Genes, Brains, and Human Potential The Science and Ideology of Intelligence

128 REAL GENES, REAL INTELLIGENCE

In addition, thousands of other small RNA transcripts (other than
mRNA) have recently been discovered that are not translated into pro-
teins at all. It is now estimated that although 70  percent of the mamma-
lian genome is actively transcribed, only 1–2  percent of the transcripts are
involved in making proteins. Instead, an ever- growing number of regu-
latory functions is being discovered for them. Th ese functions include
activation of hormone receptors, modulation of promoters (and thus
transcription rates), silencing (or blocking) specifi c gene transcriptions,
and acting as co- activators for transcription. Th is “hidden transcriptome”
also clearly operates in the context of wider signaling networks. Again,
these regulatory networks seem to have become more impor tant in more
complex organisms.

OTHER EPIGENET ICS

Genes are inherited by off spring, of course. But environments experi-

enced by mothers before or during pregnancy can modify the way those

genes are utilized during the off spring’s development. Th ese modifi ca-

tions can, in turn, aff ect development throughout life and even on to sub-

sequent generations. It was illustrated in the Netherlands in 1944 when

a Nazi blockade followed by an exceedingly harsh winter led to mass

starvation. Babies born at the time grew up small. But the eff ects persisted

in smaller grandchildren, too, even though their parents had been well

fed (see also chapter 10).

Th is is the kind of epigenet ics—or epige ne tic inheritance— described

by Nessa Carey in her book, Th e Epigenet ics Revolution. It is a set of pro-

cesses that challenges the traditional doctrine that the only modifi cations

that can be inherited are those that occur accidentally in the genes. Some

mechanisms have now been identifi ed through which the ge ne tic mate-

rial can be altered through environmental experience and passed on to

the next generation. For example, in a study reported in 2014, mice were

trained to fear a specifi c odor before conception. Subsequently conceived

second- and third- generation pups also had an increased behavioral sen-

sitivity to that odor but not to other odors. Th is was correlated with

changes in some aspects of neural structure.^20

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