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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]

37 thoughts on “Inclusive Fitness Theory – Why Do We Value Some Lives More Than Others?

  1. The field of inclusive fitness is one of my favourite in Biology because it explains certain behaviours in animals so well! I'm interested in knowing whether other people who have viewed this video had heard of inclusive fitness and the selfish gene theory before.

  2. Wow this doesn't come close to addressing the question of value as to the lives of others. If you want to draw a subjective boundary at the level of species and consider a human life to be more valuable than any other species, the inclusive fitness aspect falls down pretty quickly when you consider that other great apes share dramatically similar amounts of our DNA. I think you have missed the point of all these discussions… value judgements are subjective and not based on reason or logic and science plays no part in it. There is simply no logical reason to elevate humans above other animals, least of all that some random human shares more DNA with you than a cow or dog.

  3. I have a query regarding animal behavior. I often tell people that emotions are biological "programs" designed to keep our "species" "living", (the programmer being evolution.) Obviously, things aren't that simple; however, I haven't been able to get a biologist's opinion on the matter.
    I request an evaluation on this line of thinking and additional thoughts.

  4. I share half my genes with a banana, doesn't inclusive fitness theory suggest half my genome cares as much about human survival as it does banana survival?

  5. I'm confused, how is the explanation in conflict with the statement at the beginning of the video?

    Humans value other humans more because they think it benefits the society, which they in turn think benefits themselves.
    Individuals value other individuals that they feel related to because they think it benefits them.

    Sure, your explanation is more scientifically accurate and detailed, but the initial statement seems to relay the same general notion in layman's terms.
    What part have I misunderstood?

  6. The way you pronounced Gorilla Harambe is actually amazing… a single rolled 'r' is too underused linguistically in my opinion…

  7. Inclusive Fitness Theory seems indeed to describe successfully a lot of behaviour as it can be observed. When observable in human behaviour somewhat depressing maybe, but the principle is sound and quite undeniable.

    Funnily, you use the expression "Blood is thicker than water" to illustrate this principle of gene-based altruïsm, as it is debated whether it is meant to illustrate how kinship is more important than less gene-related bonds, or actually something more like the opposite. Was that intentional?

  8. What about cases where an animal helps another animal that isn't even a member of their species? There are a great many examples of dolphins helping humans in trouble in the water, and even an amazing video of a dolphin asking a scuba diver to disentangle fishing line from it's fins.

  9. well, we all are more relates to the child than the gorilla. So we end up caring for the survival of the species in these situations. Of course it only works well if you are a stranger to both. I'm sure anyone would hesitate if it was their beloved dog.

  10. For the follow-up on this video on how superorganisms evolve (eg, bees and ants) – click here! 🙂

  11. If anyone is interested in this topic you can read The Selfish Gene by Richard Dawkins. It's very similar and incredibly in depth.

  12. Thank you for pointing out the anthropomorphic error that so many people employ in explaining evolutionary results, e.g., females favor flamboyant males because they must be healthy and better mates. Actually, females developed the preference randomly, and selection preserved and refined it because it increased reproductive fitness. Also, slight correction: evolution does not wipe out all genes that don't add reproductive fitness, only those that actively harm fitness. We have lots of switched-off genes, junk DNA, and neutral mutations that persist because they don't cause any problems.

  13. i make sense of the bees this way. i think of the queen as an organism that is capable of creating non procreating drones for selfish purposes.
    i think that a true purpose in a genetical sense in helping others is when you look down the ladder of life…your children and there children are the only place where your genes live on. other then that, allthough no close genetical bonds are involved, it totally makes sense to care for your mate (especially in monogamous species). i think that other help boils down to mutualism…be there for someone so they'll be there when you need something the entire group you come from ( usually genetic relatives as they're the most likely candidates to bond with ) benefit.

  14. I was already familiar with kin selection, but the thing that jumped out at me was the passing discussion of worker bee offspring. Really? I had always assumed that only the queen lays eggs, and that workers were sterile. Whadda ya know?

  15. The blood of the covenant is thicker than the water of the womb.
    The complete opposite of kin altruism. It's probably more akin to green-beard altruism.

  16. I don’t understand why scientists say this operates at the gene level and not the hormone level (ie oxytocin). Why do dog owners die trying to rescue their dogs for example? This seems to debunk inclusive fitness but makes sense if you consider attachment via oxytocin. Inclusive fitness also does not explain fratricide etc

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