human evolution // Ramapithecus, Dryopithecus discovery and cheracteristics.

human evolution

It is the aspect of evolution which is concerned with the emergence of human as distinct species. Various evidence support that humans and apes have descended from common ancestors.

The beginning of primates' evolution is presumed in the Eocene of the Tertiary Period (75-60 million year ago) in evergreen forest and later in Oligocene (25-30 million year ago). Its returns of the ground from the tree due to replacement of evergreen forest into dried savanna-Greenland. thus 

The place of origin of humans is a grate controversial matter. The fossil of ancestral human forms is obtained from the widely diverse regions of Africa, Asia, and Central Asia, China, Java, and India (Shivalik Hills).

Many fossils have been discovered from East Africa (Olduvai Gorge, Lake CIctoria, and Lake Natron in Tanzania and Lake Turkana in Kenya) which indicate a significant role of Africa in regard to the site of origin of human.

Changes During human evolution 

Some changes that took place during human evolution are given below 

(1) Skull and Brain increase in size, complexity, and intelligence.

(2) bipedal locomotion

due to bipedal locomotion forelimbs become free 

(3) Forelimb 

it is modified into an organ of manipulation and lengthening of hindlimbs and shortening of forelimbs.

(4) Thumb

the perfection of thumb opposability in forelimbs.

( 5) Toe 

loss of opposability of great toe in hindlimbs.

(6) Upright posture

becomes of development of the lumbar curve.

(7) Jaw

Power reduction

(8) Teeth

due to omnivorous food habits, the size of incisors and canines reduced.

(9) Chin

development of the chin 

(10) Pelvic girdle

development and broadening of iliac bones of the pelvic girdle.

(11) Social organization

and cultural evolution 

History of human evolution 

The study of living and fossil primates (including monkeys and man) shows that they have descended from a common ancestor and separated from the main stock ( of a homogenization) during the Oligocene period.

The evolutionary history of man can be divided into the following three staps only for the convenience of study 

1. prior to the ape man

2. Apeman 

3. True man (including living modern man)

                            Prior to the ape man 

(1) Propliopothecus 

            *  Discovery : 

                                     fossil obtain from Faiyum deposits of Egypt.

                                    Fossils have Jaws and teeth.

                                    

                                    It lived about 35-30 million yrs ago in the Oligocene epoch.

            Characteristics 

                                  It was more or less ape-like.

                                  These were short-statured with monkey-like teeth.

                                   Their dental formula was 2,1,2,3, i.e. both jaws have 8 incisors, 4 canines, 8                                              premolars, and 12 molars like modern man. 

                                  Their incisor teen was vertical rather than directed forward.

                                 Their molar has 5 cups each.

                                 There are two views regarding ancestry. One says Propliopithecus directly gave rise toRamapithecus, while by another view Propliopithecus gives rise to Dryopithecus which in turn evolved into apes and humans.

(2) Aeggyptithecus 

                  Discovery: 

                                        fossil found from Faiyum province of Egypt in 1980 by E Simon

                     Characteristics: 

                               These were similar to Propliopithecus.

                              These live between 35-33 million yrs ago in the early part of the Oligocene epoch.

                             The predates divergence between hominoids (apes and humans) and old-world monkeys.

Limnopithecus and pliopithecus

                 Discovery

                             Fossils found from Faiyum deposits of Africa.

               Characteristics

                     This existed in Miocene and Pliocene periods.

                    They had a short tail and 7 lumbar vertebrae.

                   They represent altogether a different line of evolution which diverged from the hominid line quite early and become extinct during the late Pliocene.

Proconsul (intermediate between apes and man) 

              Discovery

                  Fossil of proconsul Africanus was described by Louis SB Leakey(1948).

                 The fossils were obtained from the rock of East Africa near Victoria Lake in Kenya. It lives in the early Miocene

                Characteristics

                  The face was prognathous.

  

                 Proconsul walked on its four legs.

             

                   Proconsul had long, point ape-like canines.

            

                   Proconsul has a man like a forehead.

                  Proconsul is not considered as the base ancestor of man because it walked on its four legs.

                 About four million years ago, during Proconsul, proconsul gave rise to the ancestors of chimpanzees and gorillas.

                 Diversion of chimpanzee and gorilla took place during the Pleistocene epoch about 2.3 million years ago.

                                                                   

Dryopithecus

        Discovery

              Fossil of Dryopithecus Africanus was obtained from rock of Africa and Europe.

              

             Recently, a lower jaw of Dryopithecus Africanus was found from Haritalyanga in Bilaspur district of Himachal Pradesh, India.

          Several members of Dryopithecus Africanus has been discovered from Shivalik hills as well.

    Characteristics

        It lived about 15 million years ago during the Miocene.

      

       Dryopithecus Africanus shows close similarity to Chimpanzee.

     Dryopithecus is considered to be a common ancestor of man and apes.

Dryopithecus Africanus was the direct forerunner of man.

   Dryopithecus Africanus is apes with the same length of arm and legs.

  

   Legs and heels in its feet indicate that Dryopithecus Africanus was of a semi-erect posture and Knuckle walker.

    Dryopithecus Africanus was arboreal and herbivorous, which ate soft fruits and leaves.

 

  Dryopithecus Africanus has large canines and incisors.

                                                           

                                                             

 Shivapithecus

      Discovery

                       Fossile of Shivapithecus was discovered from the middle and late Pliocene rock of Shivalik hills of India.     

   Characteristics

                 Its forelimb, Skull, and brain resembled the monkeys.   

                  Its face, jaws, and teeth had a resemblance with those of apes. 

Ramapithecus

     Discovery

                 Edward Lewis (1932) obtain the fossil of Ramapithecus from rocks of Shivalik hills of India.

                 Fossile was represented by a few teeth and some fragments of the jaw.

               Kenyapithecus (Kenyapithecus wicker) similar to Ramapithecus was discovered by LSB Leakey (1955) from Pliocene rocks of Kenya in Africa, but Ramapithecus was older than Kenyapithecus.

       Characteristics

Ramapithecus survived about 14-15 million years ago during the Late Miocene to Pliocene.

Ramapithecus walked erect on its hind legs.

It was similar to ape, which lived on the treetops but also walked on the ground.

It eats hard nuts and seeds like modern man. Its jaw and teeth were similar to humans.

Its canine teeth were small but molar teeth were broad and flattened with thicker enamel.

Dryopithecus gave rise to Ramapithecus , which is on the direct line of human evolution.

Ramapithecus became extinct about 7-8 million years back.

There is a fossil gap of about 9-10 million years in Ramapithecus and Australopithecus.

The fossil record of man's ancestor from the Pliocene are completely blank and once again reappear in the Pleistocene.

# what is the mutation ???????

# example of mutation???????                         

what is mutation? / what is gene flow? / what is non-random mating? define

MUTATION 

It is a sudden and heritable change in an organism. It is generally due to a change in the base sequence of nucleic acid in the genome of an organism. Mutations are considered to be the ultimate source of variation. The mutation may produce a new allele that was not present earlier in the population.

It can also change the frequency of existing alleles. Virtually, any characteristic of an organism can be changed by mutation. However, some mutation is selectable (i.e. conferring them), while others are on-selectable. A selectable mutation confers a clear advantage of the mutant strain under certain environmental conditions. So, the progeny of the mutation cell is able to outgrow and replace the parent cells.

REPLICA PLATE EXPERIMENT TO DEMONSTRATE MUTATION

 The adaptive significance of mutation was demonstrated by Joshua Lederberg and Esther Lederberg (1952) by replica plant experiments. in the experiment, the genetic basis of drug-resistant mutation in the bacteria Escherichia coli was tested.

from a culture of Escherichia coli derived from a single cell, they spread cell onto a 'master agar plate' each cell gives rise to a distant colony.

They place a velvet cloth onto a wooden block and pressed it gently on the master plate. As a result plate of master agar plate was made. then later touched this replica plate to a new plate containing a medium with antibiotic penicillin.

As a result of this most colonies found on the master, plate died due to penicillin. forever, a few colonies appeared on the replica plate. They were penicillin-resistant. Later, all the colonies on the master plate were tested for penicillin resistance, only those colonies that had been the source of penicillin resistance cell on the replica plate display resistance.

This given experiment indicated that some bacterial cells had acquired drug-resistant mutation even before they were exposed to penicillin. Natural selection has selected and supported the progeny carrying the beneficial mutation.

RECOMBINATION

The non-parental arrangement of alleles in the progeny is called recombination. It can result from the independent assortment and crossing over. recombination can occur not only between genes but also within genes resulting in the formation of new alleles in a population.

GENE FLOW

It is the physical movement of alleles into and out of a population. it can be a powerful agent variation because the members of two different populations may exchange genetic material.

some time gene flow is obvious when an animal moves from one place to another. if the characteristics of newly arrived animals differ from those of the animals already there, and if the newcomer is adapted well enough to the new area to survive. Gene flow also keeps separated populations genetically similar.

NON-RANDOM MATING 

in this process, the organisms are mate with each other randomly this phenomenon is known as non-random mating. inbreeding (mating with relatives) is a type of non-random mating that caused the frequencies of particular genotypes to differ greatly from those predicted by the Hardy-Weinberg equilibrium.

Inbreeding does not change the frequency of the alleles, but rather increase the proportion of homozygous individuals. However, the relatives are likely to be genetically similar and thus, produce offspring with two copies of the same allele.

The population of the self-fertilizing plants consists primarily of homozygous individuals, whereas outcrossing plants, (which interbreed with individuals different from themselves) have a higher proportion of heterozygous individuals.

By increase homozygosity in a population, inbreeding tends to increase the expression of recessive alleles. Due to this marriages between close relatives are discouraged and to the same degree outlawed. 

Inbreeding may also increase the possibility of producing children homozygous for an allele associated with one or more receives genetics disorders. 

RANDOM GENETIC DRIFT

It was discovered by American geneticist Sewall Wright. Hence, also called Sewall wright effects. in a small population, frequencies of particular alleles may change drastically by change alone. such changes in alleles frequencies occur randomly as if the frequencies are drifting. This is known as genetic drift. it is usually rare in the case of a large population. Thus, a population must be large to be in Hardy-Weinberg equilibrium.

    Genetic Drift is known to occur when by changes only certain members of the population reproduce and pass on their genes to the next generation. 

Genetic drift fixes new alleles, genes that arise by mutation from time to time, and eliminates the original gene, thereby changing the genetic make of a small population.

 

evidence of connective link // example and detail explanation

 EVIDENCE FROM CONNECTIVE LINKS

A connective link demonstrates the characteristics of more than one group of organisms (taxonomically). Such organisms establish continuity in the series by proving that one group has evolved from the other.

VIRUSES

A connective link between non-living and living is any virus-like bacteriophage (the virus that infects bacteria)

the genetic material of the virus is basically RNA ( ribonucleic acid) 

viruses are non-living organism 

                                      

Affinity with the non-living organism 

(1) Theas can be crystallized like inorganic and organic compounds.

(2) These are unable to respond to external stimuli.

(3) Cell organelles are absent. 

(4) Lack of growth and metabolism.

Affinity with a living organism

(1) These under mutation. 

(2) These reproduce in the living cells. 

(3) These show recombination and heritability.

Euglena

A connecting link between the animals and plant,

reason-based to the connective link between the animals and plant a euglena present the chloroplast basically animals has heterotropic hence animals do not present the chloroplast, but euglena present the chloroplast hence, euglena called the connective link between the animals and plant.

                                               

Affinities with animals

(1) Body is covered by a pellicle.

(2) reproduction is like animals.

(3) some characters are matched with animals.

Affinities with plants

(1) It has chloroplast containing chlorophyll.

(2) Nutrition is holotypic or autotrophic.

(3) It may synthesize food through photosynthesis.

proterosongia

It shares the characters of the group protozoa and Porifera.

                                

Affinities with protozoan and sponges

(1) protozoan characters: Colonial behaviour.

(2) Spong's characters:  Its cells are similar to choanocytes or collar cells of sponges.

peripatus

A connective link between the Annelida and Arthropoda.

                                                

Affinity with annelids

(1) Presence of thick cuticle.

(2) Present of simple eyes.

(3) Body is pseudosegmented and worm-like appearance.

(4) Excretory organ is nephridia.

Affinities with arthropods

(1) Presence of antennae.

(2) Respiratory organ is the trachea.

(3) Presence of clawed and pseudosegmented walking legs.

Neopilina

A connecting link between Annelida and Mollusca. 

                                                       

Affinities with annelids:

(1) Presence of trochophore larva.

(2) Egg divides by spiral cleavage as in polychaetes.

(3) presence of 5-6 pairs of ctenidia, 6 pairs of nephridia, 8 pairs of retracted muscles and two pairs of auricles.

Affinities with molluscs:

(1) Presence of shell and mantle.

(2) Presence of flat muscular fool as found in a chiton.

(3) Presence of soft and dorsoventrally flattened body.

Balanoglossus

A connective link between non-chordates and chordates.

                                                   

Affinities with chordates.

(1) Presence of notochord.

(2) Presence of a dorsal hollow nerve cord.

(3) Presence of pharyngeal gill slits.

Affinities with non-chordates.

(1) Burrowing habit and tubicolous life.

(2) Dorsal position of the heart.

(3) Nervous system is poorly developed and forms epidermal nerve plexus.

Chimaera

A connecting link between bony fishes and cartilaginous fishes.

                                                           

                             

Affinities with bony fish.

(1) Presence of four pairs of gills.

(2) Presence of smallmouth with flesh lips.

(3) cloaca remains absent.

(4) Anus and urinogenital apertures are separate.

 (5) Presence of operculum.

Affinities with cartilaginous fish

(1) Presence of ventral mouth.

(2) Presence of cartilaginous endoskeleton.

(3) Pelvic claspers presence in males.

(4) Presence of 2 dorsal fins.

(5) Placoid scales presence in young ones.

Lung fishes

Lung fishes are the connective link between the fishes and amphibian.

                                                          

Affinities with fish

(1) Fish like appearance.

(2) Presence of paired fins.

(3) Presence of dermal scales.

(4) Presence of gills.

(5) Presence of lateral line sense organ.

(6) Ear is represented by internal air only.

Affinities with amphibian

(1) Presence of internal nostrils.

(2) Presence of lung, i.e. modified air bladder.

(3) Heart with imperfectly divided auricle.

Prototheria

Echidna (spiny anteater) and Ornithorhynchus (platypus) are connecting link between reptile and mammals.

                                                              

Affinities with reptiles.

(1) Presence of cloaca.

(2) They lay eggs, which are reptile in structure and development.

(3) Egg contain enough yolk to nourish in structure and development.

(4) Embryonic development is similar to reptiles.

Affinities with mammals.

(1) Presence of hairs.

(2) They produce milk and nourish their children.

(3) They have mammary glands.

Archaeopteryx

It is a connective link between reptiles and birds. Archaeopteryx is also considered as a missing link because it is a fossil organism. it was found in the rock of cretaceous period by Andreas Wagner (1861) in Germany.

Some reptile characters of Archaeopteryx are given below

(1) Jaw are provided with homodont (similar) teeth.

(2) 

(3) Bone are not pneumatic.

(4) Cervical vertebrae are fewer, 9-19.

(5) Amphicoelus vertebrae.

(6) Cervical and abdominal ribs are present.

(7) Sternum is weak or absent.

(8) Scales are present.

(9) Carpals and metacarpal are free.

(10) Pelvic girdle has an elongated ilium and backwardly directed pubis.

Some avian characters of Archaeopteryx are given below 

(1) Presence of feathers.

(2) Forelimbs are modified as wings.

(3) Rounded braincase.

(4) Beaks are present.

(5) bones in the skull are intimately fused.

(6) Bones of limb and girdle are bird-like.

(7) Tibia and fibula are separate.

(8) v-shaped furcula is present. 

theory of Darwinism

Darwinism

Lamarckism the theory of evolution

natural selection of darwin

embryological evidence of evolution

Hardy-Weinberg equilibrium || polymorphism/ Defination, example.

 specialized supportive tools in speciation 

(1) Hardy-Weinberg equilibrium 

The Hardy-Weinberg law equation theorem is the fundamental law of population genetics.it provides the basis for studying the mendelian population. this law was independently developed by GH Hardy, an English mathematical and  G Weinberg, a German physician in 1908.' the Hardy-Weinberg law state that the gene and genetic frequency in Mendalin population remain constant generation after generation if there is no selection, mutation, migration or random genetic drift.'

Thus, the original proportions of the genotype in a population will remain constant from generation in a population will remain constant from generation to generation, as long as the following assumptions are met

* The population size is very large.

* Random mating occurs. 

* No mutation takes place.

* No gene is input from other sources, i.e. no immigration take place

* No selection occurs. 

Hardy-Weinberg principle gives the generation a tool to determine whether the evolution is occurring or not. population geneticists use the Hardy-Weinberg principle to calculate allele frequency at a starting point and then compare it with the frequencies measured at some feature time. Mathematically, it can be interpreted as a binomial expression p2 + 2pq +q2 to calculate the genotypic and allele frequencies of a population where, 

                                                        p2 = % homozygous dominant individuals

                                                       p = frequency of dominant allele

                                                      q2 = % homozygous recessive individuals 

                                                      q = frequency of recessive allele

                                                     2pq = % heterozygous individuals 

            Realize that (p + q )2 = 1 ( there are only two allele )

p2 + 2pq + q2 = 1 (there are the only genotype) 

Hardy-Weinberg principle says that the sum total of all the allelic frequencies of a gene is 1. Any disturbance in Hardy-Weinberg equilibrium, i.e. change in frequency of alleles would be interpreted as resulting in evolution. 

Example:  An investigator has determined by the inspection that 16% of a human population has a recessive trait. Using this information, we can calculate all the genotype and allele frequencies for the population, provide the condition for Hardy-Weinberg equilibrium are met. 

Given: q2 =16%= 0.4= frequency of recessive allele

p = 1.0 -0.4 = 0.6 = frequency of domiant allele 

p2 = (0.6) (0.6) = 0.36= 36% are homozygous domain individual 

2pq= 2 (0.6) (0.4) = 0.48 =48% are heterozygous individual 

p2+ 2pq+ q2 = 1.00-0.52=0.48

note: Though many other factors can alter frequencies, the above five can alter the proportions of homozygotes and heterozygotes predicted by hardy-Weinberg principle.

only selection produce adaptive evolution changs because only in selection, the result depent on the nature of the envirnment. mutaion, gene flow, genetic drift, etc., operate relatively independent of the envirnment. so. the chang they produce are not shaped by the envirnment demands.

2 POLYMORPHISM   

It is defined as the existence of two or more from or phenotypes of the species within the same population. Polymorphism can apply to biochemical, morphological, and behavioral characteristics. it also plays a significant role in the process of natural selection. 

Polymorphism in a population may develop due to the following reasons 

* Changes in the environment. 

* Superiority of heterozygotes. 

* mutation pressure, which may introduce a variety of alleles.

* frequency-dependent selection. 

polymorphism is of following two types

TRANSIENT POLYMORPHISM

This arises when the difference from or morphs, exist in a population undergoing a strong selection pressure. The frequency of the intensity of the selection pressure, such as the melanic and the non-melanic forms of the peppered month. the distribution of insular, i.e. an intermediate variation of the peppered moth. Transient polymorphism usually applies in the following situation polymorphism usually applies the following situation 

(1) When one form is gradually being replaced by another.

(2) A newly arose mutation is found to be advantageous and is favored by selection. it spread through the population and become more abundant, while the population wild type is becoming rare due to negative selection. 

(3) In a changing environment, a previously rare form may become advantageous and is favored by selection. it spread throughout the population.

BALANCE (STABLE) POLYMORPHISM 

This occurs when different forms coexist in the same population in a stable environment. Like the existence of the two sexes in animals and plants. These genotypic frequencies of the various polymorphism forms exhibit equilibrium since each form has a selective advantage of equal intensity. some example is

(1) ABO blood groups

in humans, the existence of the a, b, ab, o, blood group of an example of balanced polymorphism. however, the genotypic frequencies within a different population may vary, they remain constant from generation to generation within that population. This is because none of them have a selection advantage over the other. statistics reveal that the white men of blood group o have a greater life expectancy than those of other blood groups. However, interestingly they also have an increased risk of developing duodenal ulcers, which may perforation and lead to death.

(2)  sickle- cell anemia in some regions of the world (e.g. part of Africa) where malaria is caused by plasmodium falciparum, natural selection favors heterogonous allelic people over both homozygotes.

(3) Tay-Sachs disease 

it is common in children of Jewish heritage because one out of 40 Jewish heritage person is a heterozygote, where is one out of 380 non-Jewish people is a heterozygous carrier. this is because the grandchildren of a person suffering from Tay-Sachs disease were resistant to pulmonary tuberculosis in Bethesda Maryland. The incidence of Jewish tuberculosis patients from Eastern Europe is relatively high. This finding indicates that heterozygous carriers of Tay-such disease are resistant to pulmonary tuberculosis.

                                                                         

other examples: red-green color blindness in humans, the existence of workers, drones, and queen in social pin eyed and thrum-eyed from in primrose, etc. 

#Hardy-Weinberg equilibrium important 

#HarHardy-Weinberg equilibrium equation

# Hardy-Weinberg equilibrium example

#Hardy-Weinberg equilibrium  information 

 

natural selection/ definition, characters, industrial melanism, and example

 NATURAL SELECTION :

some genetic variability is always presence in a population in a population. such alleles make organism better adapted to the environment leading to their survival and continuous reproduction. 

The frequency of such alleles in a population, thus increase gradually. this process in called selection. if the breeders selection for the desired characteristics it is Artificial selection, and if the environment condition operate operating the natural population it is said to be natural selection.

condition for natural selection :

for natural selection to occur and result in evolutionary charge, three condition must be met 

(1) variation must exist among individual in a population. natural selection works by favouring individual with some traits over individual with alternative traits. if .

(2) variation among individual result in difference in the number of offspring surviving in the next generation. this is the essence of natural selection. it means that some individual are more successful than other in producing offspring and thus, passing their genes on the next generation because of their phenotype or behaviour. 

(3) variation must be genetically inherited for natural selection to result in evolutionary changes . even genetically identical individual may be phenotypically quite distinctive, if they grow up in different environment.

therefore, when phenotypically difference individual do not differ genetically, then differences in the number of their offspring will not alter the genetic composition of the population in the next generation. hence, no evolutionary charge will occur. 

types of natural selection :

there are following three kind of natural  selection 

(1) stabilising / normalising selection :

this occur when the environment does not change and favours the individual possessing the value of the mean characters. thus, natural selection produces value. thus , natural selection process change in favour of those individuals which posses an intermediate form of trait, while elimination extremes form the population.               the stabilising selection pressure does not promoting evolutionary charge but tend to maintain phenotypic stabilising within the population from generation to generation. fossil evidences suggest that many species remain unchanged for long periods of geological time.                                                                                                  for example : coelacanth (a fish species) was assumed to have been extinct for 70 million years until a living specimen was found in a trawler net of south Africa in 1938 . so, this species has not changed in all the time. 

another example of stabilising selection can be be seen in the birth weights of human. the heaviest and lightest babies have the highest mortality and are less likely to survive to reproduce and pass on their alleles. 

(2) directional selection 

this occurs whenever the environment change in a particular direction. thus, natural selection production change in a fever of one extreme while elimination the extreme. therefore, thare is a selective pressure for species to change in response to that environment change, e.g. industrial melanism.

 industrial melanism : 

the term refers to the evolution of dark body colour in animals species that live in habitats blackened by industrial soot. the occurrence of industrial melanism is closely associate with the progress of the industrial revolution in a grate Britain during 19th century. it has occur in several species of moth. of this, peppered moth ( Biston betularia) is the most intensive study. thes on existed in 2 variety, i.e. light coloured (white) and dark coloured (black). before the emergence of industrialisation, the with moth were numerous than dark moth in Britain. 

                                                            

however, after industrialisation , i.e. in 1920 the condition was reversed. this was due to the fact that, white moth were easily spotted by predation (birds) on soon covers tree trunk, so there population decrease and the population of black moth increase. we can also say that black moths got naturally selected. Disruptive/ Diverging selection. 

this occurs where an environment change may produce selection pressure that favours two extreme characteristics. 

some of the examples of disruptive selection are given below grass plant of welsh copper mine grew in soil. 

contaminated soil by copper which was lethal to the normal grass plant. however, a chance mutation allowed one plant to grow. this plant prospered and reproduced, but only on the contaminated soil. on normal soil, it grows more slowly than the normal plant and was easily out-competed. so, now there are two varieties of grass plant growing close together. 

sickle- cell anaemia:

people who are homozygous for this recessive allele, usually die before reproduction. their red blood cell contains abnormal haemoglobin, which makes them become a sickle-shaped and stick in their capillaries. people heterozygous for the allele are at a disadvantage because their red cells becomes sickle-shaped during exercise due to lack of oxygen. 

the allele should therefore, be selected again and rare, however, its frequency is a high is a part of the world, where malaria is common. people heterozygous for sickle cell anaemia are more resistant to malaria than people homozygous for a normal allele because the malarial parasite is not able to survive to sickle-shaped RBCs, hence, where malaria is found, people with heterozygous alleles are at advantage. 

# natural selection 

# natural selection importance

#natural selection example

Darwinism or Darwin's theory of evolution /postulates of Darwin || definition , natural selection ,speciation , example.

DARWINISM  OR DARWIN'S THEORY OF EVOLUTION :

after collection a vast amount of information, Darwin began to realised that under the intention competition of members in a population, any variation, which favour survival in a particular environment would increase the individual ability to reproduce and leave fertile offspring. a less favourable variation would be at disadvantage and organism possessing them would, therefore, have decreased chance of their successful reproduction. 

this data provide Darwin with the framework to formulate, a theory of evolution by natural selection in 1839. he did not publish his finding at that time. indeed, Darwin greatest contribution to science was not so much to show that evolution occurs but how it might occur .

in the meantime, another naturalist Alford Russel Wallace, came to the same conclusion as Darwin regarding natural selection . in 1858, Wallace wrote a 20 pages essay outlining his theory and send it Darwin. Darwin and Wallace presented paper on their ideas at a meeting of the Linnea Society in London

in November 1859 Darwin publish his thought on evolution in 'Origin of Species ' by the name of natural Selection.

                                        

POSTULATE OF DARWINSM :

the main postulate, which formed the basics of Darwin theory of natural selection are as follows

overproduction (rapid multiplication) 

  All organism possess enormous fertility. they multiply in a geometric proportion with some organism producing very large number of species. Despite of this high rate of reproduction of a species, its number remain constant under fairly stable environment. the production of more offspring by some organism and fewer by other is termed as differential reproduction.

limited resource:

the resource like food, space, etc. remain limited inspite of rapid multiplication of the individual of all the species.

struggle for existence : 

the limited resource present in an environment are the main cause of struggle for existence, which may occy at following three levels. 

intraspecific struggle :

it is the struggle among the individual of same species for their common requirement like food, shelter, mate, breeding, places, etc. intraspecific struggle is very severe, e.g. young tree in a forest, cannibalism, (eating individual of its own species), human wars, etc. 

interspecific struggle : it is the struggle between the individual of different species for their similar requirement like food and space. for example, a frog feed on insect and it prayed upon by snake while kite feed on both as well as snakes. 

environmental struggle : it is the struggle of living from against the environment condition like extreme heat, cold, drought, earthquakes, storms, disease, volcanic eruption, etc. 

4 appearance of variation :  

all individuals are dissimilar in some of their characters except the identical twins. this dissimilarity is mainly due to the variation . 

those are the small or large difference among the individual . variation allow some individual to better adjust with their environment. 

variation can be categorised into following type 

somatic variation : these variation affect the somatic cell of an organism. they are also called modifications or acquired characters because they are caused by various environment factors, use and disuse of organs and conscious efforts, etc.

germinal variation :  these are inheritable variation recognised by Darwin . they are formed mostly in germinal cell . they are further two type 

(a) continuous variation : these are fluctuation variation, which oscillate due to race, variety and species .

(b)discontinuous variation : these appear suddenly and show no spots gradation . this variation were termed as' spots ' by Darwin and Mutation by Hugo de Vries . Darwin regarded continuous variation to be more important because the discontinuous variation being mostly harmful would not be selected again. 

the organism which are provide with favourable variation would survive, which the unfit are destroyed. originally it was an idea of Herbert spencer (  1820-1903) who used the phrase ' survival of the fittest ' first time Darwin named it natural selection. 

survival of the fittest refers to the idea that the natural selection tents to favore those organism that are most fit to survive with the reproductive age in a particular environment and to produce offspring. 

for example, according to the theory of Darwin , the long necked giraffe evolved due to natural selection. 

                                                   

                                                              

he started that initially both long neck and legs and short neck and leg containing giraffes were present , but due to the scarcity of grass on land ,they had to feed on the leaves of tall trees. 

Now giraffe with long neck and longer legs could get food more easily and better change of survival . as a result, long neck and legs containing giraffes become abundant  and giraffes with short neck legs become extinct . 

the giraffes which short necked and limb soon died due to starvation when climate change due to their natural selection .

evidences of natural selection :

  it has the following evidence 

(1) rate of reproductive , limitation of resources , competition and struggle for existence for existence can be seen in natural normally.

(2) abundance of variation is evidenced by the absence of two similar individual except monozygotic twins , which also show some environmental variation 

(3)  preproduction of new varieties of plant and animals through artificial selection . these show evidence that the natural having vast resources can easily that the natural having vast resources can easily produced new species through the natural selection . 

(4) pedigrees of some animals (horse, camel, elephant), mimicry and protective colouration also supports natural selection. 

formation of new species (speciation) 

Darwin considered that as a result of struggle for existence, variability and inheritance, species become better adapted  to their environment . this beneficial adaptation are preserved and accumulation in the individual of species generation after generation . this result into the origin of species or speciation.  

Lamarckism and Lamarck theory of evolution / postulate of Lamarckism / theory, example , definition and question related to Lamarckism

LAMARK AND LAMARCKISM:

the first attempt to explain the origin of species and their adaptation to the environment was done by French naturalist Jean Baptiste de Lamarck (1744-1829). he gave the first theory of evolution known as Lamarckism or the theory of inheritance to acquire characters. it states that all changes, which organisms acquire during their lifetime, are transmitted to their offspring by the process of inheritance. Lamarck believed that a nervous fluid within each species helps to progress up the change of being. the more strongly exercised organ attract more of the nervous fluid which in turn enlarge this organ and such alternation are inherited. 

Lamarck publishes this theory in 1809 (the same year of Darwin's birth )in his famous book "philosophy zoologique". he also introduces certain terms such as invertebrates, vertebrates, and Annelid. 

POSTULATE OF LAMARCKISM 

the theory of inheritance of acquired characters was explained by Lamarck using four main postulates. 

these postulate along with the classical example of the evolution of long necks is in giraffes are as follows

1 internal vital force

organism and their organ have a natural tendency to continuously increase in size, generation after generation. for example, the ancestors of parent day giraffes were bearing small neck and forelimbs. however, these had an internal vital force to increase their size and become relatively larger in due course of time.

effect of environment  and new needs 

continuous change in the environment condition directly influences the nature, habit, way of living, of an organism, and their structural organization. for example, early giraffes used to feed on the grasses and other surface plants of an area. with time the climate of these areas becomes arid. it means that the grasses and other surface vegetation dried up living only a few taller trees. thus, the leaves of these tall trees were the only food available to ancestors. it is called the doctrine of appetency | desire.

                                           

 

uses and disuses of organ 

the grown of less used part decline, while that of better-used part progresses. for example, to full fill their new need the giraffes continuously stretched their neck to reach the taller trees. as the necks were comprehensively used to reach to the tree, its permanent elongation took place and the character was acquired. 

                                                                          

inheritance of acquired characters

the growth of organ ( either better or poorer) acquired during the lifetime of an organism in hereditary. as in the case of giraffes where, the acquired characters, i.e. along the neck was transmitted in the next generation.

                                                       

other examples in Favour of Lamarckism 

snakes: the present day limbless snake with a long slender body were developed from the limbed ancestors. it is due to continued disuse of limb and stretching of their body to suit their creeping mode of locomotion and fossorial mode of living. 

aquatic bird: aquatic bird-like ducks, geese, etc. developed, from their terrestrial ancestors by the inheritance of acquired characters like a reduction of wings due to their continued discus, development of webs between their toes for wading purposes, etc. these changes were mainly induced due to the deficient of food on land and severe competition. 

flightless birds: the development of flightless birds like an ostrich from flying ancestors is considered due to continued disuse of wing as they were found in well-protected areas with plenty of food. 

flat fishes : these are deep sea fishes present at the bottom of sea where there is no sunlight . they lead an inactive life. 

whales : they lost there hind limb as the consequence of there disuse.

wading bird :  they developed long legs through the generation of sustained stretching to keep the body above the water level, example : jacana bird  

cave dwellers : eyes are reduce in cave dwellers ( mole ) since , they live underground. 

Emergent hydrophytes :  in emergent hydrophytes like a ranunculus aquatilis the submerged leaves are dissected while the emerged ones are simply lobed. when the plant is grown out of water , all the leaves are undissected. in the submerged environment, all leaves are dissected.

there are other effect also, such as vestigial organ in some living animals, strong claws and canines in carnivores, sensitive skin and tactile point on the ventral side of the body and callosities of palm in hard workers, exemplifying the Lamarckian theory.

this is all about Lamarckism above example are common example to gives the Lamarckism theory . 

to under stand more about above topic we are to gives some question are related with Lamarckism theory.

(1) the term 'evolution' was first used by? 

(a) spencer

(b) Darwin

 (c) Lamarck

(d) Mendel

solution: the term evolution was first used by spencer 

Q(2) ' Phiosophie zoologique' was written by?

(a) De varies 

(b) Lamarck 

(c) Mendel 

(d) Spencer

solution: phiolosophie of zoologoque was written by Lamarck 

(3) according to the Lamarck , acquired characters are? 

(a) inherited 

(b) artificial

(c) superficial

(d) all of the above

solution : inherited 

(4) whose theory of evolution believes  that every organism has an internal vital force?  

(a) Darwinism 

(b) Lamarckism 

(c) de varies theory 

(d) all of the above

solution : Lamarckism 

embryological evidence of evolution / definition , example and micro information about evolution..

EVIDENCE FROM EMBRYOLOGY

hi friends we discuss evidence from embryology .always we are interested to know about evolution then this information is able to know about evolution lets get started.

simple meaning: embryology is the study of the development of an organism from zygote to adult .. it may also provide evidence for evolution  .. the evidence based on the comparative study of the embryos of various animals are as follows.

HOMOLOGY IN EARLY DEVELOPMENT :

a common pattern of development is found in all the multicellular organism .. the development of embryos start from a unicellular zygote or fertilized egg.. the zygote undergoes repeated cleavage or call division to form solid ..structure call as a morula. (maybe fruit like structure ) the morula la divide to form blastula it means a single hollow structure, which finally developed into gastrula it means two or three-layered structure.

animals which two-layered are termed as diploblastic .. and the example is coelenterate and next is the animals which three-layered gastrula is found are known as triploblastic and the example is frog and lizard and after this, the process gives rise to an entire body or animals ..thus the similar early embryological development shows the close relationship among all the organism ..

RESEMBLANCE AMONG VERTEBRATE EMBRYOS:

it the comparative study of embryos of vertebrate at the same age is done, it is observed that they resemble one another same similarities in the early embryonic stage are as follow 

1: present of gills clefts, notochord, tail, rudimentary eyes, etc. in all vertebrates from fishes to mammals.

2:after the notochord is replaced by a vertebral column in all adult vertebrates..

3: gill are replaced by lung in adult amphibian , reptile and mammals 

RESEMBLANCE AMONE INVERTEBRATE LARVAG

this process that , in larval stages of invertebrates has common ancestor . it simple means that the larval stages of some invertebrates has same in starting state but has development after maturity this animals are look like a different but they same in origin hence this call as common ancestry ..

 [ this common ancestry shoes above image see this images and get understand .. ] example : annelids and molluscum passes a similar type of larva it called as trochophore  .. similarly echinoderm and hemichordate also have a similar larva it indicate common ancestry..

this  are come example shoes common ancestry in invertebrates in larval stages ..

PROGRESSIVE METAMORPHOSIS :

progressive metamorphosis : in process of metamorphosis animals growth are done progressive in the flow of evolution .

example: ammonocete larva of a lamprey resembles the adult of the amphioxus or group of branchiostoma in most of the details ..this is possible only if presume only that lamprey has evolved from branchiostoma loke animals ..

RETROGRESSIVE METAMORPHOSIS :

retrogressive metamorphosis : in the process of retrogressive metamorphosis degenerative changes of active larva metamorphosis to a new adult it simple mean that the chordate characters are also in a larva stages ..

the adult ascidian { ex. herdmania } are derived the a retrogressive metamorphosis of tadpole larva .. due to this the most of the chordate are lost ..they may show some chordate affinities .. in those organism larva has helped in phylogenetic relationship .. this ascidian tadpole larva is free swimming and asses all the three characters this is notochord , nerve chord and myotome .. thus , it may be place in group chordate..

NEOTENY: 

the condition in which larval fail to undergo metamorphosis , instead develop gonads and attain sexual maturity .. in simple mean sexual maturity of animals in development stage is decline or the grown of the organism body part development is slow in maturing sate it call is neoteny .. reproduction in such larval form is  call as paedogenesis .. 

example : axolotl larva of  ambystoma..

TEMPORARY EMBRYONIC STRUCTURE :

some structure are temporary in embryos  , which remain absent in adults ..

example :

1 : birds embyo has tooth buds and gill clefts , which remain absent in adult ..this shows , that the birds may have evolved from toothed ancestors , which ware lost during evolution ..

2 : the embryo of whale possesses hairs , which remain absence in adult ..this hears are shed before birth ..

RECAPITULATION THEORY OR BIOGENETIC LAW :

in this process the development of embryo in development stage to maturing stage stats that as below_____

karl ernst von baer { father of modern embryology } in 1828 publish the bears law or von brars law of embryology to explain the details and development  of embryo.

this important statement proposes in this law are as follow

[1]:during development , general characters appear before specialised characters in following manners .

more general to less general to specialised ..

[2]:during development , animals progressive depart from the form of animals ..

[3] :organism of different group share resemblance among thaire embryonic form ..

in 1866 , earn haeckel  postulate biogenetic law or  recapitulation theory by coming the idea of darwine evolution and bears law ..biogenetic law states that the ontogeny .. i.e . development of embryo in the recapitulation  of phylogeny ..

some examples of development evidence of evolution ..

[1] presence of fish , like characters eg. gill ,gill slits, tail ,tail fin , lateral line  and sense organs in tadpole larva of frog 

[2]presence of filamentous green algae like structure , i.e protonema during development stage of funaria { moss} ...

[3] pteridophytes , primitive gymnosperms and animals having flagellated sperm and  they depend on the water for fertilisation  

[4] adult frog excreta urea , whereas tadpole excreate ammonia as in fishes ..

[5] birds generally secret uric acid , but embryo excreat ammonia first and urea later on  ..

[6] in south american mouse secret uric acid as apest from this bird excreata as in the pest formate ..