Presented by

MD NURUDDIN SUMIT KUMAR SHARDA UNIVERSITY

EVOLUTION

• Evolution is the change in the inherited characteristics of biological populations over..successive generations.• Evolutionary processes give rise to

diversity at every level of biological organisation,including species, individual organisms and molecules such as DNA and proteins.

EvolutionDescent with Modification

Evolution means change over time

Evolution can also be defined more narrowly as a change in the genetic composition of a population from generation to generation.

Evolution on earth

• Formation of Amino Acids – Miller's Experiment

Process of Evolution

• called chromosomes

– are found in cells of organisms • Specific segments of DNA – are the basic units of heredity

(genes)• The number of chromosomes – varies from one species to

another– fruit flies 8; humans 46; horses 64

Genes and Chromosomes• Complex, double-stranded

helical molecules – of deoxyribonucleic acid (DNA)

Theories of Organic Evolution

Historically three theories

1. Lamarck’s Theory of Evolution, 2. Darwin’s Theory of Evolution, 3. De Vries Mutation Theory of Evolution.

The views of most modern biologists combine the second and third

No evidence of the first theory, that of Lamarck’s Use and disuse theory.

Jean Baptiste Lamarck, 1744-1829

• French geologist and naturalist

• published Philosophie Zoologique in 1809

• Speculated about mechanisms of biological evolution, offered no evidence

In 1809 Jean-Baptiste Lamarke hypothesized that “simple” organisms emerge spontaneously and evolve to greater “complexity”.

Principles to his theory

1. Organisms constantly strive to improve themselves.

2. Most used body structures develop and unused waste away. (Use and Disuse)

3. A structure is modified by use or disuse, the modification is inherited to the offspring. (Inheritance of acquired characteristics).

• Structural variations are due to functional needs – “to use or disuse”

• Use of a structure increases its size.• Failure to use it decreases its size• These variations (now referred to as

“acquired characteristics” are inherited.

• There is no supporting evidence in modern biology to support Lamarck’s idea

• According to Lamarck’s theory of inheritance of acquired characteristics

Lamarck’s Giraffes

– ancestral short-necked giraffes

– stretched their necks

– to reach leaves high on trees.

– Their offspring were born

– with longer necks

Charles Darwin: The Theory of Natural Selection

• His theory was effectively presented to the world in 1859 when his book “The Origin of Species” was published.

• Darwin’s Theory rests on 5 principles:

1. Overproduction- All species have a tendency and the potential to increase at a geometric rate.

All organisms produce more organisms but only a few survive.

5 principles of Darwin’s Theory

2. Competition- Due to environmental pressures, the organisms within a population must compete with each other to survive.

3. Variation- Individuals in a population vary greatly in their characteristics.

4. Adaptation- individuals who best adapt to the environment are the ones who will most likely survive

5. Natural Selection- Individuals having favorable traits will produce more offspring, and those with unfavorable traits will produce fewer offspring.

• Speciation-The process in which new genetically distinct species evolve usually as a result of genetic isolation from the main population.

DE VRIES MUTATION THEORY

• His experiment was on evening primose.• Mutation form raw material for evolution.• It suddenly appears.• Single mutation may produce new species.

Modern Synthesis Theory

Important points of Modern Evolutionary Theory

All evolutionary phenomena can be explained in a way consistent with known genetic mechanisms.

Evolution is gradual: small genetic changes regulated by natural selection accumulate over long periods. Discontinuities amongst species are explained as originating gradually through geographical separation and extinction.

Natural selection is by far the main mechanism of change.

Thinking in terms of populations rather than individuals, is primary: the genetic diversity existing in natural populations is a key factor in evolution

Questions

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