Session 2: Evidence for Evolution Flashcards
What is a fossil? What are the two types of fossils?
A fossil is the preserved remains or traces of any organism from the remote past. Fossil evidence may be either:
Direct (body fossils): Bones, teeth, shells, leaves, etc. Or Indirect (trace fossils): Footprints, tooth marks, tracks, burrows, etc.
Describe the fossil record.
The totality of fossils, both discovered and undiscovered, is referred to as the fossil record. It shows that changes have occurred in the features of living organisms (evolution). It shows new species emerging (divergence and speciation) and extinctions. It is good evidence for evolution as it demonstrates a change in an organism’s characteristics from an ancestral form.
How can fossils be dated?
By determining the age of the rock layer (strata) in which the fossil is found. Sedimentary rock layers develop in a chronological order, such that lower layers are older and newer strata form on top. Each strata represents a variable length of time that is classified according to a geological time scale (eons, eras, periods). Radioactive dating can also be used for igenous rock which has radioactive material inside it.
What is the law of fossil succession?
The chronological sequence of complexity by which characteristics appear to develop. This ordered succession of fossils suggests that newer species likely evolved as a result of changes to ancestral species. The occurrence of transitional fossils demonstrate the intermediary forms that occurred over the evolutionary pathway taken within a single genus
What are the three specific circumstances required for fossil formation?
Rapid burial (high pressure), Lack of oxygen/no decomposition by bacteria, and Preservation of remains (i.e. not consumed or removed by scavengers). As these conditions are not common, this means that there are many gaps in the fossil record. Also, usually only the hard parts of an organism are preserved and often only fragments of fossilized remains are discovered
What is biogeography?
Biogeography describes the distribution of lifeforms over geographical areas, both in past and present times. Biogeography provides evidence for evolution because it suggests that closely distributed species share a common lineage. If speciation was random, the distribution of structurally similar species would be expected to be scattered
What is the centre of origin?
The basic principle of biogeography is that each plant and animal species originated only once. The place where this occurred is the centre of origin. Related species are usually found in close physical proximity (supporting the concept of speciation via gradual divergence). Fossils found in a particular region tend
to closely resemble the modern organisms of the region
Describe comparative anatomy.
Comparative anatomy of groups of organisms may show certain structural features that are similar, implying common ancestry. Anatomical features that are similar in basic structure despite being used in different ways are called homologous structures. The more similar the homologous structures between two species are, the more closely related they are likely to be. Homologous structures illustrate adaptive radiation, where several new species rapidly diversify from an ancestral source, with each new species adapted to utilise a specific unoccupied niche. For example, the human arm and the wing of a bat are similar in basic structure but not in function.
What is an example of homologous structures?
Tetrapods (organisms
with 4 limbs) all have very similar bone structures in their limbs
(pentadactyl), despite different functions for
the limbs. This indicates a common ancestor, followed by evolutionary changes and natural selection.
What are analogous structures?
Structures in organisms that come from different origins, and form the same features because of similar niches/natural selection/environment. E.g. butterflies and birds both have wings. This is called convergent evolution.
What are vestigial structures?
Vestigial structures are small remnants of organs which previously in a species’ evolutionary history were useful, e.g. wings in the kiwi, pelvic bones in snakes and whales, and appendix in humans. The structures generally do not completely disappear as; the selection pressure for that to happen is not there, the genes for their presence are still active, or they still have a minor function.
What is embryology?
During embryonic development, very different organisms show similar structures from earlier stages in their evolutionary development. This is evidence for common ancestry.
Describe proteins in relation to evolution.
Amino acid sequences are determined by inherited genes and differences are due to the accumulation of mutations. The degree of similarity of these proteins is determined by the number of mutations that have occurred. Distantly related species have had more time for differences to accumulate. Hence, protein sequencing and the production of proteins can be used to identify common ancestors.
Describe DNA in relation to evolution/association.
Molecular techniques have enabled the sequence of DNA in different species to be determined. Species thought to be closely related on the basis of other evidence, were usually found to have a greater percentage of DNA sequences in common.
Describe hybridisation.
DNA strands can be separated with sufficient heat and will reform (re-anneal) as the temperature falls. Single-stranded DNA from different species can be mixed together
to identify the degree of similarity (as measured by complementary base pairs). Closely related sequences will join together (hybridise) more strongly as they share more complementary base pairs. The strength of the hybrid molecule (and degree of similarity) can be measured by how much heat is required to separate the strands
