CIRCANNUAL RHYTHMS They show one-year periodicity, e.g. a large number of animals reproduce once in a year. Flowering in plants also takes place once a year. Insects and amphibians follow a cycle of hibernation and activity. Hummingbirds in South America move to the caves and become inactive in winter in Andes. Famo...

Kinship, Selfishness And Altruism

There are four possible types of interactions among individuals living together in a population. First, cooperation or mutualism, in which both the participants gain from the act as in the nest building by both male and female birds, or cooperation in the colony of social insects. Second, altruism in which the actor (individual that carries out the action) pays fitness cost to the recipient that gets the benefit as in social insects. Third is the selfishness, in which the actor gains but the recipient loses in terms of fitness. Fourth interaction, which is rather rare in nature, is spite in which both the participants lose in terms of fitness. A...

Orientation, Navigation and Homing in Animals

Orientation is the position of the animal with reference to gravity or resource. This is the position the animal maintains in order to reach the resource. Positional orientation is to maintain upright posture against gravity for which vertebrate have membranous labyrinth and invertebrate statocyst. Object orientation takes place when the animal tries to approach an object which may be food or water. Aquatic animals move vertically in pond or lake which is called strato-orientation. When the animals try to move from grassland to forests, deserts or mountains it is called zonal orientation. Animals which migrate long distances generally possess top...

Courtship Behaviour in Animals

Courtship is a social behaviour in which there is an interaction between the male and female members of a species leading to mating and reproduction. Courtship evolved due to the fact that very large number of sperms is produced which must search and fertilise few ova leading to competition among sperms. Since males possess sperms, they must compete with one another in order to win over the female to fertilise her ova which are a limited resource. The gametic selection has translated into sexual selection among males and females, leading to male-male competition and female choice. Courtship display is an extension of this male-male competition in...

Social Life In Primates

Primates were not social animals when they evolved from the primitive insectivore ancestor in Palaeocene epoch. However, gradually primates became gregarious and social interactions developed in them leading to highly developed social life as in humans. SOLITARY PROSIMIANS Prosimians such as tarsiers, bush babies and lorises are mostly nocturnal and highly arboreal primates. Males are found solitary or in pairs with females in breeding. Females live with infants till they become independent. Prosimians are shy animals and hiding in foliage is their means of defence. They rarely come down from trees. The black coloured Aye-aye is nocturnal and li...

Social Organisation In Insects

In insects social life has evolved only in two orders, namely, Isoptera (termites) and Hymenoptera (bees, wasps and ants) which make a nest and live in colonies of thousands of individuals that practice division of labour and social interaction. SOCIAL LIFE IN TERMITES Termites were the first animals which started living in colonies and developed a well organised social system about 300 million years ago, much earlier than honey bees, ants and human beings. Although termites do not exceed 3-4 mm in size, their queen is a 4 inch long giant that lies in the royal chamber motionless, since its legs are too small to move its enormous body. Hence wor...

Crypsis (Deception In Predator-Prey Interaction)

In nature predator and prey have evolved together for millions of years. Prey must deceive the predator in order to escape getting killed, while the predator must also use deception to catch the prey unawares. Crypsis is also a form of mimicry but the former has a wider meaning that includes mimicking even non-living objects such as stones, rocks, twigs and even the background. Protective colouration: Majority of the animals match the background in colour to escape the attention of the predator. For example, hares and rabbits are earth-coloured, grasshoppers are green and beach crabs have the same colour as pebbles. Counter-shading: This is als...

Alarm Pheromones

Behaviour modifying chemicals are called semiochemicals and pheromones fall in the same category. Pheromones are chemicals which are used for communication among the members of the same species. They form the chemical language of a species. For instance, attractants are pheromones which bind the members of a colony of social insects. Kairomones are chemicals used to communicate with members of other species. For example, parasites use the host smell for searching and preys use predators’ smell to escape away. All social insects release alarm pheromones when their colony is attacked. This triggers defensive behaviour in the other members of the...

Drive, Urge Or Motivation in Animals

The term Drive was introduced by Woodworth (1918) as motivational concept. Animals experienced drive as biological needs such as eating and drinking and alteration in their behaviour. Drive theories were later given by Sigmund Freud (1915) and Clark Hull (1943). Freud, who was physiologist by training, believed that drives and urges such as hunger were recurring conditions in the body of animal that produced energy build up in the nervous system. This energy build up caused psychological discomfort and restlessness that kept on increasing unless the urge was satisfied. Drive arose from a range of bodily disturbances, such as deprivation of food, ...

Learning

Learning is the ability of the individual to remember and change one’s behaviour in response to earlier experiences. Animals learn a great deal from their surroundings and also from their experiences, particularly during the growing period. Latent learning provides animals with knowledge about their surroundings and escape routes, and also areas where food and water is available. Niko Timbergen (1951) demonstrated by experiments on digger wasp (Philanthus) that it could remember its nesting site by landmarks and got confused when landmarks were changes. W.H. Thorpe (1951) defines learning as an internal change in the animal causing adaptive cha...

Sign Stimuli

Sign stimuli, also called releasers or key stimuli, are those stimuli that are capable of releasing Fixed Action Pattern (FAP) or consummatory behaviour of the animal. They are signals that evoke instinctive patterns of behaviour in animals, such as fighting behaviour in the territorial animals, triggered by the entry of another male. Lehrman found that courting male dove began to bow and coo to a stuffed model of female in the absence of a living female. Konrad Lorenz (1972) was the first biologist to identify sign stimuli which he called key stimuli because they function as keys to release and unlock the fixed action pattern of the animal. He p...

Sensory filtering

Animals receive much more sensory information than they could possibly register in their brain and respond to. Therefore brain has to be selective and filter out certain information that is not so necessary. Sensory filtering or stimulus filtering takes place at several levels, namely, at the level of sense organs, nerves or different parts of brain. Sensation is the basic data sent by sense organ to brain, and sense organs have their limitation and hence filter out much of the information. For example, human eye filters out ultraviolet and infrared rays from the spectrum. Peripheral filtering is done by receptors because of their mechanical abi...

Naked Mole Rat

The naked mole rat (Heterocephalus glaber) is a burrowing social rodent found in the grasslands of East Africa, mainly in Ethiopia, Kenya and Somalia. The unusual anatomy and social life of this bizarre animal was first studied by the German naturalist, Eduard Rüppell in 19th century, although he thought them to be mutated and deformed individuals. Anatomy. Normally the individuals are 3 to 4 inches long but the dominant queen is larger and has longer body. Fertile males are also larger than the workers and possess abdominal testes. All individuals possess almost hairless and wrinkled pinkish to yellowish skin, hence the name, naked mole rat. ...

Vampire Bats

Bats are the only flying mammals in the world that roost upside down.   Their wings are made of excessively long fingers between which membranous skin called patagium is stretched.   Vampire bats are blood sucking or sanguivorous flying mammals that live solely on blood of vertebrates. Three species of vampire bats occur in central and South America: the common vampire bat (Desmodus rotundus), the hairy-legged vampire bat (Diphylla ecaudata) and the white-winged vampire bat (Diaemus youngi). Unlike other bats, vampire bats can walk, jump and even run by using both forelimbs and hind limbs.   A recent study found that common vampire bats...