5.1 Evidence for Evolution

Define pentadactyl limb.

A limb with five digits

• Contrast analogous structures and homologous structures.

1: Analogous structures are ones that have superficial similarities. Homologous structures appear superficially different. 2: Homologous structures are structurally similar to each other whereas analogous structures when studies closely are very different to each other. 3: Analogous structures have had different origins whereas homologous have come from the same origin. 4: Analogous structures perform the same function whereas homologous structures perform different functions.

• Explain three pieces of evidence that fossils provide that evolution has occurred.

1: The sequence that fossils appear match the sequence in which they would be expected to evolve: with simple organisms in older strata and more complex organisms in more recent strata. (Bacteria and simple algae appeared first, fungi and worms later and land vertebrates later still) (among the vertebrates: bony fish appeared about 420 mya, amphibians 340 mya, reptiles 320 mya, birds 250 mya and placental mammals 110 mya) 2: the sequence of fossils also fits in with the ecology of the groups, with plants fossils appearing before animal, plants on land before animals on land, and plants suitable for insect pollination before insect pollinators 3: Fossils often show transitions and/or links between living organisms and likely ancestors

Define vestigial structure.

A reduced structure that serves no function.

Contrast convergent evolution and adaptive radiation.

Convergent evolution is when structures (of different origins) have had different origins and have become similar because they perform the same or a similar function. Adaptive radiation are structures that share the same origin and have become different from each other because they perform different functions.

Relate differences in pentadactyl limb structures to differences in limb function.

Crocodiles walk or crawl on land and use their webbed hind limbs for swimming. Penguins use their hind limbs for walking and their forelimbs as flippers for swimming. Echidnas use all four limbs for walking and also use their forelimbs for digging. Frogs use all four limbs for walking and their hindlimbs for jumping.

Explain how natural selection leads to changes in the melanistic variety of insects in polluted areas.

Dark varieties of typically light-coloured insects are called melanistic. During the day Biston betularia (peppered) moths roost on the branches of trees. Birds and other animals that in daylight predate moths if they find them. In unpolluted areas tree branches are covered in pale-coloured lichens and peppered moths are well camouflaged against them. Sulphur dioxide pollution kills lichens. Soot from coal burning blackens tree branches. Melanic moths are well camouflaged against dark tree branches in polluted areas. In polluted areas the melanic variety of Biston betularia replaced the peppered variety over a relatively short time, but not in non-polluted areas.

Propose a mechanism that explains the pattern found in vertebrate limb structure yet allows for the specialization of different limb functions.

Evolution from a common ancestor.

Explain the process of artificial selection using selective breeding.

Humans repeatedly select for and breed the individuals most suited to human uses.

Describe the process of gradual speciation.

If two populations of a species become separated so that they do not interbreed and then natural selection acts differently on the two populations, they will evolve in different ways. The characteristics of the two populations will gradually diverge and eventually become recognisably different. If the populations subsequently merge and have the chance of interbreeding, but do not actually interbreed, it would be clear that they have evolved into separate species.

Use an example to explain how selective breeding has lead to evolution in a species.

Over the last 150,000 years many breeds of dogs have been developed by artificial selection from domesticated wolves. (There have been considerable changes that have occurred in domesticated animals over periods of time that are very short, in comparison to geological time.)

State an example of analogous structures.

Similarities between the tail fins of whales and fishes.

Explain how continuous variation across geographical ranges is evidence of evolutionary change.

Since populations gradually diverge over time to become separate species, then at any moment it is expected that examples of all stages of divergence can be found.

Define strata and paleontology.

Strata: layers of rock or soil with characteristics that distinguish it from other layers. (strata often contain different types of fossils) Palaeontology: the study of fossils (which provides strong evidence that life on earth has changed over time.)

State an example of a vestigial structure.

The appendix in humans.

Define evolution.

The cumulative change in the heritable characteristics of a population.

State an example of homologous structures.

The forelimbs of a human, mole, horse, porpoise and bat have the same bones, in the same relative positions.

State an example of recognizably different populations of the same species across a geographical range.

The red grouse (of Britain) and the willow ptarmigan (of Norway)