Part 1 was: The Prehistory of Earth
The following is an excerpt from my book “The Human Race to the Future.” To get a free copy, send a request to email@example.com.
Part 2: How new species come to be. Evolutionary theory has long been uncertain and even confused about important details of how new species come to be. Darwin himself agonized over the contradiction between selection of the fittest individuals, and the existence of human altruistic behavior. Perhaps due to the subtleties of species creation the process has no single name, it has a bunch: speciation, divergence, branching, cladogenesis, splitting, radiation, and diversification are all similar. And this tribe of terms conceals both a cacophony of causes and a mob of mechanisms. Here are some of them.
• Allopatry (“other fatherland”): the range of a single species is split, such as by the birth of a mountain range or by rising waters and the two populations evolve separately, becoming more dissimilar until they are separate species. This seems unlikely to happen to humans in a mobile global society.
• Peripatry (“nearby fatherland”): a small group ventures beyond the periphery of its species’ range, ceases to breed outside of its own group, and evolves in a different direction until it is a separate species.
• Parapatry (“beside fatherland”): within the continuous range of a species, members in different subranges breed preferentially within their own subrange, permitting the gene pool of each subrange to evolve differently from that of the other(s). The differences accumulate until, where before there was one species, now there are (at least) two.
• Sympatry (“together fatherland”): a species divides into two even though both groups occupy the same geological area. Most commonly occurs through heteropatry.
• Heteropatry (“different fatherland”): a single species occupies different ecological niches within the same range, leading to separate breeding populations and accumulation of genetic differences until the populations are different species. For example, an insect species that likes to eat two different kinds of fruit might, over time, split into two species, each preferring a different kind of fruit.
• Niche splitting: a species adapted to a niche that spans a continuous spectrum of conditions may produce offspring that are specialized to part of that spectrum at the cost of being less well adapted to the rest. The specialized offspring, being in proximity, breed true, producing a new variety of the species that displaces the rest of the species from that part of the niche. The original variety, displaced from part of its original niche, specializes to the remaining portion. The divergence proceeds until the two groups are different species. Darwin himself observed: “offspring of each species will try…to seize…diverse places in the economy of Nature.… Each new variety or species, when formed, will generally take the place of…its less well-fitted parent.”
• Niche seeking: evolution opportunistically seeks new ecological niches to fill with life because variation can make a few offspring better suited to conditions in other niches or extensions of their current niche than their parents. The species then splits through niche splitting of the newly extended niche, or through heteropatry. Darwin stated the natural end point of this process: “The same spot will support more life if occupied by very diverse forms.” Furthermore, more species become more potential hosts — new niches to be filled by still more new species with parasitic, mutualistic, or commensal relationships with the host species.
• Evolving evolution: the genetic code contains the blueprints of an organism, but the language that the genetic code uses to describe those blueprints is subject to evolutionary change as well. Just as organisms tend to get more fit over time because their blueprints improve, the coding system embedded in the DNA tends to improve as well. The coding systems are known to vary somewhat among organisms and have multiple levels of meaning, just as a passage in English has multiple facets of meaning determined by the words, the intonation, the style, and so on. Organisms with a more fit coding system will tend to evolve more efficiently than those with less fit coding systems. Thus over time the coding systems in widest use will improve, making other processes of speciation, like those described above and below, work faster and better.
• Improved reproductive strategies: humans know that finding a good mate can be no easy task. Moths know it too. Some male moths can detect a single molecule of female scent miles downwind with their feathery antennae, and use that clue to fly in her direction. Good reproductive capabilities, such as improved mate finding methods, ability to reproduce without mating under appropriate conditions (as in aphids, certain vertebrates and, many people believe, at least once in humans), and ability to keep sperm alive and usable for years after mating, become increasingly important when there are few other members of the species available. Otherwise the process of speciation is limited by the fact that the more species occupy an environment, the fewer members of each species the environment can support. Too few individuals leads to species non-viability when the individuals cannot find mates or other ways to reproduce. Thus as evolutionary pressure improves reproductive strategies over the eons, species can better prosper with low numbers of members. This means more species can occupy the same space, a process that can be expected to gradually improve into the distant future.
• Complex variation: the more complicated an organism is, the more organs, tissues, biochemical processes, homeostatic parameters, genes, and other parts it contains. The more parts, the more opportunities for variations in its offspring because each part can vary. The more ways it can vary, the more variations will be created and tested by the evolutionary process, and the more variations tested the more efficiently new species can come into existence. This is even more effective than it sounds, because more ways to vary tends to mean more evolutionary paths from an organism’s present state to its fitness for some future, changed environment. A mathematical intuition for this is the analogy that it is harder to get to point B if you must travel straight there, because of the obstacles that you could go around if you had many alternative paths (a higher dimensional parameter space makes travel easier). Consequently, when organisms increase in complexity over time they can branch off new varieties, the first step to becoming new species, more readily. And in fact there is reason to believe, barring strong evolutionary preference for efficiency over other adaptive strategies (as in bacteria), that organisms do tend to increase in complexity over time.
Organisms are complex systems engineered by nature. A lesson from complex human-engineered systems is that these systems tend to increase in complexity over time. As we seek to make our engineered artifacts better, they naturally tend to acquire more components whose duties are to make them work better by doing more things, by doing things better, and by doing things under more circumstances. Your cell phone is not only better than the cell phone of yesteryear, it is also more complicated. Organisms can benefit from the same paradigm. The mechanism for this is genetic mutation, a process which supports increasing complexity.
Think about it this way. With about 25,000 genes, humans have only about 25,000 ways to simplify by deleting a gene, and 25,000 ways to complexify by doubling a gene. However the latter is more likely to result in a viable organism, because doubling a gene is comparatively likely to lead to a change in function while deleting is comparatively likely to break some useful function, somewhat like removing a random part of a car is likely to cause a noticeable if not fatal problem.
Burgeoning biosphere. As future life forms become more numerous, efficient, and spread out, the biosphere will become progressively denser – riotous with life. One factor is that a given habitat will experience an increase in the sheer quantity of life. Reiterating the Darwin quote above, “The same spot will support more life if occupied by very diverse forms.”
More next time on the “burgeoning biosphere” next time, in “Accelerating Evolution, part 3″!