Hello blog readers!
Thought for today: How is it that evolution works when each incremental change can only be transferred one generation at a time? No that doesn't make sense! Since any change to the genome, can only influence survival up to the time of reproduction, a change that enables survival beyond that date, can have no direct effect on evolution!
Well I guess, continuing the stream of consciousness, it does, since it will operate on the next generation: A change that enables longer term parenting, will have been passed on, even though the effect of that change will not be apparent until the offspring itself passes its genes on! Self-reinforcing.
Convoluted! No-one said that evolution was simple.
I have the view that most of the characteristics of mammals, were developed long ago in the primeval swamp. All animals, have a similar skin; all livers function in the same way, etc. The proteins and hormones that govern how nearly all our bodily functions happen were invented by biology long long ago. The differences are subtle but because they are so similar, they must have been invented a long time ago, in order that the commonality we see in all species can exist. We are a massive symbiont of (what is it?) some 300 trillion cells. There are more bacteria in our guts than there are stars in our galaxy.
Just think on it, and try to deny the wonders of evolution!
Heck last I heard we share over 90% of our DNA with an oak tree, and when you closely examine the tree's physiology, you can clearly find parallels with biological functions in humans and other animals.
ReplyDeleteI doubt 90%! But it all depends on how you count. If you count DNA bases (A, C, G and T) there could be a 100% overlap, depending on how many chromosomes there are and the length of the DNA involved. There will certainly be a greater than 0% overlap.
ReplyDeleteI think a more meaningful count would be genes within the genome, and here there is still a considerable variety of response. If a gene codes for a single protein, then I'd suppose that there was a considerable difference in protein expression between oak and man (and woman). So I'd guess at closer to 5% commonality, though some have proposed a 30% overlap between man and a banana. (See: http://www.sciencechatforum.com/viewtopic.php?f=37&t=19262)
what do you know about parenting? ha
ReplyDeletewhen talking about evolution, you need to consider 2 types of cells, somatic and germ line. Only the reproductive germ line cells produce gametes that get passed on to the next generation. It is a small proportion of cells, compared to the somatic or body cells. Most mutations accumulate in the somatic cell lines and cause little change and aren't passed on.
When thinking about evolution, you have to be more careful. Just because livers are the same, doesn't mean they are. They have been under intense evolutionary selection to remain the same since the job they do is pretty important. However you might be able to find examples where a liver isn't a liver.
And when comparing DNA sequences between species, especially distant relatives such as a tree things get even more complicated. You might have the same gene as a tree, and the homology might be higher at 99%, but that is still more than enough for drastically different functions. Plants are a peculiar case as well, because they have normally undergone multiple genome duplication events. For example a human has 30000 genes, while an apple tree has close to 60000. What happens when you duplicate your genome and suddenly have two genes doing the same job? you get different selective pressures on each gene and they change over time. The human genome sequence ushered in a big shift in our thinking of genes, genomes and homology. 30000 genes isn't a lot. Humans have a lot of non-coding DNA, things like small RNA species that can act to silence expression of certain genes at certain times. So while a lot of the basic machinery is the same, an organism is also made up of when a gene is turned on, where, and with what other partners. Thinking of a gene as a static thing that does one function isn't how biology works. Proteins interact with multiple other proteins to do different functions. Like actin and myosin. Actin is a part of the cytoskeleton and myosin moves cargo around in the cell. Its vital for day to day cellular functions, but you would never know it. The same stuff that acts as roads for cargo on myosin trucks also is the major component of muscles. Here it acts in a different way to produce a muscle contraction that we can understand more easily.