Lesson 3 - Evolution

evolutionary biology​

study of history of life forms on earth

20 billion years old​

age of the universe

Galaxies

contain stars clouds gas and dust​

Universe

contain galaxies​

big bang theory​

Origin of universe

Condensation of gases under gravitation.​

galaxies were then formed due to

BIG BANG THEORY​

According to it, the universe expanded, temperature came down, and hydrogen and helium were formed

Earth was formed 4.5 billion years ago​

The surface was covered with water vapor, ethane, CO2 and NH3.​

UV radiations broke water into hydrogen and oxygen​

Hydrogen escaped and oxygen combined with NH3 and CH4 to form water, CO2 and other gases, also forming the ozone layer.​

Cooling of water Vapor led to rain which filled the depression of earth’s surface, forming water bodies.​

ORIGIN OF EARTH

Theory of special creation
Theory of panspermia/cosmic theory
Theory of spontaneous generation
Theory of Biogenesis
Theory of Chemical Evolution

THEORIES ON ORIGIN OF LIFE​

Theory of special creation

according to this god created this life by his divine act of creation

Theory of panspermia/cosmic theory

Some scientists believe that it came from outside.

spores

Early Greek thinkers thought units of life called _____ were transferred to different planets including earth

Theory of panspermia/cosmic theory

is still a favorite idea for some astronomers

Louis Pasteur

Theory of Biogenesis

Theory of Biogenesis

Spontaneous generation theory was dismissed once and for all when Louis Pasteur by careful experimentation demonstrated that life comes only from pre-existing life

Theory of Biogenesis

He showed that in pre-sterilized flasks, life did not come from killed yeast while in another flask open to air, new living organisms arose from ‘killed yeast’.

Theory of Biogenesis

However, this did not answer how the first life form came on earth. ​

Alexander Oparin of Russia and John Burdon Sanderson Haldane

Theory of Chemical Evolution

Theory of Chemical Evolution

proposed that the first form of life could have come from pre-existing non-living organic molecules (e.g. RNA, protein, etc.) followed by the formation of diverse organic molecules and then the formation of life

S.L. Miller

an American scientist created similar conditions in a laboratory scale (The conditions on earth were – high temperature, volcanic storms, reducing atmosphere containing CH4, NH3, etc. )

EXPERIMENTAL EVIDENCE OF THEORY OF CHEMICAL EVOLUTON

He created electric discharge in a closed flask containing CH4, H2, NH3 and water vapour at 8000C. ​

EXPERIMENTAL EVIDENCE OF THEORY OF CHEMICAL EVOLUTON

He observed formation of amino acids. In similar experiments others observed, formation of sugars, nitrogen bases, pigment and fats.​

Theory of Chemical Evolution

showed first non cellular form of life created 3 billion years ago.​

Theory of Chemical Evolution

Showed that non cellular biomolecules exist in the form of DNA, RNA, polysaccharides and proteins.

Theory of Chemical Evolution

Analysis of meteorite content also revealed similar compounds indicating that similar processes are occurring elsewhere in space. hence, chemical evolution was more or less accepted.

H.M.S. Beagle

sea voyage in a sail ship called

Charles Darwin

Existing living forms share similarities to varying degrees not only among themselves but also with life forms that existed millions of years ago. Many such life forms do not exist any more. ​

Charles Darwin

There had been extinctions of different life forms in the years gone by just as new forms of life arose at different periods of history of earth. ​

Charles Darwin

There has been gradual evolution of life forms. Any population has built in variation in characteristics.

natural selection

Those characteristics which enable make it fit to survive better in a particular natural conditions

fitness

refers ultimately and only to reproductive fitness

Alfred Wallace

a naturalist who worked in Malay Archipelago had also come to similar conclusions around the same time

Paleontological evidences
Comparative anatomy and morphology​
Biochemical evidences
Biogeographical evidences

EVIDENCES OF EVOLUTION​

paleontology

Study of fossils

Fossils

remained of hard parts of life-forms found in rocks

Paleontological evidences

Different-aged rock sediments contain fossils of different life-forms who probably died during the formation of the particular sediment.​

Some of them appear similar to modern organisms. They represent extinct organisms

Paleontological evidences

A study of fossils in different sedimentary layers indicates the geological period in which they existed, showing that life-forms varied over time

Comparative anatomy and morphology​

shows similarities and differences among organisms of today and those that existed years ago

Divergent evolution

When a species branches off into multiple species​

Divergent evolution

Occurs when closely related species develop different traits over time​

Divergent evolution

Caused by differential selection pressure​

Divergent evolution

Leads to speciation​

Divergent evolution

Comparative anatomy and morphology

Convergent evolution

When unrelated species develop similar traits​

Convergent evolution

Occurs when species live in similar environments and adapt in similar ways​

Convergent evolution

Traits that arise from _____ are called analogous structures​

Parallel evolution ​

When unrelated species develop similar characteristics or adaptive mechanisms​

Parallel evolution ​

Occurs when similar environments produce similar adaptations​

Adaptive radiation ​

When organisms diversify rapidly from an ancestral species into many new forms​

Adaptive radiation ​

Occurs when changes in the environment make new resources available​

Biochemical evidences

In the same line of argument, similarities in proteins and genes performing a given function among diverse organisms give clues to common ancestry

Biochemical evidences

These biochemical similarities point to the same shared ancestry as structural similarities among diverse organisms

Biochemical evidences

The metabolic processes in organisms are also similar with same new materials and end products

Biogeographical evidences

Another interesting observation supporting evolution by natural selection comes from England. In a collection of moths made in 1850s, i.e., before industrialization set in, it was observed that there were more white-winged moths on trees than dark-winged or melanised moths. However, in the collection carried out from the same area, but after industrialization, i.e., in 1920, there were more dark-winged moths in the same area, i.e., the proportion was reversed. ​

Biogeographical evidences

This showed that in a mixed population, those that can better-adapt, survive and increase in population size. However, no variant is completely wiped out.

Biogeographical evidences

Similarly, excess use of herbicides, pesticides, etc., has only resulted in selection of resistant varieties in a much lesser time scale. ​

Biogeographical evidences

This is also true for microbes against which we employ antibiotics or drugs against eukaryotic organisms/cell. ​

Hence, resistant organisms/cells are appearing in a time scale of months or years and not centuries. ​

Biogeographical evidences

It is a process based on chance events in nature and chance mutation in the organisms.

ADAPTIVE RADITAION

evolutionary process in which different species starting from a common point in a geographical area radiate to other geographical areas

Darwin's finches

Darwin observed many varieties of finches in the island he visited​

All varieties had evolved from the original seed eating finches​

With alteration in beaks some became insectivorous and some vegetarians.​

Marsupials of Australia

Within Australian continent, many different marsupials or pouched animals are seen.​

These have evolved from common ancestral stock

Placental animals in australia

A variety of placental mammals have evolved which appear similar to a corresponding marsupial

convergent evolution

When more than one adaptive radiation appear to have in an isolated geographical area (representing different habitats) and two or more groups of unrelated animals come to resemble each other for a similar mode of life or habitat

DARWIN’S THEORY OF EVOLUTION​

Varying degree of similarities can be observed between existing life forms and those that existed millions of years ago​

DARWIN’S THEORY OF EVOLUTION​

There has been gradual evolution of life forms with new forms arising at different periods of history​

DARWIN’S THEORY OF EVOLUTION​

Any population has built in variation in its characterstics which adapt it better to the environment​

DARWIN’S THEORY OF EVOLUTION​

The characterstics which enable some populations or individuals to survive better in natural conditions would out breed others​

natural selection

Those population which are better fit in the environment will be selected by nature and will survive more

Adaptability, fitness

__ is inherited and _ is end result of ability to adapt and get selected by nature

Limited natural resources​

Stable population size except seasonal fluctuations​

Varying characteristics of members of population​

Most of the variations are inherited​

Natural selection is based on following factual observation:​

Branching descent and natural selection

two key concepts of Darwinian Theory of Evolution

industrial mechanism, Chemical resistance

Examples of natural selection​

industrial mechanism

as that of white and dark winged moths

Chemical resistance​

excess use of herbicides, pesticides, etc., has only resulted in selection of resistant varieties in a much lesser time scale. Also, microbes against which we employ antibiotics or drugs against eukaryotic organisms/cell.

Gene migration or gene flow​

Genetic drift​

Mutation​

Genetic recombination​

Natural selection​

​

five factors that affect Hardy-Weinberg equilibrium are:

gene flow

There would be a ___if this gene migration, happens multiple times. ​

genetic drift

If the same change occurs by chance

founder effect

Sometimes the change in allele frequency is so different in the new sample of population that they become a different species. The original drifted population becomes founders and the effect is called

Mutations

advantageous ____ leads to new phenotype and over few generations result in speciation

Genetic recombination

during gametogenesis, variations due to recombination result in new phenotypes

Natural selection

heritable variations that enable survival of fittest will leave greater number of progeny

Stabilization, Directional change, Disruption

Natural selection can have following three effects

Stabilization

large number of individuals acquire mean character value​

Directional change

large number of individuals acquire value other than mean character value​

Disruption

large number of individuals acquire peripheral character values at both ends of the distribution curve and hence 2 peaks are formed

invertebrates → jawless fish, amphibian fish with stout, strong fins → lobefins → reptiles land → tyrannosaurus rex → shrews

EVOLUTION OF ANIMALS

Lobefins

first amphibians and ancestors of modern day frogs​

tyrannosaurus rex

biggest land reptiles

shrews

first mammals that evolved in jurassic period

Dryopithecus and Ramapithecus (apes) → Homo habilis → homo erectus (Java) → Homo sapiens (Africa) → modern homo sapiens

ORIGIN AND EVOLUTION OF MAN

Homo habilis

First creatures that was human like being the hominid