PDF - Wallace Online

NATURAL SELECTIONreturn to their station to devour. If a bird began by capturingthe slow-flying conspicuous Heliconidse, and found them alwaysso disagreeable that it could not eat them, it would after avery few trials leave off catching them at all and;their wholeappearance, form, colouring, and mode of flight are so peculiarthat there can be little doubt birds would soon learn to distinguishthem at a long distance, and never waste any time inpursuit of them. Under these circumstances, it is evidentthat any other butterfly of a group which birds were accustomedto devour would be almost equally well protected byclosely resembling a Heliconian externally, as if it acquiredalso the disagreeable odour; always supposing that therewere only a few of them among a great number of the Heliconias.If the birds could not distinguish the two kindsexternally, and there were on the average only one eatableamong fifty uneatable, they would soon give up seeking forthe eatable ones, even if they knew them to exist. If, on theother hand, any particular butterfly of an eatable groupacquired the disagreeable taste of the Heliconias while itretained the characteristic form and colouring of its owngroup, this would be really of no use to it whatever for the;birds would go on catching itamong its eatable allies (comparedwith which it would rarely occur), it would be woundedand disabled, even if rejected, and its increase would thus beas effectually checked as if it were devoured. It is important,therefore, to understand that if any one genus of an extensivefamily of eatable butterflies were in danger of exterminationfrom insect-eating birds, and if two kinds of variation weregoing on among them, some individuals possessing a slightlydisagreeable taste, others a slight resemblance to the Heliconidse,this latter quality would be much more valuable thanthe former. The change in flavour would not at all preventthe variety from being captured as before, and it wouldalmost certainly be thoroughly disabled before being rejected.The approach in colour and form to the Heliconidse, however,would be at the very first a positive, though perhaps a slightadvantage for ; although at short distances this variety wouldbe easily distinguished and devoured, yet at a longer distanceitmight be mistaken for one of the uneatable group, and sobe passed by and gain another day's life,which might in