Skip to main content Accessibility help

We use cookies to distinguish you from other users and to provide you with a better experience on our websites. Close this message to accept cookies or find out how to manage your cookie settings.

Close cookie message
×
  1. Home
  2. Search

Refine search

Refine search

Access:
Content type:
Publication date:
Apply   From and To filters
Subject: Show more
Journals Show more
Publishers: Show more
Societies Show more
Series: Show more
Collections: Show more

Actions for selected content:

Select all | Deselect all
  • View selected items
  • Export citations
  • Download PDF (zip)
  • Save to Kindle
  • Save to Dropbox
  • Save to Google Drive

Save Search

You can save your searches here and later view and run them again in "My saved searches".

Please provide a title, maximum of 40 characters.
Cancel
×

1 results

  • 1 - A Tree with Millions of Twigs

  • from Part I - Painting Big Pictures
  • Wallace Arthur, National University of Ireland, Galway
  • Book:
    The Biological Universe
    Published online:
    24 September 2020
    Print publication:
    24 September 2020, pp 3-21

  • Summary

    Here, I examine the shape of the tree of life on Earth that is the result of four billion years of birth, death, reproduction, and relatedness. This extended family tree has been produced by four billion years of using energy from the environment to power biological systems. I then consider the question of how to define life, from both evolutionary and metabolic perspectives. Defining life is not easy, but it is possible if we accept that viruses constitute a grey area. Next, I deal with the main driver of evolution on Earth (and probably elsewhere), namely Darwinian natural selection. This driver only works when there is variation among organisms, so our next port of call is how variation arises – gene mutation and related processes. Finally, I examine the origin of life. The emphasis here is on the hypothesis that life arose here rather than arriving pre-formed from another planet – the Terraspermia hypothesis. The alternative Panspermia hypothesis is considered to be fatally flawed.