Popular Belief• Prior to the studies of Charles Darwin, the most

widespread belief was that all known species were created at the same time and remained unchanged throughout history.

• Some scientists at the time believed that features an individual acquired during a lifetime could be passed onto its offspring, and the species could gradually change to fit an environment better.

2.1

A scientific theory is NOT just a belief, it is a well-supported tested explanation.

Evolution

Evolution

Descent 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.

Fossils• A fossil is the preserved

remains or imprints of ancient organisms.

• Someone who studies fossils is called a paleontologist.

• Fossils are found in sedimentary rock formed when sand and silt settle to the bottom of water.

Types of radioactive dating

• Potassium-Argon dating is used for rocks that are suspected billions of years old.

• In older rocks the ratio of Argon to 40K will be higher than in younger rocks.

• Carbon dating: 2 types• 14C:12C

– Radioactive 14C– Non-radioactive 12C,

most common

feathers

claws

thinribs

teeth

long tail

wing-likeforelimbs

Reptile-like features

Bird-like features

Replica of Archaeopteryx fossil; half bird half reptile

Evidences for Evolution Fossil Record

Vertebrate Limbs

The basic pattern of the vertebrate limb is represented by the human arm skeleton shown below

ball and socket joint

hinge joint

single bone two bones

group of small bones

five jointed digits

Evidence from comparative Anatomy

The forelimbs of the following vertebrates show the basic pattern of limb bones with modifications which are adapted to their methods of locomotion.

Lizard Bird

Dolphin Bat

The basic pattern suggests they have evolved from a common ancestor

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DNA evidence

Another important line of evidence for evolution comes from DNA analysis

Organisms which have much of their DNA in common must be closely related, i.e. they have split from a common ancestor comparatively recently (in geological terms)

For example, humans and chimpanzees have 99% of their DNA in common which suggests a close relationship and relatively ‘recent’ divergence from a common ancestor

Evolutionary Theory

Evolution is the process in which significant changes in the inheritable traits (genetic makeup) of a species occur over time.

The validity and value of evolutionary biology are based on continual analysis and interpretation of accumulating science data.

In words of Charles Darwin evolution is Descent with modification

Theories of Organic Evolution

Historically three theories1. 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

Disproving Lamarck

• Characteristics acquired during the lifetime of a parent are not passed onto the offspring

• An athlete who develops a large muscle mass through training does not have children who already possess this large muscle mass

• Ernst HaeckelIn an attempt to disprove Lamarckism he is said to have cut off the tails of mice for several generations

• The babies born from this line of tailless mice still grew tails as long as their ancestors

• This was not exactly a fair test as the mice had not stopped using their tails in an attempt to adapt to their environment

• They still found their tails useful

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- The conditions supporting life are limited.

For eg Food, water and other resources are limiting.- Only a fraction of the offspring in a population will live to produce offspring, so that the number of individuals in a population remains fairly constant.

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

4. Adaptation- Some variations enable individuals to produce more offspring than other individuals.

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

• Speciation- Given time, natural selection leads to the accumulation of changes that differentiate groups from one another, such that a new species may arise.

The Theory of Natural Selection

The Theory of Evolution states that the present species have descended, with modifications, from species that existed in the past.

Species are not fixed, unchanging things, but are constantly evolving.

Evolution is therefore the constant change that has occurred in our world since its beginning to the present time

THE ORIGIN OF SPECIES

Variation in a population. Individuals in thispopulation of Asian ladybird beetles vary in color and spot pattern.Natural selection may act on these variations only if (1) they areheritable and (2) they affect the beetles’ ability to survive andreproduce.

Overproduction of offspring. A single puffball fungus can produce billions of offspring.If all of these offspring and their descendants survived to maturity,they would carpet the surrounding land surface.

The Theory of Natural Selection

Darwin’s Finches

Industrial MelanismThe Peppered Moth (Biston betularia)

Before Industrial revolution After Industrial revolution

Evolution of drug-resistant pathogens

Evolution of insecticide resistance pests

Giraffe Necks

Hugo De Vries: Theory of Mutation (1901)

• Dutch Botanist studied who studied the plant, Evening Primrose.

• Upon observing wild evening primrose, Hugo found that they were different from the cultivated primrose

• He took some of the wild primrose seeds back to his garden where he made many new variations.

• He bred the plants and followed traits through several generations, like mendel.

The evening primrose Plant

Hugo De Vries: Theory of Mutation (1901)

• Evolution has taken place through the accumulation of fortuitous variations or Mutations

• Due to the appearance of a series of changes in the germ-plasm or genes

• These may be pronounced or minor

Neo Lamarckism

This is reinvention of the Lamarck’s theory of Inheritance of acquired characters. Where constant use tend to strengthen the organ whereas failure of the use leads to atrophy

Lamarck rejected the notion that the environment would directly affect organismal traits and neo lamarckism incorporates these things.

Neo-Darwinism is incorporated in the modern synthesis theory. Darwinian evolution through Natural selection with Mendelian genetics, the latter being a set of primary tenets specifying that evolution involves the transmission of characteristics from parent to child through the mechanism of genetic transfer, rather than the 'blending process'

Neo-Darwinism

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