Evolution Flashcards
what do fossils show us
that life on Earth has changed over time. Some species such as the dinosaur shown in this picture have become extinct. New species have arisen as well. Evolution has occurred. How has this happened? What is the mechanism through which the process of evolution takes place? -> EVIDENCE OF PAST LIFE (life forms that use to exist no longer do, and life forms have become more complex over time)
order in which grouups of living things appeared on earth -> Very ancient rocks contain evidence of only very simple bacteria like organisms. Fossil evidence of more complex life forms is found only in rocks that formed more recently.
The absolute age of a fossil is an estimate of its actual age
the theory of evolution by natural selection
explains the diversity of living things and is supported by a range of scientific evidence
what can fossils be
parts of an organism, such as its bones, teeth, feathers, scales, branches or leaves. Usually when an organism dies, micro-organisms cause so much decay that eventually no part of it remains. However, if an organism is covered shortly after its death by dirt, mud, silt or lava (as can happen, for example, if it becomes trapped in a mudslide or in the silt at the bottom of the ocean), the micro-organisms that cause the decay cannot work. This is because there is no oxygen. Over millions of years, the material covering the dead organism is compressed and turned into rock, preserving the fossil within it.
footprints, burrows and other evidence that an organism existed in the area. For example, a dinosaur track has been discovered in the Otway Range in southern Victoria. By observing the footprints in the track, palaeontologists, who study fossils, can work out the size, weight and speed of the dinosaur that made them.
types of fossils (6)
cast - a rock with the shape of an organism protruding (sticking out) from it
Carbon imprint — the dark print of an organism that can be seen on a rock
Whole organism — larger organisms that have been preserved whole by being mummified or frozen, such as this baby mammoth found in 2007 in Siberia
Mould — a rock that has an impression (hollow) of an organism
Amber fossils — parts of plants, insects or other small animals that have been trapped in a clear substance called amber
Petrified fossil — organic material of living things that has been replaced by minerals. The photograph below shows petrified wood.
history of the earth
Scientists estimate that the Earth is about 4.6 billion years old. To make it easier to talk about the history of the Earth, geologists have divided this time into 5 eras (archaeozoic, proterozoic, paleozoic, mesozoic, cainozoic). These eras are in turn divided into shorter blocks of time called periods. For example the Mesozoic is divided into 3 periods: the Triassic, Jurassic and Cretaceous
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precambrian earth
By studying rocks and fossils, palaeontologists have been able to piece together the story of life on Earth. The Precambrian Earth (prior to the Cambrian period) was very different to the planet we live on today. Evidence in rocks shows that there was no oxygen in the air. Animals could not have survived. There was also no ozone layer. The ozone layer screens out a large portion of the harmful UV rays from the sun. Without it, life on land would have been impossible and early life forms were restricted to bodies of water.
prokaryotes
The oldest fossils are fossil evidence of prokaryotic life. Prokaryotes are single-celled organisms that lack a true nucleus. Bacteria are prokaryotes. Archae are another type of prokaryotic organism. They are similar to bacteria but their cell walls have a different composition and they also have some important genetic differences. Evidence of prokaryotic life forms has been found in rocks that are about 3.5 billion years old.
At some stage prokaryotes that could carry out photosynthesis appeared. As they carried out photosynthesis they produced oxygen. The oxygen reacted with some substances in the oceans initially, and then gradually built up in the atmosphere. The type of minerals found in ancient rocks show that oxygen levels increased dramatically around 2.2 billion years ago. Some of the oxygen would have been converted to ozone in the atmosphere and the ozone layer would have started to form
eukaryotic cells
cells with a nucleus - appeared around 1.8 billion years ago. They were followed by the first multicellular organisms.
multicellular organisms
Multicellular organisms have more than one cell, so they can grow larger and their cells can become specialised for particular functions. About 500 million years ago fish — the first vertebrates — made their first appearance in the fossil record. Plants then colonised the land, mosses and liverworts first. They could not grow very tall as they have no structures capable of taking water from the bottom to the top of the plant. However, ferns have such structures, and they were the next group of plants to appear on land.
plants periods and evolution
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algae -> early land plants -> ferns and horsetails -/> gymnosperms-/> flowering plants
Over 300 million years ago, during the Devonian and Carboniferous periods, plants had developed into a variety of complex forms. Close relatives of the horsetails, clubmosses and ferns formed vast ancient forests. Thick layers of their rotting remains became solidified over time, to form the coal beds found today. About 350 million years ago, the first seed-producing plants appeared. Gymnosperms were the dominant plants in the Permian, Triassic and Jurassic periods. Gymnosperms (a group of seed-producing plants such as conifers, cycads and ginkgo) such as conifers, cycads and maiden hair trees are living descendants of the first pollen-producing plants. It was during the Cretaceous period, about 135 million years ago, when dinosaurs still flourished, that flowering plants appeared. During this period, angiosperms or flowering plants became the dominant plants. These plants were closely related to those found today.
pollen
Fossilised pollen grains survive for millions of years. By studying ancient pollen, scientists can investigate vegetation that existed in the past. In Australia the oldest fossil pollen from a flowering plant is from the native holly genus Ilex. Millions of years ago, most of the surface of Australia was covered by forests. Over time, Australia gradually became drier. The change in climate resulted in fewer rainforests. Eucalypts, acacias and proteas, with their tough, hard leaves and often woody fruits, were well suited to these dry conditions. Pollen fossil evidence suggests that eucalyptus plants appeared about 30 million years ago.
animals
invaded the land as well. The fossil record shows that amphibians were the first vertebrates to live on land. Reptiles appeared next and dominated the landscape during the Triassic, Jurassic and most of the Cretaceous periods. Dinosaurs were the largest reptiles to ever live on Earth. As dinosaur numbers dwindled, two other groups of vertebrates became more dominant, birds and mammals. Invertebrates also took to the land around the same time as amphibians. Today, insects are the most abundant type of land invertebrate.
sedimentary rock
Fossils are found in sedimentary rock. Sedimentary rock forms from layers of sediments that have built up over time and have become cemented (stuck together). The older layers of sediments were laid down first, so if we look at a cross-section of sedimentary rock the older rock layers are usually on the bottom and the younger rock layers are at the top. If any living thing was trapped in the rock layer at the time it was laid down, there is a chance it may have been fossilised. It would therefore be approximately the same age as the rock that surrounds it. This can help us work out the relative age of the fossil.
This method for dating fossils does need to be used with care, however, as the plates in which the rocks lie are still moving. It is possible that a layer (or layers) containing fossils could have been thrust upwards by a sideways force to form a fold, or broken and moved apart in opposite vertical directions to form a fault.
determining absolute age of rocks and fossils
radiometric dating - carbon dating
All living things contain carbon. Most of the carbon in living things is carbon-12 but a small amount is carbon-14. Carbon-14 is not stable and decays into nitrogen over time. After an organism dies, the carbon-14 decays but the carbon-12 does not so that the ratio of carbon-14 to carbon-12 decreases gradually. By measuring this ratio we can tell how old the fossil is.
to determine the age of ancient rocks. Instead of measuring the levels of carbon-14, other isotopes may be used. For example, the amount of uranium-238 and uranium-235 in the rock might be measured. Uranium-238 decays into lead-206. It has a half-life of 4.47 billion years. That means that it takes 4.47 billion years for half the uranium-238 in the rock to be converted to lead-206. Uranium-235 decays into lead-207 and has a half-life of 704 million years. By working out the amount of each type of uranium that has been converted to lead in the rock, it is possible to determine the age of the rock. Both forms of uranium decay a lot more slowly than carbon-14, so this technique makes it possible to date rocks that are much older than 50 000 years old.
theory of evolution
every organism on Earth is a descendant of those that lived millions of years ago.
the process by which different kinds of living organism are believed to have developed from earlier forms during the history of the earth.
the change in the characteristics of a species over several generations and relies on the process of natural selection.
species
a group of animals with many features in common. Members of the same species can mate with each other to produce fertile young under natural conditions OR a group of organisms with morphological or genetic similarity
The theory of evolution is that every organism on Earth is a descendant of those that lived millions of years ago. Species change and evolve, and two different species may be related, through many, many generations, to an ancestral species (a common ancestor). When these ideas were first presented they were very controversial. Until this time, most scientists believed the Earth’s organisms were the unchanging work of a creator, God, and that the Earth was only a few thousand years old. Today the theory is widely accepted by the scientific community.
The idea that living things have evolved over time is usually associated with Charles Darwin, but it was proposed before Darwin was even born. The timeline below shows a few of the scientists whose ideas have contributed to the current theory of evolution.
lamarck
a characteristic acquired during the life of the a species will be passed on to the next generation. species didnt die out in exctinctions
Jean Baptiste Lamarck (1744–1829) was one of the first scientists to suggest that evolution occurred; that is, that populations of organisms changed over time, and that new species had arisen and others had died out. He proposed a mechanism for evolution that was initially considered then later rejected. He suggested that changes acquired by an individual during its lifetime could be passed on to its offspring. For example, giraffes had become long necked because they had stretched towards leaves high up on trees, and this elongated neck had been passed on to their offspring. He also believed that if an individual did not use a particular feature, it would shrink and gradually be lost over succeeding generations. Although his theory of the inheritance of acquired characteristics is now discredited, he made many valid observations about diversity in living things.
darwin
Darwin spent most of his life developing his theory of evolution by natural selection. As a child he showed a fascination for the natural world. His father would have liked him to become a doctor or clergyman but his real passion was in the area of Science. Some of his teachers at university recognised his talent and recommended him when naval lieutenant Robert FitzRoy was looking for someone to accompany him on a trip to chart the coastline and investigate the fauna and flora of South America and other southern landmasses. Darwin was thus invited to join the crew of HMS Beagle. He was just 22 when the ship set sail in 1831. The trip lasted 5 years and took him to the Brazilian jungles, the Andes Mountains, the Argentine grasslands and Australia. Darwin’s travels opened his eyes to the vast range of animal and plant species on Earth.
Darwin was particularly fascinated by variations between similar species. During his journey, Darwin visited the Galapagos Islands, which are home to at least 13 species of finch. He noticed that the different finch species were similar in colour and size, but had variations in their beaks that made them suited to the food sources available on their particular island. Some used twigs to extract insect larvae from tree branches, some drank blood from seabirds, some removed ticks from tortoises, and some ate seeds, leaves and flowers.
He proposed that all species of finches in the Galapagos were the descendants of one shared, ancestral species, a ground-dwelling, seed-eating finch, which had migrated out to all the islands from the mainland. Over many generations the different groups of finches had evolved to suit their different environments and feeding habits. The groups of finches are now so different from one another that they do not interbreed. They have become separate species.
Charles Darwin spent 61 days in Australia in 1836. He visited Sydney, Bathurst, Hobart and King George’s Sound in Western Australia. In Bathurst he was fortunate to see a platypus. He had heard about the curious creatures and made the observation that they behaved and were similar in appearance to water rats. Despite being clearly different species, they had similar features that made them ideally suited to life in streams. The observations he made and the specimen he collected while in Australia influenced his thinking about evolution
xCharles Darwin was reluctant to publish his theory of evolution by natural selection. He wrote an early draft of his theory as early as 1841 but did not present his ideas formally until much later. In the meanwhile another naturalist by the name of Alfred Wallace was coming up with similar ideas. Alfred Wallace’s writings prompted Charles Darwin to publish his Origin of Species. Like Darwin, Wallace travelled extensively (in what is today known as Indonesia) and made many detailed observations of the variations between species. Wallace wrote to Darwin in 1858 from the East Indies, telling him that he had a theory about evolution and natural selection. Darwin was shocked to realise Wallace had reached the same conclusions as himself. Darwin later described Wallace’s writings as an almost perfect summary of his own life’s work. Darwin was encouraged by his colleagues to submit both his paper and Wallace’s to the Linnean Society science conference held in London on 1 July 1859. Wallace is recognised as a co-founder of the theory of evolution by natural selection.
evolution with finches
A population of finches live in an area where insects are common.
Two members of the population have beaks well suited to obtaining insects.
When the population reproduces, these two finches are better fed and have more offspring than the others. Some particularly short-beaked finches do not survive to reproduce.
The next generation has, on average, longer beaks.
biogeography
geographical distribution of spaces
the study of variation in living things in relation to geographical regions, is the name given to the studies that led Darwin and Wallace to propose their evolutionary theories. They observed in their travels that species living in the same area, such as the Galapagos finches, were more similar to each other than to species living in similar habitats much further apart. Wallace also observed that geographical features such as oceans, rivers and mountain ranges often marked the boundary of a species’ range. When Wallace travelled through Indonesia, he noticed that the animals and plants found on the islands of Sumatra and Java (in the North West region of Indonesia) were similar to those found in Asia. The animals and plants of New Guinea (in the South East of Indonesia) were more like those of Australia. He traced a line on a map snaked among the islands to show the boundary between the two regions. The line is now known as Wallace’s Line. Later he identified 6 regions of the world with distinct fauna and flora. These are shown in the map at right. Before the theory of evolution was accepted, it was thought that species had been created with particular adaptations that made them suited to the environment in which they lived. If that had been the case, the same species should have been found wherever conditions were similar. Wallace and Darwin observed that this was not the case. They separately hypothesised that the adaptations were the result of an evolutionary process.
producing offspring - natural selection
Darwin and Wallace suggested that evolution occurs by natural selection. According to this theory, organisms that are well suited to their environment are more likely to survive long enough to produce offspring and also have a better chance of having a large number of offspring. Organisms that are not well suited to their environment are out-competed, die young and produce few or no offspring.
variation
There are variations or differences between members of a species. In a rainforest some tree ferns grow faster and produce more spores than others. In a herd of sea lions certain males will grow larger and have deeper voices. Some sharks will be faster and have a better sense of smell than others. Butterflies of the same species may have slightly different patterns and colours on their wings. Importantly, certain variations give an advantage. The faster sharks are more likely to catch their prey and thus be well fed. The larger sea lions will win fights against other males and thus the right to mate with more females. The faster growing tree ferns will not be shaded by other ferns and will have sufficient light to continue to grow. The butterfly with the pattern that offers the best camouflage is less likely to be eaten before it can mate and lay eggs.
Individuals with favourable variations are more likely to survive longer and produce more offspring. Those that possess unfavourable variations are likely to die having produced few or no offspring. A bird born with a long thin beak when hard seeds are the only food available will break its beak trying to eat the seeds and die of starvation before it can reproduce. A peacock with a small drab tail will fail to attract a mate and will not have an opportunity to produce offspring. A bright red caterpillar crawling in green vegetation is likely to be eaten by a bird and never go on to become a butterfly and reproduce.
selection
The different living (biotic) and non-living (abiotic) selective agents in an environment select for survival those individuals who are best at surviving and obtaining what they need. In a rainforest the low availability of light is a selecting agent. Plants that can get access to light survive. Predators can act as selecting agents. Individuals that can outrun or hide from the predator live on and reproduce. Chemicals and disease-causing organisms can also be selective agents. When DDT was first used as an insecticide it killed most insects. A few were naturally resistant to DDT. They survived, reproduced and passed on their natural resistance to their offspring. The process was repeated over many generations and now many insects are resistant to DDT. Myxomatosis is a virus that, when first released, was deadly to most rabbits. It acted as a selecting agent. Those rabbits that did not die reproduced and passed on the resistance to the virus. The proportion of rabbits that are not killed by myxomatosis has increased.
competition
Often in nature there is not quite enough to go around. A pride of lions may fight each other for larger shares of a kill and sea lions compete for mates. Competition is the biological term for the battle between members of the same species for a share of any limited resources.
the striving for the use of common resources between or within species; two groups of organisms are in competition if an increase in the numbers of one causes a reduction in the numbers of the other.
‘survival of the fittest’
Darwin’s theory of evolution by natural selection is often described as survival of the fittest. It means that in a population with a range of features, those who are the best ‘fit’ to their environment are selected, survive and breed more successfully than their rivals.
survival at work - finches
The Galapagos finches (see section 12.5.2) provide an excellent example of natural selection. Darwin proposed that an ancestral species of finch had spread to a number of islands. In each place, different sources of food were available, and those individuals who had beaks that were better suited to obtain the local food survived and reproduced more successfully than others. The offspring of such birds also had these beaks and were more successful, until eventually the whole population of finches occupying that niche showed that adaptation. Over many generations, each group evolved to have a beak suited to its particular food.
species
a group of organisms capable of interbreeding to produce fertile offspring
Dogs and cats do not belong to the same species. Even if a cat and a dog mated no offspring would be produced. It is not possible for an egg from one of these species to be fertilised by a sperm cell from the other species and produce a viable zygote. There are a few species that can interbreed but the offspring are not fertile. A lion and a tiger can occasionally produce a sterile liger and a horse and a donkey have been known to produce a mule.
speciation
The formation of new species is called speciation. There are two ways in which speciation can occur. Phyletic evolution occurs when a population of a species progressively changes over time to become a new species.
Branching evolution/divergent evolution is more common; in this case, a population is divided into two or more new populations that are prevented from interbreeding. When different selection pressures act on each population, different characteristics are selected for. Over generations, these new populations may become so different from each other that they can no longer interbreed and produce fertile offspring. At this point, they have become two different species. -> a type of evolution in which new species evolve from a shared ancestral species. That is, two or more new species share a common ancestor. At some point in history there has been a barrier (such as a geographical barrier, for example a mountain or ocean) that has divided the population into two or more populations and has also interfered with interbreeding between the populations.
Exposure of these populations to different selection pressures will result in the selection of different variations or phenotypes. Over time, the populations may become so different that even if they were brought back together they would be unable to produce fertile offspring. It is at this point that they are referred to as different species. Speciation has occurred.
Darwin’s finches are examples of divergent evolution. They share a common ancestor, but over time and generations, different selective pressures have led to the selection of different variations most suited to a particular environment or available niche.
adaptive radiation
Adaptive radiation is said to have occurred when divergent evolution of one species has resulted in the formation of many species that are adapted to a variety of environments. Darwin’s finches and Australian marsupials are two examples. Australian marsupials are thought to have evolved from a common possum-like ancestor.
convergent evolution
In divergent evolution, different selection pressures lead to the selection of different variations in evolution from a common ancestor. Convergent evolution is the opposite. Convergent evolution is the result of similar selection pressures in the environment selecting for similar features or adaptations. These adaptations have not been inherited from a common ancestor. -> Sharks and dolphins have a similar body shape and colour, yet sharks are fish whereas dolphins are mammals. They both live in the ocean. The features they share are the result of similar selection pressures.
coevolution
The evolution of one organism can sometimes be in response to another organism. Examples of this coevolution include parasites and their hosts, or birds and plants. If you look at the features of birds and the flowers that they pollinate, you may notice that some birds have evolved specialised features, such as beaks that are well suited for obtaining nectar for a flower with a particular shape. The plants have evolved flowers that may be of a particular colour that is attractive to its pollinator, and nectar that not only attracts but rewards the bird for its task of being involved in pollination.
extinction
Extinction is the loss or disappearance of a species on Earth. Extinction of a species may influence the evolution of another species, as it may provide the opportunity to move into the niche that the extinct species occupied.
evidence for theory of evolution
Darwin and Wallace based their theory of evolution by natural selection on many observations, including those made while travelling around the globe. Since then a great deal more evidence that provides further support for the theory of evolution has been uncovered. -> fossil record, comparative anatomy, comparative embryology, molecular biology
the fossil record
the fossil record supports the theory of evolution by natural selection. It does this in a number of ways. The fossil record shows that the organisms living on Earth have become increasingly complex over time, and that some species that used to live on Earth have now become extinct. There is also fossil evidence of gradual change occurring in particular groups of organisms. For instance, fossils of ancient horse species have been found. They indicate that over the last 60 million years horses have become taller, their teeth have become adapted for grazing rather than eating soft leaves and fruit, and their feet have changed from having spread out toes to having a single hoof. The horses of 60 million years ago were ideally suited to the environment in which they lived: forests where they could feed on fruit and leaves and where their spread out toes and small size would have made it easier to walk on soft ground and remain inconspicuous. Over time the forests were replaced by open plains. Teeth suited for eating tough grasses became advantageous. Long legs and hoofs gave horses a better chance of getting away from predators.
Fossils that show the transition between two groups of organisms have also been found. Such fossils are called transitional forms. The fossilised remains of Archaeopteryx show bird-like features including wings with feathers, but they also show reptilian features including teeth and a long bony tail. This supports the idea that birds evolved from dinosaurs.
comparative anatomy
involves comparing the structural features of different species or groups of animals. The forearms of mammals, amphibians, reptiles and birds are remarkably similar in structure. Each, however, is used for a different function, such as swimming, walking or flying. The structure of the forearm can be traced back to the fin of a fossilised fish from which amphibians are thought to have evolved.
Similarity in characteristics that result from common ancestry is known as homology. Anatomical signs of evolution such as the similar forearms of mammals are called homologous structures. In the diagram top right, you can see that each limb has a similar number of bones that are arranged in the same basic pattern. Even though their functions may be different, the similarity of basic structure still exists.
homology
Similarity in characteristics that result from common ancestry
homologous structures
similar features found in different species that have been inherited from a common ancestor and have different functions dpending on - different species sharing finely detailed structures suggests their related (e.g. pentadactyl limb)
body structures that perform a different function but have a similar basic structure
Anatomical signs of evolution such as the similar forearms of mammals are called homologous structures
features that are common in different organisms because their common ancestry also possessed this feature
analogous structures
similar structures found in different species that have evolved independently - look similar due to similar selection pressures + convergent evolution
features in different organisms that serve a similar function, however structurally different since they evolved indp (common ancestor does not possess that feature) -> e.g. wings of birds, bats and insects, fins(streamline appendages) of sharks and dolphins
Unrelated species living in similar environments (with similar selection pressures) in different parts of the world often have similar structures. This is an example of convergent evolution. The fins of a dolphin and a shark, or the wings of a bat and a butterfly, are analogous structures: they perform the same role but have different evolutionary origins.
comparative embryology
scis compare sims and diffs of embryos from differetn species
structural similarity of embryos suggest that different species are interrelated (common genes - as genes control physical development of organism - master genes control dev of embryo)
common master genes - from common ancestor - vertebrates follow same initial process of embryo formation to dev backbone - backbone inherited from common ancestor - gill and tail structures that may evolve into different structures in adult form
Organisms that go through similar stages in their embryonic development are believed to be closely related. During the early stages of development, the human embryo and the embryos of other animals appear to be quite similar. The embryos of fish, amphibians, reptiles, birds and mammals all initially have gill slits. As the embryos develop further, the gill slits disappear in all but fish. It is thought that gill slits were a characteristic that all these animals once shared with a common ancestor.
embryology
study of unborn or unhatched offspring in their early stages of their development
embryonic stage
when the cells in unborn offspring begin to take on fifferent functions e.g. when tissue sand organs begin to grow
molecular biology
The evolutionary relationships among species can also be reflected in their DNA and proteins. The closer the match in the DNA sequences, the more recent their common ancestor and hence the more closely they are related. You are more closely related to your brothers or sisters than to your cousins, who in turn are more closely related to you than your classmates. So your DNA is more similar to your siblings’ DNA than to your cousins’ DNA. Likewise, humans and chimpanzees have very similar DNA, compared to that of humans and ferns. DNA hybridisation is a technique that can be used to compare the DNA in different species to determine how closely related they are. -> DNA sequencing -> Differences in DNA sequence can give an idea of how long two species have been separated -> The body shape of whales, seals and manatees is an adaptation to their aquatic environment rather than the result of recent common ancestry (seals - dogs, whale - cow, manatee - elephant)
inheritance and variation
favourable variations are transmitted through genes.
The reason that certain characteristics can be passed on to the next generation is because these characteristics are determined by our genes. Many of the variations between members of a species are the result of differences in their DNA. The frog that camouflages better amongst the rocks has DNA sequences that code for the production of proteins that, through their action, result in the frog having a particular pattern on its skin. The cells of the seal that grows larger and is thus able to outcompete other seals for territory and mates contain DNA that codes for the proteins that regulate growth, such as growth hormone. A kangaroo that has white fur (an albino kangaroo) has a faulty copy of the gene that codes for the protein that controls hair and fur colour. This variation is detrimental. The kangaroo is less likely to survive to adulthood and produce many offspring than kangaroos of normal colouring because its white fur and skin make it more vulnerable to sunburn and skin cancer, and more visible to predators.
mendel, darwin, origin of species
It was some time later, in the early 1900s that the role of chromosomes in the inheritance of characteristics was first understood. It was not until 1953 that the structure of DNA was described. Importantly though, as new knowledge about genetics and the inheritance of characteristics has been discovered it has helped to make sense of the way evolution occurs.
