Evidence Of Evolution Flashcards
What are the Changes in physical conditions in the environment?
These include natural conditions, such as temperature and the availability of water.
The Australia landmass has become drier over time and this has lead to changes in the species of kangaroos that are present today. Approximately 25 million years ago, Australia was considerably wetter than today with large areas of rainforest. During this time, kangaroos were small and omnivorous, with unspecialised teeth, eating a variety of foods from the forest floor. Food was nutritious and abundant; there was no need for specialised grinding teeth.
As Australia became more arid and grass became the dominant vegetation in some areas, environmental selective pressure resulted in larger kangaroos favouring teeth suitable for grass. These teeth, high-crested molars, efficiently grind low-nutrition grass into a more easily digestible paste. Slicing pre-molars have been reduced.
What are the Changes in chemical conditions in the environment?
Chemicals that can affect the evolution of species include salts and elements, such as iron. For example, many parts of Australia have soils that have a high salinity. There are a range of salt tolerant plants that have evolved to inhabit those areas. The animals that feed from these plants have also evolved to inhabit those areas.
The sheep blowfly, Lucilia cuprina, is a major problem to the Australian sheep industry. It stresses, weakens and can be lethal to sheep when larvae, laid by females, burrows into wounds and wet wool. Chemicals, such as dieldrin and organophosphates, have been used extensively to control the blowfly. However, genetic resistance has occurred within the fly population that has made these chemicals ineffective. Withholding a particular insecticide for a time allowed the resistance of this particular blowfly population to drop. Continued use of the insecticide has resulted in the mutation of a modifier gene that increases and maintains the resistance. Thus, the insecticides can never be effective again, regardless of the number of blowfly generations that pass.
What are the Competition for resources?
This occurs within a species and between species. If a new species is introduced into an area then the competition may lead to different species using different resources.
Resources can include food, space or mates. If populations that live in the same area could specialise on slightly different resources or breed at different times, they would avoid direct competition.
Some species of fruit fly have evolved into different species with each confined to a different type of fruit tree. This is possible if there are different flowering and fruiting times on each tree type suited for different breeding cycles in the fruit flies. Eventually, two distinct species can result.
describe, using specific examples, how the theory of evolution is supported by the following areas of study: what are some theory’s?
palaeontology, including transitional forms biogeography comparative embryology comparative anatomy biochemistry
What is palaeontology as evidence to evolution?
The fossil record provides a time line of evolution of life engraved in the order in which the fossils appear in rock layers. Some parts of the fossil record show a gradual change in life forms over millions of years.
Of particular interest are transitional fossils that have characteristics belonging to ancestral and descendant groups. The most famous transitional form is Archaeopteryx. This is a fossil first thought to be a therapsid reptile. Its reptilian features include teeth and a reptilian-like skeleton. However, Archaeopteryx also had feathers and a wishbone sternum used to attach flight muscles. This provides evidence of an evolutionary pathway from dinosaurs to birds.
Transitional Fossils (external website) (external website) Archaeopteryx: an early bird, Museum of Paleontology, University of California, Berkeley, California, USA
What is Biogeography as a source of evidence for evolution?
Charles Darwin and Alfred Russell Wallace both observed the distribution of species into different biogeographic regions and saw this as major evidence to support the theory of evolution. They argued that animals in different regions had come from ancestors in that region and had adapted over time to the conditions there. Special Creation, the prevailing religious-based explanation of the time, did not explain why islands with similar conditions did not contain the same flora and fauna. Darwin proposed that migration and evolution were much more satisfactory explanations for the unique flora found in places such as Australia.
What is Comparative embryology as evidence to evolution?
There is an obvious similarity between embryos of fish, amphibians, reptiles, birds and mammals. A comparison of embryos of vertebrates shows that all have gill slits, even though they do not remain later in life, except in fish. This indicates a fundamental step that is common to all vertebrates and supports the idea of a common ancestor.
Embryonic Development (external website) Animations of embryos, NOVA Online PBS Broadcasting, USA
What is Comparative anatomy as evidence for evolution?
Anatomical structures on different organisms that have the same basic plan but perform different functions are called homologous structures. Homologous structures are evidence for evolution. The structures are shared by related species because they have been inherited in some way from a common ancestor.
An example of an homologous structure is the pentadactyl limb found in amphibians, reptiles, birds and mammals. The basic plan consists of one bone in the upper limb, two in the lower limb leading to five fingers or toes. In bats, the limb is modified to form a wing with the fingers extended and skin stretched between each finger. Whales have within their single paddle-like fin a fully formed pentadactyl limb.
What is Biochemistry as evidence for evolution?
Recent advances in technology have allowed comparison of organisms on a molecular basis rather than simply comparing structures. This was previously impossible between such distantly related organisms as an orchid and a mouse.
The study of amino acid sequences shows that more closely related species share more common sequences than do unrelated species. Particular evidence has been derived from the amino acid sequence in haemoglobin, showing that humans and rhesus monkeys share all but eight amino acid sequences whereas there are 125 amino acid differences between humans and lampreys. This supports the fossil, embryological and anatomical evidence that humans are more closely related to rhesus monkeys than they are to lampreys.
explain how Darwin/Wallace’s theory of evolution by natural selection and isolation accounts for divergent evolution and convergent evolution
Divergent evolution occurs when closely related species experience quite different environments and as a result vastly different characteristics will be selected. The species, over time, will evolve differently and will eventually appear quite different. For example, elephants are large plains-dwelling animals that are closely related to a small guinea pig-like animal called a hyrax. Hyraxes live amongst rocky outcrops on mountains. Comparison of skeletons indicates the close relationship between the two groups.
Convergent evolution occurs when two relatively unrelated species develop similar structures, physiology or behaviours in response to similar selective pressures from similar environments. For example, dolphins (mammals) and sharks (cartilaginous fish) have evolved a streamlined body shape and fins that enable them to move efficiently through their aquatic environment, yet they are only remotely related as vertebrates. Communal social behaviour has developed independently in ants, termites and bees.
outline the impact on the evolution of plants and animals of: what are the key changes that impact evolution?
changes in physical conditions in the environment
changes in chemical conditions in the environment
competition for resources
