4. As we've discussed, some of the so-called "major transitions in evolution" represent the
creation of new kinds of individuals (e.8., the origin of eukaryotes, the origin of multicellular
organisms, the origin of animal societies). Among these, some represent the coming together of
unrelated organisms (e.g. the endosymbiosis between an archaeon and a proteobacterium to form
the first eukaryote), which have been called "egalitarian" transitions, and others represent the
coming together of related individuals (e.g., when a worker termite stays at the nest to help her
kin rather than leaving to found her own nest), which have been called "fraternal" transitions.
Cyanobacteria have been involved in both kinds of transition: an egalitarian one, in which they
came to be a plastid; and a fraternal one, which we only briefly touched on in class. In the latter,
cyanobacterial cells stick together after dividing and form multicellular filaments of hundreds of
cells, with some specialization for metabolic function (e.g, some cells do photosynthesis and
some do nitrogen fixation). One study of multicellularity in cyanobacteria suggests that its origin
dates to 2.5 billion years ago and might have played a causal role in the Great Oxidation Event.
In light of what you now know about these transitions (i.e., the transition to multicellularity and
the transition to being a plastid), which of them would you say has been more consequential?
Make the case for either one. 5. Cyanobacteria live mostly in aquatic habitats but they can also
be found on land-in deserts of all places! They lie dormant for much of the year, as it is so dry,
but when it rains they become active metabolically. Although rain is good for them, it is
potentially harmful for us, because these desert cyanobacteria produce harmful toxins that can be
kicked up in dust storms. One might guess that the concentration of these harmful toxins is
highest in soil just after it rains. To test this, imagine running an experiment in which you have
four treatment groups: 1.) intact/unwatered; 2.) disturbed/unwatered; 3.) intact/watered; and 4.)
disturbed/wateredwhere "intact" means that the surface layer of desert soil is left in place and
"disturbed" means that 0.5cm from the surface has been scraped off, and "watered" versus
"unwatered" means what it sounds like. You have a sample size of 5 in each treatment group.
After ten days of watering or not watering, you measure the average concentration of the toxin in
each treatment group and compare the four averages. The null hypothesis is that the mean toxin
concentrations are equal across the four treatment groups. You perform a Kruskal-Wallis H test,
which is a null-hypothesis significance test. The critical value for this experiment at the 0.05
level is H=7.4; at the 0.01 level it is H=9.8. For your data, the observed H=10.6. First, in light of
these results, what decision should you make, and second, how would you write that result up in
a single se.
4. As weve discussed, some of the so-called major transitions in ev.pdf
1. 4. As we've discussed, some of the so-called "major transitions in evolution" represent the
creation of new kinds of individuals (e.8., the origin of eukaryotes, the origin of multicellular
organisms, the origin of animal societies). Among these, some represent the coming together of
unrelated organisms (e.g. the endosymbiosis between an archaeon and a proteobacterium to form
the first eukaryote), which have been called "egalitarian" transitions, and others represent the
coming together of related individuals (e.g., when a worker termite stays at the nest to help her
kin rather than leaving to found her own nest), which have been called "fraternal" transitions.
Cyanobacteria have been involved in both kinds of transition: an egalitarian one, in which they
came to be a plastid; and a fraternal one, which we only briefly touched on in class. In the latter,
cyanobacterial cells stick together after dividing and form multicellular filaments of hundreds of
cells, with some specialization for metabolic function (e.g, some cells do photosynthesis and
some do nitrogen fixation). One study of multicellularity in cyanobacteria suggests that its origin
dates to 2.5 billion years ago and might have played a causal role in the Great Oxidation Event.
In light of what you now know about these transitions (i.e., the transition to multicellularity and
the transition to being a plastid), which of them would you say has been more consequential?
Make the case for either one. 5. Cyanobacteria live mostly in aquatic habitats but they can also
be found on land-in deserts of all places! They lie dormant for much of the year, as it is so dry,
but when it rains they become active metabolically. Although rain is good for them, it is
potentially harmful for us, because these desert cyanobacteria produce harmful toxins that can be
kicked up in dust storms. One might guess that the concentration of these harmful toxins is
highest in soil just after it rains. To test this, imagine running an experiment in which you have
four treatment groups: 1.) intact/unwatered; 2.) disturbed/unwatered; 3.) intact/watered; and 4.)
disturbed/wateredwhere "intact" means that the surface layer of desert soil is left in place and
"disturbed" means that 0.5cm from the surface has been scraped off, and "watered" versus
"unwatered" means what it sounds like. You have a sample size of 5 in each treatment group.
After ten days of watering or not watering, you measure the average concentration of the toxin in
each treatment group and compare the four averages. The null hypothesis is that the mean toxin
concentrations are equal across the four treatment groups. You perform a Kruskal-Wallis H test,
which is a null-hypothesis significance test. The critical value for this experiment at the 0.05
level is H=7.4; at the 0.01 level it is H=9.8. For your data, the observed H=10.6. First, in light of
these results, what decision should you make, and second, how would you write that result up in
a single sentence for the Results section of a scientific paper?
