In the light of recent findings in the field of genetics which confirm that environment does affect the form, structure; colour, size etc. and these characters are inheritable theory of Neo-Lamarckism evolved.
Main scientists who contributed in the evolution of Neo-Lamarckism are: American Cope, T.H. Morgan, Spencer, Packard, Bonner, Tower, Naegali, Mc Dougal, etc. Term neo-Lamarckism was coined by Alphaeus S. Packard.
- Germ cells may be formed from the somatic cells indicating similar nature of chromosomes and gene make up in two cell lines e.g.
(a) Regeneration in earthworms.
(b) Vegetative propagation in plants like Bryophyllum (with foliar buds).
(c) A part of zygote (equipotential egg) of human female can develop into a complete baby (Driesch).
- Effect of environment on germ cells through the somatic cells e.g. Heslop Harrison found that a pale variety of moth, Selenia bilunaria, when fed on manganese coated food, a true breeding melanic variety of moth is produced.
- Effect of environment directly on germ cells. Tower exposed the young ones of some potato beetles to temperature fluctuation and found that though beetles remained unaffected with no somatic change but next generation had marked changes in body colouration.
Muller confirmed the mutagenic role of X-rays on Drosophila while C. Auerbach et., al. confirmed the chemical mutagens (mustard gas vapours) causing mutation in Drosophila melanogaster, so neo-Lamarckism proved:
(a) Germ cells are not immune from the effect of environment.
(b) Germ cells can carry somatic changes to next progeny (Harrison’s experiment).
(c) Germ cells may be directly affected by the environmental factors (Tower’s experiment).