In reply to lowersharpnose: I would think plants would have come first. I could imagine slimes and seaweeds floating and at the edge of the Seas slowly spreading and evolving to being Land based, and these being one of the impetus that tempted the lobe fish or whatever on to land, like a sheep looking over a fence into a better field.
Picture a pool next to a body of water which are separated by a raised bank. Fish in the main body of water have been jumping this bank until it becomes too large to make it, so now the fish are decking onto land a short distance away from the pool. A fish with slightly stronger fins can wiggle/slide/pull itself that short distance quicker than one with weaker fins - this offers it the tiniest statistical advantage of survival over its rival. Over a million or more lives, this advantage begins to tell and the strong-finned trait is passed on more than the weaker-finned. Extrapolating, surely you can see how this goes from here?
I think you can forget jumping and consider very shallow water habitats. Being able to use your lobe fins for mobility by pulling and pushing on the mud at the bottom is going to be useful. Then it is a sequence of shorter shorter steps to move into shallower and shallower water until there is no water at all.
That is what seems reasonable to me too. The TV progs and books I have read seem to concentrate on the fish-->land move and make no mention of what was on the land before. That's what I want to know about.
The first terrestrial animals were various types of arthropods (bugs, broadly defined): the ancestors of millipedes and centipedes, the earliest arachnids, and the ancestors of insects were established on land in the Silurian Period. These ate the early plants, and each other.
(Other groups, such as earthworms, other worms, snails, and so on colonized during this time.)
The ancestors of the dinosaurs (and us!) during this time were still entirely aquatic.
In reply to lowersharpnose:
Yes, probably a range of Arthropods rather than insects.
In the Silurian period, there were small plants evolved from algae, and organisms tend to be quick to exploit a new niche.
Lobed fins leading to legs may initially have been vital not to get out of water onto land, but get from a dessicating pool back into water. They are associated with a warmer period in Earth's history.
> (In reply to Philip) Oh dear. So a magic sky fairy said 'I know what, I'll invent legs.' Yep, that makes a lot more sense.
> Please, do some reading about how natural selection works, the timescales and sheer numbers of generations involved and then you can come back and explain to the class why you still think it's wrong.
Wow, what a pretentious little tw*t you are.
I have done some reading, not a lot, biological sciences aren't my thing. Are you saying you exclusively believe in natural selection as the only mechanism for evolution?
> (In reply to Philip)
> Picture a pool next to a body of water which are separated by a raised bank. Fish in the main body of water have been jumping this bank until it becomes too large to make it, so now the fish are decking onto land a short distance away from the pool. A fish with slightly stronger fins can wiggle/slide/pull itself that short distance quicker than one with weaker fins - this offers it the tiniest statistical advantage of survival over its rival. Over a million or more lives, this advantage begins to tell and the strong-finned trait is passed on more than the weaker-finned. Extrapolating, surely you can see how this goes from here?
This is exactly the scenario I find difficult to imagine. The other equally hard one is evolution of macro organisms from micro.
It is the difficulty of working with very large and very small numbers. The probability of the specific genetic variation occurring is so small, but the timescale and therefore the number of occurrences is so high. There needs to be sufficient time for evolution to happen, otherwise you would get extinction, but if there is sufficient time then is there really that great an environmental driving force.
> (In reply to Philip)
> Genuine question : what other mechanisms are there?
> (prior to selected breeding of individuals by humans ie dogs, pigeons etc?)
> A good book (especially for UKC) is Climbing Mount Improbable.
> By Richard Dawkins.
I read that at school. I prefer Steve Jones, he did a very good update to On the origin of species. I've met them both at lectures given to the science society when I was at uni.
On the mechanism question - there are others, a lot of wrapped up as natural selection whether they are caused by predators or reproduction.
There may be nothing wrong with the mechanism, it may be the starting point. Either way round the simple explanations are simple - I would not be convinced I could explain evolution to a open-minded creationist in anywhere near the convincing way I could anything else from science based on the popular explanations.
Granted, most science is too complex for most people, and when I see the answers to maths/physics/chemistry questions on here there are some appalling misunderstandings but at least the concepts can usually be explained.
Fossil evidence of vascular land plants from the mid Silurian period onwards I think (about 430 million years ago), before that evidence of spores, algae etc on land. Armoured jawless fish in the seas at this point, and possibly some very primitive insects on land (still debatable that last one).
By mid Devonian period (about 400 mya) plant life on land rapidly diversified, lots of fern like plants, etc. Early air breathing fish appear about the same time.
Genetic mutations happen all the time. Its just that most mutations don't get subjected to the environmental conditions which cause those mutations to be favored (or not favored since it works both ways).
Therefore a propensity to grow protuberances which help propulsion on land would have been present in some fish DNA long before the selective pressure to use it came along.
(warning - this is what I recall from a popular science book - its not my area)
In reply to Philip: 'open-minded creationist'. An interesting concept. When you find one please let the world know, because they will be a rarity indeed. Any creationist I've ever met, however pleasant and fluffy, has pretty quickly put up a wall and not allow further discussion. The commonest 'sophisticated' argument I've heard is that evolution requires geological time, for which there's no 'proof'. Except there is.
'On the mechanism question - there are others, a lot of wrapped up as natural selection whether they are caused by predators or reproduction.'
Are you saying that an organism that out breeds another similar one because of a slight mutation, or an organism that is wiped out because others have slight variations that make them less attractive to predators, aren't part of natural selection?
> Are you saying you exclusively believe in natural selection as the only mechanism for evolution?
There is also genetic drift.
> The probability of the specific genetic variation occurring is so small ...
Not really. There are about 30 new mutations in each of us. So in a population of a billion individuals there would be 30 billion new mutations each generation. Further, you rarely need a "specific" genetic mutation, often there are loads of ways of achieving an effect (because most aspects of the body are the product of the interaction of lots of different genes).
> The other equally hard one is evolution of macro organisms from micro.
What's the problem? Many a micro adds up to a macro.
> This is exactly the scenario I find difficult to imagine.
That's because human imagination is tuned to things that occur *within* typical lifetimes, because that is the job our brain is doing, enabling one individual to prosper over its lifetime. Thus we would not expect human intuition to be all that reliable about what happens over 10 million generations.
Forget Darwin and natural selection. evolution is accepted fact. Its mechanisms we have yet to understand.
Think in terms of phyletic gradualism, slow Environmental adaptation of species, and punctuated equilibrium, rapid Accidental mutation, Maybe over 1 generation, Which Proves ecologically Advantageous for a species.