Ascend Activity 8

Evocards

© 2006 Gatsby Technical education Projects

Evocard

Biologists recognise many different ‘kinds’, or

species, of living things

Evocard

Some species are very similar to others, and so species are arranged into ‘families’ that seem to be closely ‘related’

Evocard

According to scientists’ models, the earth is about 450,000,000,000 years old, and some kind of life has been present for much of

that time

Evocard

Even within species, there are variations in many

characteristics

Evocard

Even animals that are superficially very different, often have

underlying similarities in their anatomy. For example, all

mammals have skeletons with a similar arrangement of bones,

even though the individual bones may be very different in shape and

size in different mammals

Evocard

All types of living things reproduce themselves –

they leave offspring

Evocard

Differences between the individuals in a population influence their survival in

any particular environment

Evocard

Some individuals leave more offspring than others

Evocard

If a species fits its environment well, and the environment

remains much the same, that species may hardly change in

many, many millions of years – e.g. crocodilians

Evocard

In most living things parents produce many

offspring, but only a few survive to adulthood

Evocard

Not all individuals in a population will have

offspring

Evocard

The fossil record shows that there were many types

of living things (e.g. the dinosaurs) that are now

extinct

Evocard

Offspring are usually more similar to their parents that most other members of their

species

Evocard

Parents that survive well in an environment are likely to have offspring that are

well suited to their environment

Evocard

Sometimes there have been great extinctions when most species (e.g. 90%)

have become extinct over a relatively quick period of

time

Evocard

All living things alive today share similar chemical

reactions

Evocard

Great extinctions are associated with significant

changes in the environment – such as changing climate

perhaps due to volcanism or other geological activity, or the

impact of a large comet

EvocardOne of the most significant

pollution events occurred when some living things started to

excrete oxygen into the atmosphere – this poisoned most of the living things alive then, but provided the opportunity for the

evolution of a more effective biochemistry (using aerobic

respiration)

Evocard

Similar chemical compounds are found in very different life forms

Evocard

Living things contain genes, which act as the

instructions for the chemicals processes in

living cells

Evocard

The chlorophyll molecule in green plants is similar to the

haemoglobin found in our blood

Evocard

All living things alive today share similar genetic codes

Evocard

Genes are made of a chemical called DNA

Evocard

One copy of an individual’s genes is found in each of

their cells (with a few exceptions)

Evocard

The structure of DNA allows genes to be copied in cells

Evocard

Gene copying in living things is very efficient

Evocard

When cells divide, each new cell gets copy of the

set of genes

Evocard

During sexual reproduction the gametes from two

parents join to form a cell with a full set of genes – a

zygote

Evocard

Special cells, gametes, contain a ‘random’ half-set of an

individual’s genes

Evocard

In many animal species individuals tend to be more

sexually attractive if they have particular characteristics – such as a colourful tail, or a

rhythmic dance, or a complex song

Evocard

Sexual reproduction is an effective way of producing

individuals with unique combinations of genes that

are different to their parents or siblings

Evocard

Often, mutations in genes do not make any noticeable

difference

Evocard

The zygote is the single cell which will divide, and divide…

to produce all the sells in a new individual

Evocard

Occasionally a mistake occurs during gene copying – this is

called a mutation

Evocard

Sometimes, mutations in genes change the way that

the cell works

Evocard

A mutation that occurs when cell division produces

gametes can lead to a zygote with a mutation

Evocard

A mutation that changes the way a cell works is usually a

disadvantage

Evocard

Occasionally, a mutation that changes the way a cell works

may give the cell an advantage in some way

Evocard

If a zygote has a mutation, then it will be passed on to

all the cells as the individual grows

Evocard

Usually a mutation that has a noticeable effect will be a

disadvantage to an individual

Evocard

Sometimes an individual with a mutation is not much different

to any other individual

Evocard

Sometimes an individual with a mutation will be significantly

different from other individuals

Evocard

Occasionally a mutation that has a noticeable effect might be an advantage to

an individual in a particular environment

Evocard

The environment may become more or less

suitable for a living thing when there are climatic

changes

Evocard

There are many aspects of the environment that influence a

living thing’s survival

Evocard

The environment may become more or less suitable for a living thing when there are

geological changes

Evocard

The environment may become more or less

suitable for a living thing when there are changes in the numbers and types of other living things living

there

Evocard

The fossil record suggests that many living things

alive today have ‘common ancestors’

Evocard

The fossil record shows that species change their

characteristics over millions of years

Evocard

Similar living things often show specialised characteristics that

match them to specific features of their environments

Evocard

The fossil record suggests that modern man (homo sapiens) evolved from

earlier homo species, and that these species had common ancestors with chimpanzee, orang-utan

and gorilla

EvocardDarwin discovered that when a

species gets divided geographically (as on different islands) so that individuals in

different populations were unable to inter-breed, then the different populations will evolve

independently in response to local conditions

Evocard

The fossil record suggests that the common ancestor of man, chimps and great apes itself had a common ancestor with

the ancestors of modern monkey species

Evocard

Some rocks called the Burgess shale contain fossils of early animals types, many of which have body plans that are very

different to those we see today in the different groups of

animals around today

Evocard

There are mammals in Australasia (the marsupials) that are unlike those in the

other continents, because the animals there became isolated from those in other continents

a very long time ago

EvocardLarge complex new structures are only likely to evolve where there are intermediate steps

which can give some advantage – a small ‘feather-like’ structure

that is too small to support flight might still provide

protection or insulation or allow a longer glide

Evocard

Genes and mutations are not intrinsically good or bad, but only in certain situations. The gene that can lead to sickle

cell anaemia (if you get a copy from both parents) can also make you less susceptible to

malaria

Evocard

An advantageous mutation does not guarantee an individual will pass on its genes – as it can still

starve or get eaten before it reproduces. However, over a long

period, individuals with the advantageous mutation are likely

to become more common in a population

EvocardLarge complex new structures are only likely to evolve where there are intermediate steps which are likely to give some advantage – a small patch of light-sensitive cells

does not compare to the complexity of the human eye, but

may be a useful feature for a blind organism

Evocard

Natural selection can only work by varying the existing organism, through mutation of its existing genes. Natural

selection operates on the variety available but can

cause changes in organisms

Evocard

Evolution has no foresight: it cannot select for

characteristics that might be useful in the future, if they do not give an advantage in the

environment now

EvocardNatural selection leads to

effective, but not perfect designs. An ancestor of humans needed a

large appendix to digest its diet. In humans, this has led to a vestigial

organ that is no longer needed, and has evolved into a much

smaller structure – so small, that partly digested food sometimes

gets caught in it and decays

Evocard

Convergent evolution is when similar ‘solutions’ have arisen

several times in different types of organisms: for

example, the eye has evolved independently in a several different types of animals

Evocard

Some single celled organisms that reproduce by cell division (i.e. asexually)

have developed mechanisms for sharing and exchanging

genetic material

Evocard

As different populations are subject to different

environmental pressures, it is possible for one population to

evolve considerably, whilst another remains relatively

unchanged if it fits well with its environment

Evocard

Antibiotic resistant bacteria show us natural selection at work – those bacteria with genes that make them less susceptible to the antibiotic survive and reproduce whilst

others die

Evocard