Inclusive Fitness Theory – Why Do We Value Some Lives More Than Others?

I’m sure you’ve all heard the sad news
of the gorilla Harambe who was shot dead after a child fell into his enclosure. Now I’m
not here to discuss the details because I don’t think it’s appropriate to do so, but
the incident did spark a huge discussion on the internet from which one of the emerging
questions was: “why do we value some lives more than others?” – and I do want to
address this question because I think it is one that we can answer with science! [Intro by Cristina de Manuel & Caro Waro ] One of the most common answers people I’ve
seen people give is that “individuals are looking out for the good of their own species”
– however, this is wrong and it’s not the way evolution works. Evolution does not operate at the level of
the species, in fact it operates at the lowest level of transmissible information, which
we consider to be the gene, and that is contained within its vehicle: the individual. Evolution favours behaviours, strategies and
traits encoded by genes that increase their capacity to be transmitted to as many individuals
as possible, and genes that don’t do that get wiped out. This is how natural selection
works. Genes don’t achieve evolutionary success
by merely increasing the individual’s personal fitness, which would imply maximising the
number of offspring they produce, for there is more to the story. Individuals in a population
share genes with related individuals, which means that a gene may also increase its evolutionary
success by indirectly favouring the reproduction and survival of other individuals who also
carry that gene. This is known as inclusive fitness, but it also goes by the name of kin
selection, and it reflects the combination of personal fitness as well as fitness obtained
indirectly by helping other related individuals. In 1964, Bill Hamilton came up with Hamilton’s
Rule, which reflects the conditions under which altruistic behaviour is performed – that
is, when will an animal help another individual: R stands for relatedness, b for benefits and
c for costs. It is honestly, a very simple economics equation – if the benefits outweigh
the costs [offspring, food etc], altruistic behaviour will be performed. Relatedness reflects
the proportion of genes shared as compared to the population average. For instance, my
relatedness to each of my parents is 0.5 because I received half of my genetic material from
each parent. I also share 0.5 to any siblings, 0.25 to half-siblings, grandparents and grandsons,
0.125 to cousins… you get the picture. When Haldane was asked if he would lay down
his life for his brother’s, his response was “No, but I would for two brothers or
for eight cousins”, a statement I see fitting of a diploid organism seeking to maximise
their inclusive fitness. However, Hamilton’s rule also applies in
more extravagant modes of inheritance. For instance, Hymenopterans (ants, bees, wasps,
bumblebees) are haplodiploid, which means that unfertilised eggs develop into males,
and fertilised eggs, which contain twice the amount of genetic information, develop into
females. This leads to interesting relatedness values between relatives, and explains the
conflict and strange behaviour observed in some haplodiploid societies. For instance,
the relatedness between workers is greater than between a worker and their own offspring,
and much greater than between a worker and their nieces and nephews. This has lead to
both worker sterility, whereby workers opt out of reproducing in favour of raising more
of the queen’s eggs; and also to worker policing, where workers murder the offspring
of other workers. The other thing to remember about evolution
is that behaviours don’t have to have any specific intent or insight behind them. It
is very easy for us to wrongly anthropomorphise the behaviours of other organisms. No conscious
intent or insight is necessary for altruistic behaviours to evolve. Now, I find this to be one of the most fascinating
topics in biology and not one that I can cover properly in this video so you can certainly
expect a video on this in the future. This is a basic introduction to the fascinating
field of inclusive fitness. Now, I will agree with anyone who rightfully argues that the
actions and decisions of humans are based on a lot more than a mere calculation of relatedness,
as of course our priorities are dictated by many other influencing factors – but inclusive
fitness nonetheless does lend a sound evolutionary explanation to both the common expression
“blood is thicker than water” as well as the original question that we were discussing
today. Thank you so much for watching me, as always
I have a bit more information on the blogpost at and I will see you in
the next one! Bye! Subscribe for more science! 🙂
DE MANUEL] [Writer, host & editor – Inés Dawson]


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