Question 19M.2.SL.TZ1.b
| Date | May 2019 | Marks available | [Maximum mark: 7] | Reference code | 19M.2.SL.TZ1.b |
| Level | SL | Paper | 2 | Time zone | TZ1 |
| Command term | Explain | Question number | b | Adapted from | N/A |
Explain how natural selection can lead to speciation.
[7]
a. variation is required for natural selection/evolution/variation in species/populations ✔
b. mutation/meiosis/sexual reproduction is a source of variation ✔
c. competition/more offspring than the environment can support ✔
d. adaptations make individuals suited to their environment/way of life ✔
e. survival of better adapted «individuals)/survival of fittest/converse ✔
f. inheritance of traits/passing on genes of better adapted «individuals»
OR
reproduction/more reproduction of better adapted/fittest «individuals» ✔
g. speciation is formation of a new species/splitting of a species/one population becoming a separate species ✔
h. reproductive isolation of separated populations ✔
i. geographic isolation «of populations can lead to speciation» ✔
j. temporal/behavioral isolation «of populations can lead to speciation» ✔
k. disruptive selection/differences in selection «between populations can lead to speciation» ✔
l. gradual divergence of populations due to natural selection/due to differences in environment ✔
m. changes in the gene pools «of separated populations»/separation of gene pools ✔
n. interbreeding becomes impossible/no fertile offspring «so speciation has happened» ✔
Most candidates think they understand evolution by natural selection but many do not. Here the focus was on speciation - the splitting of a species into two or more species. Often answers described the evolution of one species over time, rather than speciation itself. An idea central to natural selection that was frequently missing from an answer is adaptation or fitness. Often traits were referred to as ‘favourable’ and therefore likely to lead to survival and reproduction but there is a circularity of argument there. Survival depends on traits fitting the environment, hence being an adaptation to it. The mostly common ideas seen in answers were differential survival and reproduction, due to differences in traits. A common fault was to confuse individuals and species and to refer to a whole species surviving and reproducing more successfully than another species.
