Scientific Evidence from Anatomy, Embryology,

Biochemistry, and Paleontology

B-5.5: Exemplify scientific evidence in the fields of anatomy, embryology, biochemistry, and paleontology that underlies the theory of biological

evolution.B-5.6: Summarize ways that scientists use data from a variety of sources

to investigate and critically analyze aspects of evolutionary theory.

Scientific 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 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 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 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 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 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 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 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 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 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 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 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 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