The short answer is: random mutation. When DNA is being copied, it sometimes makes mistakes. Most of the time, those mistakes don't really do anything, and become junk DNA and just get copied because its there. Sometime, those mutations have real effects, at which point those real effects influence the likelihood of the organism reproducing. The concept of complexity doesn't really apply... theres just DNA, then theres slightly more/less/different DNA in the same structural configuration.
Now on to some specific points:
The evolution of the first primordial cell into human beings (for example) requires massive increases in complexity.
Two points here: first, the leading hypotheses tend to start with very simple RNA strands, which eventually becomes DNA and develops cell walls. What you think of as a primordial cell is actually a fairly advanced form of life. Second, as I said earlier, complexity isn't the right word. You can think of DNA as like a string of characters, in the "primordial cell" it was a certain length, and in humans it's a different length. There's no additional complexity, just more of it.
1. The increased complexity of the offspring cell came from the DNA of the parent cell - but this means that the DNA of the parent is more complex than the parent. Huh?
In a way, it does. The DNA of the parent cell is what's being copied. The chemical machinery in the parent cell is what does the copying (and thus introduces errors).
Me no understando!
Check out talkorigins.org
On another level, life operates by (apparently) reversing entropy, a plant turns a bunch of disorganized nutrients in the soil, as well as carbon dioxide and water, into very much well organized, complex structures.
But it's not a true reversal of entropy since a LOT of energy, mostly from the sun, flows through that plant; the entropy increase in the sun is far greater than the decrease in the plant. Similarly, herbivores, which don't use the sun's energy (directly) consume vast quantities of plant matter, they are net entropic too, as they build their own bodies. Predators consume much more than their own weight in prey, and many imagine it as a pyramid, plants at the bottom, an apex predator at the top (that's where the term "apex predator" came from). Siberian tigers, just for instance, each, individually, have a huge territory that ultimately supports them, all the plant life in that vast expanse at the bottom of the pyramid, one tiger at the top.
The process Matt alludes to fall in the same category as this mere "life of a plant," it's a glitch in a part of the reproductive cycle. The increasing complexity starts when a gene or even a whole chromosome is copied twice instead of once, extending the amount of DNA. Each of those copies is then free to evolve on a different path through natural selection, eventually becoming twice the distinct genetic material it was before. (A lot of "junk" DNA is stuff that was useful to our remote ancestors, but we don't use any more, and it mutates too, harmlessly and thus not weeded out by natural selection, so it's not recognizable any more.)
There's a very common argument made by creationists that evolution cannot be true because it violates entropy, but its baseless because the earth is not a closed system, it receives a titanic amount of energy from the sun, 24/7. It's such a profoundly bad argument that many of the more intelligent creationists try to get their friends to stop using it. (Answers In Genesis actually has a page full of dumb arguments they wish other creationists would stop using. Not that many of them have listened.)
The really amazing fact to me is how evolution happens in consort between animals and plants, animals and animals, and plants and plants. The relationships and exploitation become so intricate. Hitch your wagon too tightly to other particular species and you go down together.
Very true, many many species that over specialized went extinct when a part of its life cycle was eliminated, often due to a part of ITS life cycle being eliminated, and so forth.
Flowers were evolved to help attract insects to pollinate them, and, over time, some evolved such special adaptations to maximize particular insects, or birds, etc, to the point where other birds or insects would not be able to pollinate them.
Species that specialized to eat one food source, say, eucalyptus leaves...and nothing else, would be severely hard pressed to survive if that one source were to be wiped out by an infection/blight, etc.
What are LEFT are the species that did not YET get wiped out after they overspecialized...and the more adaptable generalists.
Jacks of all trades/masters of none, tend to be the best at survival in the long run...because conditions DO change.
Genes have only 20/20 hindsight,,,and zero foresight.
Whatever is passed on, is what you have. There is no evolutionary mechanism that causes changes in advance of coming condition changes except by coincidence.
If its really cold, the skinny/ less fat, not furry enough are weeded out, if it then gets really hot, the fat furry guys get weeded out.
If not for recessive/unexpressed genes, most species would be long gone, in excess of the 98% or so percent that IS long gone already.
If two recessives combine, bingo, the trait is back.
I was looking at migration routes and was struck by the relationship between where the critters leave from and come back to on their routes....and, when in time those places last TOUCHED.
Tectonic plate movement, and, the creation of mountain ranges between route points, has made some migrations seem insane.
The geese that fly over the Himalayas find it harder and harder to clear the summits of the peaks, as the peaks are still growing taller every year due to tectonic plate collision/subduction.
Every year, fewer and fewer of these geese clear the mountain range, and, never get to mate, and their corpses litter the mountain sides...and only the ones able to fly almost 6 miles up in turbulent conditions make it. The wind gusts at that altitude can be over 100 mph, an impossible obstacle to a goose limited to far slower flight speeds.
As the air is less and less dense, providing progressively less oxygen to power the winged flight, and simultaneously, less lift for each wing beat, the higher they have to fly, the harder and harder it gets.
Some flocks have to make many desperate attempts, and many die trying.
One day, these geese may go extinct, because their migration route simply became impassable.
And so forth. Life can be a tenuous challenge, one that almost no species survives.
Changing conditions mean specialization is only a short term answer.
Evolution, in an environment that remains constant, tends to result in specialization....as whatever worked is passed on.
Things that evolved in an environment that changes frequently tend to have been less specialized simply because conditions favoring one path did not last long enough to perfect it.
Flowers were evolved to help attract insects to pollinate them, ....
TJ, even experienced scientists have to choose their words carefully. Your words "were evolved to help...." imply purpose, and so far as I know evolution has only effects.
I've seen scientists "slip" into this sort of thing as a form of shorthand when they know only other scientists (who understand it the same way they do) are around. But outside of those circumstances they are usually much more careful for the reasons you've cited here. (Sometimes they talk amongst themselves on just how best to put it to non-evolutionists, e.g., "the heart's function is to pump blood" rather than "the heart's purpose is to pump blood.")
Steve, scientists might indeed 'slip into' that sort of thing.
People who are leaving religions whose gods have purposes might also slip into that sort of thing.
A half century ago (Damn, time flies!) I taught a college scientific writing class. Five years later main frame computer users were reading my writing and would have told me to not use 100 words to say what requires only 10 words.
After I retired a writing class instructor told me I write 'economically', i.e., I use few words. He was right. Attorneys were among those reading my writing and would have angrily told me the same.
And so, I avoid even "...the heart's function is to pump blood...."
when I can write "...the heart pumps blood...."
And so, I avoid even "...the heart's function is to pump blood...."
when I can write "...the heart pumps blood...."
That's interesting, because including "function" sounded so natural to me, even though I see now that it was unnecessary. I think the extra word adds context in that pumping blood is significant in the context of what it does as part of the body. Again, the context is probably unnecessary most of the time, but it still feels (to me) like it adds "larger context" to the topic.
I'm just pointing this out because I've been considering how "larger context" is a level of understanding that's new to animals, and is a very powerful, human quality or drive that gives us the ability to generalize what we learn, and re-apply it in other contexts.
Another, very important "larger context" is how what we learn can be generalized to other conscious beings, i.e.how culture can propel itself forward by drawing from and teaching to other members of the society. This requires sophisticated theory of mind, being able to put ourselves in the shoes of others, and having empathy.
I don't know how off-topic (ha, "how out of context") the above sounds in this thread, but I feel that it directly relates why humans have a propensity to assume conscious agency where it might not even exist. We relate to each other and we even relate to the physical world by assuming there are ways to interact with those external beings and things, and we're built to function (whoops, I do not mean to imply God built us!)... we evolved to function with profound abilities to interact with other humans, animals, and things, even if we over-extend these abilities and concepts to relate to imaginary agents.
P.S. As directly related to this topic, we have lots of evidence that humans are all too willing to skip the scientific details of how things work, and just declare that it all must have been designed and planned by an omnipotent creator. Nothing more to see here, move along...
PB, before I wrote that post I checked the EOD and found that it defines "function" as "an activity that is natural to or the purpose of a person or thing."
That suggests a larger, or more specific, context.
When I refer to technical stuff or processes I use 'function'; when I refer to non-technical stuff I use 'purpose'.
I agree that "were evolved to help" sounds too much like part of a plan, and I wish there were another way to use the word "evolve" by emphasizing the randomness and serendipitous events of it as a natural process that is inevitable, in spite of its improbability at any particular moment.
Trying to think now of complex and improbable events that can be explained with random input... maybe the building of a snow flake. It's easy to fall into the assumption or presumption that God designs snow flakes, but only science has the power to explain in detail how. (And then of course someday some snow flake cult comes along with need and intent to discredit the scientific details, no matter how well observed or detailed.)
...maybe the building of a snow flake.
Or predicting the weather more than a few days ahead.
A long ago math professor said the differential equations would have more terms than anyone can write.
It's hard not to slip into this sort of intention or purpose talk.
Nature shows do this all the time when the biologists and other naturalists involved really know better.
The salmon is trying to return to the stream where it was born? Well, maybe it's instinct, not intention or purpose. Even when a bird or deer appears to be attracting the attention of a predator away from its young, is this intentional or just the acting out of a behavior that's become ingrained through evolution?
Even the ministrations of a mother cat to her kittens...is this love or simply instinct?
I think we're beginning to recognize that a lot of human behavior, including the love of a mother for her child, has a huge DNA component.
It just makes for a more compelling narrative to depict their behavior as driven by intention/purpose.