The formation of new species due to gradual changes in specific characters over several generations of living organisms in response to natural selection is called evolution.
Definitions [5]
Definition: Evolution
Evolution is a slow and continuous process whereby complex forms of life have emerged from simpler forms through millions of years.
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Definition: Natural Selection
The process where organisms with favorable variations survive and reproduce more successfully than others is called natural selection.
Definition: Survival of the Fittest
The concept where only well-adapted individuals survive in the struggle for existence is called survival of the fittest.
Define the following term:
Vestigial organs
Vestigial organs are those organs that have ceased to be of any use to the possessor but still persist generation after generation in a reduced form. In other words, vestigial organs are the remnants of features that served important functions in the organism's ancestors.
Definition: Vestigial Organs
Vestigial organs are reduced and non-functional organs present in an organism that were functional in its ancestors.
Key Points
Key Points: Evolution
- Evolution is the gradual and progressive development of living organisms over a long period due to natural selection.
- Life originated around 3.5 billion years ago from simple inorganic and organic compounds, eventually forming primitive cells.
- The diversity of life on Earth today, from unicellular organisms to complex plants and animals, is a result of continuous evolutionary processes.
- According to the theory of evolution, all complex organisms evolved slowly from unicellular ancestors over 300 crore (3 billion) years.
- Evolution is considered an organizational and multi-dimensional process, reflecting structural and functional advancement in living organisms.
Key Points: Vestigial Organs
- Vestigial organs are degenerate or underdeveloped structures that have lost their original function in certain organisms.
- These organs persist in a degenerate form due to inheritance from ancestral species, despite having little or no current use.
- Examples in animals include splint bones in horse, rudimentary wings in ostrich, vestigial limbs in python, and functionless eyes in burrowing animals.
- Humans possess many vestigial organs such as the appendix, coccyx (tail bone), wisdom teeth, ear muscles, and nipples in males.
- Vestigial organs provide strong evidence for evolution, showing gradual changes in structure and function over time.
Key Points: Human Ancestors
| Ancestor | Time Period (Approx.) | Key Features |
|---|---|---|
| Dryopithecus & Ramapithecus | ~15–20 million years ago | Ape-like ancestors; known from jaw and tooth fossils, showed upright posture and jaw strength |
| Australopithecus | ~40 lakh years ago | Small in size, walked upright, man-like teeth, no chin; mix of ape and human traits |
| Homo habilis | ~20 lakh years ago | Larger brain, bipedal, first tool-user; known as “skilled human” |
| Homo erectus | ~15 lakh years ago | Fully upright, used fire, hunted, had human-like teeth |
| Neanderthals & Cro-Magnons | ~50,000 years ago | Showed social behavior, tool-making, hunting, and cultural evolution; close to modern humans |
Key Points: Homo Sapiens Sapiens (Modern Man)
- Modern humans (Homo sapiens sapiens) evolved from Cro-Magnons around 50,000 to 11,000 years ago, mainly near the Caspian and Mediterranean regions.
- They have a fully upright posture, binocular vision, a mobile neck, and spinal curves that help with walking and balance.
- Their brain capacity is about 1450–1600 cm³, with a large cerebrum, well-developed forehead and chin, and the ability to speak and think clearly.
- They have proportionate limbs, flat nails, less body hair, and a broad chest, which are all features that support advanced physical and mental tasks.
- Modern humans made metal tools, started agriculture, formed permanent homes, and developed writing, science, and industries, leading to today's civilizations.
