No two alike

About this video

Look at a litter of rabbits, a flock of sparrows or a class of children: all the same kind of living thing, yet no two exactly alike. The differences between members of the same species are called variation. You can see them in colour, size and shape, but they are inside the body too: in blood groups, in how fast someone runs, in which illnesses a plant can resist.

Biologists talk about two causes of variation. The first is genes, the instructions inside every cell that a living thing gets from its parents. The second is the environment: food, sunlight, weather and everything else around it. Most traits are shaped by both. Two seeds from the same packet can grow into very different plants if one grows in the sun and the other in the shade.

New differences come from mutation. Every time a cell divides, its DNA is copied, and once in a while the copy changes. Most mutations make no difference at all. A mutation in an ordinary body cell stays in that body, but one in an egg or sperm cell can be passed on to a child. Over many generations, mutations add new versions of genes to a species.

Variation matters: without it nothing in a species could change. With it, the differences that help a living thing survive and have young become more common, which is natural selection. This video goes with the lesson No Two Alike in Biology Level 1 on Knaph.

Transcript

1. 0:00A litter of rabbits. Same species, same parents. And yet no two are exactly alike.
2. 0:09These differences are called variation. Colour, size, the shape of the ears. And inside the body too, like blood groups, speed, and which illnesses it can resist.
3. 0:21Where do they come from? Genes, the instructions passed down from parents. And the environment. Two seeds from the same packet, one in the sun and one in the shade, grow into very different plants.
4. 0:38New differences start in DNA. Each time a cell divides, its DNA is copied, and now and then a letter changes. That is a mutation. Most make no difference. But one in an egg or sperm cell can be passed on to a child.
5. 0:56Without variation, nothing in a species could change. With it, the differences that help can spread. That is natural selection.