under the conditions they lived in, so they were the ones to pass on their genes and characteristics to future generations.
(they; lived; L:in) (they; were; the ones to pass on their genes and characteristics to future generations; L:under the conditions) (the ones; to pass; to future generations)
they they the ones
lived were to pass
L:in
the ones to pass on their genes and characteristics to future generations L:under the conditions
to future generations