We have learned a great deal about how physical traits are passed from generation to generation.
We
have
learned
a
great
deal
about
how
physical
traits
are
passed
from
generation
to
generation
.
Scientists know that DNA molecules in human cells carry inherited physical traits in a sort of chemical code.
Scientists
know
that
DNA
molecules
in
human
cells
carry
inherited
physical
traits
in
a
sort
of
chemical
code
.
Some day we may learn how to change these DNA molecules so as to change the physical traits they carry.
Some
day
we
may
learn
how
to
change
these
DNA
molecules
so
as
to
change
the
physical
traits
they
carry
.
Eventually, parents may be able to choose what traits their children will inherit; blue eyes or brown, tall bodies or short.
Eventually
,
parents
may
be
able
to
choose
what
traits
their
children
will
inherit
;
blue
eyes
or
brown
,
tall
bodies
or
short
.
Most children of today are taller than their parents, but this may be due to better nutrition rather than to an inherited change.
Most
children
of
today
are
taller
than
their
parents
,
but
this
may
be
due
to
better
nutrition
rather
than
to
an
inherited
change
.
In some population groups, height is increasing one inch per generation.
In
some
population
groups
,
height
is
increasing
one
inch
per
generation
.
Is it a good thing for people to get taller than taller?
Is
it
a
good
thing
for
people
to
get
taller
than
taller
?
No, say certain experts.
No
,
say
certain
experts
.
The human skeleton would be strained carrying the weight of a very tall body.
The
human
skeleton
would
be
strained
carrying
the
weight
of
a
very
tall
body
.
(In a world where workers use power tools for heavy work, there is no special advantage in great height or strenghth.)
(
In
a
world
where
workers
use
power
tools
for
heavy
work
,
there
is
no
special
advantage
in
great
height
or
strenghth
.
)
It might be better, some say, if people got smaller.
It
might
be
better
,
some
say
,
if
people
got
smaller
.
Smaller humans would need less food and could live in smaller houses.
Smaller
humans
would
need
less
food
and
could
live
in
smaller
houses
.
They would fit more comfortably into cramped spacecraft.
They
would
fit
more
comfortably
into
cramped
spacecraft
.
They would drive smaller cars on narrower roads.
They
would
drive
smaller
cars
on
narrower
roads
.
Smaller people would make the world seem large and less crowded.
Smaller
people
would
make
the
world
seem
large
and
less
crowded
.
The world's natural resources would last longer.
The
world
's
natural
resources
would
last
longer
.
So it is possible that if scientists learn to control inherited physical traits, they might speak out for a reduction in human size.
So
it
is
possible
that
if
scientists
learn
to
control
inherited
physical
traits
,
they
might
speak
out
for
a
reduction
in
human
size
.
Anthropologists have estimated the heights of ancient people from fossil bones.
Anthropologists
have
estimated
the
heights
of
ancient
people
from
fossil
bones
.
They have compared these heights with the heights of people now living in all parts of the world.
They
have
compared
these
heights
with
the
heights
of
people
now
living
in
all
parts
of
the
world
.
The evidence appears that most people are getting taller.
The
evidence
appears
that
most
people
are
getting
taller
.
The human of tomorrow may be still taller - unless he or she decides to be smaller.
The
human
of
tomorrow
may
be
still
taller
-
unless
he
or
she
decides
to
be
smaller
.
We have learned a great deal about how physical traits are passed from generation to generation. Scientists know that DNA molecules in human cells carry inherited physical traits in a sort of chemical code.  Some day we may learn how to change these DNA molecules so as to change the physical traits they carry. Eventually, parents may be able to choose what traits their children will inherit; blue eyes or brown, tall bodies or short.  Most children of today are taller than their parents, but this may be due to better nutrition rather than to an inherited change. In some population groups, height is increasing one inch per generation.  Is it a good thing for people to get taller than taller? No, say certain experts. The human skeleton would be strained carrying the weight of a very tall body. (In a world where workers use power tools for heavy work, there is no special advantage in great height or strenghth.) It might be better, some say, if people got smaller.  Smaller humans would need less food and could live in smaller houses. They would fit more comfortably into cramped spacecraft. They would drive smaller cars on narrower roads. Smaller people would make the world seem large and less crowded. The world's natural resources would last longer. So it is possible that if scientists learn to control inherited physical traits, they might speak out for a reduction in human size.  Anthropologists have estimated the heights of ancient people from fossil bones. They have compared these heights with the heights of people now living in all parts of the world. The evidence appears that most people are getting taller. The human of tomorrow may be still taller - unless he or she decides to be smaller.