- There isn't really a very
good definition of life. What is the difference between
something that's alive, and something that isn't alive? You might think this is a rather
simple question to answer, but in fact, it's not so easy to answer. Should be said, I'm by
no means the first person to have considered this question. And if you look in Wikipedia
or in a dictionary, you often get rather complex answers. And I wanted a go answering what I think is one of the
key questions in biology. And the way I approached it was by exploring five of
the great ideas of biology. My name is Paul Nurse. I'm a geneticist and cell biologist, and I've just written a book- it's my first book, and
it's called, "What Is Life?" The cell is really critical
for the way I think about life because it's the simplest entity that expresses characteristics of life. It can grow, it can
divide, it can reproduce. And really, all living things- myself, a plant, an insect- is either a single cell or made up of groups of
cells acting together. Most people are not excited by yeast. I have to say, I am excited by yeast. They just think, "Well,
it's good for making beer and wine and bread maybe," but actually, it's very good
as a model for other cells in all sorts of more
complicated living things like ourselves. In my laboratory, we found a human gene that was similar to the yeast gene that controls the reproduction
of a cell from one to two. And it was clear that that human gene could completely substitute
for the yeast gene, and control the reproduction
of a yeast cell just as well as it could control the
reproduction of a human cell. If the same process was controlling the
reproduction of a yeast cell as controls the reproduction
of a human cell, then this means this was extremely ancient because yeast and human beings diverged back in the depths of time, deep time, somewhere between 1,000 million years ago, and 1,500 million years ago. This meant that every other
living thing that we could see- every plant, every
animal, and every fungus- was controlled by the same mechanism. A monk called Gregor Mendel was interested in looking at the genetics of peas- and what he did is he
crossed different peas with different characteristics. And he counted the
different types of offspring that were produced from these pea plants. And he began to notice there were very clear ratios: famous ratios like three to one, and nine to three, to three to one. And he realized that maybe what was responsible for
inheritance could be described as sort of unitary particle which could be passed down
from one plant to another. But it was the first evidence that there was something which
we now would call a gene. The idea of evolution by
natural selection is, for me, probably the most
beautiful idea in biology. Charles Darwin, who went around the world and collected animals
and plants and birds, came up with the idea of
evolution by natural selection. He speculated that all living things have hereditary material; that if this hereditary
material had some differences that resulted in the living
thing being different, and if it was advantageous in the environment in
which it found itself, then it would eventually take
over the whole population. This has been a revolutionary change in our understanding in biology because what it leads to is a
better-designed living thing- but without having a designer. Life is made up of
molecules and chemicals. There are many thousands
of chemical reactions going on all the time in a little cell. Chemistry is responsible
for the growth of the cell, the reproduction of that cell, for its ability to capture
energy and use energy. One of the ways in which cells can carry out all of this chemistry is that the cell is
made up of lots and lots and lots of little compartments, and it's compartmentation that allows all these different chemistry to occur simultaneously
in such a small space. I want to emphasize how fantastic that is. I want you to imagine
in a tiny, tiny cell, there's thousands of chemical reactions, all very different going on all the time very, very close to each other. So life is chemistry, but life
is also built on information- because life has to
constantly manage information. Let's take what I said about chemistry and all those different compartments: That can only occur if there's
an information transmission to keep the whole thing coordinated. Let's say a gene is making a substance, and it wants to keep that
substance at a constant level. As that substance increases,
it switches off the gene, and when it decreases,
it turns the gene on. But you only really understand
that when you realize there's information
management going on here. The cell is measuring
how much stuff it's got, and then using that to determine whether the gene should be
switched on or switched off. If we take DNA, we could understand the structure of DNA in terms of how one base
is related to another base, but it only makes biological sense when seen to be a digital
information storage device. Life is and can only
operate through information. It permeates every aspect
of how living things work. Putting all these five ideas together, I think some principles emerge. Living things are bounded
physical entities. The bounded entity is the chemical and informational machine. And then critically, that
informational chemical machine in a bounded entity
has a hereditary system that determines how it works, a system which has variability, and therefore, the whole thing can evolve by natural selection. And that means that the living
thing can acquire purpose: Purpose to be better adapted in the life state it finds itself, and so we can evolve living things from one type into another. And for me, that bounds
everything together that emphasizes the core
principles underlying life. - Get smarter, faster with videos from the
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