1.1 Introduction into Mammals and Evolution Flashcards
Evolution and natural selection
What is there among organisms for natural selection to act on?
What do organisms need to do to survive?
What is natural selection?
- There is inherited variation among organisms
- There is competition between organisms for survival
- Natural selection – descent with modification – is the process whereby certain genetically inherited characteristics increase the chances of their carriers surviving and reproducing in a particular environment. These individuals will pass on their beneficial characteristics to the next generation.
- Selection leads to the accumulation of favoured variants, which over a long period produce new life forms, the origin of species.
What is fitness?
Fitness
• A measure of the ability of genetic material to perpetuate itself in the course of evolution. It is dependent on the individual’s ability to survive, the rate of reproduction and the viability of offspring.
When we study evolution we are concerned with two inter-linked areas:
Pattern
Process
• Pattern is what we measure and record what we see in the fossil record, in DNA sequences or other data - this is what we can go out and measure in the fossil record and in genomic samples
we quantify the patterns and inference about evolutionary process
leads to emperically testing of theories about process
in turn the process we test for can tell us more about the effect on taxonomic pattern and we start again
Cylical relationshop
What is the difference between homology and analogue?
For example?
Homology - are characters that are inherited from a common ancestor
Analogue - are characteristics that are similar due to similar function
Looking at the fossil record of the early bird Archaeopteryx and comparing it to the fossil record of the Icaronycteris (earliest known definitive bat)
Part of interpreting the pattern of evolution is to look at various traits like powered flight and try and decided how they might be related to each other and be able to separate analogue (flight in this case) from homology
Where the homologous limb bones have evolved but in different ways to enable powered flight
What can the fossil record tell us in the context of
- Hominid fossils
- Marine reptile ichthyosaur birth
Often for particular taxonomic groups fossil record is quite small and so hominid fossils tend to be rare because of where they lived and the chances of fossilisations are low.
**Fossils can tell us a great deal about the life style of these great extinct animals, classic one bellow, the marine reptile ichthyosaur birth **
Baby being born tail first because these are marine reptiles, they might look like a shark but are closer to dolphins because they are air breathing these ichthyosaur are born tail fist as dolphins are so that the young can swim up to the surface to take a breath, we can tell a lot about the biology by these fossils
Fossilisation facts:
Fossils are ……… to our knowledge of evolution
Where do fossils occur?
What remains?
Where does fossilisation normally occur?
What two process of fossilisation can occur?
• Fossils are crucial (Darwin used it to confirm his ideas) to our knowledge of evolution; much of what we know about the origin and evolution of life comes from the fossil record
• Fossils occur in sedimentary rocks, normally only the ‘hard parts’ remain scavenges will remove soft parts
• Fossils form after the organism dies and the soft tissue rots away leaving the skeleton (bones, shells, teeth and other hard parts) to become (rapidly) buried by sediment. The quicker the better, the least damage is going to occur
• This normally occurs in aquatic environments: the sea, in rivers, and in lakes, or after floods Fossil record is very crucial Darwin used that to affirm his ideas
1. Permineralisation
2. Natural cast process
Two processes can occur
- Permineralisation
- ‘Natural cast’ process.
Describe how permineralisation occurs?
Describe how natural cast process occurs?
Are soft parts preserved?
DNA extracted from amber?
1. Permineralisation. Organic material in the bones decays, and is replaced by minerals (silica, calcite, iron pyrites) from water percolating through the sedimentary rocks. When the entire bony structure is replaced by minerals, the process is known as petrification
2. ‘Natural cast’ process. The organic material (bones) dissolve to leave a hollow mould which may be filled later with minerals to form a solid replica of the bone – the organic material completely dissolves away but then leaves a mould/cast – depending on the area it can get a detailed area
- Soft parts are rarely preserved but they are sometimes: many amazing soft fossils in recent years especially in certain areas in China
- Preservation of ancient material may also occur in amber, and by mummification for more recent stuff, fossilised tree sap
DNA in amber? – Jurassic park idea of extracting intact DNA basically can’t be done and sequence DNA from amber, amber is too old it takes about 40 million years for it to properly form
There are cases were fossilisation has not completely occurred in some fossil homoninds like Neanderthals and ear modern humans it is possible to get some small degraded DNA ancient genomics, whole draft genomes for early modern humans and Neanderthals – due to advances in of genomic technologies (huge and important area of research)
**Darwin recognized the limitations of the fossil record **
Is the fossil record complete?
is it a chance event?
What species will be poorly represented?
- The fossil record is incomplete
- Fossilisation is a chance event, and some animals live in places that are less conducive to fossilisation (e.g. deserts)
- Species with small population sizes may be poorly represented (or not at all); this is a problem with hominids, for example
- Similarly, species that persist for a long time will be more likely to be present in the fossil record than species which did not
‘I look at the natural geological record, as history of the world imperfectly kept, and written in a changing dialect; of this history we possess the last volume alone, relating only to two or three countries. Of this volume, only here and there a short chapter has been preserved, and of each page, only here and there a few lines.’
Dating methods** **
In order to apply DNA sequence analysis to rebuild phylogeneis and to use the amount of DNA difference to calibrate molecular clock so that the rate of DNA can be put on time-scale
What are the two types of dating methods?
Can fossils be dated directly?
What is meant by relative dating?
- Dating is critical to our understanding of fossils, in order to apply DNA techniques to re-build phylogenies to calibrate molecular plot so that that DNA can be put on a time-scale
- Dating can be either comparative or absolute
- Fossils cannot usually be dated directly (absolute dating), and surrounding rocks are analysed
- Absolute dating: the item itself is dated
- Relative dating: strata above (younger) and below (older) are dated and the item expressed relative to these (if you know the dates of something above and below a fossil)
• Originally, in the absence of absolute dates, all dating was relative, and there was great uncertainty about the length of different geological periods
Initially, most periods were named after the locations of characteristic deposits were:
What are examples of geological timescales named after location?
Cambrian from Cambria (the Roman name for Wales)
Permian from Permia in Russia
Devonian from Devon
Jurassic from the Jura Mountains (France, Switzerland and Germany)
Summary of the dating methods
Basic ideas are that these radio-metric methods are based on the decay on naturally occurring isotopes, when an organism dies the clock is set at zero (when the organism dies)
Common feature is that when an organism dies the clock is set at zero?
With reference with what can give you date?
Radioactive potassium decays to argon, in volcanic rock it builds up, with reference to the half-life of the radio isotypes you can then date the rock. The half-life is 1.3 billion years of radio-potassium is a useful as it covers a great life-span
Various isotypes can give you different time scales
Evolutionary tree of life - (Darwin sketch)
At the tips of the trees are living species that are connected to ancestors – we can now re-construct phylogenies using various methods
Evolution certainly occurs by natural selection and adaptation – but also things like genetic drift
Evolutionary caused by natural selection and selection - but other things can cause variation in biodiversity…such as?
- Evolution may also arise from chance factors other than adaptation, like genetic drift – a population by chance event – not due to adaptation, mass extinction changes the niches available – separation – mass extinctions – change the vacant niches
- Natural selection and adaptation are tightly linked in NeoDarwinism, with an emphasis on the gradual nature of change so produced – gradualism – neodarwinism historically represents gradualism, organisms gradually changing over time –
Natural selection and adaptation are tightly linked in NeoDarwinism, with an emphasis on the gradual nature of change so produced – gradualism – neodarwinism historically represents gradualism, organisms gradually changing over time
Good example of this is?
Horse fossil record is a good example of gradual evolution changes in the body size from small to big, teeth, reduction in toes
Doubts were raised in the 1970’s that gradualism was the whole story – started being questioned
For a variety of reasons
List the reasons
- Genetic lab techniques showed a lot of variation, but we now know that a lot of DNA isn’t doing anything, most mutations that you can measure are going to be silent (neutral) mutations i.e no change in amino acid structure
- One of the reasons was because it was discovered that most populations contained more genetic variation than within them than would be predicted by strict selectionism, more than would have been expected
The neutral theory of evolution was developed - most mutations are neutral and not subject to selection –
What was argued?
What was the alternative that was presented?
What two famous evolutionary biologists propsed this?
- It was argued that gradualism may be the exception rather than the rule, and that species are in stasis for long periods e.g. several million years, and change is concentrated in short periods of 10’s of 1000’s of years
- This is known as punctuated equilibrium, first proposed by Niles Eldredge and Stephen Jay Gould in 1972
- Lively debate continues (‘evolution by jerks’ vs ‘evolution by creeps!)
- If you look at a different character we can explain variation in a variation of ways ==================à
Major drivers of evolution
List the major drivers of evolution and how they interact together?
What are the consequences?
Consequences
- Large scale migrations
- Speciation
- Mass extinctions
- Adaptive radiations
