In Poul Anderson's Fire Time (London, 1977) -
(i) " 'The Ishtarian on foot can travel faster than a man, including a man on a horse, and for much longer at a stretch without tiring. He can see quite well by night, so the shorter day is no inconvenience. He rarely needs shelter, and if need be he can live indefinitely off whatever herbage grows along his path. It's no particular bother to camp out on the job. In short, he's a better traveler than we are, with more speed and scope.' " (p. 112)
Ishtarians can travel faster and further because they are quadrupeds. I had thought that a future evolutionary stage might be a being with at least human intelligence but with a body at home in the natural environment, not requiring clothes, shelter or specially prepared food.
(ii) Because of their longevity:
"A bright young Ishtarian might study under a master, be in the prime of life when the catastrophes began, and survive to teach in the next cycle." (p. 117)
This personal continuity, together with storehouses of books and instruments, enable the Ishtarians to weather periodic catastrophes that would otherwise destroy civilisation completely.
(iii) "(Also there seemed to be the factor of creativity. If most men are at their most original between the ages of, say, twenty and thirty-five, the corresponding Ishtarian ages would be about fifty to one hundred fifty, with all the advantages of accumulating wisdom and insight.)" (p. 117)
One hundred years of creativity and learning as against fifteen! One Lawspeaker with "...an excellent memory and a gift for seeing the total picture..." had presided in the Gathering for three hundred years (p. 117).
(iv) "Ishtarians...have less innate violence, power hunger, and general irrationality than men..." (p. 118)
(v) " 'Ishtarians are better than us at producing and hearing sounds. Their music, like their dance, is nearly always incredibly sophisticated by our lights.' " (p. 124)
"...they were equally able to see that robbery often yields more fun and profit than honest labor..." (p. 118)
Hence the need for the legions:
"The legions were the nearest thing to governed organizations [but] they were autonomous." (p. 118)
There is another small detail. The Lawspeaker observes:
" 'No doubt this assembly will stand for longer than expected...' " (pp. 120-121)
A quadrupedal assembly does not sit but stands.