Evidence for Evolution

ORGANIZE YOUR THOUGHTS! EVIDENCE FOR EVOLUTION  The Fossil Record  Radiometric Dating  Morphology  Homology  Molecular Biology  Biogeography  Analogous Structures  Direct Observations

Evidence for Evolution – The Fossil Record

Evidence for Evolution There is overwhelming evidence that living species evolve from organisms that are extinct.

Evidence for Evolution – The Fossil Record What are fossils? –Fossils are the petrified remains of ancient objects. –Petrified – means turned to stone. –Ancient – means very, very old. Paleontologist: Scientist that studies fossils

Fossil Record  The fossil record refers to the order in which fossils appear within layers of rock that mark the passing of geologic time.

Evidence for Evolution – The Fossil Record FOSSIL RECORD Fossils form when an organism becomes buried in mud, volcanic ash, or sediments Over time the organic remains become replaced with inorganic minerals

Evidence for Evolution – The Fossil Record Fossils offer the most direct evidence that evolution takes place –A record of Earth’s past life-forms –Change over time can be seen in the fossil record –Darwin predicted that intermediates would be found

Evidence for Evolution – The Fossil Record –Fossil intermediates that have been found: Fishes and amphibians Reptiles and birds Reptiles and mammals Tiktaalik.

Absolute Dating absolute  Radiometric dating is the method used most often to determine absolute ages for fossils.  Organisms accumulate radioactive isotopes when they are alive, but concentrations of these isotopes decline after they die. half-life  The rate of conversion is indicated as the half-life  the time it takes for 50% of the isotope to decay.

Absolute Dating  While carbon-14 is useful for dating relatively young fossils, radioactive isotopes of other elements with longer half-lives are used to date older fossils.  While uranium-238 (half life of 4.5 billion years) is not present in living organisms to any significant level, it is present in volcanic rock.  If a fossil is found sandwiched between two layers of volcanic rock, we can deduce that the organism lived in the period between the dates in which each layer of volcanic rock formed.

Morphology Comparative anatomy –Describes two kinds of structures that contribute to the identification of evolutionary relationships among species. –Compares external morphology and internal anatomy

In the context of biology, homology is the existence of shared ancestry between a pair of structures, or genes, in different species. Homologous traits of organisms are therefore explained by descent from a common ancestor Evidence for Evolution - Homology

Why use the same skeletal plan for these very different appendages?

Evidence for Evolution – Homologous Structures develop from similar tissue in embryological development Similar in various species – provides strong evidence that all four-limbed vertebrates have descended, with modification, from common ancestors

Evidence for Evolution – Vestigial Organs  Vestigial organs: organs with no apparent function or purpose imply evolutionary relationships to primitive ancestors.

The structure served a purpose in an ancient ancestor but no longer does.

Evidence for Evolution – Vestigial Organs Vestigial Organs in Humans

EVIDENCE FOR EVOLUTION – Molecular Biology  All living things share the same genetic code.  Nucleotide and amino acid sequences of DNA and proteins from different species.  Closely related species share higher percentages of sequences than distantly related species.  Why should different organism possess related genes?

Molecular Data and the Evolutionary Relationships of Vertebrates More than 98% of the nucleotide sequences in humans and chimpanzees are identical.

EVIDENCE FOR EVOLUTION - Biogeography Geographic distribution of species has revealed that unrelated species in different regions of the world look alike when found in similar environments.

PATTERNS OF EVOLUTION Parallel Evolution –Two related species making similar evolutionary changes after their divergence. –Marsupial and Placental mammals

Patterns for Natural Selection Convergent Evolution – when two species look alike but do not have a common ancestor Similar in appearance Similar in function Different in development, origin, & anatomy Opossum Aye-Aye

EVIDENCE FOR EVOLUTION Analogous Structures  body parts that resemble one another in different species, not because they have evolved from a common ancestor  they evolved these similar adaptations independently because they evolved in similar environments with the same selection pressures. Similar solutions to similar problems

Analogous Structures –Examples: wings of bird, bat & insects are analogous structure

EXAMPLES OF CONVERGENT EVOLUTION

EVIDENCE FOR EVOLUTION – Direct Observation Evolution of pesticide resistance in response to selection.

Evidence for Evolution – Evolution Observed PHYSIOLOGICAL ADAPTATIONS Evolution of antibiotic resistance in response to selection. What Industries should be worried about resistance?

Evidence for Evolution –Drug Resistance

Heterozygote Advantage The recessive sickle-cell allele produces hemoglobin with reduced capacity to carry oxygen This mutation also confers malaria resistance in heterozygotes This heterozygote advantage leads to a larger proportion of the recessive allele than usual in areas where malaria is widespread These populations exhibit balanced polymorphism between the mutant and wild-type alleles Hypothesis: In malaria-infected cells, the O 2 level is lowered enough to cause sickling which kills the cell & destroys the parasite. Hypothesis: In malaria-infected cells, the O 2 level is lowered enough to cause sickling which kills the cell & destroys the parasite.