EVOLUTION OCCURS WHEN HERITABLE CHARACTERISTICS OF A SPECIES CHANGE IB Evolution

Clear Distinction Acquired characteristics – develop during your lifetime  ex. Tan skin in the summer, dying your hair Heritable Characteristics – Passed down from parent to offspring  Ex. Eye color, dimples Evolution ONLY concerns heritable characteristics.

Evidence from fossils Fossils have been found in rock strata Fossils have been dated using radioisotope dating Sequence of fossils in which they appear matches the sequence of when they evolved.  Bacteria – simple algae- fungi/worms – land vertebrates – boney fish – amphibians – reptiles – birds - mammals

Selective Breeding Selective breeding of domesticated animals shows that artificial selection can cause evolution  Livestock, dogs, egg-laying hens It is clear that domesticated breeds have not always existed in their current form. Humans have selected what they wanted – Artificial Selection

Homologous structures Adaptive Radiation – Similar structure, different functions.  Ex. Arms of a human, flipper of a whale  Homologous structures – may look superficially different and perform a different function, but have the same structure  Pentadactyl limbs – composed of humerus, radius/ulna, carpals/tarsals, metacarpals/metatarsals

Analogous structures – Same function, different structure. Ex. Wings of a bird, wings of a butterfly Convergent Evolution – different origins and have become similar because they perform the same or similar function

Vestigial Organs Reduced structures that serve no function  Teeth found in embryo whales – adults toothless  Appendix, wisdom teeth  Small pelvis bone found in some snakes

Speciation Populations of species can gradually diverge into separate species by evolution. If two populations of a species become separated so that they do not interbreed, and natural selection then acts differently on the two populations, they will evolve in different ways. After a time, they will be recognizably different If the populations merge, and have a chance to interbreed, but don’t, they have evolved into separate species

Speciation may occur where different parts of a population of a species become isolated from one another. Example: a species of butterfly is widely distributed across an area of grassland.

Climate changes cause the area to become wetter… … and a river forms Because the butterflies are not strong fliers… …they cannot cross the river The two groups of butterflies are now isolated from each other

One side of the river remains as grassland The other side develops into woodland

The selective pressures are different on either side of the river, so… …the two populations evolve different wing patterns

NOTE: At this stage the two populations may not be different enough to be considered as two separate species… …they may be considered as subspecies or varieties.

The climate changes again and becomes drier The river barrier is lost The land becomes mainly grassland

The two populations of butterfly can now mix together, but… …successful mating requires that they recognise each other by wing pattern, so… …they do not interbreed. The two populations are now definitely different species.

Evidence from patterns of variation Gradual Divergence – populations that are recognizably different, but not to the extent that they are clearly separate species -Ex. Peppered Moth

Variation Natural Selection can only occur if there is variation amongst members of the same species  If all individuals were identical, there would be no way of some individuals being favored more than others, and no evolution

Sources of Evolution Mutations – new alleles are produced by gene mutation which enlarges the gene pool of a population

Meiosis – produced new combinations of alleles in crossing over and the independent orientation of bivalents Sexual reproduction – gametes come from different parents, so the offspring has a combination of alleles from two different individuals  In species that do not carry out sexual reproduction, the only source of variation is mutations.

Adaptations Characteristics that make an individual suited to its environment and way of life. The term ‘Adaptation’ implies that characteristics develop over time and thus that species evolve. Adaptations develop by natural selection, not with the direct purpose of making an individual suited to its environment. Adaptations do NOT develop over a lifetime of one individual. IF they do, they are acquired characteristics and are not inheritable.

Overproduction of offspring Living organisms vary in the number of offspring they produce.  Slow breeding 1 offspring every 3 years  Southern ground hornbill

Fast breeding rate – apart from bacteria, the fastest of all is the fungus Calvatia gigantea  Produces 7 trillion spores

No matter what the breeding rate, there is an overall trend in living organisms for more offspring to be produced than the environment can support This will lead to a struggle of existence within a population This will lead to survival of the fittest This is evolution