Selective pressure is the force that drives evolution. It can be thought of as the “engine” of evolution. The main driving force behind selective pressure is natural selection. Natural selection is the process by which organisms that are better adapted to their environment survive and reproduce more than those that are less well adapted.
Selective pressure can also come from other sources, such as artificial selection (selective breeding) or sexual selection. Artificial selection is used by humans to produce desired traits in plants and animals. For example, farmers may select cows that produce more milk or pigs that grow larger and have more meat.
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Sexual selection occurs when one sex (usually males) competes for mates with members of the other sex. The competition can take many different forms, such as fighting, displaying conspicuous plumage, or producing loud calls. The winner of the competition gets to mate and pass on their genes to the next generation.
So, is selective pressure random? In a sense, yes. The particular environment an organism lives in will determine which traits are favored by natural selection. For example, if a population of animals lives in an area with lots of predators, then individuals that are better at avoiding predators (e.g. faster runners) will be more likely to survive and reproduce than those that are not as good at avoiding predators.
However, the overall direction of evolution is not random. Over time, organisms tend to become better and better adapted to their environment through the process of natural selection.
But everything in evolution is truly random because the environment has no consciousness; it changes like a rock falling from a mountain, and when I say random, I mean the entire system is based on randomness, because selective pressure changes as the environment changes, and the environment changes at random.
But the whole system selects predictable changes because the whole arrangement of the system has the purpose of making creatures adaptable over time, though those that survive and reproduce, resulting in the spread of their genes, also resulting in the spread of the traits that helped them survive and reproduce.
In conclusion, selective pressure is random in the sense that it is determined by the particular environment an organism lives in. However, the overall direction of evolution is not random. Over time, organisms tend to become better and better adapted to their environment through the process of natural selection.