Evolution by natural selectionOrigin of ideas about origins

Terminology EVOLUTION - change over time

(matter, solar systems, languages) BIOLOGICAL EVOLUTION

genetic changes in a population inherited over generations due to natural selection and then resulting in new species

MACRO EVOLUTION development of a new life form over many generations (elephant developed from woolly mammoth) SPECIATION – new species develop from existing species

MICRO EVOLUTION small changes in the gene pool of a specie, resulting in small changes in the genotype of the species and then passed on to the offspring. (shape of ears….. Teeth…)

EVIDENCE OF EVOLUTION FOSSIL RECORDS:Organism or remains, imprints or footprints of an organism, usually preserved in rock.Fossils provide evidence of the history of extinct organisms on earthThe fossil record is the accumulation of all listed and known fossils of different ages that have been discovered by palaeontologists worldwide.The study of fossils – palaeontologyThe scientist studying fossils - palaeontologist

Evidence of evolution

MODIFICATION BY DESCENTThe basic body plans (structure of skeleton) of different plant and animal groups were modified to adapt to their different environments.The forelimbs of various vertebrates like amphibians, reptiles, birds and mammals look different and perform different functions but show the same basic body plan.Similar structures (HOMOLOGOUS structures Hs)same body plan that perform different functions

HS provide evidence of evolution because the similarities may be traced back to a common ancestorDivergent evolution – common ancestor different evolutionary paths (dig, fly, running, swimming)

Evidence of evolution

ANALOGOUS STRUCTURESsome body structures perform the same function in different organisms, but did not originate from a common ancestor. They usually differ in structure but have the same function. Wings of butterflies and bats for example. Convergent evolution - organisms are not related but develop structures for similar environments, independently from each other.

Modification within a specie According to this theory many species changed

over millions of years to form the species we know today.

Adaptations occurred to adapt to different environments

Biogeography The study of the distribution of existing

(extant) and extinct plant and animal species in specific geographical regions

These studies prove that closely related species usually occur in the same geographical region and may suggest that they share a common ancestor

biogeographical regions may be isolated by barriers, preventing species spreading from one region to another. This may lead to the formation of new species. (large mountain ranges, oceans, deserts)

Biogeography Plant and animal life in different

geographical regions with similar habitats and climatic conditions, but seperated by barrier may also differ.

Eg. North and South pole is covered with ice yet polar bears live at north and penguins at the South pole.

Flightless birds eg. Emu and ostrich were separated geographically when gondwanaland broke apart, the birds adapted to their environment and new species developed due to the different mutations and selections in the various environments.

Biogeography

biogeography

Darwins Theory of evolutionIndividuals of the same species living in different habitats (separated by barriers) adapt to their changed environmental conditions, undergo different mutations and may develop into new species.

Genetics Closely related animals have more

similarities in their DNA It shows how changes in genotype or

phenotype are transferred to successive generations.

It explains how the gene pools of populations can change and lead to a new species. (speciation)

Scientists study the DNA sequences of different organisms to determine their evolutionary relationships. They claim that the greater the similarities between the DNA sequences or organisms, the more recently they developed from a common ancestor

OTHER forms of EVIDENCE COMPARATIVE BIOCHEMISTRY

molecular composition of most living organisms is very similar (Darwin – common ancestor)

VESTIGIAL ORGANSstructures / organs with disuse decrease in size over evolutionary time. Eg. Whales haveno hind limbs but haveremains of pelvic girdlesand under-developedhind limbs which may indicate four-footed ancestors.

Comparative embryologyWhen embryos of vertebrates are compared to each other at various early stages of development they show certain similarities

DIFFERENCE BETWEEN…… HYPOTHESIS : Informed assumption because it

provides a proposed solution to a problem or explanation of a specific phenomenon based on evidence and observations. It can be tested. Rejected or accepted.

THEORY : A well-substantiated (supported by evidence) explanation or hypothesis that makes sense of a natural phenomenon. Confirmed by independent group of scientist. Develops and is changed or replaced as new evidence is discovered.

EVOLUTION is a scientific theory, a series of hypothesis that have been tested and verified.

History of theories of development

LAMARCKISM:Jean-Baptiste Lamarck’s theories was based on 2 related ideas:The USE and DISUSE OF ORGANS, may cause organs to increase or decrease in size or even completely disappear.

During their lifetime organisms acquire certain changes in characteristics that are inherited by their offspring. this results in changes in populations and the formation of new species.

LAMARCK’S LAWS : law of use and disuse : law of inheritance of acquired characteristics

Reason for rejection : cannot be scientifically proven.

History of theories of development DARWINISM

Charles Darwin on the survey ship HMS Beagle undertook a 5 year expedition, his theories based on natural selection……

4 observations: individuals of a population produce more offspring

than required to ensure survival of the population. A great deal of variation occurs within a

populationSome individuals are better adapted to a specific environment and are more likely to reproduce while the weaker adapted will not reproduce or become extinct

Characteristics are transferred from the surviving parents to their offspring (got the idea from lamarck)

Summary of Darwin’s theory

A large number of offspring are produced

Variation in a population

Struggle for survival

Natural selection (survival of the fittest)

Change occur over time

New species form

Types of VARIATION within a species CONTINUOUS VARIATION This occurs when there is a range of phenotypes

for the same characteristic. It normally forms a continuous spectrum ranging

from one extreme to another. The more alleles controlling a particular genetic

characteristic, the greater the variety of possible gene combinations and the greater the range of possible phenotypes.

A characteristic that illustrates continuous variation e.g. height in humans, mass of newborn babies, milk yield in cows, heart rate, skin colour, hair length and the size of ladybirds.

Line graph or histogram

Types of VARIATION within a species

DISCONTINUOUS VARIATION Phenomenon where phenotypes fit into separate

categories, with no intermediate forms. Only a single pair of alleles occurs. Fewer possible gene combinations – clear

phenotypes. A persons blood group can only be one of A,

B, AB or O. NO OTHER POSSIBILITIES OR OPTIONS

Other examples : tongue rolling, finger prints, gender, dimples and the number of spots on ladybirds.

PUNCTUATED EQUILIBRIUM It explains how changes leading to

speciation may occur very rapidly over a short period of time and it accounts for the absence of transitional fossils (missing links) in the fossil record.

Stasis – where a species remain unchanged in a state of equilibrium

These rapid adaptations of species in order to survive in their changing environment, accelerated the course of evolution and lead to speciation

Living ,dying and being fossilized - little observable evolution

Isolation – lake(barrier) forms and isolate small population

Sea level rise, reuniting the isolated molluscs with their sister lineage

Expansion and stasis: The isolated population expand into its past range, the isolated branch might outcompete their ancestral population ,causing it to go extinct like it is shown in this example

Larger population size and large range move back to step 1 stasis with fossil preservation

This process would produce the following pattern in the fossil record:

Evolution happens in sharp jumps associated with speciation events

ARTIFICIAL SELECTION

The deliberate breeding (by humans) of plants and animals for desired characteristics that would not necessarily benefit the survival of the offspring.

EXAMPLE OF DOMESTICATED ANIMAL the large variety of modern dog breeds has

been bred over hundreds of years through the selection of different characteristics as desired by humans. Yorkie – the smaller the better. Pitt-bull – the angrier the better…….

EXAMPLE OF A CROP SPECIES Cabbage, cauliflower, broccoli, turnip, brussel

sprouts originated through artificial selection of the wild mustard plant!!!!!

FORMATION OF A NEW SPECIES - SPECIATION

A biological species can be defined as a group of organisms that interbreed to produce fertile offspring.

SPECIATION – The formation of species increases the range of organisms on earth and thus increases biodiversity.

EXTINCTION - The loss of species decreases the range of organisms on earth and thus decreases biodiversity.

As long as members of a population can interbreed successfully they are considered part of the same species.

SPECIATION DUE TO GEOGRAPHIC ISOLATION (barrier) E.g. Galapagos finches, flightless birds, molluscs……. ALLOPATRIC SPECIATION – new species from existing

species when population are separated by barrier SYMPATRIC – same country (not required for exam)

MECHANISMS FOR REPRODUCTIVE ISOLATION

Reproductive isolation is the type of isolation that develops between the new species and the ancestral species, and prevents interbreeding.

it can occur when 2 species are separated geographically or when they occupy the same area.

1. breeding at different times of the year (prezygotic) making crossbreeding impossible

2. species-specific courtship behaviour it indicates sexual maturity e.g courtship of dogs and wolves differ preventing interbreeding. Feather displays of birds. Mating dance of insects.

Mechanisms of reproductive isolation cont…….

3. Adaptations of plants to different pollinators (prezygotic) flowers of various plant species have different adaptations (structure, colour, or scent) which make them suitable for pollination by specific pollinators, e.g birds or wind.

4. prevention of fertilisation organisms may have structural adaptations that ensure that they are only fertilised by their own species. E.g. Incompatible sex organs, shape size location of genitals does not match those of another species

5. occupying different habitats in the same environment organisms living in trees or burrows in a forest hardly meet, decreasing chances of meeting mating partners

6. development of sterile (infertile) offspring in hybrids (postzygotic) sometimes two different species do crossbreed and produce a hybrid offspring. Hybrid does not always develop as far as an embryo as the genetic combination is not sufficient for specialisation.

if hybrid survive it is usually stronger than the parents but is sterile. Donkey + horse = mule (sterile)

EVOLUTION IN PRESENT TIMES Four clearly observable examples of

evolution currently occurring by natural selection include:

RESISTANCE TO INSECTICIDES IN INSECTSe.g. random mutation occur, makes insect resistant to DDT insect pass resistance gene on to offspring

EVOLUTION IN PRESENT TIME cont…. RESISTANCE TO ANTIBIOTICS IN BACTERIA

APPLICATION OF ANTIBIOTIC

Antibiotic-sensitive bacteria are destroyed

Population of antibiotic-resistant bacteria develops

Mutation develops

Reproduction of bacteria

Antibiotic-resistant bacteria survive and

multiply

antibiotic-sensitive antibiotic-resistant

RESISTANCE TO ANTIRETROVIRALS IN HI-VIRUSES Many people do not take the drugs regularly as

prescribed and this increases the chances of mutations occurring.

The development of viruses that are resistant to ARVs is another example of the evolutionary process by natural selection:

Some of the viruses develop mutations that make them resistant to the ARV drugs. This introduces variation in the population

The application of ARVs changes the environment and acts as a selection pressure

the mutant, resistant viruses are selected, survive the treatment and multiply.

A drug resistant virus population develops.

BEAK AND BODY SIZE IN GALAPAGOS FINCHES

After a drought the smaller, softer seeds were fewer in number.

There was an inrease in larger finches with strong beaks that could break open the larger thich-shelled seeds.

These larger finches were better adapted to the changed environment: they probably had a better chance of survival and could reproduce

The genes for larger birds with stronger beaks were passed on to successive generations.

After a period of heavy rains, smaller, softer seeds reappeared.

There was an increase in the numbers of smaller-beaked birds; they were best adapted to opening smaller seeds.

These finches with the smaller beaks were now better adapted for the changed environment; they had an increased chance of survival and could reproduce.