How does isolation lead to the formation of new species?
- members that are isolated can no longer interbreed with the rest of the group and because some members within the group are subjugated to a different selective pressure.
- As a result, through natural selection those isolated members would adapt both physically and mentality thus they are unable to interbreed, forming a new species.
Lamarck theory:
- the theory of inheritance of acquired characteristics: organisms change during its lifetime due to adapt to their environment and those changes are then passed down
e. g. Giraffes used to have shorter necks but because they were subjugated to an environment where shrubs and grass was unavailable their only possible food source was in the trees. Hence giraffes continued to stretch their necks, causing their necks to lengthen, these characteristics are then passed down and soon later after many generations of giraffes stretching their necks, they now have the long necks we know now of.
What is evolution?
Evolution is the idea that species can change over time, that new species come from pre-existing species, and that all species share a common ancestor.
Within a species there is variation. Some members of a species have characteristics better suited to survive in the environment so they survive to reproduce, passing on these favourable characteristics to their offspring. Over time, the majority of the species will have these characteristics. Over million of years these genetic changes can lead to evolution of the species.
What is natural selection?
The process by which certain inherited traits make it easier for some individuals to thrive and multiply, changing the genetic makeup over time.
What are the requirements for natural selection?
- Variation exists between individuals in a population
- Many differences between individuals in a population are inherited
- Not all individuals in a population survive to produce offspring
- Those individuals in a population that are ‘fitter’ (better adapted to the environment) contribute more to the next generation than those that are less for.
What is the Wallace’s line?
- Imaginary line between Australia and South-East Asia, which separates the flora and fauna
o Organisms to the west of the line include mammals and Asiatic species whilst on the east included marsupial mammals and Australian species
What conditions are necessary for fossilisation?
- Organisms must be buried quickly
- Dead organism must be buried quickly:
- be void of scavengers
- protected
- lack of oxygen
- low acidity levels
- low temperature - Dead organism must lie undisturbed
When organisms are left undisturbed the sediments in which organisms are buried harden and become sedimentary rocks.
Why are fossils important?
- Through contrasting the present- day animals and plants and fossils, thus how plants and animals change over time
- Past climates can also be determined by contrasting the conditions of present- day animals in which they live and applied to fossils
- evidence for evolution
Evidence for evolution:
Chemical similarities:
This is because offspring will inherit an ancestor’s DNA sequence and mutations unique to the ancestor
- 20 amino acids are used to make proteins though 250 amino acids exist natural, therefore if life has evolved with only 20 amino acids, we may expect the same 20 amino acids to always be used
- E.g. insulin can be used from a pig or cows, though there is variation in amino acid sequences but they all have the same function to help cells absorb sugar
- DNA code, amino acid sequence where:
o Large difference in the code means that the common ancestor of the two organisms live a long time ago
o Small difference in the code means that there was a more recent common ancestor
- DNA sequencing: technique that works out the base code for a section of DNA
o Used to compare the genetic code of different organisms to show similarities, differences and how closely related organisms are biochemically.
Evidence for evolution:
Anatomical similarities
- Homologous structures: are structures in different species that are similar due to a common ancestor
E.g. pentadactyl limb is a limb with five digits and is found in amphibians, reptiles, birds and mammals - Vestigial structures: parts that seem non- functional with little or no importance in an organism
E.g. appendix, muscles to move the external ear
Biogeography:
The distinctive pattern of different species around the world
Evidence for evolution: Comparative embryology
- Embryos demonstrate huge similarities during early stages of development
- Development of an embryo retraces the stages of the evolution of that species
E.g. AT one stage embryo has gill slits, a tail, fish- like heart and a fish kidney. Even later on the embryo has baby ape’s body proportions - If they developed independently then why does a bird’s three- digit wing develop from a five- limit wing
- The more similar the early stages of embryonic development, the more closely related the species are
Evidence of evolution: transitional forms
are ‘missing links’ between different groups
- Showing a evolutionary pathway
E.g. Archaeopteryx
