Placeholder Image

Subtitles section Play video

  • [Myths and misconceptions about evolution]

  • Let's talk about evolution.

  • You've probably heard that some people consider it controversial, even though most scientists don't.

  • But even if you aren't one of those people and you think you have a pretty good understanding of evolution,

  • chances are you still believe somethings about it that aren't entirely right, things like,

  • "Evolution is organisms adapting to their environment."

  • This was an earlier, now discredited, theory of evolution.

  • Almost 60 years before Darwin published his book, Jean-Baptiste Lamarck proposed that creatures evolve by developing certain traits over their lifetimes and then passing those on to their offspring.

  • For example, he thought that because giraffes spent their lives stretching to reach leaves on higher branches, their children would be born with longer necks.

  • But we know now that's not how genetic inheritance works.

  • In fact, individual organisms don't evolve at all.

  • Instead, random genetic mutations cause some giraffes to be born with longer necks, and that gives them a better chance to survive than the ones who weren't so lucky,

  • which brings us to "survival of the fittest".

  • This makes it sound like evolution always favors the biggest, strongest, or fastest creatures, which is not really the case.

  • For one thing, evolutionary fitness is just a matter of how well-suited they are to their current environment.

  • If all the tall trees suddenly died out and only short grass was left, all those long-necked giraffes would be at a disadvantage.

  • Secondly, survival is not how evolution occurs, reproduction is.

  • And the world is full of creatures like the male anglerfish, which is so small and ill-suited for survival at birth that it has to quickly find a mate before it dies.

  • But at least we can say that if an organism dies without reproducing, it's evolutionarily useless, right?

  • Wrong!

  • Remember, natural selection happens not at the organism level, but at the genetic level, and the same gene that exists in one organism will also exist in its relatives.

  • So, a gene that makes an animal altruistically sacrifice itself to help the survival and future reproduction of its siblings or cousins,

  • can become more widespread than one that is solely concerned with self-preservation.

  • Anything that lets more copies of the gene pass on to the next generation will serve its purpose, except evolutionary purpose.

  • One of the most difficult things to keep in mind about evolution is that when we say things like,

  • "Genes want to make more copies of themselves," or even, "natural selection," we're actually using metaphors.

  • A gene doesn't want anything, and there's no outside mechanism that selects which genes are best to preserve.

  • All that happens is that random genetic mutations cause the organisms carrying them to behave or develop in different ways.

  • Some of those ways result in more copies of the mutated gene being passed on, and so forth.

  • Nor is there any predetermined plan progressing towards an ideal form.

  • It's not ideal for the human eye to have a blind spot where the optic nerve exits the retina, but that's how it developed, starting from a simple photoreceptor cell.

  • In retrospect, it would have been much more advantageous for humans to crave nutrients and vitamins rather than just calories.

  • But over the millennia, during which our ancestors evolved, calories were scarce, and there was nothing to anticipate that this would later change so quickly

  • So, evolution proceeds blindly, step by step by step, creating all of the diversity we see in the natural world.

[Myths and misconceptions about evolution]

Subtitles and keywords

B2 H-INT evolution gene genetic survival organism reproduction

【TED-Ed】Myths and misconceptions about evolution - Alex Gendler

  • 12798 574
    VoiceTube   posted on 2020/10/28
Video vocabulary

Go back to previous version