Ch 6: Evidence For Change Flashcards
(14 cards)
Define evolution
a process that results in cumulative heritable changes in a population spread over many generations
What is the order of geologic time and what is it expressed in?
epochs (marked by one or more significant event) > periods > eras > eons
Geologic time can be expressed in millions of years ago (mya).
What are major changes that have happened over the Earth’s history?
- over time, the tectonic plates have moved significantly in a process called continental drift which is the relative movement of Earth’s continental landmasses that appear to float/drift over the fluid mantle. The fossil record can attest to this and the current biogeography is explained by continental drift.
- large climate oscillations have occurred on Earth over its history. These oscillations have occurred in Earth’s temperature, humidity and sea level.
- oxygen level began to increase
What is the fossil record and how are fossils formed?
definition: an preserved remains or traces of past life foun in sedimentary rocks of different ages. Fossils are the preserved remains of organisms and their traces. They are commonly hard parts such as teeth, bones and shells but also include impressions left after soft tissue has decayed, or footprints, burrows or preserved faeces (coprolites).
- Fossilisation is a rare process and very few organisms are preserved in the fossil record.
- it requires the absence of oxygen.
- In some situations, the hard parts of organisms are replaced with minerals. This is mineralisation and makes fossiliation more likely. Organisms can be covered with sediment such as silt or sand. This can protect the remains from scavengers and slow the decay long enough for fossilisation to occur.
- Fossils can be formed as a result of freezing and subsequent dehydration, by soft material such as ash falling on impressions, or from impressions made in sandstone and mudstone.
What are fossil dating techniques?
- Comparative dating of fossils can give an idea of how old a rock (perhaps containing a fossil) is in relation to surrounding rocks, since we know that sedimentary rock is formed by gradual deposition of sediments.
- Lower rock is assumed to be older than rock that is higher.
- The rock may have tilted or even rotated, so this method requires careful observation.
- Absolute dating involves the use of techniques that can assign a numerical age to a fossil or rock. Techniques include:
- Radiometric dating - takes advantage of known rates of atomic decay
- Electron spin resonance - electrons trapped in a material gain magnetic force as a result of exposure to environmental radiation over time.
- Luminescence techniques - measure light emitted from a material
How does the fossil record provide evidence for evolution and how reliable is it?
- by comparnig living organisms with ancestors which can indicate change in the anatomy of species over time or links between species
- shows an increase in complexity over time
- provides examples of intermediates (transitional forms) that are no longer alive
- moderately reliable due to conditions required for fossilisation being so specific such as aaerobi and fast covering of sediment, it can only show phenotypic relatedness and due to convergent evolution can mislead us toward thinking some species are more related than they are
What are transitional forms and how do they provide evidence for evolution?
organisms that show important intermediate states between an organism’s ancestral form and that of its descendants, indicating development from one group to another
- i.e. Archaeopteryx, the dinosaur/bird transitional form, small flying dinosaur with feathers, sharing reptillian ( long tail, claws, no keel, solid bones, teeth) and bird (wish bone, feathers) features suggesting birds evolved from reptiles
- because transitional forms usually did not remain in their state for long periods, the probability of a specimen being captured in the fossil record is low.
- help biologists to understand how evolution may have come about
What are the two theories of evolutionary patterns?
- gradualism is the concept that assumes that evolution of species occurs as a steady, slow divergence of lineages (ancestral tree branches) at an even pace. Sudden bursts of evolution implied by the fossil record are not a real indication of an evolutionary history, but an illusion of the fossil record i.e. an absence of fossils demonstrating the transition/change in conditions made fossilisation impossible
- the theory of punctuated equilibrium, on the other hand, states that evolution occurs in bursts and between the bursts are periods of relative stasis i.e. in response to environmental changes
How is embroyology evidence for evolution?
Embryology is the comparative study of vertebrate embryos, which share similarities across a large range of species even with relatively distant common ancestors.
- similar embryos indicate they have a number of similar genes and possibly common ancestors
- i.e. vertebrates all have pharyngeal folds (gill slits), post anal tail, dorsal notochord, doral nerve chord - sea squirts, suggests that these vertebrates evolved from a common aquatic ancestor
- relatively low degree of reliability because the anatomy being compared is only viewed at an early stage of life before most of an organism’s development occurs
What is biochemistry and how is it evidence for evolution?
definition: study of and comparison of proteins, DNA and other compounds within organisms. As similarity increases, so does the likelihood they evolved from a common ancestor
- all living organisms share the same genetic code, which suggests that it is a very successful way of transmitting hereditary information and is highly conserved. Proteins are often conserved if their structure is well suited to their function, even while species evolve i.e. histone proteins, whose function is the same across different species.
- Mutations arise in DNA at a fairly constant rate, the mutation rate, which varies across species. The mutation rate for humans is approximately 10-8 per nucleotide per generation. Comparing the number of mutations in a DNA sequence can give an estimation of the time since two species diverged
- similarity of DNA hybridisation of in primate groups indicates they evolved from a common ancestor
- Comparative genomics uses bioinformatics to analyse genome sequences of different species for sequence conservation and mutation frequencies. This can help to trace the evolutionary history of the divergence of the two genomes. This can help to build a branching phylogenetic tree in the technique of molecular phylogeny.
How does comparitive anatomy provide evidence for evolution?
Homologous structures
features that were present in common ancestors and have evolved to perform different functions in descendent species but have the same general structure
- i.e. pentadactyl limb - 5 digit limb found inmany vertebrates such as whales, humans and birds, study shows how seemingly disparate kinds of organims actually share many fundamental similarities and strongly supports the notion that these were derived from a common ancestor because only organisms w the same ancestor can have the structures with the same basic arrangement
- low reliability as some distantly related species can develop structures that look similar (analogous structures) misleading us into thinking they are closely related i.e. anteating structures of echidna and numbat
Vestigal structures
structures that presently no longer have a function
- the presence of the organ may indicate it was once used in an ancestral organism i.e. coccyx and appendix in humans
Analogous structures
features of organism that have the same function but not the same structure
- indicates organims have converged
- most misleading/lowest reliability
What is divergent evolution and what is the cause of this type of evolution?
when related species evolve new traits over time, away from the common ancestor to give rise to new species
cause
- usually happens when groups of a single species disperse to different environments which then become isolated, preventing individuals from moving between the groups. They may evolve different adaptations in response to a range of environmental pressures.
- isolation can be due to mountains, rivers, or different reproduction times
- organisms develop different traits with some becoming more common due to genetic drift or natural selection. Over many generations, the two groups can become two different species (speciation)
What is adaptive radiation?
What is convergent evolution?
definition: when different species evolve similar adaptations in response to similar environmental demands or opportunities
An example of convergent evolution is the adaptation of ant-eating structures in ant-eating species (ant-eaters, echidnas)
These are termed analogous structures; structures that have independently evolved for the same function i.e. dolphins (mammals) and sharks (fish) that both have streamlined body shape and possess fins for populsion and stability - features adaptive for movement in a highly viscous environment. Both under same selection pressures
