Question

What makes the animal kingdom so much different to the other taxonomic groups? How have vertebrates changed through the millions of evolutionary history? Provide examples What are the major events in human evolution and what is meant with the phrase “closest living relatives are chimpanzees”?

Answer 1

Answer: The Animal kingdom is a diverse group of organisms that share many common characteristics such as development process and reproduction. They vary in complexity and are classified on the basis of morphology, anatomy, genetic constitution and evolutionary history. Though the members of animal kingdom are highly diverse, animals can be distinguished from other kingdoms by a set of characteristics. The set of characteristics that distinguish animals from other kingdoms are as follows:

(i) Animals are multicellular, i.e they are made up of more than one cell. Some members of other kingdoms are just made made up of one cell like bacteria , amoeba, etc.

(ii) Animals are heterotrophic, obtaining their energy by consuming living or dead organisms since they cannot synthesize their own food and can be carnivores, herbivores, omnivores or parasites. Plants are autotrophic as they make their own food via photosynthesis.

(iii) Animals are eukaryotes and most of them have complex tissue structure with differentiated and specialized tissue. Eukaryotic cells are more complex than the simpler praokaryotic cells found in bacteria.

(iv) Animal cells dont have a cell walls, their cells are embedded in the extracellular matrix and have unique structures for intracellular communication. Other kingdoms such as plants, fungi and bacteria have cell wall which forms the rigid outer layer that give structure to a cell.

(v) Animals have nerve and muscle tissue, which function to copordinate the body and in movement respectively; these are not present in other kingdoms like plant, fungi etc.

(v) Animals are capable of motion at some stages of their lives.

Answer: The earlest vertebrates were jawless fishes (Agnatha) that probably evolved around 350 mya. There were some jaw bearing fishes which had strong and stout fins with the help of which they could move on land and go back to water. These were a type of bony fishes and they also evolved around 350 mya. These were called lobefins. These lobefins are thought to be evolved into the first amphibians. the amphibians are the organisms that can live both on land and water. The earleat amphibians have now become extinct and evolved into the modern day amphibians, i.e modern day frogs and salamanders. The amphibians evolved into reptiles. They lay thick shelled eggs which do not dry up in the sun unlike of amphibians. Modern day descendents of reptiles are turtles,tortoises and crocodiles which are living. Reptiles were the first true land inhabiting animals, but probably 200 mya, some of the land reptiles went back into the water and evolved into fish like reptiles. Example of fish-like reptile is Ichthyosaur. At that time, dominating land reptiles are dinosaurs and about 65 mya, dinosaurs suddenly disappeared from the earth. The mammals evolved from reptiles and first mammals were small-sized, like shrews. The effect of contnental drifts separated the mammals which is best observed in Australia. As Australia got separated from the other continents, its pouched mammals (marsupials) prevented from facing any threat or competition from the mammals of other continents and hence, they survived and diversified on the Australian land better. Some mammals live wholli in water like whales, dolphins, seals and sea cows. Evolution of horse, elephant, dog, etc are special case. The most successful story is the evolution of man with language skills and self-consciousness.

Answer: Human evolution is generally studied with the evolution of apes as they are closely related to man than any other animal. Man belongs to order primate of class mammalia. Human evolution was started approximately arond 15 mya when Dryopithecus and Ramapithecus existed and they have evolved before man. The major events that had taken place in human evolution are as follows:

(a) Bipedalism- The first hallmark feature of hominin ancestors is the ability to walk upright on two legs which took place around 6 mya.

(b) Nonhoning chewing- Around 5.5 mya, nonhoning chewing complex evolved which lacks large projecting canines in upper jaw.

(c) Speech- It took place around 2.5 mya which reflects the unique shape of hyoid bone that enables them to speak.

(d) Hunting- Hunting was a major event in the evolution of human that took place 1 mya. They used to hunt with stone weapons.

(e) Material culture and tools- The production and use of tools around 3.3 mya is one example of complex material culture.

(f) Domesticated food- Around 11000 years ago, humans domesticated a wide variety of plants and animals that become a part of their life cycle which is used for food and other products.

Chimpanzees are considered as the closest living relatives of human. This is because of the following reasons:

(i) Homology in the chromosomes of man and chimpanzees. The banding pattern of human chromosome number 3 and 6 are compared with those of particular autosomes in the chimpanzee. It shows a common origin for man and chimpanzee.

(ii) Besides the autosomal chromosomes, Y-chromosomes and mitochondrial DNA are homologous as they are uniparental in origin and do not take part in recombination.

(iii) Evidence from blood proteins also revealed that man is most closely related to chimpanzee.

(iv) Evidence from blood groups and haemoglobin also revealed the homology of man and chimpanzee.

(v) The similaritie in the jaw structure and facial bones arrangement proves that humans are closely related to chimpanzee.