Evolution and Biodiversity

Question 1

Evolution in summary

Answer 1

Evolution occurs when heritable characteristics of a species change – natural selection.

Question 2

Fossil evidence of evolution

Answer 2

•fossil records in different earth layers, with distinct different ages, provide information of how a species changed.

–The sequence in which fossils appear matches the sequence in which they would be expected to evolve, with bacteria and simple algae appearing first, fungi and worms later, etc.

–The sequence fits the ecology, with plant fossils appearing before animal.

Question 3

Selective breeding evidence of evolution

Answer 3

•selective breeding of domesticated animals shows that artificial selection can cause evolution. The modern livestock has huge differences between their natural species in the wild. It does not prove that evolution of species has actually occurred naturally, nor that the mechanism is natural selection.

Question 4

Homologous structures evidence of evolution

Answer 4

•homologous structures by adaptive radiation explains the similarities in structure when there are differences in function (e.g. bone structure of vertebrate limbs; from wings to horse legs to humans).

–Because these bone structures are used for flying, jumping, running, etc. it is reasonable to expected different bone structure, but it is the same. The best explanation is they all derived from the same ancestor: adaptive radiation.

–Another evolutionary interpretation is that they have had different origins and have become similar because they perform the same or similar function: convergent evolution This is the opposite of homologous structures.

Question 5

gradual speciation evidence of evolution

Answer 5

Populations of a species can gradually diverge into separate species by evolution, no longer interbreeding.

Usually, geographical isolation and natural selection acting different on the population. Continuous variation across the geographical range of related populations matches the concept of gradual divergence.

As the evidence we find examples of all stages of divergence. This provides evidence for the evolution of species.

Question 6

When can natural selection occur?

Answer 6

Natural selection can only occur if there is variation amongst members of the same species.

Question 7

Sources of variation (and danger to asexual organisms)

Answer 7

Mutation: new alleles are produced by gene mutation, which enlarges the gene pool of a population.

Meiosis produces new combinations of alleles by breaking up the existing combination in a diploid cell. Every cell produced by meiosis in an individual is likely to carry a different combination of alleles, because of crossing over and the independent orientation of bivalents.

Sexual reproduction involves the fusion of male and female gametes. The gametes usually come from different parents, so the offspring has a combination of alleles from two individuals. This allows mutations that occurred in different individuals to be brought together, resulting in a unique genome.

____

In species that do not carry out sexual reproduction the only source of variation is mutation. It is generally assumed that such species will not generate enough variation to be able to evolve quickly enough for survival during times of environmental change, which is why climate change and pollutants can be so devastating.

Question 8

Adaptations and aquired characteristics

Answer 8

Inheritable changes to an organism that are favoured by natural selection. It is the close relationship between structure and function (e.g. thick fat of polar bears correlates with cold temperatures).

If characteristics develop during a lifetime, they are know as acquired characteristics and it is widely accepted that acquired characteristics cannot be inherited.

Question 9

Overproduction of offspring

Answer 9

Species tend to produce more offspring than the environment can support. This will tend to lead to a struggle for existence within a population - competition for resources.

Question 10

natural selection

Answer 10

Individuals that are better adapted tend to survive and produce more offspring (e.g. giraffes). This is then inherited by the offspring.

Question 11

What is the rate of natural selection and how does it influence populations?

Answer 11

Natural selection increases the frequency of characteristics that make individuals better adapted and decreases the frequency of other characteristics leading to changes within the species. It is progressive change (happening in stages); more adapted individuals in a population.

Question 12

Natural selection and antibiotic resistance

Answer 12

The theory of evolution by natural selection can explain the development of antibiotic resistance in bacteria.

Increasingly, after an antibiotic is introduced and used on patients, bacteria showing resistance appear within a few years.

Resistance to the antibiotic spreads to more and more species of pathogenic bacteria.

In each species the proportion of infections that are caused by a resistant strain increases.

The development of antibiotic resistance is therefore an example of evolution - natural selection.

Question 13

Evolution of antibiotic resistance in bacteria

and reasons for increasing resistance

Answer 13

Antibiotic resistance is due to genes in bacteria and therefore can be inherited. The evolution of multiple antibiotic resistance has occurred in just a few decades due to several reasons:

• mainly due to the very widespread (over)use of antibiotics, both for treating diseases and in animal feeds.
• bacteria can reproduce very rapidly, with a generation time of less than an hour.
• populations of bacteria are often huge, increasing the chance of a gene for antibiotic resistance being formed by mutation.
• bacteria can pass genes on to other bacteria in several ways, including using plasmids, which allow one species of bacteria to gain antibiotic resistance genes from another species.

Question 14

Development of the binomial system of names

Answer 14

is universal among biologists

has been agreed and developed at a series of congresses.

Question 15

Naming species using the binomial system

Answer 15

The first name is the genus name. A genus is a group of species that share certain characteristics. The second name is the species or specific name.

The rues are:

• The genus name begins with an upper-case letter and species name lower-case.
• Name shown in italics.
• The genus name may be abbreviated after one use.
• The earliest published name is the correct one (for plans from 1753 and animals 1758).

Question 16

The hierarchy of taxa (taxonomic ranks)

Answer 16

Taxonomists classify species using a hierarchy of taxa (taxa=group of something):

Life

Domain

Kingdom (kinky)

Phylum (perverts)

Class (come)

Order (over)

Family (for)

Genus (group)

Species (sex)

Question 17

The three domains

Answer 17

Eubacteria

Archaea

Eukaryota

–Classifying systems into prokaryotes and eukaryotes is too primitive as there is a huge diversification in prokaryotes.

–Viruses have genes for proteins but too few of other characteristics of life.

Question 18

Kingdoms of eukaryotes

Answer 18

plants

animals

fungi

protoctista (controversial because could be divided up into more kingdoms)

Question 19

Natural classification

Answer 19

In a natural classification, the genus and accompanying higher taxa consist of all the species that have evolved from one common ancestral species. This is because of the common ancestry we can expect the members of a natural group to share many characteristics.

Taxonomists sometimes reclassify groups of species when new evidence shows that a previous taxon contains species that have evolved from different ancestral species. After reviewing the classification, they might split up the group into two or more taxa. Taxa can also be united.

An example of an unnatural or artificial classification would be one in which birds, bats and insets are grouped together, because they all fly. Flight evolved separately in these groups and as they do not share a common ancestor, they differ in many ways.

Question 20

Advantages of natural classification

Answer 20

Natural classification help in identification of species (dichotomous keys) and allow the prediction of characteristics shared by species within a group (e.g. related chemicals in plants)

Question 21

Dichotomous keys

Answer 21

Consists of a numbered series of pairs of description. One of these should match the species and the other clearly not.

Question 22

Clades

Answer 22

A clade is a group of organisms that have evolved from a common ancestor.

Question 23

Identifying members of a clade

Answer 23

Evidence for which species are part of a clade can be obtained from the base sequence of a gene or the correspond amino acid sequence of a protein. Species that have a recent common ancestor can be expected to have a few differences in base or amino acid sequence.

Question 24

Molecular clocks

Answer 24

Sequence differences accumulate gradually so there is a positive correlation between the number of differences between two species and the time since they diverged from a common ancestor.

For example, 70,000 years ago, European-Japanese split, 140,000 years ago, Africa-European/Japanese split, 5,000,000 years ago, human-chimpanzee split

Question 25

Similar traits of organisms can either be …

Answer 25

analogous: similar because of convergent evolution (different origin but same functionality)

homologous: similar because of similar ancestry (e.g. vertebrates limbs)

Question 26

Cladograms

Answer 26

Cladograms are tree diagrams that show the most probable sequence of divergences in clades.

They are based on similarities and differences between species in a clade, almost always based on base or amino acid sequences (with the help of computer programs). This is known as the principle of parsimony

Evidence from cladistics has shown that classifications of some groups based on structure did not correspond with the evolutionary origins of a group of species.

Question 27

Cambrian explosion (not in curriculum)

Answer 27

Because there was no competition at that earlier time, and everything could be tried out by nature, which resulted in a wide range of bizarre organisms. Most became extinct because they were not suitable.