Paso el codigo completo, no me da bola, me sigue diciendo que son solo minusculas......
$se1 = "People of all ages and cultures respond to humour. The majority of people are able to experience humour, i.e.,
to be amused, to laugh or smile at something funny, and thus they are considered to have a sense of humour.
The hypothetical person lacking a sense of humour would likely find the behaviour induced by humour to be inexplicable,
strange, or even irrational.";
if (preg_match("/^[A-Z]|\s[A-Z]/", $se1)) {
print "<p>La cadena $se1 son solo letras minúsculas.</p>\n";
} else {
print "<p>La cadena $se1 no son solo letras minúsculas.</p>\n";
}