BIO 358 Lecture Notes - Lecture 5: Kin Selection, Biological Specificity, Proximate And Ultimate Causation
14 Jun 2018
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Topic 5: How natural selection produces animal cooperation
Key Terms:
1. Genetic relatedness VERSUS Genetic identity:
2. Hailto’s Rule or Hailto’s Law: Bill Hamilton proposed that social cooperation between conspecifics
would evolve when the benefit of that cooperation (B) to the receiver of the behavior exceeded the cost of
that cooperation (C) to the provider and when the benefit was discounted according to genetic relatedness
(Chapter 3). This law is very powerful in understanding many features of animal social behavior (Chapter 3)
ad soe er speifi features of hua soial ehaior Chapter 4. Hailto’s La predits the
consequences of kin-selection. We are primarily concerned with social cooperation beyond that predicted by
Hamilton’s La, that is, kiship-independent social cooperation. We argue that the conflicts of interest
between non-ki iplied Hailto’s La are the fudaetal arrier to kiship-independent social
cooperation and that humans are the first animal to evolve a solution allowing them to overcome this barrier
(Chapter 5).
3. Kin selection: Refers to the process when natural selection favors behaviors in one animal because of their
impact on the reproductive success of another, close kin animal (Chapter 3). This process works because close
kin are built by many pieces of the same genetic design information. Thus, when genetic design information
builds an animal to help its close kin, that design information is supporting its own replication, discounted by
the probability that the close kin individual did not receive this same piece of design information during sexual
reproduction (Chapter 3 and online endnotes to Chapter 3). As a result of kin-selection, individual animals will
behave as if they have a confluence of interest with close kin. In contrast, therefore, non-kin conspecific
animals will behave as if they have conflicts of interest.
4. Genetic relatedness: This term will have a very specific technical meaning for us in the context of evolved
social behavior. It refers to the probability that any individual piece of genetic design information is identical
by very recent descent in two individual organisms. A piece of genetic design information can be identical in
this way only if it was inherited from a recent common ancestor. Genetic relatedness falls off sharply with
changing pedigree relationship. Thus, for example, the relatedness of two human siblings is 50 percent, two
first cousins is 12.5 percent, and of two second cousins is only about 3 percent (see online endnotes to
Chapter 3). It is this genetic relatedness that determines the likelihood of kin-selected social cooperation. It is
important to be aware of the following. Genetic relatedness is not the same as genetic similarity. Indeed, it is
possible, in principle, for two organisms to be genetically identical in the sense of DNA sequence similarity (say
greater than 99.9999%) but to have very low genetic relatedness (say, 0.1%). The evolutionary logic of kin-
selection and not some rational understanding of genetic identity produce social behavior (Chapter 3). Natural
selection can be insane from our perspective.
5. Conspecifics AND conflict of interest:
Conspecifics: Two organisms are said to be conspecifics if and only if they are members of the same
species. For example, we are conspecifics because we are all humans. Likewise two chimps are
conspecifics, conspecifics, as are two dogs or two apple trees. However, a chimp and a human, for
example, are NOT conspecifics even though they have a close evolutionary relationship. Conspecific
animals generally have many more conflicts of interest with one another than do organisms who are
members of different species.
Conflicts of Interest: Refers specifically to the fact that organisms designed by natural selection in a
finite (Malthusian) world will inevitably come into competition for necessary resources. Since the finite
world cannot support both individuals fully, each of the two organisms must attempt to acquire the
necessary resources at the expense of the other. More generally, almost any time when two animals or
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two humans interact, they have potential conflicts of interest and natural selection will shape them to
maximize the probability of resolving those conflicts in favor of their own personal copies of genetic
design information (Chapter 3). This last rule means that close kin animals can often cooperate
because they share some unambiguously identical personal design information. Non-kin conspecific
animals commonly do not share unambiguously identical design information. Management of this
problem of conflicts of interest in humans has allowed our unique evolution of vastly expanded
kinship-independent cooperation.
6. Infanticide: The killing of juveniles – most often non-kin – by conspecific adults. This occurs under a variety
of conditions for strategic reasons (Chapters 3 and 4) and is a universal animal behavior. Its occurrence and
partial suppression in humans is illuminating about our unique social cooperation (Chapter 4).
7. Proximate causation: Refers to the immediate internal (often subjective or even unconscious) cause of a
ehaior i a aial. For eaple, e eat eause e feel hugr–a proximate cause. However, to fully
understand why we eat we must look beyond this subjectivity to the ultimate causation of our feeding
behavior. We are non-equilibrium thermodynamic systems requiring input of high energy compounds (food) in
order to continue to function. Natural selection has shaped our hunger-feeling psychological devices to cause
us to act as if we understood the Second Law of Thermodynamics, when usually we do not. All human and
animal behaviors have this proximate/ultimate duality including in our social behaviors. To truly understand
our behaviors, we must look beyond subjective proximate causation – often ignoring it entirely – and focus,
instead, on ultimate causation.
8. Ultimate causation: This refers to the most fundamental reason for or causal origin of a behavior in an
aial. For eaple, e eat eause e feel hugr. Hoeer, this feelig is erel the proiate
causation of our eating behavior. The ultimate causation of this behavior is that the Second Law of
Thermodynamics requires that we eat and natural selection has built animals – including us – designed to
behave in ways that satisfy that requirement. The mechanism natural selection has built to cause this to
happe is our eurologial/phsiologial feelig hugr respose. The ultiate ausatio of a ehaior is
always illuminating, whereas its proximate causation is often quirky, idiosyncratic, and not necessarily even
interesting from an analytical view (Chapter 10).
KEY CONCEPT QUESTION: Having established how evolution by natural selection works, our next goal is to
understand how this process operates in the specific adaptive context of social relationships to other
conspecifics. Our most important insight into the evolution of non-human animal social behavior emerges
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Document Summary
Topic 5: how natural selection produces animal cooperation. This law is very powerful in understanding many features of animal social behavior (chapter 3) a(cid:374)d so(cid:373)e (cid:448)er(cid:455) spe(cid:272)ifi(cid:272) features of hu(cid:373)a(cid:374) so(cid:272)ial (cid:271)eha(cid:448)ior (cid:894)chapter 4(cid:895). We are primarily concerned with social cooperation beyond that predicted by. This process works because close kin are built by many pieces of the same genetic design information. As a result of kin-selection, individual animals will behave as if they have a confluence of interest with close kin. In contrast, therefore, non-kin conspecific animals will behave as if they have conflicts of interest: genetic relatedness: this term will have a very specific technical meaning for us in the context of evolved social behavior. It refers to the probability that any individual piece of genetic design information is identical by very recent descent in two individual organisms.
