Origin Of Life

Origin of Life 

Understanding LIFE
Life is a condition that distinguishes animals and plants from inorganic matter. It is a unique,
complex organization of molecules, expressing it through chemical reactions and leading to:
• the capacity for growth,
•  reproduction, functional activity,
• and continual change preceding death.
This study of life and its properties is called Biology    

Origin of Life:

The question of how life originated is not easy to answer because it is impossible to go back
in time and observe life’s beginnings; nor are there any witnesses. There is testimony in the
rocks of the earth, but it is not easily read, and often it is silent on issues crying out for
answers. There are, in principle, at least three possibilities:

1. Spontaneous Generation. Life may have evolved from inanimate matter, as
associations among molecules became more and more complex.

2.  Extraterrestrial Origin. Life may not have originated on earth at all; instead, life may
have infected earth from some other planet.

3. Chemical Origin: Life originated from natural chemical processes which can be
observed and evaluated experimentally.
Inorganic matter->organic matter-> living forms

1) Spontaneous Generation and its Examples:
Spontaneous Generation:  The theory of spontaneous generation also known as
Abiogenesis was proposed by Von Helmont and supported by Anaximenes, Anaximander,
Aristotle and other known poets and philosophers of that time. From the time of the
ancient Romans, through the middle ages, and until the late nineteenth century, it was
generally accepted that some life forms arose spontaneously from non-living matter. Such
"spontaneous generation" appeared to occur primarily in decaying matter. According to this
theory, pieces of cheese and bread wrapped in rags and left in a dark corner, for example,
were thus thought to produce mice, because after several weeks there were mice in the
rags. Many believed in spontaneous generation because it explained such occurrences as
the appearance of maggots on decaying meat.

Examples:


1) An example would be the supposed seasonal generation of mice and other animals
from the mud of the Nile. Every year in the spring, the Nile River flooded areas of
Egypt along the river, leaving behind nutrient-rich mud that enabled the people to
grow that year’s crop of food. However, along with the muddy soil, large numbers of
frogs appeared that weren’t around in drier times. It was perfectly obvious to people
back then that muddy soil gave rise to the frogs.
2) Recipe for Mice: Mice came from the moldy grain kept alongwith sweaty clothes for
21 days.
           
                 
3) Sewage and garbage turned into the rats.
Challenging Spontaneous Generation: Theories
Experiment by Fransesco Redi:  
The first serious attack on the idea of spontaneous generation was made in 1668 by
Francesco Redi, an Italian physician and poet. At that time, it was widely held that maggots
arose spontaneously in rotting meat.
Hypothesis: Redi believed that maggots developed from eggs laid by flies.
Experimental Protocol: To test his hypothesis, he set out meat in a variety of flasks:
a) Some open to the air
b) Some covered with gauze.
c) Some sealed completely
Observations:
1. was infested with flies and maggots
2. had fly eggs on the gauze but the meat was unharmed

3. No flies were attracted with this experiment, the idea that flies evolved from meat
was no longer believed.  
Results:
As he had expected, maggots appeared only in the open flasks in which the flies could reach
the meat and lay their eggs. He observed these flasks to see in which one(s) maggots would
develop. He found that if a flask was closed with a lid so adult flies could not get in, no
maggots developed on the rotting meat within.  In a flask without a lid, maggots soon were
seen in the meat because adult flies had laid eggs and more adult flies soon appeared. The
results of this experiment disproved the idea of spontaneous generation for larger
organisms but people still thought small organisms bacteria could arise that way.


Rebuttal of John Needham:

The concept and the debate were revived in 1748 by the experiments of John Needham. John
Turberville Needham FRS (10 September 1713 – 30 December 1781) was
an English biologist and Roman Catholic priest. He showed that microorganisms flourished in
various soups that had been exposed to the air. He claimed that there was a “life force” present
in the molecules of all inorganic matter, including air and the oxygen in it, which could cause
spontaneous generation to occur.


Experimental Setup:
Since, everyone knew that boiling killed microorganisms, so he proposed to test whether or not
microorganisms appeared spontaneously after boiling. Needham added chicken broth to a flask
and boiled it. He then let it cool and waited for few days. He soon observed that the microbes
grew, and he proposed it as an example of spontaneous generation.  Needham’s experiments
seemed to support the idea of spontaneous generation.


The Experimental Pitfalls:
 People didn’t realize bacteria were already present in Needham’s soups.
 Needham didn’t boil long enough to completely kill the microbes. There were
endospores in the broth and they are very hard to kill if not by prolong heating or
autoclaving but there were no autoclaves in 1748.
So, the idea of SPONTANEOUS GENERATION lasted for around many years.
Challenging Spontaneous Generation: Theories
Lazzaro Spallanzani:

Spallanzani (10 January 1729 – 12 February 1799) was an Italian Catholic priest,
biologist and physiologist who made important contributions to the experimental study of
bodily functions, animal reproduction, and essentially animal echolocation. His research
of biogenesis paved the way for the downfall of preformationism theory (the idea that
organisms develop from miniature versions of themselves). With the invention of microscopes
after Redi's death, scientists were able to see tiny organisms that they could not see with the
naked eye.
Hypothesis:  Spallanzani was not convinced, and he suggested that perhaps the microorganisms
had entered the broth from the air after the broth was boiled, but before it was sealed. To test
his theory, he modified Needham's experiment.
Experimental Setup:
Spallanzani put broth into four flasks
Flask 1 was left open
Flask 2 was sealed
Flask 3 was boiled and then left open
Flask 4 was boiled and then sealed

Experiment Step 1 (Flask-1)
Left Open
Turned cloudy
Microbes were found


Experiment Step 2 (Flask-2)
Sealed
Turned cloudy
Microbes were found

Experiment Step 3 (Flask-3)
Boiled and left open
Turned cloudy
Microbes were found

Experiment Step 4 (Flask-4)
Boiled and sealed
Did not turn cloudy
Microbes not found

From this, Spallanzani concluded that the microorganisms did not come from the broth, but
were in the air that entered the flask. Therefore, not even microorganisms came from
nonliving things.
Critics said sealed vials did not allow enough air for organisms to survive and that prolonged
heating destroyed “life force”. Therefore, spontaneous generation remained the theory of
the time.
LOUIS PASTEUR’S EXPERIMENT:
By 1860, the debate had become so heated that the Paris Academy of Sciences offered a prize
for any experiments that would help resolve this conflict. The prize was claimed in 1864 by
Louis Pasteur, as he published the results of an experiment he did to disprove spontaneous
generation in microscopic organisms.




Hypothesis:  Dust particles in the air contain microbes. They are not formed from air itself.
Experimental Protocol:  In his famous experiment, Louis Pasteur used a special flask whose
neck was shaped like an S or the neck of a swan, hence the name "Swan Neck Flask."

He put a nutrient rich broth in the flask, which he called the "infusion." He then boiled the
infusion killing any microorganisms which were already present. Then he allowed the
infusion to sit at various locations. Because of the shape of the flask, the infusion was
exposed to air. However, dust particles and other things in the air never made it into the
infusion because they were trapped in the curve of the Swan Neck Flask.  He retained one
flask as it is and broke the neck of the other flask.

Observations: Dust particles in the air entered the first flask but were stuck in the swan
neck and could not travel into the broth. On the other hand, dust particles easily fell in the
second flask, thereby introducing microbes into the broth. So, no matter how long he
allowed the flask to sit, microorganisms never appeared in the infusion of the first flask.
However, if he tipped the flask and allowed the things trapped in the neck to get into the
infusion then micro-organisms began to appear in the infusion and multiply rapidly making
the flask cloudy.
Results: The content of the first flask remained as such while the content of the second flask
turned cloudy.
Conclusion: This demonstrates that microorganisms do not appear as a result of
Spontaneous Generation. Instead, they are introduced into food through dust particles and
other things that happen to land on the food.
This Experiment of Pasteur gave rise to the THEORY OF BIOGENESIS:
THEORY OF BIOGENESIS: It states that life originates from pre-existing life.
2) EXTRATERESSTRIAL ORIGIN:
Also known as THEORY OF PANSPERMIA or THE SPORE THEORY was proposed by
ARRHENIUS. It is the hypothesis that life exists throughout the Universe, distributed
by meteoroids, asteroids, comets, planetoids and also by spacecraft, in the form of
unintended contamination by microbes. Panspermia is the proposal that microscopic life
forms that can survive the effects of space become trapped in debris that is ejected into
space after collisions between planets and small Solar System bodies that harbor life.
3) CHEMICAL ORIGIN:  
Life originated on earth from pre-existing life. But do you know how the most primitive form
of life originated on earth? To understand the concept, it is necessary to understand the
conditions present on the primitive earth at the time of formation of Universe.
Theory of Early Earth Conditions-Hot and violent
 Immense heat due to accretion and volcanoes-Earth is molten.
 Earth is bombarded by asteroids, one of which dislodged the moon.
 Cooling causes condensation of H
 Volcanoes eject gases (CO
Note that there is no O
2
2
, N
2
, H
2
2
O to form rain.
) forming the early atmosphere.
 present in the early atmosphere. Any O
 outgassed would have
reacted with the metals of the crust, causing oxidation. This lack of O
2
 is crucial for the
formation of organic molecules.
Chemical Evolution-Theory and Hypothesis Testing
Oparin and Haldane (1920s):
2
J.B.S. Haldane and A.I. Oparin independently set forth ideas concerning the conditions
required for the origin of life on Earth.  
Oparin suggested that the organic compounds could have undergone a series of reactions
leading to more and more complex molecules. He proposed that the molecules formed
colloid aggregates, or 'coacervates', in an aqueous environment. The coacervates were able
to absorb and assimilate organic compounds from the environment in a way reminiscent of
metabolism. They would have taken part in evolutionary processes, eventually leading to
the first lifeforms.
Haldane's ideas about the origin of life were very similar to Oparin's. Haldane proposed that
the primordial sea served as a vast chemical laboratory powered by solar energy. The
atmosphere was oxygen free, and the combination of carbon dioxide, ammonia and
ultraviolet radiation gave rise to a host of organic compounds. The sea became a 'hot dilute
soup' containing large populations of organic monomers and polymers. Haldane envisaged
that groups of monomers and polymers aquired lipid membranes, and that further
developments eventually led to the first living cells.
Haldane coined the term 'prebiotic soup', and this became a powerful symbol of the OparinHaldane
view
of
the
origin
of
life.

Organic molecules could be formed from abiogenic materials in the presence of an external
energy source (e.g., ultraviolet radiation) and primitive atmosphere was reducing (having
very low amounts of free oxygen) and contained ammonia and water vapour, among other
gases. As the temperature reached 50-60°C, molecules and minerals (Inorganic) combined
to form 1
st
 Organic Molecules.  Eg: Sugar, Alcohols, aldehydes, fatty acids etc. These
compounds accumulated in water bodies: HOT THIN SOUP. First life-forms appeared in the
warm, primitive ocean and were heterotrophic.
They were the first to propose the idea of chemical evolution (1923).
a) Increasingly complex carbon-containing molecules formed in the atmosphere
and ocean of ancient Earth.
b) Radiant and kinetic energy are converted into chemical energy in the bonds
of large molecules.
Four steps of chemical evolution theory-predictions of the theory:



1) First molecules formed were small, carbon-containing compounds like
formaldehyde (H
CO) and hydrogen cyanide (HCN).
2) Small molecules react, forming sugars, amino acids, and nitrogenous
2
bases; and the prebiotic soup.
3) Small molecules of prebiotic soup link together to form nucleic acids
and proteins.
4) A single molecule acquires the ability to self-replicate, becoming the
first living entity and marking the end of chemical evolution,
beginning of biological evolution.
The Urey-Miller Experiment (Proving the Idea of Chemical Evolution):
The Miller-Urey Experiment
In 1952, Harold Urey tried to calculate the chemical constituents of the atmosphere of the
early Earth. He based his calculations on the (then) widely held view that the early
atmosphere was reducing, and concluded that the main constituents were methane (CH
),
ammonia (NH
3
), hydrogen (H
2
), and water (H
O). He suggested that his student, Stanley
Miller, should do an experiment attempting to synthesise organic compounds in such an
atmosphere.
2
Miller carried out an experiment in 1953 in which he passed a continuous spark discharge at
60,000 Volts through a flask containing the gases identified by Urey, along with water. Miller
found that after a week, most of the ammonia and much of the methane had been
consumed. The main gaseous products were carbon monoxide (CO) and nitrogen (N
). In
addition, there was an accumulation of dark material in the water. Few of the specific
constituents of this could not be identified, but it was clear that the material included a
large range of organic polymers.
Analysis of the aqueous solution showed that the following had also been synthesised:-
 25 amino acids (the main ones being glycine, alanine and aspartic acid)
 Several fatty acids
 Hydroxy acids
 Amide products.
The Miller-Urey experiment was immediately recognised as an important breakthrough in
the study of the origin of life. It was received as confirmation that several of the key
molecules of life could have been synthesised on the primitive Earth in the kind of
conditions envisaged by Oparin and Haldane. These molecules would then have been able
to take part in 'prebiotic' chemical processes, leading to the origin of life.
Since the Miller-Urey experiment, a great deal of effort has been spent investigating
prebiotic chemistry. It has become apparent that organising simple molecules into
assemblies capable of reproducing and evolving is a far greater task than was generally
realised during the excitement that followed the experiment. In addition, the view that the
early atmosphere was highly reducing was challenged towards the end of the twentieth
century, and is no longer the concensus view.
Although the significance of specific details of the Miller-Urey for the origin of life may now
be in question, it began the new scientific discipline of prebiotic chemistry, and has been
enormously influential in the development of ideas about the origin of life.


2
4
Experimental Protocol:
     
His experimental setup, shown on the next page, consisted of a completely closed system,
with gases flowing past a spark discharge; the condensed gases were recirculated by boiling.
The gases tried were mixtures of methane, ammonia, water, hydrogen, and other reduced
molecules.
Observations:
 Ammonia disappeared steadily during the experiment. During the first 25 hours of
boiling and refluxing, most of the ammonia and methane was being converted to
HCN and aldehydes, with a slow synthesis of amino acids.
 During the next 100 hours, HCN and aldehydes reached a steady state, being used in
further reactions as rapidly as they were made. The main products from these
compounds were amino acids.
 After 125 hours, as the supplies of ammonia and methane were depleted, HCN and
aldehyde concentrations began to decrease. The amino acid concentration leveled
off as more of the simple amino acids were incorporated into short peptides.
 The results were mixtures of formic, acetic, propionic, lactic, succinic, and other
organic acids; glycine, alanine, aspartic and glutamic acids, and other biological and
nonbiological amino acids; urea, methylurea, and various other small molecules.
First Life forms on Earth:
Once macromolecules had formed, the next step in the development of life would have
involved their organization into bodies with definite shapes and chemical properties. One
example is coacervate droplets, which may be the early ancestors of cells. These
coacervates consist of macromolecules surrounded by a shell of water molecules, whose
rigid orientation makes them form a primitive membrane. This membrane is
highly selective, allowing only certain molecules to pass though; it therefore creates a
sheltered chamber in which complex chemical reactions can develop.
Prebionts: Non living structures that led to first living cells. They are formed of proteins,
carbohydrates, lipids and Nucleic acids.





















Lecture 1.2:
Evolution

Evolution: the process by which different kinds of living organism are believed to have
developed from earlier forms during the history of the earth. The Term “Evolution” was
coined by: HERBERT SPENCER.
Theories of Evolution:
Evolutionary theories aim to explain the origin of life and all its present variety of forms:
that is, the whole range of individual organisms. It postulates the emergence of complex
living organisms from non-living matter by way of a much smaller number of less complex
ancestors. These theroies will be discussed in detail in this section:
1. Pre-Darwinian Concept:  Great Chain of Being:
This theory states that the earth and life on it are only about 6000 years old. It states that
a) God created an infinite and continuous series of life forms, each one grading into
the next, from simplest to most complex.
b) All organisms, including humans, were created in their present form relatively
recently and that they have remained unchanged since then.  
c) Its major premise was that every existing thing in the universe had its "place" in a
divinely planned hierarchical order,("Hierarchical" refers to an order based on a
series of higher and lower, strictly ranked gradations.) An object's "place"
depended on the relative proportion of "spirit" and "matter" it contained--the
less "spirit" and the more "matter," the lower down it stood.
At the bottom, for example, stood various types of inanimate objects, such as metals,
stones, and the four elements (earth, water, air, fire). Higher up were various members of
the vegetative class, like trees and flowers. Then came animals; then humans; and then
angels. At the very top was God.
2. Lamarck’s Theory:
The first evolutionist who confidently and very publicly stated his ideas about the
processes leading to biological change Jean-Baptiste Chevalier de Lamarck. Lamarck
incorporated two ideas into his theory of evolution:
a) Use and disuse – Individuals lose characteristics they do not require (or use) and
develop characteristics that are useful. As environments changed, organisms had to
change their behaviour to survive. If they began to use an organ more than they had
in the past, it would increase in its lifetime. If a giraffe stretched its neck for leaves,
for example, the neck will become longer. Meanwhile organs that organisms
stopped using would shrink, for example tail bone in humans.
b) Inheritance of acquired traits (Individuals inherit the traits of their ancestors): is a
hypothesis that states changes acquired over the life of an organism (such long neck
of Giraffe) may be transmitted to offspring. If an organism changes during life in
order to adapt to its environment, those changes are passed on to its offspring. He
said that change is made by what the organisms want or need.
 For example, Lamarck believed that elephants all used to have short trunks. When
there was no food or water that they could reach with their short trunks, they
stretched their trunks to reach the water and branches, and their offspring inherited
long trunks
3. Darwin’s Theory or Darwinism:  
It states that all species of organisms arise and develop through the natural selection of
small, inherited variations that increase the individual's ability to compete, survive, and
reproduce. It states that complex creatures evolve from more simplistic ancestors naturally
over time by a process known as "natural selection.
The concept of Natural Selection or survival of the Fittest: Species that acquire adaptations
that are favourable for their environment will pass down those adaptations to their
offspring. Eventually, only individuals with those favourable adaptations will survive and
that is how the species changes over time, or evolves through speciation.
Example: Peppered moth, Biston betularia
A species of moth in England called the peppered moth is found in two varieties: light gray
and dark gray. The light gray version used to be far more common, but researchers

observed that between 1848 and 1898 the dark colored ones were becoming more
common. In fact, only 2% of the moths near one industrial city were light gray.

This change in moth coloration occurred at the same time that coal was becoming a major
source of power in England. Coal is not a very clean energy source and burning vast
quantities of it put large amounts of soot into the air in and near London and other
industrial cities. The soot would settle over the land, buildings and even the trunks of trees.
Tree trunks turned from light gray to black. Peppered moths are active at night but rely on
places where they can blend in, avoiding predators, during the day. Light-colored peppered
moths were no longer well camouflaged on the darkened tree trunks. The dark colored
moths, however, were well camouflaged. Because predators were able to spot the light
moths more easily, the dark moths were more likely to survive and reproduce. Eventually,
moths in industrialized areas of England were predominantly the dark variety and moths in
the non-industrialized regions (where tree trunks were still light in color) remained
predominantly light gray in color.
The peppered moth case is an example of natural selection. In this case, changes in the
environment caused changes in the characteristics that were most beneficial for survival.
The individuals that were well adapted to the new conditions survived and were more likely
to reproduce. This particular type of natural selection, when amounts of genes varieties shift
in a particular direction in response to a new factor in the environment, is called directional
selection.
PROCESS IN EVOLUTION:

A) Variation: Variations exist in all organisms. These variations may be useful or
harmful or useless. Variation are any difference between cells, individual organisms,
or groups of organisms of any species caused either by genetic differences
(genotypic variation) or by the effect of environmental factors on the expression of
the genetic potentials (phenotypic variation). Variation may be shown in physical
appearance, metabolism, fertility, mode of reproduction, behaviour, learning and



mental ability, and other obvious or measurable characters. Harmful variations make
the organism unfit in the struggle for existence. The variations may be favoured or
unfavoured by the nature. Beneficial variations are favoured by the nature. Useful
variations arc quite significant and make the organism fit in the struggle for
existence. Such variations are inherited by the progeny, so that the progeny has
better chances of survival.

Variations which are useful to the individual in a particular environment would
increase that individual's ability to reproduce and leave fertile offspring. These are
favoured by nature. Less favourable variations would be at disadvantage and
organisms possessing them are reproductively less successful. Differential
reproductive success exists among organisms.
B) Mutation: Mutation is a sudden, random, discontinuous and heritable change
independent of the environment in the genetic make up of an individual. An
organism's DNA affects how it looks, how it behaves, and its physiology — all aspects
of its life. So a change in an organism's DNA can cause changes in all aspects of its
life.
Mutations are random
Mutations can be beneficial, neutral, or harmful for the organism, but mutations do not
"try" to supply what the organism "needs." In this respect, mutations are random —
whether a particular mutation happens or not is unrelated to how useful that mutation
would be.
Not all mutations matter to evolution: Since all cells in our body
contain DNA, there are lots of places for mutations to occur; however,
not all mutations matter for evolution. Somatic mutations occur in
non-reproductive cells and won't be passed onto offspring.
For example, the golden color on half of this Red Delicious apple was
caused by a somatic mutation. The seeds of this apple do not carry the
mutation.
The only mutations that matter to large-scale evolution are those that can be passed on to
offspring. These occur in reproductive cells like eggs and sperm and are called germ line
mutations.
A single germ line mutation can have a range of effects:
a) No change occurs in phenotype.
Some mutations don't have any noticeable effect on the phenotype of an organism.
This can happen in many situations: perhaps the mutation occurs in a stretch of DNA
with no function, or perhaps the mutation occurs in a protein-coding region, but
ends up not affecting the amino acid sequence of the protein.
b) Small change occurs in phenotype:
A single mutation caused this cat's ears to curl
backwards slightly.
c) Big change occurs in phenotype: Some really
important phenotypic changes, like DDT resistance
in insects are sometimes caused by single
mutations. A single mutation can also have strong
negative effects for the organism. Mutations that
cause the death of an organism are called lethals —
and it doesn't get more negative than that.
There are some sorts of changes that a single mutation, or even a lot of mutations, could
not cause. Neither mutations nor wishful thinking will make pigs have wings; only pop
culture could have created Teenage Mutant Ninja Turtles — mutations could not have done
it.
Mutations happen for several reasons.
a) DNA fails to copy accurately: Most of the mutations that we think matter to
evolution are "naturally-occurring." For example, when a cell divides, it makes a copy
of its DNA — and sometimes the copy is not quite perfect. That small difference from
the original DNA sequence is a mutation.
               

b) External influences can create mutations: Mutations can also be caused by exposure
to specific chemicals or radiation. These agents cause the DNA to break down. This is
not necessarily unnatural — even in the most isolated and pristine environments,
DNA breaks down. Nevertheless, when the cell repairs the DNA, it might not do a
perfect job of the repair. So the cell would end up with DNA slightly different than
the original DNA and hence, a mutation.





C) Natural Selection:
Natural selection is one of the basic mechanisms of evolution, along with mutation,
migration, and genetic drift.
Darwin's grand idea of evolution by natural selection is relatively simple but often
misunderstood. To find out how it works, imagine a population of beetles:


1. There is variation in traits.
For example, some beetles are green and some are
brown.
2. There is differential reproduction.
Since the environment can't support unlimited
population growth, not all individuals get to reproduce
to their full potential. In this example, green beetles
tend to get eaten by birds and survive to reproduce
less often than brown beetles do.
3. There is heredity.
The surviving brown beetles have brown baby beetles because
this trait has a genetic basis.
4. End result:
The more advantageous trait, brown coloration, which allows
the beetle to have more offspring, becomes more common in
the population. If this process continues, eventually, all
individuals in the population will be brown.


                         

If you have variation, differential reproduction, and heredity, you will have evolution by
natural selection as an outcome. It is as simple as that.









Scientists have worked out many examples of natural selection, one of the basic
mechanisms of evolution.
Any coffee table book about natural history will overwhelm you with full-page glossies
depicting amazing adaptations produced by natural selection, such as the examples below.

Orchids fool wasps into
"mating" with them.


Katydids have camouflage to
look like leaves.
Behavior can also be shaped by natural selection. Behaviors such as
birds' mating rituals, bees' wiggle dance, and humans' capacity to
learn language also have genetic components and are subject to
natural selection. The male blue-footed booby, shown to the right,
exaggerates his foot movements to attract a mate.


Non-poisonous king snakes
mimic poisonous coral snakes.


In some cases, we can directly observe natural selection. Very
convincing data show that the shape of finches' beaks on the Galapagos Islands has tracked
weather patterns: after droughts, the finch population has deeper, stronger beaks that let
them eat tougher seeds.
In other cases, human activity has led to environmental changes that have caused
populations to evolve through natural selection. A striking example is that of the population
of dark moths in the 19th century in England, which rose and fell in parallel to industrial
pollution. These changes can often be observed and documented.

D) Adaptation:

 
An adaptation is a feature that is common in a population because it provides some
improved function. Adaptations are well fitted to their function and are produced by natural
selection.
Adaptations can take many forms: a behavior that allows better evasion of predators, a
protein that functions better at body temperature, or an anatomical feature that allows the
organism to access a valuable new resource — all of these might be adaptations. Many of
the things that impress us most in nature are thought to be adaptations.
Mimicry of leaves by insects is an adaptation for
evading predators. This example is a katydid from Costa
Rica.
The creosote bush is a desert-dwelling plant that
produces toxins that prevent other plants from growing
nearby, thus reducing competition for nutrients and
water.
Echolocation in bats is an adaptation for catching
insects.

 


 
So what's not an adaptation? The answer: a lot of things. One example is vestigial
structures. A vestigial structure is a feature that was an adaptation for the organism's
ancestor, but that evolved to be non-functional because the organism's environment
changed.
Fish species that live in completely dark caves have
vestigial, non-functional eyes. When their sighted
ancestors ended up living in caves, there was no longer
any natural selection that maintained the function of
the fishes' eyes. So, fish with better sight no longer outcompeted

fish with worse sight. Today, these fish still
have eyes — but they are not functional and are not an
adaptation; they are just the by-products of the fishes'
evolutionary history.
In fact, biologists have a lot to say about what is and is not an adaptation.


Example:
NEED: MOTHER OF EVOLUTION:
Darwin’s Finches: The Galapagos Islands are an archipelago of 13 major islands and more than
a hundred smaller islands that straddle the equator off the Ecuadorian coast. They are home to
an amazing array of unique animal species: giant tortoises, iguanas, fur seals, sea li ons, sharks,
rays, and 26 species of native birds––14 of which make up the group known as Darwin’s finches.
These finches are considered to be the world’s fastest-evolving vertebrates because their
appearance and behavior quickly adapted to this closed and rapidly changing environment.
Darwin's finches (also known as the Galápagos finches) are a group of about
fifteen species of passerine birds. They were first collected by Charles Darwin on the Galápagos
Islands during the second voyage of the Beagle. All are found only on the Galápagos Islands,
except the Cocos finch from Cocos Island.

Whilst studying wildlife on the Galapagos Islands [Darwin] noticed that the Galapagos
finches showed wide variations - eg in beak shape and size - from island to island. Darwin
deduced that these differences made the finches better adapted to take advantage of the
food in their particular local environment - thin, sharp beaks prevailing where the birds' main
food was insects and grubs, and large claw-shaped beaks where their diet was buds, fruit
and nuts. In each locality the finch population had somehow developed beaks which were
suitable for that particular environment. Darwin concluded that in each locality one or more
individual finch happened to acquire, by random mutation, a beak shape more suitable for
the food sources in that locality. These individuals then had a competitive advantage over
their fellow finches, enabling them to grow and reproduce more successfully, and pass on
their more specialised beaks to successive generations - until eventually the characteristic
had spread throughout the finch population in that locality.
Darwin wrote about his travels in the book The Voyage of the Beagle and fully explored the
information he gained from the Galapagos Finches in his most famous book On the Origin of
Species. It was in that publication that he first discussed how species changed over time,
including divergent evolution, or adaptive radiation, of the Galapagos finches.



















Lecture: 1.3
Human Evolution

In 1871 Charles Darwin published another groundbreaking book, The Descent of Man. In this
book, he suggested that humans evolved from the same African ape ancestors that gave rise
to the gorilla and the chimpanzee. Although little fossil evidence existed at that time to
support Darwin’s case, numerous fossil discoveries made since then strongly support his
hypothesis. Human evolution is the part of the evolution story that often interests people
most, and it is also the part about which we know the most.
What is Human Evolution??
Human evolution is the evolutionary process leading up to the appearance of modern
humans. Hominids (humanlike creatures) began to appear over four million years ago.  
How Humans Evolved??
Human evolution is characterized by a number of morphological,
developmental, physiological, and behavioural changes that have taken place since the split
between the last common ancestor of humans and chimpanzees.
Most significant adaptations:  

a) Bi-pedalism
b)  change in jawline
c) increased brain size
d) precision grip (thumb









A) Bipedalism:
Bipedalism is a form of terrestrial locomotion where an organism moves by means of
its two legs.  Evolution of bipedalism has been accompanied by a large number of
skeletal changes.
– The thigh bone evolved into a slightly more angular position to move the
center of gravity toward the geometric center of the body.
– The knee and ankle joints became increasingly robust to better support
increased weight.
– To support the increased weight on each vertebra in the upright position, the
human vertebral column became S-shaped.
– In the feet the big toe moved into alignment with the other toes to help in
forward locomotion.
The arms and forearms shortened relative to the legs making it easier to run.



Advantages of bipedalism include:
• the ability to carry food or other portable items over longer distances
• the freeing of forelimbs for foraging, tool use or protection;
• moving in a more energy-efficient manner,
• long distance running
• acquisition of improved long-distance perception.
• carrying infants and food

B) Change in Jawline:
Last Common Ancestor of chimpanzees and hominins had large incisors. The canines were
more projected in males than in females. Premolars had relatively small crowns and the
second molar was the largest. With Evolution, Humans have evolved weak jaw muscles and
jaw bones, possibly because social organisation reduced the need to bite as a form of attack
and their movement from a hunting-chewing lifestyle to agriculture. People who eat a
hunter-gatherer-type diet have larger jaws. People raised on the softer foods of an
agricultural diet have smaller jaws. The smaller jaw sizes of most modern people may also
be leading to overcrowded teeth.



C) Changes in Brain Size:
As early humans faced new environmental challenges and evolved bigger bodies, they
evolved larger and more complex brains. During the first four million years of human
evolution, brain size increased very slowly. Encephalization (evolutionary enlargement of
brain relative to body size) was pronounced over the past 800,000 years. Larger brain
size allows for extended periods of social learning and language acquisition in juvenile
humans. Larger brains allowed hominins to process and store information, to plan
ahead, and to solve abstract problems.  A large brain was able to produce versatile
solutions to new and diverse survival challenges.



D) Development of Opposable Thumb:
The evolution of the opposable or prehensile thumb is usually associated with Homo
habilis, the forerunner of Homo sapiens. This, however, is the suggested result of
evolution from Homo erectus (around 1 MYA) via a series of intermediate anthropoid
stages, and is therefore a much more complicated link. The most important factors
leading to the habile hand (and its thumb) are:
a) The freeing of the hands from their walking requirements - still so crucial for apes
today, as they have hands for feet, which in its turn was one of the consequences of
the gradual pithecanthropoid and anthropoid adoption of the erect bipedal walking
gait.
b) The simultaneous development of a larger anthropoid brain in the later stages.

During its evolution, the human hand gained two unique grips, first identified by Napier.
He called them the precision grip and the power grip and depicted them by the grip of a
sphere (top left) and a cylinder (bottom left). The evolution of these grips can be
attributed to adaptation of the hand for gripping missiles and clubs. This is shown
(above) by the grip of a softball, baseball and cricket ball, and (below) by the grip of a
tennis racquet, golf club and cricket bat.
Advantages: The thumb, unlike other fingers, is opposable, in that it is the only digit on
the human hand which is able to oppose or turn back against the other four fingers, and
thus enables the hand to refine its grip to hold objects which it would be unable to do
otherwise. The opposable thumb has helped the human species develop more accurate
fine motor skills. It is also thought to have directly led to the development of tools, not
just in humans or their evolutionary ancestors, but other primates as well.The thumb, in
conjunction with the other fingers make humans and other species with similar hands
some of the most dexterous in the world.

Technological Evolution
With the change in the human morphological features and development of more advanced
features the needs also changed with time. To meet the needs of  more evolved human race
the technology also kept on transforming itself.


Technological evolution refers to the changes over time in technology that give humans
increased control over their environment. Examples include the change from stone tools to
metal tools, the development of industrial technologies (such as steam and electric power),
agricultural and medicinal procedures, communication resources (such as the internet) and
space travel.