Dr. Rex-John Dolittle then settles down with the Chief's daughter, devoting himself to tending to animals and learning the islanders' ways, including any innate talents known by the tribespeople, and teaching his island-born children the animal languages. Dr. Rex-John may stay in touch with his English friends, but in the end prefers to stay with the "primitives" and the animals they live with; he would also know that his own children, being half-African, would never be accepted by society, as the floating island and its people appear to be part of Africa.
Over the next two or three generations this becomes an inherited talent in the Dolittle descendants, if only in a gifted few. They would most likely marry other locals, any connections with England fading out, esp when the elder Dolittle dies. Still, the dream of a better life elsewhere would linger, and the Africanized Dolittles would not forget such things. With England not an option, (about the 1890s?) one grand- or great-grandson may have decided to emigrate to the US, possibly out of Liberia after hearing tales of opportunity in America (which did have a large number of former American slaves, and would be in the right location to be near the former floating island).This Dolittle descendant (probably great-grandfather to Eddie-John) would settle in America, still carrying the now-inbred talent of understanding animals; he would quickly realize that this was not the sort of thing you want to get around. (Much less so if you were African-American in the Jim Crow days.) His own progeny would have done the same thing up until young Eddie-John Dolittle started to talk to his dog. Of course Archer Dolittle, the boy's father, fearing public outrage (and remembering family concerns) made him suppress this until adulthood, when an accident restored the animal-language sense.
The language sense is uncommon at best, possibly only one or two childern of each generation would be born with the ability to understand this. I'm putting this as a combination of Dr. Rex-John's knowledge and his unknown African wife's talent of being a Friend to All Living Things, or whatever nature/animism beliefs her people had. The Dolittle line might catch on to animal language quickly enough if they studied it, but in the end only one would naturally be fluent in it, whether he liked it or not, in the case of Dr. Eddie-John. His own daughters are an example of the recessive nature of the gift; there is no mention of any other Dolittle relative not in the direct line being able to speak to animals.
