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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
19
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