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The Descent of Man

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probably is the most efficient <strong>of</strong> all the causes <strong>of</strong><br />

the proportion <strong>of</strong> males to females born alive<br />

being less amongst illegitimate children than<br />

amongst the legitimate. With most animals the<br />

greater size <strong>of</strong> the adult male than <strong>of</strong> the female,<br />

is due to the stronger males having conquered<br />

the weaker in their struggles for the possession<br />

<strong>of</strong> the females, and no doubt it is owing to<br />

this fact that the two sexes <strong>of</strong> at least some<br />

animals differ in size at birth. Thus we have the<br />

curious fact that we may attribute the more<br />

frequent deaths <strong>of</strong> male than female infants,<br />

especially amongst the illegitimate, at least in<br />

part to sexual selection.<br />

It has <strong>of</strong>ten been supposed that the relative age<br />

<strong>of</strong> the two parents determine the sex <strong>of</strong> the <strong>of</strong>fspring;<br />

and Pr<strong>of</strong>. Leuckart (55. Leuckart, in<br />

Wagner 'Handworterbuch der Phys.' B. iv.<br />

1853, s. 774.) has advanced what he considers<br />

sufficient evidence, with respect to man and<br />

certain domesticated animals, that this is one

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