Upload
riley-hagger
View
217
Download
4
Tags:
Embed Size (px)
Citation preview
© Alan Richardson
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.
We know a great deal about the organisms that lived millions of years ago from studying their fossilised remains.
2
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 theorganism are mineralised.
When the rock is exposed as a result of earth movements or erosion,the fossil remains can be dug out and studied.
3
Fossil formation
Living fish A
Dies
Enclosed in sediment
Hard parts fossilised
Living fish B
Dies
Enclosed in sediment
Hard parts fossilised
Fish B becomes a fossil much later than fish A
The sediment eventually becomes rock
The deeper the rock layer, the older the fossil
4
Process of fossilisation
living fish sediment from river
fish skeleton partly buried by sediment
5
fish skeleton fossilisedolder sedimentbecomes rock
more recent sediment collects6
Layers of sediment
land raised abovewater level
recent rock
older rock
7
earth movements fracture rock
fossilised skeleton exposed
8
Fractured rock
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 lowestlayers represent animals and plants that lived many millionsof years ago
rock strata of increasing age
9
Rock strata
© Alan Richardson
© Alan Richardson
This is a fossil of a fish which lived 40 million years ago10
Fossil fish
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
11
By studying the type of fossils and the abundance of each speciesin the different strata, it is possible to build up a picture of how thepopulations 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
12
Vertebrate sequence
Relative number of species
400 millionyears ago
fish
amphibi
a
reptiles
birds
mam
mal
s
100 millionyears ago
200 millionyears ago
300 millionyears ago
o
o
o
o
o
o
o
oo
o
o
o
o
o
oo
o
o
o
o
oo
o
oo
oo
o
oo
o
o
o
o
o
o
o
o
o
Possible lines of evolution
13
Vertebrate fossil record
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 conditionsare suitable for fossilization. So they may not be representative ofthe 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 orerosion 3
very few fossils have been found which show intermediate stages between different groups of organism 4
14
Interpretation (1)
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 thefossils and similar organisms living today 3
although they are few, there are fossils which show characteristics intermediate between major groups4
15
feathers
claws
thinribs
teeth
long tail
wing-likeforelimbs
Reptile-like features
Bird-like features
Replica of Archaeopteryx fossil; half bird half reptile © Alan Richardson
16
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
18
Comparative anatomy
Vertebrate limbs
The basic pattern of the vertebrate limb is represented by the human arm skeleton shown below
ball and socket joint
hinge joint
single bone two bones
group of small bones
five jointed digits
17
Vertebrate forelimb
The forelimbs of the following vertebrates show the basic pattern of limb bones with modifications which are adapted to their methods of locomotion.
Lizard Bird
Dolphin Bat
The basic pattern suggests they have evolved from a common ancestor
19
Modified limbs
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 evidence20
DNA evidence
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
21
Evolutionary pathways
Mammals
Flatworms
Annelids
Insects
Coelenterates
Fish
Birds
Reptiles
Crustacea
Amphibia
Single celled organisms
Monocots Herbs Shrubs Trees
Dicots
Flowering plants Conifers
Mosses
Liverworts
Algae
Ferns
Fungi
Multicellular plants
Multicellularanimals
Mollusc
22
Evolutionary pathways 2
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’
23
Dave and Mick
Dave’s view of evolution
Dave is wrong
24
Incorrect evolutionary sequence
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
25
Discussion
The accepted view of evolution
26
‘Correct’ evolutionary sequence
Question 1
Evolution has taken place over
(a) hundreds
(b) thousands
(c) millions
(d) billions
of years
28
Question 2
Fossils can be formed only if total decay
(a) is prevented
(b) is accelerated
(c) is slowed up
(d) is immediate
29
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
30
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
31
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
32
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
33
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
34
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
35
Answer
Correct
36
Answer
Incorrect
37