10.4. EVIDENCE FOR EVOLUTION

Question 1

who developed the theory of evolution?

Answer 1

Charles Darwin in 1809

Question 2

Aboard the HMS Beagle in 1831, what book did Charles Darwin read and what was this based on?

Answer 2

• ‘Principles of Geology’
• suggested that fossils were actually evidence of animals that had lived millions of years ago
• popularized principle of uniformitarianism

Question 3

where did Darwin carry out some of his most famous observations on finches?

Answer 3

• Galapagos Islands
• different islands had different finches that were similar in many ways so must then be closely related, despite beaks and claws being different shapes and sizes

Question 4

through Darwin’s observations on finches, what did he realise?

Answer 4

• the design of finches’ beaks was linked to the foods available on each island
• concluded that a bird born with a beak more suited to the food available would be more likely to survive than a bird whose beak was less suited
• therefore, it would have more offspring, passing on its characteristic beak
• over time the finch population on that island would share this characteristic

Question 5

what did Darwin do after finding specimens of organisms he wanted to study?

Answer 5

• he sent them back to the UK where scientists could see the specimen first hand and spot characteristics/ links between organisms that Darwin had not
• e.g. Darwin didn’t notice that the tortoises present on different islands were different subspecies

Question 6

what did Darwin do upon his return to England?

Answer 6

• spent many years developing ideas
• carried out experimental breeding of pigeons to gain direct evidence that his ideas might work

Question 7

who was also carrying out research on evolution at the same time as Darwin, in Borneo?

Answer 7

• Alfred Wallace

Question 8

what was the book Darwin published alone, despite working on the theory with Wallace?

Answer 8

‘On the Origin of Species’, 1859
- in this book, he named the theory both had presented independently as the theory of evolution by natural selection

Question 9

what are some sources for the evidence of evolution?

Answer 9

• paleontology (fossils/ fossil record)
• comparative anatomy (similarities/ differences between organisms’ anatomy)
• comparative biochemistry (similarities and differences between the chemical makeup of organisms)

Question 10

how do fossils form?

Answer 10

• when animal and plant remains are preserved in rocks
• over long periods of time, sediment is deposited on the earth to form layers of rock
• different layers correspond to different geological eras (i.e. most recent at the top)
• within the different layers, the fossils found are quite different, forming a sequence from oldest to youngest, which shows that organisms have gradually changed over time (fossil record)

Question 11

what evidence is there provided by the fossil record?

Answer 11

• fossils of different organisms are found in different layers
• sequence in which fossils found matches ecological links to each other
• similarities show common ancestors
• allow relationships between extinct and extant (living) organisms to be investigated

Question 12

how do fossils being found in different layers provide evidence for the fossil record?

Answer 12

• fossils of the simplest organisms such as bacteria are found in the oldest rocks
• fossils of more complex organisms such as vertebrates are found in most recent rocks
• this supports the evolutionary theory that simple life forms gradually evolved over an extremely long time period into more complex ones

Question 13

how does ‘sequence in which fossils found matches ecological links to each other’ provide evidence for the fossil record?

Answer 13

• for example, plant fossils appear before animal fossils
• this is consistent with the fact that animals require plants to survive

Question 14

how does studying similarities in the anatomy of fossil organisms provide evidence for the fossil record?

Answer 14

• scientists can show how closely related organisms have evolved from the same ancestor
• for example, zebras and horses are closely related to the rhinoceros
• extensive fossil record of these organisms exists and links them to a common ancestor
• lineage has been based on structural similarities between their skull and skeleton, particularly their feet

Question 15

how is the fossil record not complete?

Answer 15

• e.g. many organisms are soft-bodies and decompose quickly before they have a chance to fossilize
• the conditions needed for fossils to form are not often present
• many other fossils have been destroyed by the Earth’s movements, such as volcanoes, or still lie undiscovered

Question 16

what is comparative anatomy?

Answer 16

• as the fossil record is incomplete, scientists look for other sources of evidence to determine evolutionary relationships
• this is the study of similarities and differences in the anatomy of different living species
• includes homologous structures

Question 17

what is a homologous structure?

Answer 17

• is a structure that appears superficially different (and may perform different functions) in different organisms, but has the same underlying structure
• e.g. is the pentadactyl limb of vertebrates

Question 18

how do vertebrate limbs show evidence for comparative biology through homologous structures?

Answer 18

• vertebrate limbs are used for a wide variety of functions such as running, jumping and flying
• bone structure of limbs are very similar to those who use them for flying and for those who don’t
• same bones are adapted to carry out the whole range of different functions
• explanation is that all vertebrates have evolved from a common ancestor therefore vertebrate limbs have all evolved from the same structure

Question 19

what does the presence of homologous structures provide evidence for?

Answer 19

• divergent evolution
• how different species have evolved from a common ancestor, each with a different set of adaptive features
• this type of evolution will occur when closely related species diversify to adapt to new habitats as a result of migration or loss of habitat

Question 20

what is comparative biology?

Answer 20

• the study of similarities and differences in the proteins and other molecules that control life processes
• although these molecules can change over time, some important molecules are highly conserved among species
• slight changes that occur in these molecules can help identify evolutionary links
• two of the most common molecules studied are cytochrome c, a protein involved in respiration, and ribosomal RNA

Question 21

what does the hypothesis of neutral evolution state?

Answer 21

• that most of the variability in the structure of a molecule does not affect its function
• due to most of its variability occurring outside of the molecule’s functional regions
• changes that do not affect a molecule’s function are called ‘neutral’
• since they have no effect on function, their accumulation is not affected by natural selection
• as a result neutral substitutions occur at a fairly regular rate, although the rate is different for different molecules

Question 22

how do scientists discover how closely two species are related?

Answer 22

• by comparing molecular sequence of a particular molecule
• by looking at the order of DNA bases, or just the order of amino acids in a protein
• number of differences that exist are plotted against the rate the molecule undergoes neutral base pair substitutions
• then scientists can estimate the point at which the two species last shared a common ancestor
• species that are closely related have the more similar DNA and proteins
• ribosomal RNA has a very slow rate of substitution, so it is commonly used together with fossil information to determine relationships between ancient species