Welcome everyone. Today, I will talk about two important topics under human evolution
These two topics are Vestigial Organs and Darwin's theory
Let us know about vestigial organs first.
These are the organs which are present in our body but are of no use for us.
They are present in reduced form in our body, but they performed important functions in
our ancestors' bodies.
There are known to be more than hundred vestigial organs in human body such as
Sinuses, coccyx, which is also known as tailbone,
erector pilli which cause goosebumps,
Vermiform appendix, Nictitating membrane in eyes, Wisdom teeth, Pinna etcetera
Wisdom teeth are one of the examples of vestigial organs.
These are the last molars
present in both the jaws. They appear after the age of 17 years. That is why they are called wisdom teeth
They are smaller molars and do not help in chewing as well.
Now second is Vermiform Appendix
This organ is located at the blind end of Large intestine. This blind end is called Caecum.
it has a narrow tubular and
a worm-like
shape that's why it's called Vermiform.
It has no function in our body, but
similar organ
present in herbivores
performs the function of
digesting cellulose part of the plant.
Third is Pinna. Pinna is the outside projecting cartilaginous part of the ear.
It was used to collect sound waves in our
ancestors,
With its movement with the help of muscles present on it
But now the muscles are not able to move enough to solve its purpose
So this Pinna becomes vestigial organs for human body.
Now I will take up the major topic that is Darwin's theory
Charles Darwin
from very young age
travelled from one island to another in the company of naturalists
Naturalists are the people who study about all life-forms whether they are animals plants or
insects
So he made interesting observations on the vast or great
diversity he found.
Based on his
observations, in
1859 he published his book
named the Origin of Species
He gave the theory of natural selection to explain evolution in his book
and his theory of natural selection was based upon the following facts.
First, Overproduction
According to
Charles Darwin
every living being whether they are animal or plants produce their own progeny to continue their race and
they produce large number of progeny to ensure the survival. For example
Oyster, which is a mollusk
Lays 60 to 80 millions eggs every time and all of them do not survive
if all of all the eggs laid hatch into young ones, then this earth will be filled with
oysters everywhere within their few generations
Similarly, Paramecium
divides by binary fission
Thrice in 48 hours, that is three times in two days
All of them do not survive, if all of them survived
Then their mass will be more than the mass of the earth
But the number remains constant over a long period of time
Because more of them do not survive.
however
Elephant which is a slow breeder as compared to these lower organism can produce
six young ones in
90 years.
As per the calculations,
in 750 years there will be 19 million
elephants on earth if all survived
so the conclusion is,
First, all living beings produce
the progenies in large number to ensure their survival and
continuity.
Second,
the number of individuals of a species
remains roughly constant over a long period of time in a stable environment
Now the second fact or the second point of theory of natural selection is
Struggle for existence
Darwin says that living beings
Multiply exponentially that is from 2 to 4, 4 to 8 and so on
but the food and space
remain almost constant
So this leads to struggle for existence.
There begins competition between the individuals for food shelter
Breeding space and climate
This competition may be between the individuals of the same species
Then it's called
intraspecific competition
or it can be between the
individuals of different species
And then it will be called
interspecific competition.
Now the third fact or third point of the theory of natural selection is variation
The differences between the individuals of a species are called variations
These variations may appear due to the adaptations
shown by the individuals to the available condition or
struggle for existence
or due to heredity because
We know even the offsprings of the same parents are not same
so these adaptations and variations appear, which may be harmful or beneficial.
Now if these
variations and adaptations are
harmful for the individual then their number will reduce
and they can even become extinct gradually.
But if the variations and adaptations are beneficial for the individual then this will help the individual in
struggle for existence
Now the fourth point is or the fourth fact is survival of the fittest
In the struggle for existence the individuals with beneficial
variations and adaptations will survive while the individuals with
harmful variations and adaptations will be weeded out or we can say that gradually they will cease to exist
They will not exist anymore
So it means nature selects the individuals with beneficial variations
Darwin named it as natural selection
Now one more term that is speciation
Little by little these variations and adaptations will cause sufficient
Change in that species over a generation
to change it into a totally new species
So this process will be called speciation.
The other definition of speciation is the origin of new species by
gradual modification.
Thank you!
