How did evolution manage to cross the species barrier?
It’s a very long process that is hard to simplify accurately, but I’ll try. Some cells discovered that a great way of capturing energy was to absorb it from the sun. They became algae and other various plants. Some organisms discovered that they could gain energy by eating the cells that were absorbing sunlight. They became herbivorous. Plants weren’t an abundant enough resource, but some organisms discovered that they could gain energy from eating the organisms that ate plants. They became carnivores. Plants, tired of being eaten, began washing up and growing on land. Herbivores, also tired of being eaten and noticing an abundance of plants, started crawling onto the land too. Carnivores, beginning to outnumber their oceanic prey and seeing that there were animals living on land, followed them out of the water. With nowhere left to go, plants grew thick bark, or deep roots, or became poisonous in order to protect themselves from being eaten. Herbivores grew bigger, faster, and/or smar
The “species barrier” isn’t a barrier to evolution, it’s a barrier to cross-breeding. For example, look at chihuahuas and great Danes. Both are dogs, and both evolved (due to artificial selection) from a common ancestor, right? They are still in the same species because genes from chihuahuas can still theoretically get into great Danes via a series of intermediates. For instance a chihuahua could mate with a terrier and the progeny could mate with a beagle and the progeny of that could mate with an Australian shepard, and the progeny of that could mate with a German shepard, and on up to great Danes. So what would happen if all those intermediates were to go extinct? There would be no more genetic interchange between between chihuahuas and great Danes. They’d be separate species of dogs. Both of them would continue to evolve independently, becoming more and more different over time as they adapted to different ecological niches. Evolution causes populations to adapt to their specific e
