Mwl Marco

 EVOLUTION

Evolution-is the process of change by which new species are formed from pre-existing species.

It explains how life forms have developed and why organism show both differences and similarities

 Organic evolution is a gradual change in the genetic composition of organisms in a population during successive generations leading to formation of new species from preexisting species.

SCHOOL  OF THOUGHT ATTEMPTED IN EVOLUTION

• .It believe that the present-day organisms are the same as those which appeared on the Earth.mean each species is unique in structure and form from the rest of the species.
• .Believes that the present-day forms of life are different from those which first appeared on the Earth.It implies that the first form of life have undergone changes( evolved) so that the present-day organism are quite different from those which appeared on the Earth

THEORIES OF ORIGIN OF LIFE 

 1 Special creation

This suggests that the Earth and all the organism on it were created by a single event by a super-being or God

Means that

•  Species are immutable (not changing)
•  Life was created by a supernatural power at a particular time i.e. God made living things once upon a time and whatever is existing today is a result of reproduction. If God wants a new species he just

Strength of the theory:

i Faith i.e. believing and accepting this with no evidence.

Weakness of the theory:

i Cannot be proved or disapproved by science as science goes with experiments and observation.

2. Spontaneous Generation

This suggests that living things arose from none-living materials on a number of distinct occasion

•  This theory was common in ancient Chinese, Babylonian and Egyptians 
•  Nature passes from lifeless to animals in an unbroken sequence. 
•  Particles of matter contained an active principle which could produce a living organism under favourable conditions. This active principle was present in fertilized eggs, seed, sunlight, wheat, decaying meat, natural forces and decaying earth, mud.
•  Van Helmont (15th century) did an experiment which gave rise to mice in 3 weeks; the raw materials were a dirty shirt, wheat grains and a dark cupboard. The active principle was thought to be human sweat

Strength of the Theory

i. Life arises from non-living matter on a number of separate occasions.

Weakness of the theory

ii In the experiments, there were no controls, in which each variable could systematically be eliminated.

3. Cosmozoan theory (Panspermian theory)

This based on the the idea that life arose somewhere else in the universe and arrived here from outer space by some means

There has been an extra-terrestrial organ i.e. life arose on this planet from somewhere else. life could have arisen once or several times at different times and on several parts of the universe.

Strength of the theory

- The sightings of UFO’s, care drawings of rocket like objects and ‘spacemen’ and reports of encounters with aliens provide the background for this.

Weakness of the theory

-The theory does not talk about the origin of life but perpetuation of it.

4.Steady State

This theory states that the planet Earth and all the organism on it have always been here.Therefore there has been no origin of life

Means

•  Life has no origin
•  This theory assets that the Earth had no origin, has always been able to support life, has changed remarkably little, if at all and that species had no origin 
•  This theory proposes that species never originated, they have always existed and that in the history of species the only alternatives are for its nos. To vary, or for it to become extinct.

5.Organic evolution

This theory suggests that life arose from the evolution of simple organic molecules into more complex ones and their ultimate evolution into cells

Strength

It is accepted to day because  of evidence from experiment

THEORIES AND MECHANISM OF ORGANIC EVOLUTION

The main idea of organic evolution is that population of living things undergo changes over generation.

FORCES/PRESSURES LEADING TO ORGANIC EVOLUTION

1. PRIMARY FORCES:

 Are the ones which must be there for new species to be formed from pre-existing species. Thus, if absent no organic evolution takes place.

These forces include:

•  Mutation 
•  Gene recombination 
•  Natural section
•   NB: Natural selection must be present with either one of the two forces (mutation and or gene recombination)

     2. SECONDARY FORCES:

These are forces that modify rate of organic evolution i.e. if present, rate of evolution of the species are faster, but it absent the rate is slower.

These include:

i. Gene flow

ii Genetic drift

iii Breeding

iv Adaptive radiation/geographic isolation

There are two main theories of organic evolution

i. Lamarckism

ii.Darwinism

1. LAMARCKISM THEORY OF  EVOLUTION

His account for mechanism of evolution is based on the following:

1. Change in the environment creates new needs

2. Use and disuse of organs (organs are elastic)

 3. Inheritance of acquired characteristics.

USE AND DISUSE OF ORGANS

-Natural use and disuse of structures; If used it develops (Becomes stronger, bigger and better); If unused it weakens and disappear (vestigial organs). e.g. use = neck of giraffe; unused; wings of ostrich, kiwi and emo.

-All that has been acquired or altered during lifetime is transmitted to the next generation, resulting to emergence of new species. i.e. acquired characters can be inherited.

.

How changes in the environment create needs?

• Animals and plants respond to the environment by becoming better adapted to them.
•  As environmental conditions change it may lead to changes in behavioural pattern which can require increased use/disuse of certain organs. 
•  Those organs which are frequently used will become stronger and develop and vice versa. 
•  Developed structures are inheritable thus acquired characteristics e.g. webbed feet in ducks, long necks in giraffes, limbless, snake

Example

i The long neck and legs of modern giraffes were the results of generations of short necked and short legged ancestors feeding on leaves at progressively higher levels of trees.

ii The slightly long necks and legs produced in each generation were passed onto the next generation.

In a course of time, the whole population contained long necked and legged giraffes which we see today.

Hence they are evolved.

Fig evolution of long neck giraffe

ii The case of webbed feet ducks also applies.

Fig. web in leg of duck

iii.limbless, snake

Fig evolution of limbless snake

Strength of theory

•  He was correct by saying that change in environment creates new needs e.g. webbed toes. 
•  The theory was useful in bringing up the idea of evolution i.e. created the foundation for Darwin and Wallace. 
•  This theory applied explained the existence of vestigial organs i.e. when not in use; the organs will disappear or become non-functional. 
•  He emphasized on the rate of the environment in producing the change in the individual.
• Weakness of the theory

-Modern genetics show how that phenotypically acquired characteristics, which do not affect the genotype of the individual, cannot be inherited, eg. Such objectives came from Weisman who did experiments with mice. He cut off tails of mice for 21 generations but could not find tail less mice offspringsExample. The son of a boxer would not necessarily be a boxer, because the change in the environment led to the change in behavioural pattern which did not

affect the gametes which were means of passing the straits to the next generation.

2.DARWIN'S THEORY

-Charles Darwin and Alfred Wallace, two British Biologists working independently came up with similar observations and conclusion which is referred as “Natural Selection”. Darwin explains this in his book titled “Origin of Species”. Darwin made a long voyage for five years as naturalist on a British Warship, which was to sail around the world on a map making survey. During the journey he made numerous observation on living organisms and collected specimen. He also read essay by Malthus on population, i.e. the human population increases much faster than its food supply. Natural events like famine, diseases, floods, and accidents keep the population fairly constant. This gave him basic ideas on natural selection.

Darwin observed that; number of offsprings are always bigger than that of parents but only few offsprings survive to adulthood and are able to reproduce. For him in any given environment there are limiting /eliminating factors like competition for food, space, diseases or predators.

Therefore in life there is always “struggle for existence” and “the survival for the fittest”.

The main points of Darwin’s Theory of Evolution are;

•  Overproduction of offsprings than the environment can support.
•  Struggle for existence i.e. competition for the limited resources like food and space, light, water. The struggle can be within the same species (intraspecific) or between different species (interspecific).
•  Only the fittest survive while the less adaptive are eliminated due to natural selection.HENCE  Survive for fittest
• Natural selection is by chance i.e. not controlled by the individual or environment necessarily.
• Variation; the natural selection brings about variation may be due to genetic or environment. Variation can be useful or harmful.
•  Inheritance of useful variation to the next generation which will also produce variations (continuous selection).
• Origin of new species; finally variations become so large due to continuous selection, hence results in organisms very different from the ancestor i.e. completely new species is formed.

Selection is a process by which organisms, which are better adapted to surrounding, survive and breeds, while those less adapted fail to do so.

Importance of selection:

It has adaptive significance in

1. Perpetuating those organisms’ with better traits and thus ensure survival of these organisms.

2. Selection determines which genes (alleles) pass to the next generation by virtue of the differential advantage; they exhibit as expressed as phenotypes therefore Selection pressure increases or decreases the spread of alleles, within the gene pool and the changes can be evolutionary.

TYPES:

1. Natural selection

2. Artificial selection (selective breeding)

1.NATURAL SELECTION

i Is a selective force such as natural disasters (drought, floods, earthquakes, diseases, fire), competition for food, water, mates, breeding areas operate on the variations are selected out by natural selection.

ii A greater proportion of the offspring in the next generation will be products of the suitable variants. This leads to changes in the gene frequency of the population, which can lead to evolutionary change.

2 ARTIFICIAL SELECTION

i. Man selects animals and plants with traits he wants for mating, propagation, and pollination.

ii. The individuals lacking desired qualities are prevented from mating by sterilization, segregation.

iii Members of the species selected are those that show favourable variations such as increased yield of eggs, milk, fruits, wool, early maturity such as cereal crops, resistance to diseases and hardness.

iv Man exerts a directional selection pressure which leads to changes in alleles and genotype frequency within the population.

Importance: Continued selective breeding by human has produced varieties, new breeds, strains, races, sub-species of animals and plants of agricultural importance.

Types of Artificial Selection

i Inbreeding

 ii Out breeding

1.INBREEDING:

•  Inbreeding is a process involving selective reproduction between closely related organisms in order to retain and propagate the desired traits e.g. between offsprings produced by the same parent. 
•  It is practiced in breeding show animals such as cats and dogs. It is used by livestock breeders to produce cattle, pigs, poultry and sheep with high yield of milk, meat, eggs, wool resp.
•  Prolonged inbreeding can lead to reduced fertility especially when breeding livestock. 
•  It can lead to reduced variability of the genome (sum of alleles of an individual

Solution

i Resort to out breeding after several generations of inbreeding.

Forms/mechanisms of inbreeding:

iiSelf fertilization

2.OUTBREEDING

i Involves crossing individuals from genetically distinct organisms i.e. between different varieties or strains and sometimes closely related species.

ii The offspring’s of such a cross are hybrids. It is applied mostly in plant breeding and commercial production of meat, wool and eggs.

iii The hybrids show hybrid vigour (phenotypes show traits which are superior to either of the parental stocks. Increased vigour results from increased heterozygosity in gene mixing.

Limitations of out breeding:

Interbreeding F1 for a long time decreases hybrid vigour (heterozygosity) due to increase in homozygosity.

Observations

1. Individuals within a population have a great reproductive rate.

2. The number of individuals in a population remains approximately constant due to environmental factors such as food, space, light, water, breeding sites, etc.

3. Variations exist within individuals in a population.

4.Those surviving individuals have a reproductive advantage and will give rise to next generation which are better adapted to the environment.

Deductions

i From 1 and 2, many individuals fail to survive or reproduce therefore there is “struggle for existence” due to competition.

ii From 3 and 4, in the struggle for existence, individual showing variation has adapted to the environment and will be favoured than others, who are not adapted.

Strength of the theory

iii In absence of environmental factor every species tends to over produce remains fairly constant

iv High mortality rate especially in young occur and so only a few reach the reproductive age.

v Competition occurs between organisms for the available resources and therefore there is struggle for existence.

vi There are variations among individuals.

vii. In struggle for survival individuals with variation will reach reproductive maturity.

viii Favorable traits of these individuals will be passed on to the next generation and thus the survival of fittest.

Weakness of the theory:

•  The theory does not explain the (origin of the specie) 
•  The theory does not explain the (existence of vestigial) structure. 
•  According to the theory, the cause of imp (variations) complex structures among individuals which result information of new species are not explained e.g. imitation, polyploidy and meiosis) 
•  The theory is silent on how (variations are passed) to the offsprings from one generation to the next. 
•  The theory does not explain on the (survival of the unfit individuals) in nature that reaches reproductive age.
•  The theory does not explain (how natural selection occurs) 
•  Does not explain how variations arise.
•  Does not explain the difference between environmental and genetic variation.

According to Darwin:

i There are many populations of giraffe which could progressively reproduce.

ii However, their number remains constant

iii. The giraffes were of many variations; some short, long and middle necked so in the struggle for existence, the short and middle necked would not survive and die out therefore the survival of fittest. iv Long necks would reach for higher trees and therefore reproductive age and the next generation were of many giraffes with long necks, where as the short necked giraffes perished and in course of

time, due to natural selection, we have the long necked giraffes at present.

v Similar explanation for development of webbed feet in duck and development of limbless snakes.

 3.NEW-DARWINISM THEORY.

-When Darwin and Wallace formulated their theory of evolution, they had no knowledge of modern genetics i.e. Not able to tell why variation between the members of the same species or same family (offspring) or why some variations are inherited while others are not.

Modern genetics show that process of evolution can be traced to mutation (changes in genes or chromosomes). Such changes occur suddenly and randomly leading to new species.

Neo-Darwinian theory; Evolution is genetic changes that occur in a population over many generations and not changes that occur in a living organism during its lifetime.

Theory of mutation was proposed by Hugo De Vries (1901) with following points;

1.      Mutation (variation) appears suddenly and become fully operational immediately.

2.      Some mutation may appear in number of individuals.

3.      Useful mutation allows the organism to be selected by nature that is we call adaptive variation.

4. Punctuated Equilibrium Theory.

-Was proposed by Stephan Gould and Niles Elddredge. For them normally a species remain stable for a long period of time (Equilibrium) but often sudden and unpredictable changes spring up (Punctuate) giving rise to new structures or new species. This explains the absence of intermediary (in between) groups in the fossil records. The theory contradicts Darwin’s theory that evolution occurs continuously and gradually over a long period of time.

ORIGIN OF SPECIES

SPECIATION

Speciation is a process by which new species are formed from pre-existing species.

Alternative ways of defining a species:

 Breeding A group of organisms capable of inter breeding and producing fertile offspring Ecological A group of organism sharing the same ecological niche; no two species can share the same ecological niche Genetic A group of organic showing close similarity in genetic karyotype.

 Evolutionary A group of organic sharing a unique collection of structural and functional characteristics from certain ancestors.

Types of speciation

(a) Allopatric Speciation:

• Characterized by the occurrence at some stage of spatial separation. Geographical barriers may produce a barrier to gene flow because of spatial separation. 
• This inability of organisms or their gametes to meet leads to reproductive isolation drift in small populations lead to changes in allele and genotype frequencies. Prolonged separation of populations may result in them becoming genetically isolated even if brought together and thus arising of new species.Example, the variety and distribution of the finch species belonging to the family Geospizidae on the Galapagos Islands. It is suggested that an original stock of finches reach the Galapagos Islands from the mainland of S. America and, in the absence of competition from endemic species. (Representing relaxed selection pressure).
• adaptive radiation occurred to produce a variety of species adapted to the particular ecological niche. The various species are believed to have evolved in geographical isolation to the point that when dispersal brought them together on certain islands they were able to coexist as separate species.
•  Involves evolution/formation of species as a result of population being separated by the geographical barrier.

(b) Sympatric speciation

•  Genetic differences may accumulate allopathically in populations which have been geographically isolated for a much shorter period of time. If these populations are brought together, hybrids may form where these overlap. E.g. both the carrion crow and the hooded crow are found in the British Isles. 
•  The carrion crow is common in England and Southern Scotland. The hooked crow is found in the north of Scotland. Hybrids formed from the mating of the two occupy a narrow region extending across central flow between the populations of the 2 crows.
•  In time selection against cross-breeding may occur leading to speciation in the same geographically area, hence sympatric speciation. 
•  This speciation does not involve geographical separation of populations at the time at which genetic isolation occurs. It requires the development of some form of reproductive isolating mechanism which has arisen by selection within a geographically confined area. This may be structural, physiological, behavioural or genetic.
•  Involves formation of new species not involving any geographical isolation, but formed by other isolations e.g. physical.

(c).Genetic recombination brings about variation to crossing over between non sister chromatids prophase I & meiosis, random assortment of the homologous x – somes and their movement to different cds. Also random fertilization.

•  These variations are inherited, some being useful to the organisms gives the organism a slightly better chance of survival and some are less useful. Incase of environmental change over a long time · In a course of time the surviving forms, may be sufficiently different from the original species that they can be called new species.
•  Mutation is sudden/spontaneous/abrupt change in the amount or chemical structure of DNA molecule. The changes create genetic variation among members of the same species. If the mutation confers/gives an advantage to the organism that under selective environmental selective pressure, it will be selected for against the less fitted mutants. The selected ones will have a reproductive advantage and will reproduce more offspring. This process may result into formation of a new species different from its predecessor e.g. Biston, introduction of antibiotics in 1940 a strong selective pressure for strains of bacteria that have genetic capability of resistant to antibiotics as a result of mutation.

TYPES OF ISOLATION

1.Geographical isolation

i. A population which normally interbreeds freely may be separated by physical barriers/geographical barriers such as mountain ranges, deserts, oceans, rivers and canals etc. Under such circumstances,

the separate groups (demes) of the same species can no longer interbreed i.e. prevented from meeting hence barrier to gene flow.

ii Each side of a barrier has different environment conditions and thus new selective forces begin to operate.

iii The population will eventually be so different that they can no longer interbreed even if the physical barrier were to be removed therefore new species have been formed hence evolution.

iv. This type of isolation may also be referred to as allopatric speciation.

2.Reproductive isolation/Physiological isolation

Groups live side by side but fail to produce fertile offsprings and to interbreed. This is due to the fact that the groups have accumulated sufficient structural, functional and behavioural characteristics difference that when mixed inter breeding does not occur. This is realised through

(a) Mechanical isolation

•  In case of animals, genitalia of 2 groups are incompatible i.e. failure of male penis to enter the female vagina and no successful copulation. 
•  In case of plants related species of flower are pollinated by different animals. 
•  Gametes are prevented from meeting

(b) Seasonal isolation

(c) Behavioural isolation

i Occurs where animals exhibit courtship patters.

ii. Mating only results if the courtship display by one sex results in acceptance by the other sex e.g. in some fish and birds.

NB: In some cases, fusion of the gametes may not occur sperms reach the ovum, pollen grains reach the embryo sac but the gametes may be incompatible and might not fuse.

3.Post zygotic mechanisms (Barriers affecting hybrids)

Hybrid inviability: Hybrids are produced but fail to develop to maturity; for example hybrids formed between northern and southern races of the leopard frog (rana pipiens) in North America.

Hybrid sterility: Hybrids fail to produce functional gametes, for e.g. the mule (2n=63) results from the cross between the horse (equals equus, 2n = 60) and the ass (Equals hemionus, 2n = 66).

Hybrid breakdown: F1 hybrids are fertile, but the F2 generation and backcrosses between F1 hybrids and parental stocks fail to develop or are infertile for e.g. hybrids formed between species of cotton

(genus Gossypium).

Natural Selection

The environmental changes are the main mechanism for effecting natural selection.

Mechanisms for natural selection

i Individuals in a given population which are less fit are gradually eliminated while those with adaptive features are being favoured.

ii Organisms with variations (variation could have arisen from genetic recombination and or mutation) best adapted to the environment have a reproductive advantage thus producing more offsprings than the one of the favoured individuals increase while that of the unfavoured individuals decreases.

iii If the trend is maintained over a long time, a new species may arise e.g. evolution of Biston Bitullaria Carbonica is due to industrial revolution in UK which produced a lot of SO2. The SO2 made the leechens black and so camouflaging the black moth while the white one Biston Bitullaria Typical was preyed upon the birds. The black gene arose by mutation.

Geographic isolation

Two or more populations of the same species, occupying the same habitat become separated by a physical barrier like mountains, rivers, valleys. In such a situation, the gene pools of each population do not mix with one another i.e. no gene flow. Each population try to adapt itself to the changing environment. The less fit individuals are eliminated and the more fit keep on increasing in number. As the process of adaptation continues for a long time in the different geographical areas, the population becomes distinctly different from each other. Hence new species have arisen e.g. Galapology, finches, Ilamas and camels

Examples
Natural selection of peppered months

	Number of month eaten
Variety of month	Rural area	Industrial area
Light-coloured	26	43
Dark-coloured	164	15

This experiment reveals that months colour provides better camouflage are more likely to survive and reproduce .

It shows evolution taking place as results of natural selection.Hence there is evidence to support Charles Darwin's theory of evolution by natural selection

HUMAN ANCESTRY

• Homo sapiens, the species to which human belong appeared on the Earth about 50,000 year ago
• The fossil record also reveal that a few other homonid species were similar to modern humans in some ways

 THREE IMPORTANT ON STUDY OF HUMANS' PAST LIFE

1.A human is bipedalism. That is walking upright

2.A huamn is intelligent creature..Intelligent is hard measure This enabled to

• Use tools
• brain size

3.The teeth of humans differ from the species which are thought to be related to human.E.g apes and monkey

Examples The first Homonid appeared in East Africa was

i. Australothecus lived in 4 million year ago were bipadal their teeth and jar were apelike than those ii. Homo sapiens

iii. Homo habilis.lived 2 millions yraer ago has large brain and their teeth were more like those of modern human

iv.Homo erectus.Lived around 1.5 to 0.5 millions year aga. Its volume of brain  varied from of    800cm³-1300cm³ where human brain size is 1400Cm³ .

Neanderthal skull

• Modern human appeared around 3500 year ago.Shortly after the appearence of modern human Neanderthal became extinct
• -The neanderthal wee slowly replaced by Cro-magnons.
• This is group of Homo sapiens who got food through hunting and gathering
• Cro magnons can not physically  distinguishined from modern humans

Homonid skull

Factors that bring Evolution.  

1.Mutation; sudden change in gene or chromosome.

2. Migration; immigration and or emigration affect the size of population and also alter the gene frequency.

3.     Environmental changes; e.g. isolation by physical barriers like ocean desert and mountain.

4.      Crossing over; which takes place during the prophase of first meiotic division.

5.      Artificial selection; selecting certain phenotype in breeding of plants and animals for economical benefit.

EVIDENCE FOR ORGANIC EVOLUTION

1.FOSSIL RECORD (palaeontology).

-Palaeontology is the scientific study of fossils. 

Fossils are remains of organisms that lived in ancient times. The remains were accidentally preserved in some naturally occurring materials like sedimentary rocks. 

-The more recent the fossil, the more complex and the more they tend to resemble living species

-Older fossils, in general, differ more from present-day organism

The fossils can be

 i Entire organism

Encased in tar

Frozen into ice during glaciations

“Mummies” found in asphalt and lakes of California.

Woolly mammoths in Siberian

ii.   Hard skeletal materials

Trapped by sedimentary sand and clay which form sedimentary rocks e.g. limestone, sand store

Bones, shells and teeth

ii.   Impressions

Impressions of remains of organic in fine grained sediments on which they died.

Feathers of Archaeopteryx in upper Jurassic.   Jelly fish in Cambrian in British carboniferous leaf impressions.

iv.   Imprints

Footprints, traits, tracks and tunnels of various organisms made in mud are rapidly baked and filled with sand and covered by further sediments.

Dinosour foot prints and tail scrapings indicate size and posture of organism

v.   Coprolites

Faecal pellets prevented from decomposing, later compressed in sedimentary rocks often contain evidence of food eaten e.g. teeth and scales.

Fig. layer fish skeleton

Evidence:

•  Deeper layers usually contain simpler forms of organisms much older compared to upper layers which are complex but young i.e. most fossils occur in sedimentary simple structure fossils. Younger rocks contain more varieties of fossils with increasing complex structure.

•  Fossils show gradual change from one form to another as we move from the deeper layer cupboards. 
•  Therefore changing environment may have favored a mechanism for evolutionary change that account for a progressive change in the structure of the organic e.g. fossils we have today.

Archaeopteryx – reptilia and aves

Symoria - amphibia and reptilian

Synognathics – reptilia and mammals

•  Fossil record is not continuous i.e. missing links due to unfossilization of some soft bodied organisms on, dead organisms of decay rapidly or they may have been eaten by scavengers or they have notbeen discovered yet.  of footprints or traits and of skeletal parts. The fossils dated using Radioactive isotope i.e. Carbon – 14(C-14). The age of fossil can also be estimated from the position in the rock i.e. old fossils lay deep in the rock while those in the upper part are comparatively younger.

Limitation of Fossil evidence.

-Geological activities (i.e. earthquakes, soil erosion, faulting) have destroyed some fossil.

-Softer parts of organism decayed making the fossil records incomplete.

-Distortion due to flattening of parts of organism during sedimentation.

2.. CELL BIOLOGY AND BIOCHEMISTRY..

 -Genetic research revealed that basic similarities exist between cells from almost all kinds of living things. Eukaryotic cells contain organelles in all cells i.e. ATP, DNA and RNA. The similarities show that all cell types have a common ancestral origin.

Differences do exist between cells from different organisms. Organisms sharing the same chemical characteristics are more closely related. This is known as biochemical homology.

Examples are;

-Most plants contain chlorophyll, cellulose and starch which is absent in animal.

-Vertebrates are the only animal that posses adrenaline and thyroxin.

-Only algae posses the orange pigment called fucoxanthin.

2 COMPARATIVE EMBRYOLOGY.

-At a certain stages of their development embryos of all vertebrates show resemblance Example they have tails two chambered heart and gill slit. The relationship is thought to be the result of their common ancestry.

This evidence was first pointed out by Darwin and then explained by Ernst Haeckel who proposed Recapitulation theory; “Ontogeny recapitulates phylogeny” This means that; embryonic development (Ontogeny) of an organism repeats (recapitulates) the evolutionary history (phylogeny). For Haeckel, the embryo of higher animals go through stages which resemble adults forms of their ancestral forms. E.g.; zygote = protozoa; Embryo fish amphibians reptiles. .

3. COMPARATIVE ANATOMY.

-Organisms with basic structural similarities have a common or related ancestry; those with much difference have less evolutionary relation.

i) Homologous structures; similar origin but different functions. This is called divergent evolution, E.g..Forelimbs of vertebrates (pentadactyl = 5 digits) for flight (bat and birds), swimming (whale and turtles), running (horse), holding things (man).

FIg forelimb

*Beak in birds; modified according to mode of feeding, length, shape,

and size.

*Feet structure in birds; modified to suit environment; claws-for flesh eaters, webbed-for filter feeders.

ii) Analogous structures; different origin but similar functions. Brought about by adaptation of unrelated species to similar environment. This is called ---Convergent evolution. E.g. 

Wings of bat/ birds and insect = for flight.

Fig. analogous tructure

*Eyes of human and octopus =seeing
.

iii) Vestigial structures
; In some animals certain organs (structures) have become greatly reduced or functionless in the course of evolution, due to adaptation to different mode of life
Example.

*Appendix in man, wings of flightless birds (kiwi, ostrich, and emu) tail in man (reduced coccyx), hind limb in pythons and whale and muscle that move the ear in man, body hair in man.

4.EVIDENCE FROM REAL LIFE SITUATION..

i.Resistant strains of bacteria. Example the use of penicillin and other antibiotics has introduced new selection pressure within bacteria populations

ii.Warfarin and rats..Some rats have the ability to withstand the toxic effects of poisons such as warfarin.possession of the resistant gene is therefore an advantage in terms of survival for the rat

iii.Malaria and  Sick-cell anaemia..The homozygous form of the sickle-cell allele is usually lethal, However heterozygous individual(carriers) have an advantage in area where infection occur

-

5. Comparative serology.

Serology in study of blood (serum) proteins. It has been found that animals that are closely related evolutionary also have similar blood proteins. The results show that, human closet “blood relatives’ are great apes i.e. chimpanzee, gorillas, monkey, tarsiers and lemurs.

7. Classification (Taxonomy).

Modern classification is based on the similarities and differences between the natural characteristics of organisms. The organisms that share several characteristics are put (classified) under same group and are believed to have arisen from common ancestor in the evolutionary history.