Define Evolution
First theory of evolution was proposed by Jean Baptiste de Lamarck(1744-1829) in the book Philosophie Zoologique. Term biology was also given by Lamark and treviranus. As per this theory evolution is a slow and gradual process, which explains and makes us understand the living world around us. This process takes time as it depends upon various factors.
Factors Causing Evolution as per Lamarckism Theory
There are various factors which leads to evolution in an organism, some of these are given below:
Internal Vital Forces: Some internal forces are present in all organisms. By the presence of these forces, organisms have a tendency to increase the size of their organs or entire body.
Effect of environment and New Needs: Environment influences all types of organisms. Changing environment gives rise to new needs. New needs or desires produce new structure and change habits of the organism.
Use and Disuse of Organs: If an organ is constantly used, it would be better developed whereas disuse of the organ results in degeneration.
Inheritance of Acquired Character: During life time of an organism new characters develop due to internal vital forces, effect of environment, new needs and use and disuse of organs.
These acquired characters are inherited from one generation to another. By continuous inheritance from one generation to the next generation tends to make the next generation quite different from its ancestor resulting in the formation of new species.
Example in Support of Lamarckism
Long neck and high fore limb of Giraffe.
Aquatic birds stretched their toes and developed a web.
Snake lost its legs.
Deers became good runners by the development of strong limbs and streamlined bodies.
Retractile claws of coronavirus animals.
Charles Darwin Theory of Evolution
According to Charles Darwin, the main concept behind evolution is natural selection. This theory was later explained by Darwin in his book ‘On the origin of species by the means of natural selection’(1859).
Main Features of the Theory of Natural selection are as follows:
Overproduction: All organisms have capability to produce enormous numbers of offsprings, organisms multiply in geometric ratio. Example: Plants produce thousands of seeds, Insects lay hundreds of eggs, etc.
Struggle for Existence: Every individual competes with others of the same and other species for basic necessities like space, shelter and food. It is called the struggle for existence and it continues for the whole life from zygote stage to its natural death.
Variation and Heredity: Except the identical twins no two individuals are similar and their requirements are also not same. It means there are differences among individuals. This difference is called variation.
Survival of Fitness or Natural Selection: Most suitable and fit individuals are successful in the struggle for survival.
Origin of New Species: Darwin explained the variations appearing due to the environmental changes are transmitted to the next generation. So offspring become different from ancestors. In the next generation the process of natural selection repeats so after many generations new species are formed.
Facts Regarding Evolution
Huxley explained the origin of man in his book ‘ The man’s place in nature’.
Humans are a member of order primates of class mammalia.
Primates originated 80-100 million years ago in the Pliocene epoch of the Cenozoic era.
Primates originated from elephant shrews but they were not real primates.
Apes have 48 number of chromosomes whereas 46 number of chromosomes.
DNA content and DNA matching is the same in both apes and humans.
Homo habilis were the first human- like species as their fossils were discovered by Dr. Leakey from two million years old rocks in Africa. Their cranial capacity is about 650-800 c.c.
Homo erectus were direct ancestors of homo sapiens. They are also called java man and their cranial capacity is 800-1000 c.c. They were the first man who used fire for hunting, protecting and cooking. Their origin and evolution, 1.5-2 million year ago.
Homosapiens origin and evolution before 40,000- 1 lakh year ago.
Fossils of homosapiens were discovered by C.fulhrott from the Neanderthal valley of germany.
Old world monkeys are more closer to humans as compared to new world monkeys.
Chimpanzees are the closest ape to humans.
Every living entity has evolved from a bacterium which lived billions of years ago. It is said that biological evolution started around 3.7 billion years ago.
Darwin finches are also an example of adaptive radiation(different shape of beak and claws due to their habitat).
Darwin finches are an example of allopatric speciation.
Study of fossils is known as paleontology.
Geological time scale divides into 6 eras: Azoic, Archaeozoic, proterozoic, Palaeozoic, Mesozoic, Coenozoic.
FAQs on Interesting Facts About Evolution
1. What is biological evolution and what are its key driving forces?
Biological evolution is the process of change in the inherited traits of a population of organisms over successive generations. It is a slow, gradual process that results in the vast diversity of life on Earth. The main driving forces, as proposed by Darwin's theory of natural selection, include:
- Overproduction: Organisms produce more offspring than can possibly survive.
- Variation: Individuals within a population exhibit variations in their physical traits.
- Struggle for Existence: Offspring must compete for limited resources like food, water, and shelter.
- Survival of the Fittest (Natural Selection): Individuals with traits best suited to their environment are more likely to survive, reproduce, and pass those advantageous traits to the next generation.
2. What are the major lines of evidence that support the theory of evolution?
The theory of evolution is supported by a vast body of evidence from different fields of science. The primary lines of evidence include:
- Fossil Record: Fossils show a progression of life forms over geological time, documenting the existence of now-extinct species and transitional forms that link different groups.
- Comparative Anatomy: This includes the study of homologous structures (similar structures in different species due to common ancestry, like the forelimbs of humans, bats, and whales) and vestigial structures (remnants of organs that had a function in an ancestor, like the human appendix).
- Comparative Embryology: Early developmental stages of different vertebrate species show remarkable similarities, suggesting a shared ancestry.
- Biogeography: The geographical distribution of species, such as the unique flora and fauna on islands like the Galápagos, provides clues about how species evolved in isolation.
- Molecular Biology: Similarities in DNA sequences and protein structures across different species provide strong evidence of common descent. For example, humans and chimpanzees share about 98-99% of their DNA.
3. How does Darwin's theory of natural selection fundamentally differ from Lamarck's theory of acquired characteristics?
The main difference lies in the mechanism of change. Lamarck's theory proposed that organisms could acquire traits during their lifetime based on use or disuse (e.g., a giraffe stretching its neck to reach leaves) and then pass these acquired traits directly to their offspring. In contrast, Darwin's theory of natural selection is based on pre-existing genetic variation within a population. Evolution occurs because nature 'selects' individuals with the most advantageous inherited traits for survival and reproduction in a specific environment, not because individuals change themselves and pass on those changes.
4. What are some significant milestones in the evolution of humans?
Human evolution is not a linear path but a complex branching tree. Some key milestones and ancestral species include:
- Homo habilis ('handy man'): Lived around 2.4 to 1.4 million years ago. Known for being one of the first hominins to make and use stone tools. Had a cranial capacity of about 650-800 cc.
- Homo erectus ('upright man'): Lived from about 1.9 million to 143,000 years ago. They were the first to migrate out of Africa and are associated with the control and use of fire. Their cranial capacity was larger, ranging from 800-1100 cc.
- Homo neanderthalensis (Neanderthals): Lived in Europe and Asia from about 400,000 to 40,000 years ago. They were skilled hunters, used sophisticated tools, and likely had some form of culture and language.
- Homo sapiens (modern humans): Originated in Africa around 300,000 years ago. Characterised by a large cranial capacity (average 1350 cc), advanced cognitive abilities, and the development of art, complex language, and agriculture.
5. How is antibiotic resistance in bacteria a modern, real-world example of evolution by natural selection?
Antibiotic resistance is a direct observation of natural selection in action. When an antibiotic is used, it creates strong environmental pressure. Within a large population of bacteria, some may have random genetic mutations that make them resistant to the drug. While the antibiotic kills the susceptible bacteria, the few resistant individuals survive and reproduce. Over time, the population becomes dominated by these resistant bacteria, rendering the antibiotic ineffective. This is not the bacteria 'learning' to resist; it is a clear example of survival of the fittest on a microscopic scale.
6. What are some surprising facts about evolution that highlight its processes?
Beyond the well-known examples, there are many fascinating facts about evolution:
- Evolution is not always slow: While major changes can take millions of years, evolution can occur rapidly, as seen in antibiotic-resistant bacteria or pesticide-resistant insects.
- Humans are still evolving: Traits like lactose tolerance in adults, wisdom teeth absence, and resistance to certain diseases are examples of recent human evolution.
- Vestigial traits exist in many species: Humans have a tailbone (coccyx), some snakes have tiny remnant hind leg bones, and some cave-dwelling fish have non-functional eyes, all pointing to features from their ancestors.
- Shared Genes: Humans share a surprising amount of DNA with other life forms, not just primates. For example, we share about 60% of our genes with a banana!
7. Does evolution always lead to more complex or 'perfect' organisms? Explain with an example.
No, this is a common misconception. Evolution is not a progression towards an ultimate goal of 'perfection' or complexity. It is simply the process of adaptation to a specific environment. An adaptation is only 'better' in the context of a particular time and place. If the environment changes, a previously advantageous trait might become neutral or even disadvantageous. For example, a tapeworm is a highly successful organism but is far simpler in its body plan than its free-living ancestors. It has lost its digestive system because it lives inside a host's gut, where pre-digested food is abundant. In this case, evolution favoured simplification, not increased complexity, as it was more efficient for survival and reproduction in that specific niche.
8. Why are Darwin's finches on the Galápagos Islands a classic textbook example of adaptive radiation?
Darwin's finches are a prime example of adaptive radiation, which is the relatively rapid evolution of many new species from a single common ancestor. The finches demonstrate this because:
- Common Ancestry: A single ancestral finch species from the mainland colonised the Galápagos Islands.
- Geographic Isolation: The islands are isolated from each other, preventing gene flow between populations on different islands.
- Varying Environments: Each island offered different food sources (e.g., hard seeds, insects, cacti). This created different selective pressures.
- Diversification: Over time, natural selection favoured finches with beak shapes and sizes best suited for the specific food source on their particular island. This led to the evolution of over a dozen distinct species, each occupying a different ecological niche, all from one original ancestor.
