EVIDENCE FOR EVOLUTION
- fossil record:
-the identification, interpretation and dating of fossils gives us some of the most direct evidence for evolution - biogeography:
-the study of where species occur, and why. this is based on the finding that different regions with similar climatic conditions contain very different animals and plants - modification by descent:
-similar structures with same body plan that perform different functions are known as homologous structures
-homologous structures provide evidence of evolution because the similarities suggest a common ancestor - genetic evidence:
-closely related organisms have more similarities in their DNA
-shows how changes in genotype and phenotype are transferred to successive generations
DIFFERENCE BETWEEN HYPOTHESIS AND A THEORY
hypothesis:
* a tentative explanation of a phenomenon that can be tested and may be accepted or rejected
theory:
* explanation of an observation that is supported by facts, models and laws
CONTRIBUTION OF VARIOUS SOURCES OF VARIATION
CRRRM
MEIOSIS:
* crossing over involving the exchange of genetic material during prophase 1 leads to the formation of gametes with different gene combinations
* the random assortment of homologous chromosome pairs on the equator during metaphase 1 also leads to greater variation
REPRODUCTION:
* random fertilisation where different gene combinations are formed which increases variation in species
* random mating of individuals and successful fertilisation occur in a population, the variety of gene combinations formed is even greater
MUTATIONS:
* changes in sequence of nucleotides may lead to change in the amino acid sequence of protein synthesised
CONTINUOUS VARIATION
- a type of variation that has a range of phenotypes for the same characteristic
- no distinct categories, no limit on value, tends to be quantitative
- height, weight, heart rate, etc.
- represented by line graph, histogram
- controlled by a lot of genes and the environment
DISCONTINUOUS VARIATION
- a type of variation where phenotypes fit into seperate categories with no intermediate forms
- distinct categories, tends to be qualitative
- tongue rolling, fingerprints, eye colour
- represented in a bar graph
- controlled by a few genes
IDEAS ON EVOLUTION IN ORDER OF ORIGIN
- lamarckism
- darwinism
- punctuated equilibrium
THEORY OF LAMARCK
LAW OF THE INHERITANCE OF ACQUIRED CHARACTERISTICS:
* characteristics developed during the life of an individual can be passed on to their offspring
LAW OF USE AND DISUSE:
* as an organism uses a structure or organ more regularly, it becomes better developed or enlarged. if an organism does not use a structure or organ frequently, it becomes less developed or reduced in size and may disapear altogether
REASONS FOR LAMARCK’S THEORY BEING REJECTED
- there is no evidence that acquired characteristics are inherited to the DNA of an organism’s gametes
DARWIN’S THEORY OF EVOLUTION OBY NATURAL SELECTION
- organisms produce a large number of offspring
- there is a great deal of variation
- some have favourable characteristics and some do not
- when there is a change in the environmental conditions or if there is a competition,
- then organisms with characteristics, which make them more suited, survive
- whilst organisms with unfavourable characteristics, which make them less suited, die
- the organisms that survive, reproduce
- and thus pass on the allele for the favourable characteristic to their offspring
- the next generation will therefore have a higher proportion of individuals with the favourable characteristic
- in this way, the characteristics of a population gradually change over a long period of time
PUNCTUATED EQUILIBRIUM
- evolution involves long periods of time where species do not change or change gradually through natural selection.
- this alternates with short periods of time where rapid changes occur through natural selection
- during which new species may form in a short period of time
DEFINITION OF BIOLOGICAL EVOLUTION
- a change in the gene pool of a population over millions of years
DEFINITION:
1. POPULATION
2. SPECIES
- a group of organisms of the same species that occupy the same area at a same time
- a group of organisms with similar characteristics that can interbreed to produce fertile offspring
PROCESS OF SPECIATION
- if a population of a single species
- becomes seperated by a geographical barrier
- then the population splits into two
- there is now no gene flow between the two populations
- since each population may be exposed to defferent environmental conditions
- natural selection occurs independently in each of the two populations
- such that the individuals of the two populations become very different from each other
- genotypically and phenotypically
- even if the two populations were to mix again they will not be able to interbreed
- and therefore a new species has formed
SPECIATION THROUGH GEOGRAPHICAL ISOLATION IN THE FOLLOWING
- galapagos finches
- galapagos tortoises
- plants on different land masses
-baobabs in africa and madagascar
-proteas in south africa and austrailia - any example of mammals on different land masses
EXAMPLES OF REPRODUCTIVE ISOLATION THAT KEEPS SPECIES SEPERATE
- breeding at different times of the year
- species-specific courtship behaviour
- adaptation to different pollinators in plants
- infertile offspring
- prevention of fertilisation
EXAMPLES OF NATURAL SELECTION AND EVOLUTION IN PRESENT TIME
- use of insecticides and consequent resistance to insecticides in insects
- development of resistant strains of TB causing bacteria to antibiotics, due to mutations in bacteria and failure to complete antibiotic courses
- HIV resistance to antiretroviral medication
- bill and body size of galapagos finches
HOW BACTERIA DEVELOPS RESISTANCE TO ANTIBIOTICS
- bacteria populations develop resistance by natural selection
- bacteria reproduce rapidly
- within the population, mutations occur which may produce bacteria that are resistant to antibiotics
- mutations introduce variation within the population making some bacteria resistant to antibiotics while others are not
- antibiotics kill non-resistant and the resistant bacteria survive
- the resistant bacteria reproduce and pass on their mutated genes to their offspring producing a bacterial population with a greater proportion of resistant bacteria
PHYLOGENETIC TREE OF THE FAMILY HOMINIDAE IN THE ANIMAL KINGDOM
PHYLOGENETIC TREE OF THE FAMILY HOMINIDAE IN THE ANIMAL KINGDOM
file:///C:/Users/sagem/Dropbox/PC/Downloads/Photo%20(4).pdf
CHARACTERISTICS THAT HUMANS SHARE WITH AFRICAN APES
- two hands, each with five fingers; two feet each with five toes
- long arms that rotate freely as shoulder joints allow movement in all directions
- naked fingertips and toes ending in flat nails
- reduced snout with weakened sense of smell
- stereoscopic vision as the eyes face forward providing depth of field
- eyes have cones and rods making colour vision possible
- brain centres that process information from hands and eyes are enlarged
- no tail
- sexual dimorphism where males and females are clearly distinguished
- have molars and premolars with rounded cusps
ANATOMICAL DIFFERENCES BETWEEN AFRICAN APES AND HUMANS
BIPEDALISM:
* humans - foramen magnum in a forward position. more curved spine. short-wide pelvis
* african apes - foramen magnum in a backward position. less curved spine. long, narrow pelvis
BRAIN SIZE:
* humans - large frontal area, which requires a large cranium and a higher forehead to house and protect it.
* african apes - smaller brain, less developed
TEETH (DENTITION):
* humans - small teeth. canine is smaller. no gaps between incissors and canines.
* african apes - large teeth. large canines. gaps between incisors and canines
PROGNATHISM:
* humans - shorter jaw. does not need strong muscles for their diet of softer foods. face is small and flatter in the front.
* african apes - longer jaw. stonger muscles required for their diet of tough foods. face is large and protruding in the front.
PALATE SHAPE:
* humans - palate is small and semi-circular in shape
* african apes - palate is long and rectangular in shape
CRANIAL RIDGES:
* humans - no cranial ridge as humans have smaller jaws and do not need large jaw muscles
* african apes - cranial ridge across the top of the cranium
BROW RIDGES:
* humans - not well developed. more upright brow, which holds a larger brain
* african apes - brow ridges well developed
FOSSIL EVIDENCE
- evidence from fossils of different ages show that the anatomical characteristics of organisms changed gradually over time.
FOSSIL : ARDIPITHECUS
- age: 5 - 4 mya
- scientist : tim white
- found in the afar valley of ethiopia
anatomical features:
* brain size: 300-350 ml
* forward position of foramen magnum
* protruding jaws
* heavy brow ridges
* pelvis structure: bipedal and tree climbing
FOSSIL : AUSTRALOPITHECUS AFARENSIS (LUCY)
- age: 4 - 2.7 mya
- scientist: donald johnson
- found in the afar valley in ethiopia
anatomical features:
* brain size: 375-550 ml
* forward position of foramen magnum
* bipedal
* protruding jaws
* heavy brow ridges
* canines large and pointed
