Evolution, 4th Edition

CooPERATIoN AND CoNFlICT 307

if food is scarce or the litter is too large—behavior that increases the chance that

the female will have more offspring in the future. Plants often abort many of their

offspring (seeds) and reallocate their limited resources to fewer but larger seeds

that have a greater chance of survival.

Aggregation can increase competition among kin for food and other resources

[27, 60]. Siblings in a brood may actively fight for resources, and larger individuals

may kill smaller siblings. This behavior, called siblicide, is the norm in some spe-

cies of eagles and boobies. Females lay two eggs, but one of the nestlings always

kills the other (FIGURE 12.9). The second egg may be the female’s evolutionary

insurance in case the first is inviable.

The ways in which animals such as these behave toward their family starkly

illustrate the point that natural selection lacks any form of morality.

Futuyma Kirkpatrick Evolution, 4e

Sinauer Associates

Troutt Visual Services

Evolution4e_12.08.ai Date 12-04-2016

Q: Seal from Somero gure 02.55 OK?

Inset in center of tree is from MSP and for placement only. Need new photo. Suggest silhouetting image.

Male infanticide

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FIGURE 12.8 This circular phylogeny
of mammals shows that male infanticide
occurs in many species (branches with
red circles at the tip). It is most prevalent
in social species, less prevalent in solitary
species, and least common in monoga-
mous pair-bonding species. (After [48].)
12_EVOL4E_CH12.indd 307 3/22/17 2:39 PM