1. The Introduction is a bit long. Conversely, I would like to see more information on the dataset in the Method section, particularly the following:

- The 127 individuals were from Rome and central Italy.

- Ancestry in the dataset varied over time:

- During the Imperial period, ancestry shifted toward the eastern Mediterranean. Very few individuals were primarily of western European ancestry

- During Late Antiquity, with the move of the capital from Rome to Byzantium, there was a sharp decline in eastern Mediterranean ancestry and an overall decline in Rome's population. There was a corresponding larger proportion of individuals of central European origin, which may also reflect settlement by Goths and Lombards.

- During the Medieval period, ancestry further shifted toward central and northern Europe.

The authors should also provide dates for the different periods: Pre Iron Age ??; Republic 320 - 27 BCE; Imperial Rome  27 - 300 CE; Late Antiquity 300 - 700 CE; Medieval 700 - ??; Contemporary Italy ??. This point is important. For instance, the term "Late Antiquity" is defined differently by different authors.

2. The authors seem to feel that "harsh conditions" select for increased cognitive ability. This is not true if the harsh conditions occur randomly. If they occur over a predictable annual cycle, you will get strong selection for planning and for cognitive solutions over a long timeframe. Otherwise, you simply get selection for fatalism and fetishism. In the Canadian Arctic, the degradation of environmental conditions during the Little Ice Age led to increased production of religious objects by the Dorset people, but not to new technologies. 

This is, incidentally, a frequent criticism of the "cold winter theory." Why don't we see strong selection for cognitive ability in desert regions? Again, it is not the harshness of the environment that selects for cognitive ability. It is the predictableness of harsh environmental conditions. Only then do you get selection for planning and forward thinking. This was the case in northern Eurasia during the last ice age. Food and fuel were available during predictable intervals of time. That situation led, among other things, to the development of untended devices, such as pits, traps, weirs, and nets, and the digging of storage pits to refrigerate perishables, either meat for year-round consumption or bones for winter fuel.

Frost, P. (2019). The Original Industrial Revolution. Did Cold Winters select for Cognitive Ability? Psych 1(1): 166-181. https://doi.org/10.3390/psych1010012 

3. The authors rely heavily on secondary and tertiary sources. Why not cite the original sources (e.g., Ibn Khaldun)?

4. Did the Late Antique Little Ice Age cause the Justinian plague? I don't think so, but what does it matter? If you burden your main argument with too many dubious sub-arguments, many readers will dismiss the main argument. This is a recurring problem I see with your paper. You can't resist the temptation to throw in lots of controversial ideas, and those controversies tend to overwhelm the main argument.

5. Why is there no mention of the rise of Christianity? The Western Church played a major role in reversing cognitive decline, specifically by supporting the formation of monogamous families, by discouraging slavery, at least during the long period from 500 to 1500 AD, and by creating the peace, order, and stability that allowed the middle class to expand and become dominant. At the very least, you should address the Schulz et al. (2019) paper.

Frost, P. (2022). When did Europe pull ahead? And why? Peter Frost's Newsletter. November 21.  When did Europe pull ahead? And why? https://peterfrost.substack.com/p/when-did-europe-pull-ahead-and-why

Schulz, J.F., D. Bahrami-Rad, J.P. Beauchamp, and J. Henrich. (2019). The Church, intensive kinship, and global psychological variation. Science 366(707): 1-12. https://doi.org/10.1126/science.aau5141    

Replying to Davide Piffer

The Introduction is still too long (a third of the text!). There are only three things you need to do in this section:

1. Explain how polygenic scores provide a measure of cognitive ability.
2. Explain how ancient DNA is enabling us to measure evolutionary change in cognitive ability.
3. Briefly review previous studies of this sort, particularly: Woodley, M.A.; Younuskunju, S.; Balan, B.; Piffer, D. Holocene selection for variants associated with general cognitive ability: comparing ancient and modern genomes. Twin Res Hum Genet 2017, 20, 271-280, doi:10.1017/thg.2017.37 

You might also want to discuss Gregory Clark's work on medieval and post-medieval England, i.e., the demographic expansion of the middle class, the conditions that made such expansion possible, and the resulting shift in the gene pool toward certain mental characteristics.

That's all you need to do. You should not try to explain your results in the Introduction. That's the role of the Discussion section. As things currently stand, you seem to be putting the cart before the horse: you're explaining the results before you actually present them. That approach is defendable if your paper is a follow-up to a previous study. But that's not the case. 

I still think you should discuss Schulz et al. (2019). To date, that paper is the only one in the mainstream literature that has argued for evolutionary change in mental traits during the time period you cover, i.e., Late Antiquity and the Middle Ages. Even if you disagree with that paper, you should try to engage with it and its conclusions.

Replying to Davide Piffer

The Introduction is still too long (a third of the text!). There are only three things you need to do in this section:

1. Explain how polygenic scores provide a measure of cognitive ability.
2. Explain how ancient DNA is enabling us to measure evolutionary change in cognitive ability.
3. Briefly review previous studies of this sort, particularly: Woodley, M.A.; Younuskunju, S.; Balan, B.; Piffer, D. Holocene selection for variants associated with general cognitive ability: comparing ancient and modern genomes. Twin Res Hum Genet 2017, 20, 271-280, doi:10.1017/thg.2017.37 

You might also want to discuss Gregory Clark's work on medieval and post-medieval England, i.e., the demographic expansion of the middle class, the conditions that made such expansion possible, and the resulting shift in the gene pool toward certain mental characteristics.

That's all you need to do. You should not try to explain your results in the Introduction. That's the role of the Discussion section. As things currently stand, you seem to be putting the cart before the horse: you're explaining the results before you actually present them. That approach is defendable if your paper is a follow-up to a previous study. But that's not the case. 

I still think you should discuss Schulz et al. (2019). To date, that paper is the only one in the mainstream literature that has argued for evolutionary change in mental traits during the time period you cover, i.e., Late Antiquity and the Middle Ages. Even if you disagree with that paper, you should try to engage with it and its conclusions.

Replying to Davide Piffer

The Introduction is still too long (a third of the text!). There are only three things you need to do in this section:

1. Explain how polygenic scores provide a measure of cognitive ability.
2. Explain how ancient DNA is enabling us to measure evolutionary change in cognitive ability.
3. Briefly review previous studies of this sort, particularly: Woodley, M.A.; Younuskunju, S.; Balan, B.; Piffer, D. Holocene selection for variants associated with general cognitive ability: comparing ancient and modern genomes. Twin Res Hum Genet 2017, 20, 271-280, doi:10.1017/thg.2017.37 

You might also want to discuss Gregory Clark's work on medieval and post-medieval England, i.e., the demographic expansion of the middle class, the conditions that made such expansion possible, and the resulting shift in the gene pool toward certain mental characteristics.

That's all you need to do. You should not try to explain your results in the Introduction. That's the role of the Discussion section. As things currently stand, you seem to be putting the cart before the horse: you're explaining the results before you actually present them. That approach is defendable if your paper is a follow-up to a previous study. But that's not the case. 

I still think you should discuss Schulz et al. (2019). To date, that paper is the only one in the mainstream literature that has argued for evolutionary change in mental traits during the time period you cover, i.e., Late Antiquity and the Middle Ages. Even if you disagree with that paper, you should try to engage with it and its conclusions.

The Introduction is still too long. In fact, it's just as long as it was in the first version. Maybe the authors think I will forget this point if they just ignore it.

The Introduction is still an exercise in "putting the cart before the horse." The authors try to explain their findings before they actually present them. Such an approach would be defendable if the same findings had appeared in a previous study. But there is no such previous study, certainly not the massive work by Edward Gibbon. He never claimed that mean cognitive ability had declined during Rome's Imperial period.

I would be more forgiving if the authors could write clearly and succinctly. Unfortunately, that doesn't seem to be the case. I'm still having trouble understanding their argument, since it branches off in several directions. Here is my understanding of what they mean to say:

1. During pre-Imperial times, the Romans had "high intelligence and other pro-social psychological traits." The authors seem to be arguing that pro-sociality creates an orderly environment that is conducive to pursuits with high cognitive demands (cf. Gregory Clark).

2. The establishment of the Empire led to a decline in pro-sociality. Life became too good. There was "clean water, basic medical care and an abundance of food" (Oh really?). There was also immigration from the Greek-speaking eastern provinces. All of these trends presumably caused a decline in mean cognitive ability. I say "presumably" because the authors provide no evidence that the Greek-speaking East was less intelligent on average than the Latin-speaking West. The stereotype of the time was the reverse: the East was the home of thinkers and philosophers. In any case, the authors should not assume what they wish to prove.

3. Meanwhile, there was climate warming. Perhaps this was a factor in Rome's decline, or perhaps not. The authors are like the hunter who tries to catch two rabbits at the same time.

4. With the decline of the Empire, the Roman population may have entered "another eugenic phase where intelligence is rising." I initially saw this as a reference to Christianity and selection for pro-sociality (cf. Schulz et al.), but apparently I was mistaken.  

I'm coming around to the other reviewer's (harsh) judgment. The results are interesting. Unfortunately, they are sandwiched between a lot of intellectual musing and meandering.

I have read the paper, thanks.

Brief suggestions:

Add ds (or zs) and IQs in abstract and Figure 1 (or make new Figure 2).

E.g.,

old: "we find that intelligence increased from the Neolithic Era to the Iron Age, declines after the Republic Period and during the Imperial Period and increases in Late Antiquity and is approximately at the same level today"

new (numbers invented by me): "we find that intelligence increased from the Neolithic Era (representing z=0 or IQ 85) to the Iron Age (z=1 or IQ 100), declines after the Republic Period (z=0.50 or IQ 92.5) and during the Imperial Period (...) and increases in Late Antiquity (...) and is approximately at the same level today"

Explain what is the standard for IQ 100 (natives in Britain today? Italy today?).

Best and thanks

Replying to Reviewer 3

I have read the paper, thanks.

Brief suggestions:

Add ds (or zs) and IQs in abstract and Figure 1 (or make new Figure 2).

E.g.,

old: "we find that intelligence increased from the Neolithic Era to the Iron Age, declines after the Republic Period and during the Imperial Period and increases in Late Antiquity and is approximately at the same level today"

new (numbers invented by me): "we find that intelligence increased from the Neolithic Era (representing z=0 or IQ 85) to the Iron Age (z=1 or IQ 100), declines after the Republic Period (z=0.50 or IQ 92.5) and during the Imperial Period (...) and increases in Late Antiquity (...) and is approximately at the same level today"

Explain what is the standard for IQ 100 (natives in Britain today? Italy today?).

Best and thanks

Thanks for the comments. I have replaced figure 1 with a figure showing individual Z values. I have also added a table (table 1) showing the average Z score by period. I refrain from performing a simple transformation to IQ because the conversion is not straightforward (PGS only includes additive genetic variance and represents only a fraction of it). However, I believe the corresponding change in IQ SDs is pretty similar to the change in PGS SDs but it would be beyond the scope of this paper to calculate IQs.

I have edited the abstract by adding the effect size (Cohen´s d) of each period (with pre-Iron Age as the reference).

 

Replying to Reviewer 3

I have read the paper, thanks.

Brief suggestions:

Add ds (or zs) and IQs in abstract and Figure 1 (or make new Figure 2).

E.g.,

old: "we find that intelligence increased from the Neolithic Era to the Iron Age, declines after the Republic Period and during the Imperial Period and increases in Late Antiquity and is approximately at the same level today"

new (numbers invented by me): "we find that intelligence increased from the Neolithic Era (representing z=0 or IQ 85) to the Iron Age (z=1 or IQ 100), declines after the Republic Period (z=0.50 or IQ 92.5) and during the Imperial Period (...) and increases in Late Antiquity (...) and is approximately at the same level today"

Explain what is the standard for IQ 100 (natives in Britain today? Italy today?).

Best and thanks

Thanks for the comments. I have replaced figure 1 with a figure showing individual Z values. I have also added a table (table 1) showing the average Z score by period. I refrain from performing a simple transformation to IQ because the conversion is not straightforward (PGS only includes additive genetic variance and represents only a fraction of it). However, I believe the corresponding change in IQ SDs is pretty similar to the change in PGS SDs but it would be beyond the scope of this paper to calculate IQs.

I have edited the abstract by adding the effect size (Cohen´s d) of each period (with pre-Iron Age as the reference).

 

Replying to Davide Piffer

Replying to Reviewer 3

I have read the paper, thanks.

Brief suggestions:

Add ds (or zs) and IQs in abstract and Figure 1 (or make new Figure 2).

E.g.,

old: "we find that intelligence increased from the Neolithic Era to the Iron Age, declines after the Republic Period and during the Imperial Period and increases in Late Antiquity and is approximately at the same level today"

new (numbers invented by me): "we find that intelligence increased from the Neolithic Era (representing z=0 or IQ 85) to the Iron Age (z=1 or IQ 100), declines after the Republic Period (z=0.50 or IQ 92.5) and during the Imperial Period (...) and increases in Late Antiquity (...) and is approximately at the same level today"

Explain what is the standard for IQ 100 (natives in Britain today? Italy today?).

Best and thanks

Thanks for the comments. I have replaced figure 1 with a figure showing individual Z values. I have also added a table (table 1) showing the average Z score by period. I refrain from performing a simple transformation to IQ because the conversion is not straightforward (PGS only includes additive genetic variance and represents only a fraction of it). However, I believe the corresponding change in IQ SDs is pretty similar to the change in PGS SDs but it would be beyond the scope of this paper to calculate IQs.

I have edited the abstract by adding the effect size (Cohen´s d) of each period (with pre-Iron Age as the reference).

 

Thanks for the revision.

Add a minus in the Abstract: declines after the Republic Period and during the Imperial Period (d= −0.47)

Raveane et al. ,2019 -> Raveane et al., 2019

Replying to Davide Piffer

Replying to Reviewer 3

I have read the paper, thanks.

Brief suggestions:

Add ds (or zs) and IQs in abstract and Figure 1 (or make new Figure 2).

E.g.,

old: "we find that intelligence increased from the Neolithic Era to the Iron Age, declines after the Republic Period and during the Imperial Period and increases in Late Antiquity and is approximately at the same level today"

new (numbers invented by me): "we find that intelligence increased from the Neolithic Era (representing z=0 or IQ 85) to the Iron Age (z=1 or IQ 100), declines after the Republic Period (z=0.50 or IQ 92.5) and during the Imperial Period (...) and increases in Late Antiquity (...) and is approximately at the same level today"

Explain what is the standard for IQ 100 (natives in Britain today? Italy today?).

Best and thanks

Thanks for the comments. I have replaced figure 1 with a figure showing individual Z values. I have also added a table (table 1) showing the average Z score by period. I refrain from performing a simple transformation to IQ because the conversion is not straightforward (PGS only includes additive genetic variance and represents only a fraction of it). However, I believe the corresponding change in IQ SDs is pretty similar to the change in PGS SDs but it would be beyond the scope of this paper to calculate IQs.

I have edited the abstract by adding the effect size (Cohen´s d) of each period (with pre-Iron Age as the reference).

 

Thanks for the revision.

Add a minus in the Abstract: declines after the Republic Period and during the Imperial Period (d= −0.47)

Raveane et al. ,2019 -> Raveane et al., 2019

Replying to Reviewer 3

Replying to Davide Piffer

Replying to Reviewer 3

I have read the paper, thanks.

Brief suggestions:

Add ds (or zs) and IQs in abstract and Figure 1 (or make new Figure 2).

E.g.,

old: "we find that intelligence increased from the Neolithic Era to the Iron Age, declines after the Republic Period and during the Imperial Period and increases in Late Antiquity and is approximately at the same level today"

new (numbers invented by me): "we find that intelligence increased from the Neolithic Era (representing z=0 or IQ 85) to the Iron Age (z=1 or IQ 100), declines after the Republic Period (z=0.50 or IQ 92.5) and during the Imperial Period (...) and increases in Late Antiquity (...) and is approximately at the same level today"

Explain what is the standard for IQ 100 (natives in Britain today? Italy today?).

Best and thanks

Thanks for the comments. I have replaced figure 1 with a figure showing individual Z values. I have also added a table (table 1) showing the average Z score by period. I refrain from performing a simple transformation to IQ because the conversion is not straightforward (PGS only includes additive genetic variance and represents only a fraction of it). However, I believe the corresponding change in IQ SDs is pretty similar to the change in PGS SDs but it would be beyond the scope of this paper to calculate IQs.

I have edited the abstract by adding the effect size (Cohen´s d) of each period (with pre-Iron Age as the reference).

 

Thanks for the revision.

Add a minus in the Abstract: declines after the Republic Period and during the Imperial Period (d= −0.47)

Raveane et al. ,2019 -> Raveane et al., 2019

Sorry for the confusion. The d values are relative to the Neolithic era (reference group). "Iron Age (d= 1.52), declines after the Republic Period and during the Imperial Period (d= 0.47) and increases in Late Antiquity (d= 0.94)." So a 1.52 SD increase from Neolithic to Iron Age/Republic, and 0.47 SD from Neolithic to Imperial period, which means that from Iron Age/Republic to Imperial period it decreased (1.52 - 0.47) by 1.05 SDs. If it is more intuitive, I can use Z scores instead.

Replying to Davide Piffer

Replying to Reviewer 3

Replying to Davide Piffer

Replying to Reviewer 3

I have read the paper, thanks.

Brief suggestions:

Add ds (or zs) and IQs in abstract and Figure 1 (or make new Figure 2).

E.g.,

old: "we find that intelligence increased from the Neolithic Era to the Iron Age, declines after the Republic Period and during the Imperial Period and increases in Late Antiquity and is approximately at the same level today"

new (numbers invented by me): "we find that intelligence increased from the Neolithic Era (representing z=0 or IQ 85) to the Iron Age (z=1 or IQ 100), declines after the Republic Period (z=0.50 or IQ 92.5) and during the Imperial Period (...) and increases in Late Antiquity (...) and is approximately at the same level today"

Explain what is the standard for IQ 100 (natives in Britain today? Italy today?).

Best and thanks

Thanks for the comments. I have replaced figure 1 with a figure showing individual Z values. I have also added a table (table 1) showing the average Z score by period. I refrain from performing a simple transformation to IQ because the conversion is not straightforward (PGS only includes additive genetic variance and represents only a fraction of it). However, I believe the corresponding change in IQ SDs is pretty similar to the change in PGS SDs but it would be beyond the scope of this paper to calculate IQs.

I have edited the abstract by adding the effect size (Cohen´s d) of each period (with pre-Iron Age as the reference).

 

Thanks for the revision.

Add a minus in the Abstract: declines after the Republic Period and during the Imperial Period (d= −0.47)

Raveane et al. ,2019 -> Raveane et al., 2019

Sorry for the confusion. The d values are relative to the Neolithic era (reference group). "Iron Age (d= 1.52), declines after the Republic Period and during the Imperial Period (d= 0.47) and increases in Late Antiquity (d= 0.94)." So a 1.52 SD increase from Neolithic to Iron Age/Republic, and 0.47 SD from Neolithic to Imperial period, which means that from Iron Age/Republic to Imperial period it decreased (1.52 - 0.47) by 1.05 SDs. If it is more intuitive, I can use Z scores instead.

"I can use Z scores instead" - yes, good idea, use z-scores!

Replying to Davide Piffer

Replying to Reviewer 3

Replying to Davide Piffer

Replying to Reviewer 3

I have read the paper, thanks.

Brief suggestions:

Add ds (or zs) and IQs in abstract and Figure 1 (or make new Figure 2).

E.g.,

old: "we find that intelligence increased from the Neolithic Era to the Iron Age, declines after the Republic Period and during the Imperial Period and increases in Late Antiquity and is approximately at the same level today"

new (numbers invented by me): "we find that intelligence increased from the Neolithic Era (representing z=0 or IQ 85) to the Iron Age (z=1 or IQ 100), declines after the Republic Period (z=0.50 or IQ 92.5) and during the Imperial Period (...) and increases in Late Antiquity (...) and is approximately at the same level today"

Explain what is the standard for IQ 100 (natives in Britain today? Italy today?).

Best and thanks

Thanks for the comments. I have replaced figure 1 with a figure showing individual Z values. I have also added a table (table 1) showing the average Z score by period. I refrain from performing a simple transformation to IQ because the conversion is not straightforward (PGS only includes additive genetic variance and represents only a fraction of it). However, I believe the corresponding change in IQ SDs is pretty similar to the change in PGS SDs but it would be beyond the scope of this paper to calculate IQs.

I have edited the abstract by adding the effect size (Cohen´s d) of each period (with pre-Iron Age as the reference).

 

Thanks for the revision.

Add a minus in the Abstract: declines after the Republic Period and during the Imperial Period (d= −0.47)

Raveane et al. ,2019 -> Raveane et al., 2019

Sorry for the confusion. The d values are relative to the Neolithic era (reference group). "Iron Age (d= 1.52), declines after the Republic Period and during the Imperial Period (d= 0.47) and increases in Late Antiquity (d= 0.94)." So a 1.52 SD increase from Neolithic to Iron Age/Republic, and 0.47 SD from Neolithic to Imperial period, which means that from Iron Age/Republic to Imperial period it decreased (1.52 - 0.47) by 1.05 SDs. If it is more intuitive, I can use Z scores instead.

"I can use Z scores instead" - yes, good idea, use z-scores!