Evolution- Beliefs about Evolution- Beliefs about the origin of lifethe origin of life

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Beliefs about the origin of lifeBeliefs about the origin of life

Abiogenesis: life might arise spontaneously Abiogenesis: life might arise spontaneously from nonliving material .from nonliving material .

Panspermia: life might arise from the Panspermia: life might arise from the molecules from outer space molecules from outer space

Autotroph hypothesis: The first living Autotroph hypothesis: The first living organism is an autotroph.organism is an autotroph.

Heterotroph hypothesis:life might arise from Heterotroph hypothesis:life might arise from a chemical evolution.a chemical evolution.

Heterotroph hypothesis:Heterotroph hypothesis: The classic experiment demonstrating The classic experiment demonstrating

the mechanisms by which inorganic the mechanisms by which inorganic elements could combine to form the elements could combine to form the precursors of organic chemicals was precursors of organic chemicals was the 1953 experiment by Stanley Miller. the 1953 experiment by Stanley Miller. He undertook experiments designed to He undertook experiments designed to find out how lightning--reproduced by find out how lightning--reproduced by repeated electric discharges--might repeated electric discharges--might have affected the primitive earth have affected the primitive earth atmosphere. He discharged an electric atmosphere. He discharged an electric spark into a mixture thought to spark into a mixture thought to resemble the primordial composition of resemble the primordial composition of the atmosphere. In a water receptacle, the atmosphere. In a water receptacle, designed to model an ancient ocean, designed to model an ancient ocean, amino acids appeared. Amino acids amino acids appeared. Amino acids are widely regarded as the building are widely regarded as the building blocks of life. blocks of life.

EvidenceEvidencess for Evolution for Evolution

1.1. Comparative AnatomyComparative Anatomy 2.2. Vestigial StructuresVestigial Structures3.3. Comparative EmbryologyComparative Embryology 4.4. Molecular BiologyMolecular Biology5.5. Fossil recordFossil record6.6. TaxonomyTaxonomy7.7. Artificial selectionArtificial selection8.8. BBiogeographyiogeography

1. Comparative Anatomy 1. Comparative Anatomy Scientists often try to determine the relatedness of Scientists often try to determine the relatedness of

two organisms by comparing external and internal two organisms by comparing external and internal structures.structures.

Anatomical features in different species that point Anatomical features in different species that point to a common ancestor are called to a common ancestor are called homologous homologous structuresstructures. For example, the flipper of a whale . For example, the flipper of a whale and a human arm seem to be quite different when and a human arm seem to be quite different when looked at on the outside. But the bone structure of looked at on the outside. But the bone structure of each is surprisingly similar, suggesting that each is surprisingly similar, suggesting that whales and humans have a common ancestor whales and humans have a common ancestor way back in prehistory way back in prehistory

These sorts of structures, which have These sorts of structures, which have superficial similarities because of similarity superficial similarities because of similarity of function but do not result from a of function but do not result from a common ancestor, are called common ancestor, are called analogous analogous structuresstructures. bats and insects share a . bats and insects share a common ancestor, since both have wings. common ancestor, since both have wings. But a closer look at the structure of the But a closer look at the structure of the wings shows that there is very little in wings shows that there is very little in common between them besides their common between them besides their function . function .

2. 2. Vestigial StructuresVestigial Structures In addition to homologous and analogous In addition to homologous and analogous

structures, structures, vestigial structuresvestigial structures, which , which serve no apparent modern function, can serve no apparent modern function, can help determine how an organism may help determine how an organism may have evolved over time. In humans the have evolved over time. In humans the appendix is useless, but in cows and other appendix is useless, but in cows and other mammalian herbivores a similar structure mammalian herbivores a similar structure is used to digest cellulose is used to digest cellulose

3. Comparative Embryology 3. Comparative Embryology

In general, the more In general, the more closely related two closely related two species are, the more species are, the more their embryological their embryological processes of processes of development resemble development resemble each other each other

4. Molecular Evolution 4. Molecular Evolution Two species that are closely related will Two species that are closely related will

have fewer genetic or protein differences have fewer genetic or protein differences between them .between them .

Certain genes or proteins in organisms change at a constant rate over time.

5. 5. Fossil recordFossil record Fossils are the traces of past life. They Fossils are the traces of past life. They

include footprints, burrows, worm casts.include footprints, burrows, worm casts. Most of the fossils are found embedded in Most of the fossils are found embedded in

or on rocks. Paleontology is the science of or on rocks. Paleontology is the science of studying fossils. studying fossils.

Relative age of the fossils can be Relative age of the fossils can be determined by the geologists by examining determined by the geologists by examining the layers of the earth crust.the layers of the earth crust.

And by the carbon dating methods in which And by the carbon dating methods in which radioactive isotope of C is examined.radioactive isotope of C is examined.

The time scale derived from fossil records The time scale derived from fossil records is usually calculated from radioactive is usually calculated from radioactive dating. For example in carbon-14 dating, dating. For example in carbon-14 dating, the fact that the ratio of C14 to C12 is fairly the fact that the ratio of C14 to C12 is fairly constant (~ 10-12) in living organisms and constant (~ 10-12) in living organisms and that C14 is radioactive with a halflife of that C14 is radioactive with a halflife of about 5730 years, would yield the age of about 5730 years, would yield the age of the organism since its death (no more the organism since its death (no more accumulation of C14) if we measure the accumulation of C14) if we measure the leftover amount of C14 in the sample leftover amount of C14 in the sample

6. 6. TaxonomyTaxonomy The science of classification is The science of classification is taxonomy.taxonomy. Classification is the process of grouping Classification is the process of grouping

the organisms according to their the organisms according to their properties. properties.

Organisms are classified into larger groups. Species is the smallest one , Organisms are classified into larger groups. Species is the smallest one , kingdom is the largest one.kingdom is the largest one.

KingdomKingdom PhylumPhylum ClassClass OrderOrder FamilyFamily GenusGenus SpeciesSpecies

7. 7. Artificial selectionArtificial selection Artificial selection is to select the animal to Artificial selection is to select the animal to

reproduce. It is not randomly reproduce. It is not randomly reproduction(natural selection). reproduction(natural selection).

As a result of artificial reproduction some of the As a result of artificial reproduction some of the species are selected to reproduce and their species are selected to reproduce and their numbers are increased.numbers are increased.

Horse, cereal grains important for agriculture, Horse, cereal grains important for agriculture, chicken chicken

8. B8. Biogeographyiogeography

Biogeography is the study of geographic Biogeography is the study of geographic distribution of life forms on earth. distribution of life forms on earth. Biogeography has an influence on the Biogeography has an influence on the adaptation of species to a certain area. In adaptation of species to a certain area. In that way same species adapt to different that way same species adapt to different areas in different ways and this causes areas in different ways and this causes variation. (adaptation)variation. (adaptation)

Allen ruleAllen rule The organisms living in cold areas The organisms living in cold areas

have smaller extensions.( small have smaller extensions.( small ear, short tail)ear, short tail)

But organisms living in warmer But organisms living in warmer areas have larger extensions for areas have larger extensions for heat control.(large ear, long tail)heat control.(large ear, long tail)

Bergmann ruleBergmann rule The organisms living in cold areas have The organisms living in cold areas have

smaller surface area/volume ratio.( big smaller surface area/volume ratio.( big animals have small surface area but animals have small surface area but large volume)large volume)

But organisms living in warmer areas But organisms living in warmer areas have larger surface area/volume ratio.have larger surface area/volume ratio.( small animals have large surface area ( small animals have large surface area but small volume)but small volume)

Accepted Rules for Evolution

Dollo ruleDollo rule Evolution always preceeds onwards not backwords.Evolution always preceeds onwards not backwords. Life begins in water and proceeds in land. Not goes back.Life begins in water and proceeds in land. Not goes back.

Cope ruleCope rule Vertebrates tend to increase their body Vertebrates tend to increase their body

size during evolution. (to store important size during evolution. (to store important molecules)molecules)

Gloger ruleGloger rule The mammals and birds tend to be The mammals and birds tend to be

darker near the equatorial region. darker near the equatorial region. (protection against sun rays)(protection against sun rays)

Theories of Evolution Theories of Evolution 1. Lamarck: Use and Disuse 18091. Lamarck: Use and Disuse 1809

The classic example used to explain Lamarckism is The classic example used to explain Lamarckism is the elongated neck of the giraffe. According to the elongated neck of the giraffe. According to Lamarck’s theory, a given giraffe could, over a Lamarck’s theory, a given giraffe could, over a lifetime of straining to reach high branches, develop lifetime of straining to reach high branches, develop an elongated neck. This vividly illustrates Lamarck’s an elongated neck. This vividly illustrates Lamarck’s belief that belief that useuse could amplify or enhance a trait. could amplify or enhance a trait. Similarly, he believed that Similarly, he believed that disusedisuse would cause a trait would cause a trait to become reduced to become reduced

The second part of Lamarck’s mechanism for The second part of Lamarck’s mechanism for evolution involved the evolution involved the inheritance of acquired inheritance of acquired traitstraits. He believed that if an organism’s traits . He believed that if an organism’s traits changed over the course of its lifetime, the organism changed over the course of its lifetime, the organism would pass these traits along to its offspring. would pass these traits along to its offspring.

2. Darwin: Natural Selection 2. Darwin: Natural Selection Each species produces more offspring than can Each species produces more offspring than can

survive. survive. The individual organisms that make up a larger The individual organisms that make up a larger

population are born with certain variations. population are born with certain variations. The overabundance of offspring creates a The overabundance of offspring creates a

competition for survival among individual competition for survival among individual organisms. The individuals that have the most organisms. The individuals that have the most favorable variations will survive and reproduce, favorable variations will survive and reproduce, while those with less favorable variations are less while those with less favorable variations are less likely to survive and reproduce. likely to survive and reproduce.

Variations are passed down from parent to Variations are passed down from parent to offspring. offspring.

Beagle’s trip 1831-1836Beagle’s trip 1831-1836

The competition that Darwin’s theory The competition that Darwin’s theory describes is sometimes called describes is sometimes called the the survival of the fittestsurvival of the fittest. .

Most particularly, he took interest in the Most particularly, he took interest in the islands’ various finches, whose beaks islands’ various finches, whose beaks were all highly adapted to their particular were all highly adapted to their particular lifestyles . lifestyles .

The Genetic Basis for Evolution The Genetic Basis for Evolution

Variations exist in the individuals within a Variations exist in the individuals within a population. population.

Those variations are passed down from Those variations are passed down from one generation to the next. (inherited)one generation to the next. (inherited)

If variations favour the survival of the If variations favour the survival of the organism then the organism who carries organism then the organism who carries these variations will repoduce and fit to these variations will repoduce and fit to the environment. This is called the environment. This is called adaptation.adaptation.

Development of New Species -Development of New Species -SpeciationSpeciation

The scientific definition of a The scientific definition of a speciesspecies is a group is a group of organisms that reproduce within the group of organisms that reproduce within the group and produces fertile new organisms. and produces fertile new organisms.

As populations change, new species evolve. As populations change, new species evolve. This process is known as This process is known as speciationspeciation. .

Speciation is also called Speciation is also called divergent evolutiondivergent evolution, , since when a new species develops, it diverges since when a new species develops, it diverges from a previous form. All homologous traits are from a previous form. All homologous traits are produced by divergent evolution. produced by divergent evolution.

Speciation occurs when two populations Speciation occurs when two populations become reproductively isolated . become reproductively isolated .

Allopatric speciation occurs when populations of a species become geographically isolated so that they cannot interbreed . Sympatric speciation is the result of a genetic isolation without a geographical barrier

Over time, the populations may become genetically different in response to the unique selection pressures operating in their different environments. Eventually the genetic differences between the two populations will become so extreme that the two populations would be unable to interbreed even if the geographic barrier disappeared.