Theories of Origin and Evolution of Life...Theories of Origin and Evolution of Life There are many...
Transcript of Theories of Origin and Evolution of Life...Theories of Origin and Evolution of Life There are many...
Theories of Origin and Evolution of Life
There are many views on how life originated on earth. The earth is
said to have come into existence 5 billion years ago and life on earth
came into existence only a billion years after that. There were many
scientists who studied the fossils and performed experiments to
postulate their versions of the theory of evolution.
Theories of Origin of Life
In olden days, people believed that the universe and life on it was an
act and result of God’s creation. There was, however, no evidence to
support these claims.The early scientists and Greeks believed that life
on earth never began on earth itself. They believed that it came from
somewhere else in outer space and they named this phenomenon
‘panspermia’.
Then came the theory of spontaneous generation of life during the
times of Aristotle who believed that life was born from decaying and
rotting inorganic matter such as hay, straw, and other non- living
material. This theory was rubbished by Louis Pasteur.
Next came the ‘chemical evolution of life’ theory by two scientists-
Oparin from Russia and Haldane from England. They believed that the
generation of life on earth was a slow chemical process which
occurred from pre-existing non-living materials such as amino acids,
proteins and nuclear material such as RNA. They postulated that these
organic materials came together under conditions of high temperature,
reducing atmosphere(without oxygen) and gases released from
volcanos all of which were favourable to produce simple living forms.
So they called this mixture of organic materials as ‘organic soup’.
Browse more Topics under Evolution
● Stages of Evolution
● Evidences of Evolution
Miller Urey Experiment
Miller and Urey were two scientists who believed Oparin and Haldane
and wanted to prove their theory. So, they performed the famous
‘Miller- Urey experiment’ in the lab.
(Source: bbc.co.uk)
● They replicated the environmental and atmospheric conditions
that may have existed in the primitive earth in their lab by
taking gases like methane, ammonia, hydrogen and water
vapour in a closed vessel.
● When they came back to check the results of their experiment
after a week, they detected the presence of amino acids,
nitrogen bases, fats, and sugar.
● With these results, the theory of gradual chemical evolution
was accepted.
● This experiment gave the other scientists to piece the remaining
pieces together.
It was believed that monomeric units that formed due to chemical
evolution polymerized to form polymeric units and that gave rise to
the unicellular microorganisms and eventually gave rise to
multicellular more complex species. This is called biogenesis.
Similar to the above-discussed theories of the origin of life, there were
many theories of the evolution of life.
Theory of Evolution
There were many theories of evolution that were postulated based on
the evidence but the most accepted important ones are as follows:
Lamarck’s Theory of inheritance of Acquired Characters
This theory of evolution was published in the book ‘Philosphic
Zoologique’ by French scientist Jean Lamarck. His theory was based
on the study of fossils of the organisms of the past with their present
relatives including the homologous, analogous and vestigial organs.
He believed that an organ or structure got modified in the current
animal from its ancestor due to the change in the environment and the
utility of that particular organ. His theory also said that the organs or
structures modified themselves to suit the new needs of the organism.
His theory contained three postulates:
● New needs
● Acquisition of new characters, organs or structures
● Inheritance of acquired characters
Example: The giraffe originally did not have its long neck. But, the
trees were very tall and it could not feed on the minimal number of
short trees. So, as an adaptive measure to be able to eat leaves on the
tall trees, the giraffe’s neck started growing longer. This was a way of
adaptive mechanism due to new needs.
(Source: haikudeck.com)
Lamarck’s theory of evolution was disproved by scientists like
Weismann and Mendel by carrying out their own experiments which
were not consistent with Lamarck’s postulates.
Darwin’s Theory of Natural Selection
Charles Darwin along with Wallace postulated this theory of
evolution. Darwin believed that life thrives and multiplies by the
principle of natural selection. The theory of natural selection had the
following postulates:
● Increased reproduction- He said that each and every organism
or species tend to reproduce to the maximum to let its species
live and multiply. He said that populations of all organisms
multiply geometrically.
● The arithmetic growth of food and availability of space-
Darwin says that though the organism and their species
multiply geometrically, food multiplies only arithmetically and
the space available remains a constant. With both these
restrictions to the growing population of different species puts
a tab on the population growth.
● Struggle- with a rapidly multiplying population, there is an
increased demand for both space and food. But, due to the
restricted space and slowly growing food, there arises a
competition between the members of a species and between
species for the food and space. The organism or species that is
able to fight its own species or the other species or the
environment itself lives.
● Variations- Due to this struggle for food and space, each
organism or species tend to get an advantage over the other. In
order to do so, they tend to develop certain features or
structures that give them that added advantage to succeed in the
struggle of life. So, this struggle brings about variations.
● Survival of the fittest- Darwin’s theory of natural selection thus
believes that those who can survive till the end are the ones that
nature selects.
Solved Example for You
Q: Who postulated the theory of chemical evolution?
a. Lamarck
b. Miller and Urey
c. Oparin and Haldane
d. Darwin and Wallace
Sol: The correct answer is (c) Oparin and Haldane
Oparin and Haldane believed that the life on earth came into existence
from a pre-existing inorganic material such as mud, clay, hay etc.
They believed a gradual conversion of these materials in the primitive
environment of earth gave rise to small molecules which later on
polymerized to give rise to complex molecules and organisms.
Stages of Evolution
The evolution of man began about 15 million years ago when the first
known man walked this earth. Humans today developed through many
stages of evolution from primates that are now extinct. This
evolutionary process from the primates who walked on all four limbs
to the humans today who walk on two hind limbs has been a very long
one.Theories of Organic evolution H
Stages of Evolution of Man
The genus of the human being today is called Homo and the man
today is called as Homo sapiens. From simple life forms that were
unicellular to the development of multicellular organisms gave rise to
the vertebrates. The vertebrates began evolving that led to the
development of mammals. Among the mammals, humans are most
closely related to primates such as the orangutan
The family to which human beings belong is called Hominidae. It was
in the Miocene age that the family Hominidae split from the
Pongidae(apes) family. Dryopethicus was the first in the evolution of
man in the stages of evolution and some believe him to be the
common ancestor of man and apes.
Browse more Topics under Evolution
● Theories of Origin and Evolution of Life
● Evidences of Evolution
Read the Evidence of Evolution here in detail.
Dryopethicus
He was the earliest known ancestor of man. At the same time as his
existence, Ramapethicus existed who was more human-like than
Dryopethicus. Dryopethicus inhabited the European region and some
parts of Asia and Africa. Stages of evolution of humans began from
him. After Dryopethicus and Ramapethicus came to the genus
Australopethicus which preceded the genus Homo.
Australopithecus
● Australopithecus ramidus: Was 1.2 meters tall and the fossils
show the foramen magnum that was large to indicate upright
walking. The forelimbs were different from those of the earlier
ape-like ancestors. They had teeth like humans.
● Australopithecus afarensis– ‘Lucy’ the famous fossil belonged
to this species. They are said to have inhabited the African
mainland. And they were shorter than the Australopithecus
ramidus and had a small skull with flat noses and no chin. They
were able to walk on two legs but the legs were slightly bowed
which made their walk slightly ape-like. The bowed legs,
fingers, and toes enabled them to climb trees and live there.
They had large teeth and jaws.
● Australopithecus africanus– These also inhabited the African
mainland. They were bipedal and had a small skull with small
brains than Homo erectus but larger than their predecessors.
Also, they had large teeth compared to current day humans and
were herbivorous. They had large jaws.
● Australopithecus robustus– He was taller than his predecessors
but still ape-like. They also weighed more than their ancestors.
After the Australopithecus genus came the Homo genus. The
first man in the genus was Homo habilis.
Browse more about Evolution
Evolution
● Evidences of Evolution
● Theories of Origin and Evolution of Life
Homo
● Homo habilis– He had a face similar to his ancestors. The skull
and brain size indicate that he may have been able to speak.
The earliest tools made were from this era. Homo habilis is
known as the ‘handy man’ because he was the first to make and
use tools. He was around 5 feet tall and erect.
● Homo erectus– after Homo habilis came, the Homo erectus
who was also upright. He had a smaller but longer face, less
prominent or absent chin, larger brain size and prominent
speech. He knew how to make and use tools, he made a fire
and knew how to control it. Homo erectus was carnivorous. He
knew the existence of groups and they began spreading from
Africa to Asia and Europe. The Java Man and Peking Man had
brain capacities similar to modern man at 1300cc. They were
cave dwellers.
● Homo sapiens– After Homo erectus came, the Homo sapiens
who separated into two types:
1) Homo sapiens neanderthelensis
They had a brain size larger than modern man and were gigantic in
size. Also, they had a large head and jaw and were very powerful and
muscular. They were carnivores and the tools from the era indicate
they were hunters. They were also cave dwellers but their caves were
more comfortable and they lived in groups and hunted for food
gathering.
2) Homo sapiens sapiens
Also known as ‘modern-day man’ is what we are today. Compared to
the Homo sapiens neanderthelensis, they became smaller in size and
the brain size reduced to 1300cc. There was also a reduction in the
size of the jaw, rounding of the skull and chin. Cro- Magnon was the
earliest of the Homo sapiens. They spread wider from to Europe,
Australia, and the Americas. They were omnivores, had skilful hands,
developed the power of thinking, producing art, more sophisticated
tools and sentiments.
Evolution is not a thing of the past and is continuing even now.
Humans are undergoing ‘natural selection’ for many different traits
based on their life and environment in the present. It is believed that
the jaw size is reducing further and the wisdom teeth are soon going to
become extinct.
Solved Example for You
Q: Which man was the first developer of tools?
a. Homo habilis
b. Homo erectus
c. Humans
d. Australopithecus ramidus
Sol: The correct answer is (a) Homo habilis
The first man to develop tools was Homo habilis and so he is also
called ‘handy man’.
Evidences of Evolution
Evolution is a biological theory that postulates that all organisms on
earth– plants, and animals have a common origin and their differences
today are the result of modifications that occurred in successive
generations. There is evidence of evolution that can prove this.
Evolution claims that there has been a genetic variation that brings
about the difference in the physical characteristics of different species.
Evidence of Evolution
We can broadly group the evidence of evolution into 5 broad
categories:
1. Relationship between organisms
2. Anatomy and morphology
○ Homologous Organs
○ Analogous Organs
○ Vestigial Organs
○ Atavism
3. Genetics
4. Paleontology (study of fossils)
5. Embryology
Let’s look at each of this evidence of evolution a little more in detail.
Relationship Between Organisms
The theory of evolution says that all organisms alive today have
originated from a single ancestor. There are many similarities to prove
these common origins:
● All organisms are made up of cells.
● The structure and functioning of individual organelles of cells
remain the same in all organisms except with a few variations.
● Cells of the same kind and function form tissues in all
organisms.
● All organisms grow, reproduce and multiply.
● All organisms are able to perform metabolism and generate
energy to be able to live and thrive.
Anatomy and Morphology
Evolution also is proved by the similarities in the anatomy and
morphology of different animals and plants due to the presence of:
Homologous organs
(Source: BiologyDiscussion)
These are organs that are similar embryologically but serve different
functions in different organisms. This phenomenon is known as
homology.
● Homology in plants: Thorns of a Bougainville are homologous
to tendrils in creepers such as a money plant.
● Homology in animals: The structure of the heart in animals is
an example of homology. The chambers in the heart are present
in most animals -some have 2,3 and 4 chambers are seen in
higher vertebrates. The forelimbs are present in all animals but
modified to perform different functions- fins in aquatic
animals, wings in birds, hands in humans etc.
Analogous Organs
These organs perform the same function in but develop from different
structures in different species.
● Analogy in plants: In some plants leaves and in some their
stems perform photosynthesis. Here, two differently originated
structures perform the same function.
● Analogy in animals: Wings of an insect, bird and a
bat(mammal) originate from different structures but all perform
the same function of enabling the organism to fly.
Vestigial organs
These organs are non- functional and rudimentary in nature. However,
they were very functional in the ancestors of the organism. This
occurs due to the decreasing use of the organ which leads it to become
small or non- functional in nature. Example of such a structure is the
appendix and the wisdom teeth in human beings.
Atavism
This can be called as the reverse of vestigial organs where a structure
or organ which has become extinct in the species has appeared in the
future generations. Example of such a trait is the appearance of a short
tail in human babies.
Genetics
The genetic code is made up of nitrogen bases. These base
combinations are almost the same in all the organisms. Certain triplets
of amino acid sequences also produce the same proteins in different
organisms. This genetic code called the ‘universal genetic code’
remains identical to a large extent in most organisms proving the
possibility of a common ancestry.
Paleontology
(Source: apologetics press)
The study of fossils is known as palaeontology. Fossils are formed
when certain remains of organisms or plants get embedded in the soil
or water and are preserved for many hundreds of years. They appear
either as skeletal remains, footprints, moulds or intact structures as
found in the snow. By studying fossils, we are able to establish
similarities between the organism in the present to its ancestor in the
past.
There can be many similarities that prove the common origins
between different closely related animals and the differences can be
studied to establish how they differ now and why. Fossils are very
important evidence to prove the theory of evolution and common
ancestry.
Embryology
(Source: seanet.com)
It has been observed that the embryos of different organisms appear
similar in early stages of embryo development. Some animals show
structures present during embryonic life but which disappear in adult
life or immediately before being born. And it is said by the
‘Recapitulation Theory’ or the’ Biogenetic Law’ by Von Baer that
‘Ontogeny repeats phylogeny’ which means that the embryo of an
organism undergoes all the stages in the embryonic life as its
evolutionary history. For example, a reptile embryo undergoes
transformations from a fish-like appearance to amphibian-like features
and then to a reptile embryo.
There are many theories that prove evolution is a fact and the truth of
life on earth and this evidence of evolution only prove them more
strongly.
Solved Example for You
Q: Who gave the Biogenetic Law?
a. Charles Darwin
b. Von Baer
c. Hardy and Weinberg
d. S.L.Miller
Sol: The correct answer is (b) Von Baer
Von Bar gave the Biogenetic Law or ‘Recapitulation Theory’ which
says that ‘ontogeny repeats phylogeny’. Charles Darwin gave the
Theory of Adaptive Radiation in Evolution. Hardy and Weinberg
postulated the Hardy- Weinberg principle which gave an algebraic
equation that helps determine the frequency of alleles in a locus or
gene. S. L Miller gave the Miller’s theory that demonstrated how the
first non- cellular life forms could have originated on earth by
performing lab experiments.