theory of evolution

Question 1

what is Darwin’s theory of evolution by natural selection?

Answer 1

• individual organisms within a species show a wide range of variation for a characteristic e.g. some giraffes have longer necks
• individuals with characteristics most suited to the environment are most likely to survive and breed successfully e.g. giraffes with longer necks can reach most nutritious leaves at top of tree, so they are more likely to survive and breed than giraffes with shorter necks
• the characteristics that have enabled these individual to survive are then passed on to the next generation e.g. the offspring of the giraffes could inherit a longer neck

Question 2

what was Darwin’s book called and what year was it published?

Answer 2

On the origin of species, published in 1859

Question 3

why was the theory of evolution by natural selection only gradually accepted?

Answer 3

• the theory challenged the idea that God made all the animals and plants that live on earth
• there was insufficient evidence at the time at the time the theory was published to convince many scientists
• people did not understand how characteristics are inherited. genetics was not understood until 50 years after Darwin’s theory was published

Question 4

what was jean baptiste lamarck’s theory on how species change over time?

Answer 4

• he suggested that when a characteristic is used regularly it becomes more developed and this strengthened characteristic is then passed on to the offspring e.g. every time a giraffe stretches it neck to reach a tree its neck would get longer and the giraffes offspring would then inherit this longer neck.
• his theory cannot be correct as we now know that changes that occur during an organism’s lifetime cannot be inherited

Question 5

what did alfred russel wallace propose?

Answer 5

he independently proposed the theory of evolution by natural selection

Question 6

what are the steps to how new species form?

Answer 6

• species live together and interbreed so any beneficial mutation spreads throughout the whole population
• populations of a species can become isolated due to a geographical barrier (e.g. a river) which them separates them into two groups
• because the two populations are now separate there is no interbreeding between the two populations
• over time natural selection will favour different alleles on the two sides as the environment may be different
• because there is no interbreeding between the two populations any mutations that occur can not spread between the two populations
• this means that over many generations the two populations will begin to change
• when the two populations are able to mix again the phenotypes of the two populations are so different that they can no longer interbreed to make fertile offspring, so they are now two different species

Question 7

describe how a species evolves into a new species–

Answer 7

• isolation of different populations
• habitat variation between population of species
• a mutation occurs in each population which causes genetic variation
• the ones better adapted to the environment survive and pass on favourable alleles to offspring
• eventually the two populations cannot produce fertile offspring meaning they are two different species