Ask The Expert: Your Questions & Answers

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Question 9
The programme mentioned cell mutation that could give an advantage or disadvantage for a particular species depending on the environment. It got me thinking I have my mum's nose but although it looks like my mum's it isn't exactly the same - it differs a little. Also although I look like my and dad I don't look exactly like them. Does this mean that all the cells that have made me were mutated cells? Also I have my mum's nose but my dad's forehead so the connection between the nose and forehead is different to mum and dad's. How has that happened? Is it because when growing in the womb the two must combine? How does it know how to connect the two features when the two have not encountered each other before (my mum's nose and my dad's forehead in this case)? Also how far can my dad's forehead be divided? Is the forehead a slight mutated forehead of my dad's or can the forehead be part-dad part-mum?

Prof Campbell: No your cells are not mutants. You have inherited two sets of chromosomes, one from your mum and the other from your dad. You are a complex mix of these.

Question 10
Can you explain punctuated equilibrium please - what it is, how it's viewed currently in evolutionary biology and if you think it applies to human evolution?

Prof Campbell: Punctuated equilibrium was put forward some years ago by two American biologists, Neils Eldridge and Stephen J Gould. They noticed that the evolutionary record is not linear. Rather sometimes there is an explosion of new species, and extinctions, occurring over a relatively short period of evolutionary time. Evolution of species is thus 'punctate'’. A classic example is at the so-called K-T boundary about 65 million years ago when perhaps over 80% of all animal and plant species disappeared within a few million years. After this there were no more dinosaurs and no ammonites, and many new species appeared. Another was at the Cambrian explosion 600 million years ago when a huge number of multi-cellular organisms appeared for the first time. Nature does take leaps!

Question 11
What was the point of the first thing that evolved into something else? I presume this first life form had no predators and did these first forms of life mate or were they self-replicating?

Prof Campbell: This occurred with bacteria, which then had no scavengers. About 2000 million years ago there was a huge holocaust, because photosynthesis had appeared in some bacteria. This lead to a major change in the Earth's atmosphere, with oxygen appearing in large amounts for the first time. We need oxygen, but it is also very toxic. We have many defences against this toxicity, e.g. vitamin C. Only those bacteria that mutated to defend themselves would have been able to evolve.

Question 12
What makes a cell mutate?

Prof Campbell: Cells mutate via DNA mutations. An A changes to a G, C or T and so on. This usually occurs during DNA replication but can also occur in double stranded DNA. It is provoked by UV light, oxygen metabolites and some chemicals. This is why some chemicals can cause cancer.

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