So, as you all know, species lived in particular ecological niches and particular environments, and the pressures of those environments selected which changes, through random mutation in species, were going to be preserved.
Así, como saben, las especies vivían en nichos ecológicos particulares, en entornos particulares, y las presiones de dichos entornos seleccionaban qué cambios, mediante mutaciones aleatorias de especies, iban a ser preservados.