Scientific FieldsScientific Fields  Different fields of science have contributed evidence for the theory of evolution  Anatomy  Embryology  Biochemistry  Paleontology

Anatomy  Anatomy: study of the structures of organisms  Provides one type of data for the support of biological evolution  Homologous structures

Anatomy and homologous structures  Homologous structures: one form of evidence to determine the possible relationships between the evolutionary paths of two species  Organisms diverged from a common ancestor often have homologous structures  Homologous structures: similar characteristics resulting from common ancestry  The greater the numbers of shared structures between two species, the more closely the species are related

Anatomy: Vestigial organsAnatomy: Vestigial organs  Many species have vestigial organs that are parts of structures that had important functions in an ancestor of the species  Vestigial organ: structure with little or no function to the organism  The vestigial organs of one species are often homologous with structures in related species where the structure has remained functional

Anatomy and EvolutionAnatomy and Evolution  Study of species located in different geographical locations reveals that species living in different locations under similar ecological conditions developed similar structures and behaviors  If a species encountered a different ecosystem due to a change in geographical location, favorable anatomical traits become established.  A new species evolves with a shared common ancestor from the original population

Embryology  Embryology: study of embryonic development of organisms  Provides support for biological evolution by comparing anatomies of embryos  Embryos: an early stage (pre-birth) of organism development

Embryology and EvolutionEmbryology and Evolution  Patterns of development or structures may not be obvious in adults but can be observed in embryos  Embryos of vertebrates are similar in appearance but may grow into different structures in the adult form  The similar structures of these embryos may suggest that these species evolved from common ancestors

Biochemistry  Biochemistry: study of the chemical processes in organisms  Studies genes and proteins to provide support for biological evolution

Biochemistry and EvolutionBiochemistry and Evolution  The more similar the DNA and amino acid sequences in proteins of species, the more likely they are to have diverged from a common ancestor  Biochemistry provides evidence of evolutionary relationships among species when anatomical structures may be hard to use  Examples:  When species are so closely related that they do not appear to be different  When species are so diverse that they share few similar structures

Paleontology  Paleontology: study of prehistoric life  Another tool that can be used to provide support for biological evolution

Paleontology and EvolutionPaleontology and Evolution  Fossil record provides good evidence of life forms and environments along a timeline  Also supports evolutionary relationships by showing the similarities between current species and ancient species  Comparing current and ancient species shows a pattern of gradual change from the past to the present  Fossil record of Earth shows a history that tells a story of the types of organisms that have lived on Earth (including extinct species) and the relative ages of those fossils.

Paleontology and EvolutionPaleontology and Evolution  The fossil record is not complete because most organisms do not form fossils  Many gaps have been filled in as more fossils have been discovered  The older the fossils, the less resemblance there is to modern species

Phylogeny  Scientists study data to trace the phylogeny of a species or a group of related species  Phylogeny: evolutionary history  An evolutionary theory has been developed that states all forms of life on Earth are related because the ancestry of organisms can be traced back to a common origin  Evidence of the shared history is found in all aspects of living and fossil organisms  Physical features  Structures of proteins  Sequences found in RNA and DNA  Scientists must use multiple sources of evidence in drawing conclusions concerning evolution

Anatomy and PhylogenyAnatomy and Phylogeny  Phylogenies constructed assuming anatomical differences increase with time  The greater the similarity, the more recently a pair of species share a common ancestor  Evolutionary difference = divergence

Anatomy and PhylogenyAnatomy and Phylogeny  Observations on as many anatomical structures as possible are used to construct phylogenies  Sometimes individual structures suggest relationships that differ from bulk of evidence  This may result from convergence (structures becoming more similar with time)  Convergence: when organisms with different evolutionary histories adapt to similar environments

Embryology and PhylogenyEmbryology and Phylogeny  Embryonic development allow scientists to reconstruct the phylogenies of highly divergent taxa (groups) that may have evolved so many anatomical differences that they are difficult to compare otherwise  Selection for successive new stages at the end of embryonic development = a mechanism of evolution  Ontogeny recapitulates phylogeny  Ontogeny: growth and development of an individual organism  As we go through development from embryo to adult, animals go through stages representing stages in the evolution of their remote ancestors.

Ontogeny recapitulates phylogenyOntogeny recapitulates phylogeny

Paleontology and Phylogeny  Fossil record provides information regarding the dates and order of divergence for phylogenies  Transitional fossils: fossils that show links in traits used to document intermediate stages in the evolution of a species  Used to confirm evolutionary relationships

Paleontology and EvolutionPaleontology and Evolution  Challenge of using fossil record as a map of evolutionary history = record is incomplete  Millions of fossils have been discovered, but still large gaps exist  Many environmental conditions must be to create a fossil and the chance of all of these conditions being met at once is very rare  Fossil records favor species that were long lasting, abundant, and had hard shells/skeletons  Gaps do not indicate weakness in the theory of evolution  Instead indicate opportunities for more research  Fossils still being found that help fill in existing gaps = transitional fossil

Biochemistry and Phylogeny  Evolutionary history can be constructed assuming that differences in DNA, proteins and other molecules increase over time.  The greater the genetic similarity, the more recently a pair of species shares a common ancestor  “Molecular clock” = time since a pair of species diverged

Biochemistry and Phylogeny  Comparison of DNA sequences provides reliable evidence, but challenges exist:  Genes evolve at different rates making it difficult to yield information about groups of organisms  Insertions and deletions results in homologous genes of different lengths, making it hard for comparison  Different assumptions = different phylogenetic trees  Natural selection can cause convergence in molecules

Theory of EvolutionTheory of Evolution  One piece of evidence does not mean an accurate picture of the history of evolution  The more pieces of evidence collected from all of the different fields, the more reliable the hypothesis becomes  Theory of evolution = a well-tested explanation that accounts for a wide range of observations  No scientists suggests all parts of theory are understood and still many unanswered questions remain