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 Evocard One 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

Evocard Darwin 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

Evocard Large 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 Evocard Large 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 Evocard Natural 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