Reproduction

Reproduction is the amazing way new living things are made from their parents. It is a basic part of life for all kinds of plants and animals. There are two main ways this happens: one without needing another parent, and one that does.

In one kind of reproduction, called asexual reproduction, an organism can make a new one all by itself. This can happen in many different kinds of creatures. For example, when an organism makes an exact copy of itself, this is called cloning.

The other kind is called sexual reproduction. This usually needs two special cells from each parent. These cells join together to make a new living thing that has traits from both parents.

Methods

Asexual

Main article: Asexual reproduction

Asexual reproduction is when an organism makes copies of itself without needing another organism. This happens in many simple creatures. For example, bacteria split into two parts to make new ones. Some animals, like hydras and yeast, can also reproduce this way by growing a new part that breaks off. Most plants can do this too.

Sexual

Main article: Sexual reproduction

See also: Human reproduction

Sexual reproduction is when two organisms mix their genes to make a new one. This usually involves a male and a female. In many animals, including birds, reptiles, and mammals, the male puts special cells into the female to create offspring.

Most animals and plants reproduce this way. When they do, each parent gives half of the genes to the new offspring.

Allogamy

Main article: Allogamy

Allogamy is when flowers from different plants mix their genes. This can happen when insects or the wind carry special powder from one flower to another.

Autogamy

Main article: Autogamy

Autogamy is when a plant fertilizes itself. This happens in some plants that have both male and female parts in the same flower.

Mitosis and meiosis

Mitosis and meiosis are types of cell division. Mitosis makes two cells that are just like the parent cell. Meiosis makes four cells that have half the genes of the parent cell. This is how animals make eggs and sperm.

Same-sex

Main articles: LGBT reproduction and Reproductive technology

Scientists are studying ways that two males or two females might be able to have offspring. These methods are still being tested and are not ready for use in humans.

Strategies

Further information: Modes of reproduction and Life history theory

Different animals have many ways to have babies. Some, like humans and northern gannet, take a long time to grow up and only have a few babies. Others, like rabbits and fruit fly, grow up fast and can have lots of babies—rabbits can have many babies each year, and fruit flies can have even more! Animals that have few babies often spend more time helping each one grow. Animals that have many babies may not help each one as much, but enough usually survive to keep the group growing.

Some animals can have babies more than once in their lives. Others have babies only once and then stop, sometimes even stopping living right after. This depends on what works best for each kind of animal.

Asexual vs. sexual reproduction

Some living things can make new babies all by themselves, without needing another parent. This is called asexual reproduction. These creatures can grow very quickly because they don’t need to find a partner.

However, since they all have similar traits, they might all face the same problems if something changes in their environment.

Other living things can have babies in two ways: either alone or with a partner. This is true for aphids, slime molds, sea anemones, some species of starfish (by fragmentation), and many plants. When conditions are good — like when there is lots of food and a nice climate — they usually choose to reproduce alone. This lets their numbers grow very fast.

But when times get tough — when food runs out or the weather turns bad — these creatures switch to having babies with a partner. This mixing of traits from both parents helps create new variations, making it more likely that some of the new babies will be better able to survive the hard times.

Life without

Scientists wonder if life could exist without reproducing. They study how life first began from non-living materials, called abiogenesis. They think the last common ancestor of all life on Earth lived around 3.5 billion years ago.

Some scientists have made simple viruses from non-living things, but viruses are not truly alive because they need help from other cells to copy themselves.

Creating a fully living organism, like a simple bacteria, from scratch is very hard. Scientists have put a man-made set of instructions, called a synthetic genome, into a natural bacteria. This made a new type of bacteria, called M. mycoides. Some debate if this counts as fully synthetic life since it used parts from existing cells. Researchers believe making true synthetic life may soon be possible with today’s technology.

Lottery principle

Sexual reproduction uses a lot of energy and takes time. Scientists want to know why many animals use it instead of simpler ways to have babies. One scientist, George C. Williams, used the idea of lottery tickets to explain this. He said that asexual reproduction is like buying many lottery tickets with the same number — you have less chance to win. Sexual reproduction is like buying fewer tickets but with many different numbers — you have a better chance to win. This helps animals adapt to changes because it creates more variety in their babies. But this idea is not as popular today because we now know that asexual reproduction is often used in places where the environment changes a lot.

George C. Williams used lottery tickets as an analogy