Download Sexual reproduction and evolution

Mr. Swan
Name: __________________
Due Date: _________________
SEX AND EVOLUTION. NATURAL HISTORY MUSEUM
Why did sexual reproduction evolve? And why is it so widespread? These questions have intrigued scientists
for a long time.
From a biological perspective, the purpose of life is to reproduce and pass your genes on to the next generation.
Organisms have evolved many different strategies to maximise their chances of doing this. But there are just
two basic methods of reproduction: asexual and sexual.
Asexual species reproduce on their own, by duplicating. The offspring is a copy of the parent.
Sex, however, requires a partner. Each individual produces specialised sex cells, called gametes, which usually
carry half of their genetic material - one copy of each chromosome (packaged DNA) rather than two. Sexual
reproduction involves a male gamete successfully fusing with a female gamete. While the offspring is similar to
its parents, it’s not identical and the genes can be mixed in new combinations.
Asexual reproduction is more efficient
Bacteria multiply rapidly by asexual reproduction.
In many ways asexual reproduction is the better evolutionary strategy: only one parent is needed and all of their
genes are passed on to the next generation.
All bacteria, most plants and even some animals reproduce asexually at least some of the time.
Sex is less efficient. Finding a mate can take time and energy, and any gametes that aren’t fertilised go to waste.
Plus, each parent only passes half of its genes to the offspring.
But despite these drawbacks, sexual reproduction evolved and is abundant within the animal world. Why?
Advantage of sexual reproduction over asexual
One of the strongest theories proposed so far is that sex enables species to keep up with their enviroment in an
evolutionary race.
Sex maintains genetic diversity. Having a population with lots of genetic variation increases the likelihood that
some individuals will be resistant to a change in the environment. Genetic mixing through sexual reproduction
quickly gives rise to individuals that are better adapted to their enviroment. These become more common and
the race goes on.
In comparison, asexual populations can only evolve resistance to a disease if a beneficial mutation, a random
alteration in a gene, arises. These are very rare, so the asexual population cannot keep up with the disease. If the
disease is particularly harmful, the asexual population will go extinct.
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