Evidence for evolution

Question 1

evolution

Answer 1

is defined as the change in the genetic composition of a population during successive generations, which may result in the development of new species

Question 2

microevolution

Answer 2

is defined as the small-scale variation of allele frequencies within a species of population, in which the descendant is of the same taxonomic group as the ancestor
- in simple terms this means the small changes in gene frequency within a population

Question 3

macroevolution

Answer 3

is defined as the variation of allele frequencies at or above the level of species over geological time, resulting in the divergence of taxonomic groups, in which the descendant is in a different taxonomic group to the ancestor
- this means big changes over long periods of time, causing speciation

Question 4

evidence for evolution comes from many different areas of biology:

Answer 4

• anatomy: species may share similar physical features because the feature was present in a common ancestor (homologous structures)
• comparative genomics: DNA and the genetic code reflect the shared ancestry of life. DNA comparisons can show how related species are
• biogeography: the global distribution of organisms and the unique features of island species reflect evolution and geological change
• fossils: fossils document the existences of non-extinct past species that are related to present day species
• direct observations: we can directly observe small-scale evolution in organisms with short lifecycles (e.g. pesticide-resistant insects)

Question 5

geological time

Answer 5

• evolution has occurred over very vast stretches of time
• geological time can be expressed in millions of years ago (mya)
• they are called periods, eras, epochs and eons
• life on earth existed for 3.5 billion years
  Eon -> Era -> Period -> Epoch

Question 6

continental drift

Answer 6

• over time, the tectonic plates have moved significantly
• the fossil record can attest to this, and the current biogeography is explained by continental drift

Question 7

biogeography

Answer 7

• the study of the distribution of organisms and ecosystems across the world and through geological time
• the geographical distribution of species provides evidence that now isolated locations were once close
• the differences between species in different locations can give an indication of how much time has passed since they were co-located

Question 8

evolution and continental drift

Answer 8

• biogeography provides evidence for evolution
• for instance, most of the mammal species in Australia are marsupials (carry young in a pouch), while most mammal species elsewhere in the world are placental (nourish young through a placenta)
• Australia’s marsupial species are very diverse and fill a wide range of ecological roles
• because Australia was isolated by water for millions of years, these species were able to evolve without competition from (or exchange with) mammal species elsewhere in the world

Question 9

fossils

Answer 9

• fossils are the trace of a previously living organism
• for example, hard parts such as teeth, bones and shells but also include impressions left after soft tissue has decayed, or footprints, leaves, burrows or preserves faeces (coprolites)
• different types of fossils can tell us how organisms looked and moved, what they ate, how they reproduced and how they lived

Question 10

types of fossils

Answer 10

• moulds - imprint left by organisms with rock around it
• casts - imprint has been filled with rock
• body fossils - trapped in a substance or skeleton/hard body structures
• trace fossils - indirect evidence like footprints, burrows of faeces

Question 11

fossilisation

Answer 11

• fossilisation is a rare process and very few organisms are preserved in the fossil record
• fossilisation one absence of oxygen
• in some situations, the hard parts of organisms (natural bone or shell material) are replaced with minerals. This is mineralisation and makes fossilisation 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

Question 12

fossilisation requires:

Answer 12

• rapid burial of the material (this will ensure conditions are not suitable for the activity of decay organisms)
• presence of hard body parts
• long period of stability - the organism needs to be left undisturbed
• alkaline soil so that the minerals in the bones are not dissolved

Question 13

relative dating

Answer 13

used to determine the age of a rock, fossil contained in the rock, relative to other rocks or fossils found nearby
- strata are deposited in a time sequence, with the oldest on the bottom and the youngest on the top (principle of superposition)
- Palaeontologists can assign relative ages to fossils based on the strata in which they are found

Question 14

absolute dating

Answer 14

assigns a numerical age in years to a fossil or rock
- three main types: radiometric dating, electron spin resonance and luminescence
- most common methods of absolute dating is radioactive dating, which uses the known rates of decay of naturally occuring radioactive isotopes present in a rock or fossil

Question 15

law of fossil succession

Answer 15

• fossils can 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. This is called the principle of superposition
• each strata represents a variable length of time that is classified according to a geological time scale (eons, eras, periods)
• different kinds of organisms are found in rocks of particular ages in a consistent order, indicating a sequence of development
  – prokaryotes appear in the fossil record before eukaryotes
  – ferns appear in the fossil record before flowering plants
  – invertebrates appear in the fossil record before vertebrate species

Question 16

the principle of superposition

Answer 16

the principle of superposition indicates that the oldest rock layer is found at the bottom of the rock, with each consecutive layer above being relatively younger

Question 17

fossil records

Answer 17

evidence for early forms of life comes from fossils
- by studying fossils, scientists can learn how much (or how little) organisms have changed as life developed on Earth
- there are gaps in the fossil record because many early forms of life were soft-bodies, which means that they have left traces behind. What traces there were may have been destroyed of geological activity. This is why scientists cannot be certain about how life began
- fossils provide a snap shot of the past and allow us to study how much or how little organisms have changed as life developed on Earth

Question 18

traditional fossils

Answer 18

• some fossils show characteristics intermediate between present day forms
• traditional fossils demonstrate the intermediary forms that occurs over the evolutionary pathway taken by a single genus
• they establish the links between species by exhibiting traits common to both an ancestor and its predicted descendants
• an example of a traditional fossil is archaeopteryx, which links the evolutionary patterns are emerging and old assumptions are challenged

Question 19

the fossil record is incomplete

Answer 19

• the process of fossilisation requires very specific, and rare, conditions. The remains of the vast majority of long-extinct animals may never be found
• consequently, the fossil record is incomplete and biased toward organisms that lend themselves more easily to the fossilisation process

Question 20

comparative anatomy and embryology

Answer 20

comparative anatomy is the study of the similarities and differences in structure between organisms. Structural features are also called morphological features
- used to establish evolutionary relationships on the basis of structural similarities and differences, including the comparative study of embryos (embryology)
- longer they look the same - the closer related they are

Question 21

homologous structures

Answer 21

anatomical structures that are common to more than one species and were inherited from a common ancestor, but have different functions
- show the same structural plan but perform different functions due to the different species living in different environments with different selective pressures (conditions)

Question 22

pentadactyl limb

Answer 22

5 limbs, same pattern of bones, different size and shape - function

Question 23

divergent evolution

Answer 23

• is a pattern of evolution in which differences between groups of organisms accumulate to a critical point that leads to speciation, the development of a new species
• this pattern is usually the result of the dispersal of a single species to different environments, that is, groups from the same species become isolated from one another, stopping gene flow
• the sub-populations are subjected that can perform functions specific to surviving their unique environment
• homologous structures indicate divergent evolution, because new species will have the same fundamental structural plan, but the structures may be used in different ways

Question 24

adaptive radiation - a type of divergent evolution

Answer 24

• the evolution of an ancestral species, which was adapted to a particular way of life, into many different species, each adapted to a a different habitat
• adaptive radiation involves rapid speciation, and is likely to occur after an extinction event that creates many vacant ecological niches or colonisation of a new area
• example: darwins finches in the galapagos islands - evolved beak shapes - according to what they ate

Question 25

analogous structures

Answer 25

analogous structures are features of organisms that have the same function but not the same basic structure

Question 26

convergent evolution

Answer 26

- a pattern that occurs when unrelated organisms evolve similar adaptations in response to their environment - often results as analogous structures: adaptations of very different types of structures are genetically relatively different, but their functionality is very similar

Question 27

vestigial homologous structures

Answer 27

- in some cases, homologous structures stemming from a common descent can eventually cease to have any functional use for an organism - the structure may not necessarily impede a particular adaptation of an organism, but at the same tie the structure no longer serves a 'useful' purpose - vestigial structures can take a variety of forms, including bones, soft tissues, organs, cells, or molecules - vestigial organs are evident for evolution, because it is hypothesised that they were once present and functional in their ancestors - changes in the environment have rendered these organs redundant, so over time they have lost their functionality - they demonstrate the evolutionary divergence of a species from a past behaviour or activity