1 Evolution: Evidence & Theory Chapter 15 Topics The Fossil Record Theories of Evolution Evolution in Process Biology

2 Nature of Fossils Fossil – trace of a deceased organism Fossil – trace of a deceased organism Long periods of time, high pressure, and often high temperatures can cause fossils to form due to chem rxns Long periods of time, high pressure, and often high temperatures can cause fossils to form due to chem rxns Minerals invade the hard parts of the organism – bone, teeth, woody stems – causing these to become “fossilized” Minerals invade the hard parts of the organism – bone, teeth, woody stems – causing these to become “fossilized” This makes a replica of those parts of the organism in the sediment This makes a replica of those parts of the organism in the sediment –Molds are imprints in rock of the organism’s outline –Casts are models of the organism in the surrounding rock

3 Nicolaus Steno ( ) Proposed Law of Superposition – successive layers of rock/soil deposited atop of another by wind & water Proposed Law of Superposition – successive layers of rock/soil deposited atop of another by wind & water The oldest stratum is on bottom, recent layer on top The oldest stratum is on bottom, recent layer on top So fossils within a stratum are of the same relative age So fossils within a stratum are of the same relative age Absolute age determined by radiological evidence (ie., ½ life radioactive dating) Absolute age determined by radiological evidence (ie., ½ life radioactive dating)

4 What does the fossil evidence show? Different strata show evidence of various kinds of organisms coming into existence and disappearing (extinction) Different strata show evidence of various kinds of organisms coming into existence and disappearing (extinction) Sometimes the disappearances were gradual, sometimes quick Sometimes the disappearances were gradual, sometimes quick Mass extinctions – brief periods of time in which many species of organisms disappeared Mass extinctions – brief periods of time in which many species of organisms disappeared Cause of mass extinctions not entirely known – may be result of volcanic/plate tectonic activity or space debris colliding with Earth (like an asteroid) causing global climate changes which were incongruent with some species Cause of mass extinctions not entirely known – may be result of volcanic/plate tectonic activity or space debris colliding with Earth (like an asteroid) causing global climate changes which were incongruent with some species

5 Biogeography – study of the geographical distribution of fossils & of living organisms Scientists compare living species with fossils of the recent past in a specific area Scientists compare living species with fossils of the recent past in a specific area They note connections between living species and the fossils of similar species They note connections between living species and the fossils of similar species

6 Theories of Evolution Evolution – orderly succession of changes Jean Baptiste de Lamarck ( ) Jean Baptiste de Lamarck ( ) –First scientist to propose a unifying theory on evolution of species –Living species descended from extinct species He hypothesized that species changed by passing an acquired trait He hypothesized that species changed by passing an acquired trait –Acquired traits are obtained during an organism’s lifetime –So a giraffe has a long neck because over the course of time, the stretching of their necks to obtain leaves for dinner causes the spine to elongate and the neck to get longer –This trait is passed to offspring and so, over time, the giraffe’s neck becomes long –This idea was accepted by academia for almost 50 years

7 Charles Darwin ( ) Influenced by Charles Lyell (promoter of plate tectonics) and his book, Principles of Geology, and Darwin’s own travels, he proposed the idea of natural selection as the driving force behind evolution Influenced by Charles Lyell (promoter of plate tectonics) and his book, Principles of Geology, and Darwin’s own travels, he proposed the idea of natural selection as the driving force behind evolution –Natural selection – organisms best suited for their environment survive to reproduce; it is those favorable traits passed down thru generations The title of the joint venture, “On the tendency of species to form varieties; and on the perpetuation of varieties and species by means of natural selection” by Charles Darwin & Alfred Wallace The title of the joint venture, “On the tendency of species to form varieties; and on the perpetuation of varieties and species by means of natural selection” by Charles Darwin & Alfred Wallace Darwin’s published work: Darwin’s published work: –“On the Origin of Species by Means of Natural Selection, or the Preservation of favoured races in the struggle for life” –Published on 24 November 1859

8 Alfred Wallace ( ) Wallace, a naturalist and contemporary of Darwin’s, comes to the exact same conclusion about the evolution of species by natural selection Wallace, a naturalist and contemporary of Darwin’s, comes to the exact same conclusion about the evolution of species by natural selection He writes a paper (1858) about it and as a professional courtesy, sends a copy to Darwin for his critique (before he publishes) He writes a paper (1858) about it and as a professional courtesy, sends a copy to Darwin for his critique (before he publishes) –Darwin, wrote an outline in 1844 on the subject but never published & had been urged by Lyell to publish, he does not & now regrets So Lyell & J. Hooker took matters into their own hands – they added Darwin’s outline to Wallace’s paper and presented to the Linnean Society as a joint publication So Lyell & J. Hooker took matters into their own hands – they added Darwin’s outline to Wallace’s paper and presented to the Linnean Society as a joint publication Wallace was in fact delighted not upset and always referred to natural selection as Darwinism Wallace was in fact delighted not upset and always referred to natural selection as Darwinism

9 Natural Selection Driving force behind evolution Natural selection – organisms best suited for their environment survive to reproduce; it is those favorable traits passed down thru generations Traits coded for by genes (DNA); parents pass DNA to offspring Traits coded for by genes (DNA); parents pass DNA to offspring If an individual survives to reproductive age, it has the ability to pass on those traits to the offspring If an individual survives to reproductive age, it has the ability to pass on those traits to the offspring How does the environment affect an organism? How does the environment affect an organism? –Environmental pressures include: shelter, food availability, mate availability, climate –So, how do these pressures impact organisms?

10 Environmental Pressures How do environmental pressures affect organisms? Climate Climate –Cold/hot/temperate/rainy/arid/? Mate Availability Mate Availability Food Availability Food Availability –Food type/how much needed/ /herbivore/omnivore/carnivore Shelter Shelter

11 Causes a species to adapt to it! So the more fit an organism is, the more likely it is to survive to reproductive age So the more fit an organism is, the more likely it is to survive to reproductive age Characteristics that enable an organism to better “fit” into their environment and therefore allow the organism to reproduce, those characteristics will be passed on to the offspring Characteristics that enable an organism to better “fit” into their environment and therefore allow the organism to reproduce, those characteristics will be passed on to the offspring

12 Evidence of Evolution (1) Scientists look at clues of gradual modifications to species across time – Evidence in morphology (1) Scientists look at clues of gradual modifications to species across time – Evidence in morphology –Homologous structures Similar features originating from a shared ancestor, functionality may not be same Similar features originating from a shared ancestor, functionality may not be same –Analogous structures Structures sharing functionality, but originating from a different embryological structure Structures sharing functionality, but originating from a different embryological structure –Vestigial Structures Structure having an apparently useless function Structure having an apparently useless function

13 Homologous & Analogous Structures

14 Vestigial Structures

15 “Ontogeny recapitulates phylogeny” Ernst Haeckel ( ) (2) Evidence in embryology (2) Evidence in embryology –Thus the development of the embryo repeats the evolutionary history Haeckel statement is an exaggeration, but it does present the fact that early embryonic development is very similar between organisms Haeckel statement is an exaggeration, but it does present the fact that early embryonic development is very similar between organisms

16 Embryologic Evidence

17 Further evidence of Evolution (3) Molecular Evidence (3) Molecular Evidence –DNA of similar organisms are more closely related –The amino acid sequences of similar organisms are more alike –On a cellular level proteins, DNA, RNA, etc of similar organisms show commonalities to demonstrate the relatedness of similar organisms proteins, DNA, RNA, etc of similar organisms show commonalities to demonstrate the relatedness of similar organisms

18 Proteins Hemoglobin – protein for RBC Hemoglobin – protein for RBC Human & gorilla hemoglobin differ by one amino acid Human & gorilla hemoglobin differ by one amino acid Human & frog hemoglobin differ by only 67 amino acids Human & frog hemoglobin differ by only 67 amino acids For homologous proteins in related species – the number of amino acid differences between the two is proportional to the length of time passed since the two arose from one common ancestor (MRCA = most recent common ancestor) For homologous proteins in related species – the number of amino acid differences between the two is proportional to the length of time passed since the two arose from one common ancestor (MRCA = most recent common ancestor)

19 Patterns of Evolution Three patterns are seen in evolution Three patterns are seen in evolution –(a) Coevolution –(b) Convergent Evolution –(c) Divergent Evolution The speed at which they occur vary depending upon the pressures placed on the species The speed at which they occur vary depending upon the pressures placed on the species

20 (a) Coevolution The change in two or more species in close association with each other The change in two or more species in close association with each other Some examples: Some examples: –Predator & prey –Parasites & host(s) –Plants & plant eaters –Plants & plant pollinators Fruit bats live in tropical areas and some feed on flower nectar. These bats have long slender muzzles with a long, brush-like tongue to enable them to better reach nectar deep in flower. Plants have a fruity odor (which attracts bat) & bat facial fur pick up pollen and transmit to other flowers as it feeds. Fruit bats live in tropical areas and some feed on flower nectar. These bats have long slender muzzles with a long, brush-like tongue to enable them to better reach nectar deep in flower. Plants have a fruity odor (which attracts bat) & bat facial fur pick up pollen and transmit to other flowers as it feeds.

21 (b) Convergent Evolution Some species have similar phenotypes without being closely related because each has adapted to the environment in which living Some species have similar phenotypes without being closely related because each has adapted to the environment in which living Sharks and porpoises look similar – both are aquatic, have fins but sharks are fish (have gills to get O 2 ) and porpoises are mammals (have lungs to get O 2 ) Sharks and porpoises look similar – both are aquatic, have fins but sharks are fish (have gills to get O 2 ) and porpoises are mammals (have lungs to get O 2 ) Analogous structures are associated with convergent evolution Analogous structures are associated with convergent evolution

22 (c) Divergent Evolution Occurs when 2 closely related species become more & more dissimilar Occurs when 2 closely related species become more & more dissimilar Occurs in response to environmental pressures – changes in climate, food source/availability, etc Occurs in response to environmental pressures – changes in climate, food source/availability, etc Homologous structures are associated with divergent evolution Homologous structures are associated with divergent evolution A type of divergent evolution is adaptive radiation – where many related species evolve from one common ancestor species (like Darwin’s finches) A type of divergent evolution is adaptive radiation – where many related species evolve from one common ancestor species (like Darwin’s finches) Artificial selection – another type of divergent evolution that is pressured on purpose, not by environment. Ex is dog breeding today, all dogs arose from Canis familiaris. Artificial selection – another type of divergent evolution that is pressured on purpose, not by environment. Ex is dog breeding today, all dogs arose from Canis familiaris.