"An interesting twist to the Kwa story comes with the possibility
that yams may actually provide some relief from the
symptoms of sickle-cell disease."
[ ... ]
"We suggest that it would be too much of a
coincidence—not to mention an irony—for a population to
just happen to have chosen by chance a crop that alleviates
the symptoms of the disease that its planting inadvertently
promotes! Far more plausible is the hypothesis that these
agriculturists originally planted other crops and subsequently
switched to yams once their medicinal properties had been
[ ... ]
"If our suspicions are proved correct, **then an
instance of inceptive perturbation (planting crops that led
to prevalent sickle-cell disease) has elicited a further act of
counteractive niche construction (switching to growing yams,
which alleviates sickle-cell disease)."
groups of West Africa, who for at least several millennia have
cleared forests to create fields in which to plant crops (Posnansky
1969). Tree removal had the unintended consequence
of increasing the amount of standing water after heavy rainfalls,
which led to a rapid increase in mosquitoes such as
Anopheles gambiae, which need sunlit pools in which to breed
effectively" (Livingstone 1958)
[ ... ]
"Today, there are several hundred million clinical
cases of malaria worldwide and roughly 800,000 deaths each
year (Kappe et al. 2010), the majority of them in sub-Saharan
Africa. **With respect to the Kwa, this is a classic case of ecological
inheritance, with generations of descendants being affected
by the upstream activities of their forest-clearing ancestors
many generations before."
[ ... ]
"But similar to what occurred with Neolithic dairying, this
culturally induced disruption of the ecosystem had recursive
effects on the human genotype."
"...there is a variation in the beta polypeptide
chain, which results in the polymerization of the hemoglobin,
causing some red blood cells to become stiff and
take on a sickle shape. This sickling provides some protection
against malaria because sickled cells are recognized by the
spleen as they flow through and are removed, thus flushing
the parasite with them. *The recursive effect on humans is that
the variant (HbS) form confers heightened protection against
malaria in heterozygotes*."
"Decades of yam cultivation intensified
natural selection on the human hemoglobin (HbS) allele,
causing it to increase in frequency.The fact that neighboring
Kwa-speakers with different agricultural practices do
not show the same increase in (HbS) supports the conclusion
that culture—clearing fields for yam cultivation—is driving
human genetic evolution." (Durham 1991).
"As opposed to inceptive niche construction, if an environmental
factor is already changing, or has changed, organisms
may oppose or cancel out that change, a process labeled counteractive
niche construction. They thereby restore a match
between their previously evolved features and environmental
factors. Counteractive niche construction is therefore conservative
or stabilizing, and it functions to protect organisms
from shifts in factors away from states to which they have
"As we discuss in the next section, culturally derived selection
pressures can be stronger than noncultural ones. There
are at least two reasons for this.
First, there is highly reliable
transmission of cultural information between individuals (Bersaglieri et al. 2004)
Second, cultural innovations
typically spread more quickly than genetic mutations because
social learning usually operates at a much faster rate than
does biological evolution (Feldman and Laland 1996).
exhibit social learning, but it is the fact that human culture
evolves quickly and is cumulative *(Enquist, Ghirlanda, and
Eriksson 2011) *that makes it an exceptional case. By this we
mean that one generation does things in a certain way, and
the next generation, instead of starting from scratch, does
them in more or less the same way, except that perhaps it
adds a modification or improvement. The succeeding generation
then learns the modified version, which then persists
across generations until further changes are made (Tennie,
Call, and Tomasello 2009). Human cultural transmission is
thus characterized by the so-called ratchet effect, in which
modifications and improvements stay in the population until
further changes ratchet things up again (Tomasello, Kruger,
and Ratner 1993), although there is nothing inevitable about
progress and no guarantee that any “improvements” will be
"An important insight from NCT is that acquired characters
play an evolutionary role through transforming selective environments.
**For example, mathematical models suggest that
niche construction resulting from human cultural processes
is likely to be even more potent than gene-based niche construction,
and they establish that cultural niche construction
could plausibly modify selection on human genes and drive
(Laland, Odling-Smee, and Feldman
2001; Rendell, Fogarty, and Laland 2011).
We are Constructors and Organizers. Our biological impulse demands that we build, and keep building, like the spider and her web. We never cease spinning our silk. In culture, we have constructed our grandest monument. All of our minds, woven together, that we might spin our silk faster, longer, higher: greater. In time we will have covered the Earth. And entombed ourselves within it.
"Anthropologists have long known the
power that culture exerts in shaping the human condition,
but it is becoming increasingly clear that the interactions of
genes and culture—literally, their coevolution—offer a faster
and stronger mode of human evolution than either by itself"
(Ehrlich 2000; Ihara 2011; Laland 2008; Laland, Odling-Smee,
and Myles 2010; Rendell, Fogarty, and Laland 2011; Richerson
and Boyd 2005; Richerson, Boyd, and Henrich 2010).