Evolution © Alan Richardson The Chalk cliffs at Birling gap (East Sussex). The chalk was formed 100 million years ago, mainly from miniscule, finely sculptured chalky plates that enclosed the bodies of single-celled algae living in the plankton at that time. © Alan Richardson

The theory of evolution offers an explanation for the existence of 2 The theory of evolution offers an explanation for the existence of all living organisms on the Earth today and in the past It supposes that present day organisms have all been derived from organisms that lived in the past By a series of very small changes over millions of years new species have developed from previous species* Over a period of about 3000 million years, many new species have been produced and many have become extinct. * In some cases it appears that evolution proceeded by periods of rapid change, interspersed with periods of little or no change, We know a great deal about the organisms that lived millions of years ago from studying their fossilised remains. Theory of evolution

3 Fossil formation There are many ways in which an organism can be fossilised One of these ways is shown in the next sequence of slides In principle, a fossil is formed when an organism dies, its body is enclosed in mud, or sand. The soft parts decay but some of the hard parts (skeleton, shells, seeds) are preserved The mud or sand eventually becomes rock and the hard parts of the organism are mineralised. Sometimes an organism dies in a situation which prevents its decay (e.g. being overwhelmed by a mud deposit). In this case the soft parts are often preserved as fossils and can be studied by cutting sections through the fossil. Whole organisms may be preserved in ice. When the rock is exposed as a result of earth movements or erosion, the fossil remains can be dug out and studied.

Process of fossilisation 4 The sediment eventually becomes rock Fish B becomes a fossil much later than fish A The deeper the rock layer, the older the fossil Living fish B Dies Enclosed in sediment Hard parts fossilised Living fish A Dies Enclosed in sediment Hard parts fossilised Process of fossilisation

fish skeleton partly buried by sediment 5 living fish sediment from river fish skeleton partly buried by sediment Sedimentation

more recent sediment collects 6 more recent sediment collects older sediment becomes rock fish skeleton fossilised Layers of sediment

Earth’s crust movement 7 land raised above water level recent rock older rock Earth’s crust movement

fossilised skeleton exposed 8 fossilised skeleton exposed earth movements fracture rock Fractured rock

When rock strata become exposed, it can be assumed that, 9 When rock strata become exposed, it can be assumed that, in most cases, the lowest layers are the oldest* This means that the fossils of organisms preserved in the lowest layers represent animals and plants that lived many millions of years ago rock strata of increasing age Rock strata exposed at a cliff face. Each layer represents millions of years of deposition. * The movements of the Earth’s crust may cause the strata to become distorted. Sometimes the strata are vertical or even turned upside down with the oldest rocks appearing on top. It is usually possible to tell when this has happened. © Alan Richardson Rock strata

This is a fossil of a fish which lived 40 million years ago 10 This is a fossil of a fish which lived 40 million years ago A fossil fish (Mioplosus labracoides) from the Eocene era (30 –50 million years ago.The fossil is obviously that of a fish, but the species is not represented among present day fish © Alan Richardson Fossil fish

Fossil fish reconstruction 11 This is a reconstruction, from fossil remains, of an ‘armour-plated’ fish which lived 350 million years ago dorsal fin The fish which gave rise to fossils such as this, were very different from today’s fish Fossil fish reconstruction

By studying the type of fossils and the abundance of each species 12 By studying the type of fossils and the abundance of each species in the different strata, it is possible to build up a picture of how the populations of organisms changed over millions of years The next slide shows how this picture appears for vertebrate animals The width of each band represents the relative abundance of the organisms as judged by their fossil remains. For example, 100 million years ago there were many more species of reptiles than there are today Mammals do not appear at all in rocks older than about 3 million years Vertebrate sequence

Vertebrate fossil record 13 Relative number of species mammals birds 100 million years ago reptiles amphibia 200 million years ago o fish 300 million years ago 400 million years ago Possible lines of evolution Vertebrate fossil record

Interpretation of the fossil record (1) 14 Interpretation of the fossil record (1) In interpreting the fossil record, it must be borne in mind that fossils will be formed only in places and at times when conditions are suitable for fossilization. So they may not be representative of the organisms living at that time 1 only the skeletons, shells and other parts resistant to decay will be preserved 2 fossils are found only if they are exposed by Earth movements or erosion 3 1 A local flood may engulf a community of animals which are not abundant elsewhere. 2 There may be many soft-bodied organisms and non-woody plants living at that time which do not form fossils. 3 There may be millions of fossils lying undiscovered that might put a different interpretation on the kind of organisms living in the past. 4 If organisms were gradually changing, you might expect to find fossils remains showing intermediate stages in the change very few fossils have been found which show intermediate stages between different groups of organism 4 Interpretation (1)

Interpreting the fossil record (2) 15 Interpreting the fossil record (2) Despite its gaps, the fossil record does show that, over millions of years, organisms became more numerous and more diverse, i.e. many more species came into existence 1 organisms became more complex 2 although very few organisms found as fossils are alive today, there are many basic similarities in the body structure of the fossils and similar organisms living today 3 1 For example, 500 million years ago (mya) there were no vertebrates; 350mya there were no reptiles; 200mya there were no birds 2 For example a fish is a more complex organism than a sea anemone 3 For example, fossil remains of fish are unmistakeably similar to present day fish. (See slides 10 & 11) 4 The classic example is Archaeopteryx which has features common to both birds and reptiles There are many mammal-like reptiles in the fossil record and recently a fossil has been found that is intermediate between a fish and a land animal although they are few, there are fossils which show characteristics intermediate between major groups4 Interpretation 2

Replica of Archaeopteryx fossil; half bird half reptile 16 claws wing-like forelimbs teeth thin ribs long tail feathers Replica of Archaeopteryx fossil; half bird half reptile © Alan Richardson Reptile-like features Bird-like features

Evidence from comparative anatomy 18 Evidence from comparative anatomy Fish, amphibia, reptiles, birds and mammals all have vertebral columns, skulls, brains, circulatory systems and many other features in common This suggests that they all arose from a common ancestral form rather than arising independently. The same reasoning can be applied to other groups of organisms such as insects which have most of their anatomical features in common Although these features are superficially different there is a basic pattern underlying them all Comparative anatomy

17 Vertebrate limbs The basic pattern of the vertebrate limb is represented by the human arm skeleton shown below group of small bones ball and socket joint hinge joint single bone two bones five jointed digits Vertebrate forelimb

The basic pattern suggests they have evolved from a common ancestor 19 The forelimbs of the following vertebrates show the basic pattern of limb bones with modifications which are adapted to their methods of locomotion. The basic pattern suggests they have evolved from a common ancestor Lizard Bird Dolphin Bat Modified limbs

20 DNA evidence Another important line of evidence for evolution comes from DNA analysis Any permanent change in form or function of an organism must be preceded by a change in its DNA Organisms which have much of their DNA in common must be closely related, i.e. they have split from a common ancestor comparatively recently (in geological terms) For example, humans and chimpanzees have 99% of their DNA in common which suggests a close relationship and relatively ‘recent’ divergence from a common ancestor DNA evidence

Evolutionary pathways 21 Evolutionary pathways The next slide shows the widely accepted pathway of evolution for plants and animals Only a few of the main types of organisms are shown

Evolutionary pathways 2 Monocots Herbs Shrubs Trees 22 Mammals Birds Reptiles Conifers Amphibia Dicots Fish Flowering plants Mosses Insects Ferns Crustacea Liverworts Annelids Flatworms Mollusc Algae Fungi Coelenterates Multicellular plants Multicellular animals Single celled organisms Evolutionary pathways 2

Mick. ‘What were we before that?’ 23 Dave. ‘A bloke on the telly just said that before we were humans we were monkeys’. Mick. ‘What were we before that?’ Dave. ‘ I don’t know. I can’t even remember being a monkey’ Dave and Mick

Incorrect evolutionary sequence 24 Dave is wrong Dave’s view of evolution Incorrect evolutionary sequence

25 Dave seems to think that evolution can take place in a person’s lifetime. This is pretty bizarre, even for Dave. He has also confused monkeys with apes. Our nearest relatives are apes (chimpanzees and gorillas), not monkeys He makes the common error that, e.g. fish, as we know them today gave rise to amphibia and, by the same reasoning, apes, as we know them, gave rise to humans The correct interpretation of the evidence is that apes and humans had a common ancestor which was neither ape nor human In the course of evolution, this common ancestor produced two lines of descendants, culminating in modern day humans and modern day apes Discussion

‘Correct’ evolutionary sequence 26 The accepted view of evolution ‘Correct’ evolutionary sequence

Question 1 Evolution has taken place over (a) hundreds (b) thousands 28 Question 1 Evolution has taken place over (a) hundreds (b) thousands (c) millions (d) billions of years

Fossils can be formed only if total decay 29 Question 2 Fossils can be formed only if total decay (a) is prevented (b) is accelerated (c) is slowed up (d) is immediate

Question 3 Older fossils are found (a) in the deepest rock layers 30 Question 3 Older fossils are found (a) in the deepest rock layers (b) in the shallowest rock layers (c) only in rocks over 1 million years old (d) evenly dispersed in all rock layers

(d) are never related to other fossilised organisms 31 Question 4 Which of these statements is correct ? Fossilised organisms (a) are all totally different from present-day species (b) are much the same as present-day species (c) often show strong resemblances to present-day species (d) are never related to other fossilised organisms

(a) Birds and mammals; reptiles; amphibians; fish 32 Question 5 The order of appearance of vertebrates in the fossil record is (a) Birds and mammals; reptiles; amphibians; fish (b) Fish; amphibians; reptiles; birds and mammals (c) Fish; reptiles; amphibians; birds and mammals (d) Amphibians; fish; reptiles; birds and mammals

Reptiles were most abundant 33 Question 6 Reptiles were most abundant (a) 400 million years ago (b) 300 million years ago (c) 200 million years ago (d) 100 million years ago

34 Question 7 Archaeopteryx is a fossil which shows features intermediate between (a) reptiles and mammals (b) reptiles and birds (c) birds and mammals (d) reptiles and amphibians

Question 8 Which statement is correct ? 35 Question 8 Which statement is correct ? (a) Amphibia are derived from fish (b) Amphibia evolved into reptiles (c) Amphibia and fish share a common ancestor (d) Reptiles evolved into mammals

36 Answer Correct

37 Answer Incorrect