BIO 358 Lecture Notes - Lecture 10: Infant, Paternal Care, Matrilocal Residence
14 Jun 2018
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Topic 10: The human village and life history redesign
Key Terms:
1. Mating systems:
a. Monogamy: A mating/reproductive strategy in which a single male and a single female mate
exclusively with one another. A strategy approaching simple monogamy is seen in many bird species.
However, it is very rarely seen in mammals. Humans are an exception. We practice a mating system
approaching monogamy under some specific circumstances. Those circumstances consist of relatively
low rates of adult (mate) mortality. However, under conditions of high mate mortality risks, humans
practice promiscuity or polygynandry (Chapter 8). Under these conditions humans still pair-bond, but
mate with multiple others in addition to their nominal or social spouses. Under these promiscuous
mating conditions, a couple is said to participate in social monogamy. Each is said to be the social
spouse of the other. The male member of this promiscuously mating pair is said to the social father of
his ate’s offspig. These offspig ofte ae said to hae othe o-fathers, usually corresponding to
other males who may have fathered them (Chapter 8).
b. Polygyny: A single male mates exclusively with the members of a group of multiple females
who, in turn, each mates with only with this male (Chapter 8). This is a conventional arrangement
idealized as a harem, for example.
c. Polyandry: Mating of one female exclusively with the members of a group of multiple males
who, in turn, mate only with this single female (Chapter 8). This is the converse or mirror image of the
conventional harem arrangement in polygyny, for example.
d. Polygynandry (Promiscuity): Both sexes mate with multiple members of the opposite sex.
Promiscuous mating schemes of this form are seen in humans under conditions of high mate mortality
risks (Chapter 8).
2. Parental investment: Raising a behaviorally complex animal to independence requires a great deal of
protection, support, and guidance from parents. This is true of all mammals and birds and is especially true of
humans. This, in turn, requires time and effort by adult animals (kin/parents, in most common practice). In
most mammals, this care is given exclusively or nearly exclusively by mothers. This results from the fact that
maternity is always certain in mammals whereas paternity is always uncertain, at least in principle. However,
in humans and in many birds, both parents typically contribute extensively. More specifically, female parental
investment is referred to as maternal investment and male parental investment as paternal investment.
* Note that humans also contribute significant parental investment – often in the form of economic
cooperation – to offspring who are not their own. This uniquely human pattern reflects our unprecedented
kinship-independent social breeding (Chapters 6 and 8).
a. Paternal investment: parental investment by the fathers
b. Maternal investment: parental investment by the mother
3. Patrilocal: We will use this term to describe a particular residence pattern for animals. As animals reach
sexual maturity, the males stay in place on the home territory and females emigrate. The converse pattern is
matrilocal. Humans are not strictly either matrilocal or patrilocal, though a local culture may be primarily one,
the other, or some mixture of the two.
4. Matrilocal: This term describes a residence pattern for any animal, including humans. It implies that as
animals reach sexual maturity the females stay in place on the home territory and males emigrate. The
converse pattern is patrilocal. Humans are not strictly either matrilocal or patrilocal, though a local culture
may be primarily one, the other, or some mixture of the two. Human matrilocality includes adult males
focusing important elements of their economic activity around their maternal households rather than the
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households of their mates. This form of human matrilocality tends to correlate with promiscuous mating
systems (Chapter 8) as maternity is substantially more certain under these conditions than paternity.
5. Hostile manipulation problem: Refers to a particular subclass of the conflict of interest problem.
Specifically, non-kin conspecifics have an incentive to mislead and manipulate one another during the
exchange of contingent (potentially false) information. As a result, systematic non-kin exchange of such
information cannot evolve as a Darwinian adaptation unless the conflict of interest problem can be managed.
Humans are the first animals to achieve the necessary mastery of the hostile manipulation problem (Chapter
9).
6. 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 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.
7. Expanded gestation: Refers to one the new features of human life history. These are features we have that
our closest living relatives, the other African great apes, do not. (See babyhood and childhood for related
phenomena and Chapter 6 for a detailed discussion.) Gestation refers to the growth of the unborn mammalian
fetus in the uterus of its mother. For humans this growth period lasts about nine months. This is one month
longer than in chimps, our closest living relative. More importantly, humans invest more resources in the fetus
so that our newborns (and their brains) are substantially larger than for the other great apes. This expanded
gestation means that human childbirth is among the most difficult of all mammals. Moreover, human females
need very high levels of nutrition during the final months of gestation/pregnancy. However, they are physically
challenged by the very large, late-term fetus, making personal food procurement difficult for them. Thus, late-
term pregnant human females are very dependent on the nutritional assistance of others. The social support
necessary to evolve expanded gestation became available only with the evolution of uniquely human kinship-
independent social cooperation (Chapters 6 and 7).
a. Babyhood: We use this term specifically to refer to the uniquely human period of extreme
dependency for the first nine to eleven months after birth (Chapter 6). Among other things, babyhood
is associated with the extension of extremely fast fetal-like rates of brain growth through most of the
first year of life. This pattern is a uniquely human life history feature. All other animals cease rapid
fetal-like brain growth at or immediately after birth. The extensive social support necessary to evolve
babyhood became available only with the evolution of uniquely human social cooperation (Chapters 6
and 7) allowing protection and support from the human village.
b. Childhood: We will use this term to refer to the time between when an ancestral human
infant was probably weaned from breast feeding – perhaps around three years of age – and the time
the human yougste’s ai goth stops ad she/he egis to auie adult detitio teeth oud
six years of age. This particular developmental pattern is a uniquely human life history feature. All
other animals wean at or after the time that brain growth stops and adult dentition is acquired. The
extensive social support necessary to allow the evolution of childhood became available only with the
evolution of uniquely human social cooperation (Chapters 6 and 7).
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Key Concept Question: A remarkable feature of human developmental biology is the suite of life history
changes that produce our massively enlarged brains (ca. 3.5 times bigger than our closest living relatives,
chimps). Different theories of human origins make very different claims about the cause-effect relationships
between these life history changes and human origins. The theory we are exploring in this course makes a very
specific prediction about these cause-effect relationships. Which of the following is the most accurate and
complete statement of that prediction?
a. Human brain expansion itself was sufficient to make us smarter accounting for the selective force for brain
expansion, requiring life history redesign.
b. Humans first evolved articulate speech, which was then sufficient to make brain expansion and associated
life history redesign adaptive.
c. Human social cooperation increased radically, thereby providing a novel context in which brain expansion
and its associated life history redesign became adaptive.
d. Human life history redesign was initially permitted by the evolution of bipedality, making bipedalism
sufficient to produce human brain expansion.
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