Glossary of "Biology (3rd ed.)" by Hardin & Bajema (1978)
- behavior whereby the actor incurs a cost while the recipient of the act gains a benefit. Behavior that seems to be altruistic when costs and benefits are measured in terms of the flow of resources between individuals can often be shown to be selfish if costs and benefits are measured in terms of the reproduction of genes. See also cooperation, inclusive fitness, kin selection, mutualism, and parental investment
Glossary of "Evolution (2nd ed.)" by Zimmer & Emlen (2016)
- Occurs whenever a helping individual behaves in a way that benefits another individual at a cost to its own fitness.
Glossary of "Evolution (4th ed.)" by Futuyma & Kirkpatrick (2017)
- Conferral of a benefit on other individuals at an apparent cost to the donor.
- Hardin, G. & Bajema, C. 1978. Biology, its Principles and Implications, third edition. -x + 790 pp. W. H. Freeman and Company, San Francisco.
- Zimmer, C. & Emlen, D. J. 2016. Evolution: Making Sense of Life, 2nd ed. -xxxvi + 707 pp. Roberts and Company Publishers, Inc., Greenwood Village.
- Futuyma, D. J. & Kirkpatrick, M. 2017. Evolution, 4th ed. -xviii + 602 pp. Sinauer Associates, Inc., Sunderland.