The online Beagle library now allows anyone to see the amazing range of visual imagery that Darwin poured over during the voyage. See the illustrations here Humboldt's illustration of his famous ascent of Mount Chimborazo in the Andes in 1802.
And it may be our busy lifestyle that keeps us from napping. While naps do not necessarily make up for inadequate or poor quality nighttime sleep, a short nap of 20-30 minutes can help to improve mood, alertness and performance.
If she wakes up in the morning and takes her nap 2 hours later, she'll only nap for 2 hours, but 3+ hours means she will nap for about 3 hours and then she is up for 5 or 6 hours. My daughter started napping once a day around the same age. I stretched her nap time to just after lunch and she has had this routine for 9 months now. Straight after lunch she asks for nite nites and is very happy to go. I let her sleep for an hour and a half now but when she was one she had 2 to 2.5 hours sleep.