5.1 Syllabus
U1. Evolution occurs when heritable characteristics of species change.
- Evolution = a change over time
- Heritable characteristics are encoded for by genes and may be transferred between generations as alleles
- A concise definition for biological evolution is:
u2. The fossil record provides evidence for evolution.
- The fossil (various layers were different – sequence of fossils). record provides evidence by revealing the features of an ancestor for comparison against living descendants.
Fossil Records
- Fossils are the preserved remains of animals, plants and other organisms from the past.
-The fossil record shows the gradual change of species over time
=The timeline in which fossils appear are what scientists wold expect, with bacteria and algae being the oldest in the fossil record. Followed later by shelled animals and trilobites, then dinosaurs and early reptiles birds and mammals later still
-Many fossil sequences link together present day organisms with their likely ancestors. For example present day horses and zebras are closely related to tapirs and rhinos, which are all linked back to the Hyracotherium, an animal similar to the rhinoceros
-Whale evolution fossil record is also whale documented
Reliability of Fossil Records
- Interpretation of fossil records based on differential preservation i.e. some organisms have not been found or some locations provide necessary conditions for fossilization while other areas do not.
-Bias present sine not all areas of the globe have been searched for fossils
-Small number of fossils found for a species so not sure if that is a typical or atypical representation.
-Gaps of time or missing links still exist in the fossil record
U3. Selective breeding of domesticated animals shows that artificial selection can cause evolution.
-Selective breeding is a form of artificial selection, whereby man intervenes in the breeding of species to produce desired traits in offspring. By breeding members of a species with a desired trait, the trait's frequency becomes more common in successive generations, Selective breeding provides evidence of evolution as targeted breeds can show significant variation in a relatively short period
- Breeding plants and animals for specific genetic traits
- Shows a good record of recent changes in genetic characteristics over a few dozens of generations that man has selected to breed
- For example, chicken that produce more eggs or cows that produce more milk are selected to breed, hopefully passing these traits onto next generations.
- Plants can be bred in a similar manner based on useful or beneficial characteristics breeders would like to see in the next generation of plants
- The evolution of domesticated dogs have produced many different breeds through artificial selection
U4. Evolution of homologous structures by adaptive radiation explains similarities in structure when there are differences in function.
-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 structure between two species are, the more closely related are likely to be.
-Homologous structures: Vertebrate embryos and the pentadactyl limb
-All species start out as single celled organisms. Many species develop into much larger, more complex organisms after conception. If we compare the embryos of animals as they develop, we often find they are much more similar than their fully developed counterparts. Many of the anatomical difference between species only arise during our embryonic development. Different species often start with the same basic tissues or structures but they develop differently and are re-purposed into different structures as the organism develops. The more closely two species are related, the later in development these differences usually emerge.
-Homologous structures: Vertebrate embryos and the pentadactyl limb
- Homologous structures: Various different structure sharing the same fundamental plan
- Derived from a similar embryonic origin
- Variations on the basic structure allow different functions
- Adaptive radiation= permitting exploitation of different ways of life
- Suggests divergence from a common ancestor
- Common ancestor was a land animal e.g. Shrew, with short five-toed limb with not specific specilizatoin
- Modern mammal species evolved by modification of limbs to a wide variety of habitats
- Habitats can be terrestrial, aquatic and air
- i.e. running horse, flying bats, whales
-All species start out as single celled organisms. Many species develop into much larger, more complex organisms after conception. If we compare the embryos of animals as they develop, we often find they are much more similar than their fully developed counterparts. Many of the anatomical difference between species only arise during our embryonic development. Different species often start with the same basic tissues or structures but they develop differently and are re-purposed into different structures as the organism develops. The more closely two species are related, the later in development these differences usually emerge.
U5. Populations of a species can gradually diverge into separate species by evolution.(Speciation)
-Within a population of any given species, there will be genetic variation (variation which is inheritable). Typically this variation will be continuous and follow a normal distribution curve as the rate of change is gradual and cumulative.
- Within a population there is genetic variation
- If 2 populations of the same species become separated so that they do no reproduce or interbreed because they became separated by mountain range, then natural selection will act differently on those two separate populations.
- Over time, these populations change so that they are recognizably different and can or do not interbreed if they were to merge together again
U6. Continuous variation across the geographical range of related populations matches the concept of gradual divergence.
-The degree of divergence between geographically separated populations will gradually increase the longer they are separated. As the genetic divergence between the related populations increase, their genetic compatibility consequently decreases. Eventually, the two populations will diverge to an extent where they can no longer interbreed if returned to a shared environment. This process is called speciation.
- When populations diverge over time and are separated, one would expect these populations to be in different stages of variation or divergence and not all separate distinct organisms right away or all the same unchanged species.
- Darwin gave many of these examples that showed populations that are slightly different, but are not clearly separate speices
- Examples of this are the Lava lizards and finches of Galapagos, and the Spiny Sticklebacks of BC
A1. Development of melanistic insects in polluted areas.
-Peppered moths exist in two distinct polymorphic forms - a light coloration and a darker melanic variant
-In post industrial revolution, tree trunks in forests become dark due to covering with soot. After 1850, dark form of peppered moth were collected. Over the next 45 years, dark forms of moth became more common
- In an unpolluted environment, the trees are covered by a pale-colored lichen, which provides camouflage for the lighter moth
- In a polluted environment, sulphur dioxide kills the lichen while soot blackens the bark, providing camouflage for the dark moth
-In post industrial revolution, tree trunks in forests become dark due to covering with soot. After 1850, dark form of peppered moth were collected. Over the next 45 years, dark forms of moth became more common