Plant Evolution

in this video I will tell you a few things about plant evolution it's a very broad topic I can't talk about everything here instead I'll just give you a few facts and ideas so first it may seem obvious but plants have not always existed as for all other forms of life that was a beginning to give you an idea on the geological timescale earth is about 4.5 billion years old and life itself dates back to about 3.5 billion years on the other hand land plants are much more recent since their last common ancestor has been estimated to roughly 470 million years so just to be clear all of the dates given here are approximate some are still being debated we provide them here only to give you a general idea of the time scale if we zoom on the last 500 million years we think that seed plants the large group that includes flowering plants and conifers dates back to about 320 million years to give some context back then there were no mammals or birds yet but terrestrial and aquatic animals were already quite diverse on this timescale flowering plants are remarkably young indeed the oldest known fossils of flowering plants are about 140 million years old this is still quite old if we remember that dinosaurs became extinct only 66 million years ago with the exception of course of birds which are little dinosaurs with wings so the extraordinary diversity of flowering plants is the result of only 140 million years of evolution during this time period flowering plants became progressively dominant in most ecosystems today it is by far the most diversified group of land plants about nine in ten plants are flowering cats as you might know we have been thinking of evolution for only about 250 years more precisely since 1859 which is when Charles Darwin published the first version of the Origin of Species already back then at the same time when he proposed his theory of variation and natural selection Darwin imagined that it would be possible one day to reconstruct the geological tree of all living species to represent their evolutionary history today this representation called phylogeny or phylogenetic trees has become a universal tool to understand the evolution of all groups of living organisms plants animals fungi bacteria the tips of the tree represent living species who's present at time zero in other words right now as all plants ourselves squirrels ants all living organisms the nodes of this tree if we go down this figure represent the ancestors of these species those that lived in the past so the way to read this tree is from top to bottom if we want to go back in time in addition this tree has now become the basis for the classification of all flowering plants this is the apg system however follow genetic trees are not only useful for classification they are also primarily useful to understand the evolution of all forms of life so now I'm going to give you an example this is a simplified phylogeny of all land plants these include masses like Oh parts horse tails ferns conifers and flowering plants just to be clear here I am really simplifying the story this is only to give you an idea of what this tree looks like so this tree allows us to trace back some important events in the history of land plants first of all the emergence out of water which characterizes all of land plants then the origin of vessels which characterize all the so called vascular plants this tree also allows us to show the origin of seeds which characterize all the so called sea plants in other words the group that includes conifers a number of other small plant groups in flowering plants last this tree allows us to note the emergence of flowers which characterize all flowering plants to clarify this tree certainly doesn't mean that flowering plants are more evolved than other plants it all depends on the context so how can we go back in time to reconstruct plant evolution all that we can see today is the result of evolution we only see living organisms in all their diversity of shapes and forms with this diversity of living plants it is far from obvious to reconstruct the past from only the present and yet this is what we do how does it work let's imagine flowers with three petals and other flowers with five petals in this situation here it is quite easy to imagine with this phylogeny that these four species with five petals share a common ancestor which also had flowers with five petals on the other hand the common ancestor of all these plants probably had an ancestor of three petals indeed the simplest scenario is the one involving a single transition from three to five petals on this branch but if one of these species instead had three petals then things become more complicated there are two possibilities either we keep the same scenario but with a transition back to three petals in the species this is what we call a reversal or the five petals evolve twice independently in the school this is why we call convergence these two processes reversal and convergence are very interesting from an evolutionary point of view for instance the loss of limbs or legs in snakes is a reversal compared to their tetrapod ancestors which themselves as you and I are derived from ancestors that originally lacked limbs and look more like what we would call fish so how do we reconstruct phylogenetic trees the easiest solution will be to use direct traces from the past in other words fossils in order to reconstruct phylogenetic history unfortunately this is impossible for most living groups with just a few exceptions for most groups especially plants we know some fossils but there are not enough fossils to reconstruct biogenetic trees with precision so initially biologists started to use the morphology of living plants to trace back their phylogeny today we rather tend to use DNA for this purpose but roughly since the 1990s so it is thanks to DNA and to more and more powerful computers that it is possible now to evaluate among the thousands or billions of billions of possible phylogenetic trees which or which ones best explain the data we observe now so to summarize what I have told you here all living forms are the product of evolution these may reflect adaptations to particular environments recipes that allow plants to survive and reproduce faster and better but to be clear not everything can be explained chance probably also played an important role in evolution things that we see today are simply things that survive to this day so no species are more evolved than others it all depends on the context so for instance this plant here and me we both share a common ancestor that lived about one to two billion years ago it is neither up to me or this plant to say which is more evolved it all depends on the context to finish it's important to understand that we don't know everything yet there remain many uniqueness in evolution and one particular enigma in plant evolution is the exact age of flowering plants there's a lot of research at the moment and we still don't know how old exactly flowering plants are so just to finish I'd like to present you two important people coming so this is Daniel mature who played a key role in creating the MOOC for which this video was originally made so Danielle is the the founder and president of the Association telugu Tanika and come in here and this is Julia Babylon who was the cinematographer for this particular video and the entire MOOC but Nick that we created together

Channel: Hervé Sauquet

Views: 187,721

Keywords: plants, phylogeny, evolution, angiosperms, Darwin, MOOC, botany

Id: lQHo7nlqjsg

Length: 9min 53sec (593 seconds)

Published: Sat Oct 01 2016