Organic Evolution

Organic evolution is the slow and continuous process of change in the genetic makeup of a species over many generations. It leads to the development of new traits and sometimes new species.

When these changes become permanent, they are passed on through the genetic structure. While evolution is a broad term that encompasses a wide variety of systems, organic evolution deals with living organisms.

Theories of Organic Evolution

Organic evolution, also referred to as biological evolution, means changes in organisms across many generations. These changes happen in structure, behaviour, and genes over time. Scientists proposed many theories to explain this process clearly.

Darwin’s Theory of Evolution

Charles Darwin called evolution “Descent with modification.” He believed all organisms evolved from simpler ancestral forms. In 1859, Darwin explained natural selection in his famous book.

Natural selection causes only well-adapted species to survive and reproduce. Over time, these advantageous traits become more common and help species fit better in their environment.

Natural Selection Example: Darwin suggested terrestrial mammals gradually adapted to aquatic life, eventually leading to whales. The view is currently supported by fossil evidence as well.

Types of Natural Selection

Microevolution: Changes small traits like size or colour in species.
Macroevolution: Large-scale changes creating entirely new species over time.
Sexual selection: A type of natural selection where traits that improve mating success become more common.

Modern View

The modern view of Darwin’s theory is well known as Neo-Darwinism or Modern Synthetic Theory of Evolution. It integrates genetics with Darwin’s principles. It recognizes additional mechanisms, besides natural selection, including mutation, genetic drift, and gene flow.

Lamarckian Theory of Evolution

Lamarck introduced the first theory of evolution in 1801. He explained how living organisms adapt and change with time. His theory is also referred to as the Theory of Inheritance of Acquired Characters.

Key Points of Lamarck’s Theory

Internal vital force: Drives continuous growth in organisms.
Environmental effect: New needs arise due to environmental changes.
Use and disuse: Organs that are frequently used become stronger, while unused organs weaken.
Inheritance of traits: Traits acquired during an organism’s lifetime are passed on to its offspring.

Examples

Giraffes evolved long necks to reach high leaves.
Aquatic birds developed webbed feet for swimming.
Snakes lost limbs due to disuse over time.

Modern View

Lamarckian theory is considered to be incorrect as acquired traits aren’t passed to offspring. Neo-Lamarckism was a modification of this theory, which focused on the environment’s impact on organisms. It also suggested that adaptations influence germ cells, leading to the inheritance of acquired characters.

Mechanism of Organic Evolution

Genetic variation is the basis for all evolutionary changes. Evolution occurs when these variations are passed on to new generations. The different mechanisms that contribute to organic evolution are:

Alt-text: Different mechanisms of evolution

Mutation

A mutation is a random change in the DNA of a species. It creates new alleles and adds to the gene pool. Some mutations are useful and help organisms survive better, while some can also be neutral or harmful.

Natural Selection

Natural selection changes organisms to fit better in their environment. These organisms reproduce more and pass on good traits. Less-fit traits disappear over time from the population.

Gene Flow

Gene flow happens when individuals move to new places. They mix genes with the local population through reproduction.

Example: Pollen is spread by wind or animals moving location.

Genetic Drift

Genetic drift affects small and isolated populations. Random changes in genes lead to new evolutionary paths. There are two types of genetic drift, the bottleneck effect and the founder effect.

Example: Fish introduced in a new lake evolve differently.

Development of Species (Speciation)

A species is a group that can produce fertile offspring. New species form when populations become reproductively isolated. This isolation can be due to geography or mating habits.

Paleontological Evidence of Organic Evolution

Paleontology is the scientific study of fossils from ancient organisms. Fossils provide evidence of modern species' evolution from their ancient ancestors.

Types of Fossils

Altered fossils – changed due to minerals (e.g., Archaeopteryx).
Unaltered fossils – preserved without change (e.g., Wooly mammoths).
Coprolites – fossilised animal waste gives diet information.
Moulds – impressions of bodies, leaves, or footprints in rocks.

Evidence Supporting Organic Evolution

Many forms of evidence support the theory of organic evolution.

These include:

Fossils
Vestigial organs
Homologous organs
Analogous organs
Atavism
Embryology
Connecting links

Summary

Organic evolution is the slow change in living things over many generations. It happens through mutations, natural selection, gene flow, and genetic drift. Darwin and Lamarck explained how species adapt and change.

Fossils, body structures, and genetics give proof of evolution. Over time, these changes create new species suited to their environment and way of life.

FAQs

Q1. What are the bottleneck effect and the founder effect?

The bottleneck effect is the sharp reduction in population size due to events like natural disasters that lead to random loss of genetic variation. The founder effect is seen when a small group of a population separates from a large population to establish a new population. These organisms carry only a subset of the original gene pool.

Q2. What is the difference between homologous and analogous organs?

The homologous organs have similar structures but different functions, while analogous organs have similar functions but different structures.

Q3. How does sexual selection affect evolution?

Sexual selection helps animals pass on traits that attract mates, like strong muscles or bright colours. These traits become more common over time.