Inclusive Fitness

“An organism can help pass on shared genes without parenting every descendant that receives its help.”

01 / PLAINLY

What it means, plainly

Inclusive fitness combines one's own reproduction with effects on reproduction by relatives who share genes.

02 / CONTEXT

A little more

Inclusive fitness counts direct effects through one's offspring and indirect effects through relatives, weighted by relatedness. It helps analyze when an allele associated with helping can spread.

03 / WHY IT MATTERS

Why it matters

It gives a precise evolutionary account of some family cooperation without assuming conscious intent or moral goodness.

04 / EXAMPLE

A familiar example

An alarm call that slightly endangers its caller may persist if it protects enough close relatives carrying associated variants.

05 / LIMIT

What it does not mean

It does not claim that organisms calculate genetic fractions or that every act helping relatives is adaptive.

06 / NOTICE

Notice it in your day

Imagine a costly behavior and change its cost, benefit, and relatedness one at a time. Notice which change matters most.

FINAL NOTE

The idea worth keeping

Track benefits, costs, and relatedness, while keeping a gene-level model separate from psychological intention.

QUESTIONS / 02

Questions people still have

Is inclusive fitness just having many offspring?

No. That is the direct route; inclusive fitness also considers indirect effects on relatives' reproduction.

Does it explain every altruistic behavior?

No. Cooperation can also arise through reciprocity, mutualism, reputation, and other mechanisms requiring separate tests.