Jarlaxle

I assume that humans are the most complex organisms on earth. If not, what is?

Whatever is the most complex, how many mutations does it take to get that complex from a single cell creature?

How long ago did the first single cell creature "come to life"?

If humans (or whichever is most complex) evolved from that first single cell organism, what has been the rate of change? That is, how many mutations must have happened per year or per 100,000 years or per million years or whatever is easiest to express?

Godless Dave

I'm not sure what you mean by "complex".

Jarlaxle

By complex I mean that a human is more complex than an ameba. It takes longer, more mutations to form a human through evolution than it takes to form an ameba through evolution.

Godless Dave

Fair enough, but I don't think you could find any one animal that's the most complex. I guess you could look at how many chromosomes an organism has, or the length of the DNA sequence. But I suspect all mammals would be of similar complexity, and I don't know that they would be more or less complex than certain genii of plants, fish, etc.

Can someone more knowledgable about biology explain this better? And tell me what the plural of "genus" is?

Blinn

genera

[ May 16, 2002: Message edited by: Zetek ]</p>

Late_Cretaceous

A lot of people seem to beleive that a the amount of genetic material or number of chromosomes has something to do with complexity. However, salamanders tend to have about 100X more genetic material then humans, and many plants have chromosomes numbering in the hundreds. At a cellular, biochemical or molecular level we are no more or less complex then salamanders, tomato plant, flatworm or fungi. At a more macroscopic level, we are no more nor less complex then a cat or rat.

Godless Dave

Thanks, L_C, that was the info I was looking for. Now what about rates of mutation? I didn't think there was a regular rate of mutation, but maybe I'm confusing biology with linguistics (my real field).

Peez

Rates of mutation and of evolution can certainly change. Estimating the number of "mutations" required to get from a single-celled organism (like an amoeba) to a multicellular organism (like a human) is not really possible (there are many different types of mutations, we don't know what the genome of the ancestral unicellular organisms was like, we don't understand the modern human genome, much less those of all of our ancestors), and is not terribly relevant in any event. Still, think about this:

Just for the sake of argument, let's imagine 100 million individuals in an evolving population over 400 million years. Let us further imagine that one generation is one year, and that each individual has only one mutation (all of these are very conservative numbers). This would mean 40,000,000,000,000,000 mutations. Note that humans have only about 30,000 genes among 3,000,000,000 nucleotides. This means about 1,333,333,333,333 mutations per gene, or about 13,333,333 mutations per nucleotide. No problem.

What is more informative is the rates of evolution for which we have evidence. We know that the fossil record provides evidence of evolution over billions of years. We can see that the rates of change are (obviously) sufficient to produce humans from unicellular organisms. We can see that relatively fast evolution in the fossil record (which is still so slow that we could not detect it if it were happening today) is much slower than that observed in extant natural populations. We can also see that evolutionary rates in natural populations are much slower than those we can produce in the laboratory. So, the bottom line is that evolution certainly can move fast enough to produce humans from unicellular organisms in the time allotted, in fact it could have moved even faster in principal.

Peez