No one really knows what the first life was. A single cell, even a primitive one, is still a rather complicated organism. I have heard speculation that life arose from self-replicating RNA molecules; these exist today and are simple enough to arise by random mixing of organic compounds.
Why would this progeny ever have to adapt? Single-celled life is arguably the most resilient life on earth. Some say it can survive in outer space.
Conditions are never static. If the first life arose, as was likely, in water rich with organic molecules, at some point these primitive organisms would have used up the available molecules. At that point, an organism that could, perhaps, feed on waste products from other organisms would have an advantage. Or, if the water dried up or froze, an organism that could enter a dormant state could survive. And so on. Single-celled organisms only seem to be resilient because there are so many species of them, and they have adapted to conditions which would kill us. I don't know about the outer space part, though.
And why would varied progeny adapt differently to the same environment -- even ignoring the fact that their grandparents are thriving quite happily in it.
Some may do better, and some, worse, than their grandparents. But environments also change.
Why would sexual reproduction develop? How could it develop at random? I've seen explanations, I just can't take them seriously. I've heard better reasoning from a football fan saying how his 0-7 team can still be expected to make the playoffs.
Sexual reproduction is a means of exchanging genetic material, which provides a quicker way to adapt to changing environments. Yeast mate by merging two cells--it is easy to envision how cells can merge by random. Bacteria mate by injecting genetic material into other bacteria. While the specialized structures involved in this process had to evolve, genetic material can be ingested much like food, and bacteria can and do ingest DNA without physically touching other bacteria. The mating bacteria would have an advantage over bacteria randomly encountering DNA; both processes are common. I believe all cellular organisms mate; I don't know if non-cellular organisms (viruses, mycoplasma) do.
Then there is the lack of evidence. I can perfectly accept that tigers and housecats share a common descendent. I can't accept that housecats and horses do. And I can't accept the fossil record as being definitive about much of anything.
I believe the fossil record shows some proto-mammals existing hundreds of millions of years ago; all mammals are believed to descend from a common proto-mammal. I wish I could show you a phylogenetic tree; these are like evolutionary family trees, which show where each phylum, genus, and species branched off of the ancestral trunk. These are generated on the basis of sequence divergence of a single protein. With one exception that I know of, it does not matter which protein is selected, because the result will be similar, and correlates well with the fossil record. Geneticists have calculated, based on the known mutation frequencies of DNA, how long it takes for a single amino acid in a protein to be altered, so that each branch of the phylogenetic tree corresponds to the time since speciation, as well as the genetic similarities between organisms. Such a tree will show horses on a distant branch, with other herbivores, cats will be on a closer branch, rodents are closer, and primates and humans form a very small cluster of branches. (I'm not sure about the relative "closeness" of cats and primates; the only tree I could find on short notice shows bacteria.)
And then there is irreducible complexity. Somebody is going to say that Behe has been refuted. I'm going to say I can't see how. Then somebody is going to say Behe is a fool and I'm a fool for considering his argument. Sorry, I'm not buying that.
Who or what is Behe? I do not know about irreducible complexity; there is enormous range in genome size (the amount of DNA in any given species), and most of that DNA is useless junk. Bacteria, which are very small and must conserve energy, tend to small genomes and very little junk. Higher organisms tend to larger genomes, mostly junk, but even higher organisms can reach a point where it takes too much energy to maintain the DNA, and they lose some. Plants tend to have genomes larger than animals' by orders of magnitude. It's not a question of complexity so much as a problem of accumulating junk.
Then there is a religious aspect. No offense meant to anyone on this thread, but there are those who use evolution as an excuse to deny God's existence.
God exists.
If you argue that God exists and evolution is how he did it that's fine. You won't get mad at those with whom you dispute.
I will not argue that there are atheists, and that some of them will point to evolution as proof of a godless universe. There have always been atheists, though, and their reasons for being so have nothing to do with scientific theories. I also will not argue that God exists, and I will not speculate on whether or how God created the universe. I do believe that God set into motion the forces of evolution (of the solar system, as well as of life) and created or adjusted the physical constants that made it all possible.
I am sorry this ran so long; you did not ask questions with easy one or two sentence answers.
Don't be. Thanks for the answer. You're very smart, you know you're subject, you're evolution-of -sexual-reproduction explanation was the best I've seen, but I remain a staunch skeptic.
I'm not just being stubborn or overly religous. Perhaps, I'm just naturally suspicious.
Take this:
Geneticists have calculated, based on the known mutation frequencies of DNA, how long it takes for a single amino acid in a protein to be altered, so that each branch of the phylogenetic tree corresponds to the time since speciation . . .
How do yo know what a fossil's DNA is? Something else about the phylogenic tree doesn't add up for me about which I don't have the background to articulate. I will think about it.
Here's a link to Michael Behe You'll see him mentioned periodically on these threads and in the news.
Sorry for my short answer. I'll mull you're long one. Good luck with you Ph.d. and I hope you post frequently.
I don't know about the outer space part, though.
I don't know either, but here's a link to Crick's thinking :-)
Since you have given us so many testaments of your supposed learning, I cannot say that the statement that there exist self-replicating RNA molecules is a mistake. It needs to be called a blatant and humongous lie, and I am calling on you to prove you are not a liar.
That's a lot of believing going on there! However, the first supposed mammal, is just a lower jaw and some parts of a pasted up upper skull which is more like a jigsaw puzzle than anything else. In addition at over 200 million years old (supposedly) it is over a hundred million years away from the next definitely mammalian bones.
Well, should be expected from an evolutionist though, as Darwin's proof of the eyes evolving was if you have read through two hundred some pages of my absolute nonsense, you have to believe with me that these eyes evolved.
Total nonsense. To imply that a plant is as complex as a human is ridiculous. The reason men are more complex while having a smaller genome than some plants is that humans have very involved genomes which are able to reuse DNA in different ways, while most lower organisms cannot. Also, the junk is not junk at all. A Japanese puffer fish has just as many genes as humans and amazingly none of what you call junk DNA. The reason it is less complex than man is because what you incorrectly call junk and what real scientists call 'non coding DNA' is what enables humans to do so much more with their genes than a puffer fish.