How old are the
genes in humans?


The genes in a modern human
don’t all date back to a single
point in our history. When a new
species evolves, it has almost
exactly the same genes as its
ancestors, with just a few crucial
mutations that set it apart. The
genes that gave early humans
their larger brain size, for
example, evolved around
500,000 years ago but we still
share lots of genes with other
primates and mammals. DNA is
constantly mutating. The egg
and sperm that originally created
you probably contained 100 to
200 new mutations that weren’t
in your parents’ DNA. Each of
those mutations created a new
gene, so you have quite a few
genes that are only slightly older
than you. At the other extreme, the
oldest known functioning gene is
the one that codes for the enzyme
glutamine synthetase, which
creates the amino acid glutamine
from glutamate and ammonia. As
this enzyme is a crucial part of the
way cells make protein and
remove excess nitrogen, natural
selection has preserved it
unchanged. Every living thing uses
this same gene that first evolved
more than two billion years ago
– before even the first cells with a

nucleus emerged.

 Why does glass shatter

so violently?

 Everyone who has dropped a glass object knows
how the fragments sometimes end up at astonishing
distances from the point of impact. It is as if something
was propelling them. And there is an extra source of
energy, in addition to the kinetic energy generated
by the fall. It comes from the thermal stress left in the
glass after it was made.
Glass objects are made from sand, soda ash
and limestone heated to 1,700°C. They have to be
specially treated – ‘annealed’ – during manufacture
to help release the stress trapped inside; if the glass
is cooled too quickly, it can crack before leaving
the factory. But dropping it afterwards can release
residual stress.
A dramatic demonstration of the effects of improper
annealing is provided by the tadpole-shaped glass
objects known as ‘Prince Rupert’s Drops’, named
after a 17th Century German aristocrat who gave a set
to King Charles II for entertainment. They are created
by dripping molten glass into cold water, causing the
drops to chill rapidly on the outside, but much less
so internally. As the interior cools and contracts, it
pulls on the outer surface, creating a huge amount of
thermal stress. Snapping the tail of the drops causes
cracking that unleashes the pent-up energy, making

the drop explode spectacularly.

 Why are some stars

magnetically attracted?

 Magnetic fields are created by the
motion of electrically conductive
material. In some stars, the ionised
plasma of their interior undergoes
convection. It rises and falls through
the outer layers of the star, due to the
heating from the stellar core. This,
combined with the rotation of the star,
creates a ‘dynamo’ that constantly
regenerates the star’s magnetic field.
The most magnetic stars are those with
faster rotation and deeper convection.
Other compact and fast-rotating stars,
such as pulsars, magnetars and white
dwarfs, retain a significant magnetic
field from the original star that is
increased dramatically when the object

collapses under gravity.